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YOUR
EYES & VISION
How the Eye
Works
Our ability to "see" starts when light reflects off an object at which we are
looking and enters the eye. As it enters the eye, the light is unfocused. The first step
in seeing is to focus the light rays onto the retina, which is the light sensitive layer
found inside the eye. Once the light is focused, it stimulates cells to send millions of
electrochemical impulses along the optic nerve to the brain. The portion of the brain at
the back of the head interprets the impulses, enabling us to see the object.
Light, refraction and its importance.
Light entering the eye is first bent, or refracted, by the cornea -- the clear window on
the outer front surface of the eyeball. The cornea provides most of the eye's optical
power or light-bending ability.
After the light passes through the cornea, it is
bent again -- to a more finely adjusted focus -- by the crystalline lens inside the eye.
The lens focuses the light on the retina. This is achieved by the ciliary muscles in the
eye changing the shape of the lens, bending or flattening it to focus the light rays on
the retina.
This adjustment in the lens, known as accommodation,
is necessary for bringing near and far objects into focus. The process of bending light to
produce a focused image on the retina is called "refraction". Ideally, the light
is "refracted," or redirected, in such a manner that the rays are focused into a
precise image on the retina.
Most vision problems occur because of an error in
how our eyes refract light. In nearsightedness (myopia), the light rays form an image in
front of the retina. In farsightedness (hypermetropia), the rays focus behind the retina.
In astigmatism, the curvature of the cornea is irregular, causing light rays to focus to
more than one place so that a single clear image cannot be formed on the retina, resulting
in blurred vision. As we age, we find reading or performing close-up activities more
difficult. This condition is called presbyopia, and results from the crystalline lens
being less flexible, and therefore less able to bend light.
Since changing the apparent refraction of the eye is
relatively easy through the use of corrective spectacle or contact lenses, many of the
conditions that contribute to unclear vision can be readily corrected.
How do we make sense of light?
Sensory interpretation
Even with the light focused on the retina, the process of seeing is not complete. For one
thing, the image is inverted, or upside down. Light from the various "pieces" of
the object being observed stimulate nerve endings -- photoreceptors or cells sensitive to
light -- in the retina.
Rods and cones
Two types of receptors -- rods and cones -- are present. Rods are mainly found in the
peripheral retina and enable us to see in dim light and to detect peripheral motion. They
are primarily responsible for night vision and visual orientation. Cones are principally
found in the central retina and provide detailed vision for such tasks as reading or
distinguishing distant objects. They also are necessary for color detection. These
photoreceptors convert light to electrochemical impulses that are transmitted via the
nerves to the brain.
Millions of impulses travel along the nerve fibers
of the optic nerve at the back of the eye, eventually arriving at the visual cortex of the
brain, located at the back of the head. Here, the electrochemical impulses are unscrambled
and interpreted. The image is re-inverted so that we see the object the right way up. This
"sensory" part of seeing is much more complex than the refractive part -- and
therefore is much more difficult to influence accurately.
What is 20/20 Vision?
You may be pleased to hear that you have 20/20 vision and think you have perfect vision.
But do you?
Not necessarily. 20/20 only indicates how sharp or
clear your vision is at a distance. Overall vision also includes peripheral awareness or
side vision, eye coordination, depth perception, focusing ability and color vision.
20/20 describes normal visual clarity or sharpness
measured at a distance of 20 feet from an object. If you have 20/20 vision, you can see
clearly at 20 feet what should normally be seen at that distance. If you have 20/100
vision, it means that you must be as close as 20 feet to see what a person with normal
vision can see at 100 feet.
Is 25/25 vision better than 20/20?
No. 25/25 means normal sharpness of vision, or visual acuity, at 25 feet just as 20/20
indicates normal vision at 20 feet.
Why do some people have less than 20/20?
The ability to see objects clearly is affected by many factors. Eye conditions like
nearsightedness, farsightedness, astigmatism or eye diseases influence visual acuity. Most
people with vision slightly below 20/20 function very well, whereas some people who have
better than 20/20 vision feel that their vision is not satisfactory. Everybody's visual
expectations are different and satisfactory vision is far more complex than just being
able to see 20/20.
If my vision is less than optimum, what can I do?
A comprehensive eye examination will identify causes that may affect your ability to see
well. We may be able to prescribe glasses, contact lenses or a vision therapy program that
will help improve your vision. If the reduced vision is due to an eye disease, the use of
ocular medication or other treatment may be needed. If necessary, referral will be
undertaken if an eye disease is found which warrants further investigation.
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Children's Vision
About 80 percent of all babies are born farsighted -- able to see objects clearly at a
distance but less clearly close up. Some five percent are born nearsighted, or unable to
see objects at a distance clearly.
Approximately 15 percent are born with nothing wrong
with the refractive parts of the eye -- the cornea and crystalline lens which bend light
and focus it properly on the retina. Farsightedness usually decreases as a child ages,
typically normalizing to a negligible value by the age of 7-8.
After a child grows and the incidence of
farsightedness decreases, that of nearsightedness increases. Many school-age children and
teens first discover they are nearsighted when they have difficulty reading the writing on
the board at school. Nearsightedness usually occurs before age 25.
Vision skills for school
Your school-age child's eyes are constantly in use in the classroom and at play. When his
or her vision is not functioning properly, learning and participation in recreational
activities can suffer.
Good vision involves many different skills working
together to enable your child not only to see clearly but also to understand what he or
she sees.
Those skills include:
Near Vision
Ability to see clearly and comfortably at 13-16 inches, the distance at which school
deskwork should be performed.
Distance Vision
Ability to see clearly and comfortably at 10 feet or more.
Binocular Coordination
Ability to use the two eyes together.
Eye Movement Skills
Ability to aim the eyes accurately, and move them smoothly across a page and quickly and
accurately from one object to another.
Peripheral Awareness
Ability to be aware of things to the side while looking straight ahead.
Eye/Hand Coordination
Ability to use the eyes and hands together.
If any of these or other vision skills is lacking or
not functioning properly, your child's eyes have to work harder. This can lead to blurred
vision, headaches, fatigue and other eyestrain symptoms.
Why thorough vision examinations are important
Don't assume your child has good vision because he or she passed a school vision
screening. A 20/20 score means only that your child can see at 20 feet what he or she
should be able to see at that distance. It does not measure any of the other vision skills
needed for learning.
Vision screenings are important but they should not
be substituted for a thorough vision examination.
Things you can do
There are things you can do to help ensure that your child's vision is ready for school
each year and to relieve the visual stress of schoolwork.
Be alert for symptoms that may indicate your child
has a vision problem. Note if your child frequently:
- Loses his or her place while reading.
- Avoids close work.
- Holds reading material closer than normal.
- Tends to rub his or her eyes.
- Has headaches.
- Turns or tilts their head to use one eye only.
- Makes reversals when reading or writing.
- Uses a finger to maintain their place while reading.
- Omits or confuses small words when reading.
- Performs below potential.
- Closes one eye while reading.
Make sure your child's homework area is evenly
lighted and free from glare. Furniture should be the right size for proper posture. During
periods of close concentration, have your child take periodic breaks. Rest breaks are also
recommended when your child is using a computer or playing video games.
To make TV viewing easier on your child's eyes:
- Be sure the room has overall soft lighting.
- Place the set to avoid glare and reflections.
- Watch from a distance at least five times the width
of the screen.
Be sure your child's hours away from school include
time for exercise and creative play. Both can help keep his or her vision skills
functioning properly.
Teach your child eye protection through these
safety rules:
- Keep away from the targets of darts, bows-and-arrows,
air guns and missile-throwing toys.
- Don't shine laser pointers into anyone's eyes. Teach
them laser pointers are not toys.
- Don't run with or throw sharp objects.
- Wear safety goggles when using chemistry sets, power
tools and household and yard chemicals. (Note: Be certain your child is mature enough to
handle these items safely, and provide proper supervision.)
Thorough vision care is important
Because a change in vision can occur without you or your child realizing it, have your
child's eyes examined every year.
A thorough eye examination should include:
- A review of your child's health and vision history.
- Tests for nearsightedness, farsightedness,
astigmatism, color perception, lazy eye, crossed-eyes, eye coordination, depth perception
and focusing ability.
- An eye health examination.
If your child's eyes need help
After assessing your child's test results, glasses, contact lenses or vision therapy may
be prescribed. He or she may also recommend preventive measures, such as mild prescription
lenses to be worn only when doing schoolwork or watching television. These may help
relieve stress on your child's eyes.
Vision therapy is prescribed for conditions that
cannot adequately be treated with glasses or contact lenses alone. By reinforcing or
re-teaching vision skills, conditions such as poor eye coordination and movement, lazy eye
and perceptual problems can be improved.
Your care and concern for your child's vision can
enrich his or her future while helping develop eye care habits for a lifetime of good
vision.
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Mature
Vision
Most changes in vision occur in the early and later years of life. Although some people
may discover they have nearsightedness -- or difficulty seeing at a distance -- as late as
their mid-20s, vision typically stabilizes during the late teen years. From then until
around age 40, vision typically changes little, if at all.
Presbyopia - Age-related loss of close-up vision
At about 40 years of age, seeing to read or do close work such as sewing may become
difficult. This is known as "presbyopia." Presbyopia, a name that comes from the
Greek words for "old eye," occurs because the crystalline lens, an essential
component of the eye's refractive, or light-bending structure, loses flexibility as it
grows thicker with age. This lack of flexibility affects the ability to focus on close
objects.
Generally, by around age 45, reading glasses may be
required for nearby tasks. If near- or farsightedness is also present, a number of vision
correction options will be evaluated to best meet your needs.
Spots and floaters
People of every age may at times see spots and floaters, which appear to look like specks
of material, cobwebs, thread-like strands or showers of brilliant crystals. During the
middle years of life, they may become more frequent. These are optical defects that occur,
as the vitreous, the jelly-like body in the main globe of the eye, becomes less jelly-like
and more liquid as time goes by. This change is not always uniform, and so the mixture of
jelly-like and liquid materials can affect the passage of light to the retina.
The result is seen as 'floaters.' Although spots and
floaters are typically not of concern, they should be evaluated promptly. If you suddenly
experience a large number of floaters, don't delay in making an appointment. A sudden
change may signify that something is wrong.
Glaucoma
For adults, it is important to schedule regular eye examinations in order to detect and
treat any occurrence of glaucoma in its earliest stages. Most types of glaucoma occur
without the presence of any symptoms and can only be detected during a routine eye
examination. Glaucoma occurs when fluid pressure inside the eye rises, cutting off the
blood supply in the very small arteries carrying food and oxygen to the retina and causing
loss of side vision or blindness if left untreated. It is a condition that can be arrested
or slowed down but not reversed, so early detection is essential. Treatment often involves
special eye drops or medicine, but, in some cases, surgery may be required. If detected
early, chances that vision can be maintained are usually very good.
Retinal disorders
Retinal disorders have a greater chance of developing in older adults, due to the aging
process. These often impair central vision. Advances in eye and health care have made
treatments more successful, with chances of maintaining good vision now better than ever.
Conditions once considered sight threatening may now be successfully treated if diagnosed
early.
Suggestions for better sight
- Be aware of your visual limitations and compensate
for them.
- You may need more light for reading and other close
tasks. Move the lamp closer to you and/or use a larger watt bulb. It is a fact that a 60
year old needs three times as much light as a 20 year old to see near work as easily.
- Side vision and reaction time may reduce with age.
Keep this in mind while driving or walking near traffic.
- Limit night driving to well-lighted roads; keep
headlights and windshields clean; and be visually aware of traffic.
- Be sure to keep glasses clean.
- Be sure to wear distance spectacles if they are
prescribed for you. While you may feel that your distance vision is as good as it was when
you were younger, very often this is not the case.
Although natural vision changes can't be prevented,
they need not mean giving up activities such as driving your car. By practicing good
health habits and having regular eye examinations, you should be able to continue an
active, productive and independent life.
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TV &
Vision
Eye care experts generally agree: Watching television will not harm your eyes or vision if
the TV room is lit properly and if you follow a few viewing tips. In fact, there is
usually less strain involved in TV viewing than in doing close work such as sewing or
reading. But TV watching for long stretches of time can leave your eyes fatigued.
What are the best conditions for TV viewing?
A normally lit room, suitable for general activities, is best. Excessively bright lighting
tends to reduce contrast on the screen and "wash out" the picture. No lights
should be placed where glare or reflections will be seen in or near the television screen.
Strongly colored lighting should not be used and surroundings should be neutral in color.
Is it all right to watch television in a dark
room? This situation is not ideal. When the room is totally dark, the contrast between
the television screen and the surrounding area is too great for comfortable and efficient
vision. When the room is softly illuminated, undesirable high contrast is kept to a
minimum.
Is it better to adjust the television set to room
lighting or room lighting to the set? Adapt the set's brightness and contrast to room
lighting -- not room lighting to the set -- after the room lights have been turned on.
Is it all right to wear sunglasses while watching
television? Generally, no. Sunglasses may shut out too much light for good vision. If
worn when not needed, they tend to make it difficult for the viewer to adapt promptly to
normal light levels. If you are bothered by brightness, consult with an eye care
practitioner about the possible need for lenses more appropriate to TV viewing.
Possible difficulties with TV viewing
Children sometimes sit close to the set. Does this hurt their eyes? While close-up
viewing is certainly not recommended, it is generally not harmful. It is best to watch
television from a distance of at least five times the width of the picture. Picture
details will appear sharper and better defined and the television lines and defects will
be less apparent. If your child persists in watching television from a short distance,
have his or her vision checked. Nearsighted (myopic) children like to sit close to the
screen.
What does it mean if the eyes water or if there
is other visual discomfort while watching television? It could indicate a problem that
needs professional attention. Some viewers, especially those over 50 years old, may find
relief with special glasses for television viewing. Discomfort could also indicate that
the drainage passages which drain tears from the eyes into the nose are partially blocked
and require examination.
What about color television for viewers with
color vision deficiencies? Color deficiency (i.e. color blindness) is generally not a
barrier to enjoying color television. However, viewers with color deficiencies may
disagree with others as to the "proper" color adjustment. A color TV picture
properly adjusted for most people may appear too green to a protanomalous (weak red)
observer, or too red to a deuteranomalous (weak green) viewer. When the set is adjusted to
"correct" its color, the resulting picture is usually unsatisfactorily tinted
for other viewers. Viewers who are severely color deficient, the so-called "red
blind" or "green blind," will see little or no difference in widely
different color mixtures, and will not be bothered by most color adjustments.
TV viewing tips:
- Make sure your television set is properly installed
and the antenna properly adjusted.
- Place the set to avoid glare and reflections from
lamps, windows and other bright sources.
- Adjust brightness and contrast controls to individual
and/or viewer's taste and comfort.
- Have the set at approximately eye level. Avoid having
to look up or down at the picture.
- Avoid staring at the screen for lengthy periods.
Briefly look away from the picture, around the room or out the window.
- Wear lenses prescribed for vision correction, if
advised to do so by your eye care practitioner.
- View from a distance at least five times the width of
the television screen.
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Reading
& Vision
Good vision is vital to reading well. And although vision may not be the only cause of
reading difficulties, it is one that is sometimes overlooked.
Eight vision skills needed to read
Reading requires the integration of eight different vision skills. Only one is checked by
the typical school eye chart test. Quick eye examinations may cover only one or two. Since
a comprehensive eye examination will cover the eight vision skills, it is a must for
anyone having trouble reading. The eight skills include:
Visual acuity, or the ability to see objects
clearly at a distance. Visual acuity is sometimes measured in a school vision screening.
Normal visual acuity is referred to as 20/20 vision (or 6/6 vision in the metric system)
-- a measure of what can normally be seen at a distance of 20 feet, or six meters. If a
problem is discovered in the screening, a thorough optometric examination should follow.
Visual fixation, or the ability to aim the
eyes accurately. One type of fixation, called direct, has to do with the ability to focus
on a stationary object or to read a line of print. The other type, called pursuit
fixation, is the ability to follow a moving object with the eyes.
Accommodation, or the ability to adjust the
focus of the eyes as the distance between the individual and the object changes. Children
frequently use this skill in the classroom as they shift focus between books and
blackboards.
Binocular fusion, or the brain's ability to
gather information received from each eye separately and form a single, unified image.
Eyes must be precisely aligned or double vision (diplopia) may result. If it does, the
brain often subconsciously suppresses or inhibits the vision in one eye to avoid
confusion. That eye may then develop poorer visual acuity (amblyopia or lazy eye).
Stereopsis, a function of proper binocular
fusion enhancing the perception of depth, or the relative distances of objects from the
observer.
Convergence, or the ability to turn the two
eyes toward each other to look at a close object. Any close work, such as deskwork,
requires this vision skill. If convergence is poor then reading becomes uncomfortable
after a relatively short period of time and double vision may result.
Field of vision, or the area over which
vision is possible. It is important to be aware of objects on the periphery (left and
right sides and up and down) as well as in the center of the field of vision.
Perception, the total process of receiving
and recognizing visual stimuli. Form perception is the ability to organize and recognize
visual images as specific shapes. A reader remembers the shapes of words, which are
defined and recalled as reading skills are developed.
Treating reading-related vision problems
When a vision problem is diagnosed, the practitioner will prescribe glasses or contact
lenses, vision therapy or both. Vision therapy involves an individualized program of
training procedures designed to help develop or sharpen vision skills and possibly develop
the eye muscles involved in focusing.
Because reading problems usually have multiple
causes, treatment must often be multidisciplinary. Educators, psychologists, optometrists
and other professionals often must work together to meet each person's needs. The
optometrist's role is to help overcome any vision problems interfering with the ability to
read. This may require the use of corrective spectacles and/or the implementation of a
variety of eye exercises. Once any vision problems are addressed, the student is better
prepared to respond to special reading education efforts.
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VISION
PROBLEMS
Astigmatism
If you experience a distortion or blurring of images at all distances -- nearby as well as
far -- you may have astigmatism. Even if your vision is fairly sharp, headache, fatigue,
squinting and eye discomfort or irritation may indicate a slight degree of astigmatism. A
thorough eye examination, including tests of near vision, distant vision and vision
clarity, can determine if astigmatism is present. Astigmatism is not a disease nor does it
mean that you have "bad eyes." It simply means that you have a variation or
disturbance in the shape of your cornea.
Astigmatism is one of a group of eye conditions
known as refractive errors. Refractive errors cause a disturbance in the way that light
rays are focused within the eye. Astigmatism often occurs with nearsightedness and
farsightedness, conditions also resulting from refractive errors.
What causes astigmatism?
Astigmatism usually occurs when the front surface of the eye, the cornea, has an irregular
curvature. Normally the cornea is smooth and equally curved in all directions and light
entering the cornea is focused equally on all planes, or in all directions. In
astigmatism, the front surface of the cornea is curved more in one direction than in the
other. With the cornea's shape more like that of an American football or rugby ball than a
basketball, the light hitting the more curved surface comes to a focus before that which
enters the eye through the less curved surface. Thus, the light is focused clearly along
one plane, but is blurred along the other so only part of anything being looked at can be
in focus at any time.
This abnormality may result in vision that is much
like looking into a distorted, wavy mirror. The distortion results because of an inability
of the eye to focus light rays to a point.
Why are corneas shaped differently?
Not all corneas are perfectly curved, just as sets of teeth are seldom perfectly aligned.
The degree of variation determines whether or not you will need corrective eyewear. If the
corneal surface has a high degree of variation in its curvature, light refraction may be
impaired to the degree that corrective lenses are needed to help focus light rays better.
The exact reason for differences in corneal shape
remains unknown, but the tendency to develop astigmatism is inherited. For that reason,
some people are more prone to develop astigmatism than others.
How does astigmatism affect sight?
The clear cornea is situated at the very front surface of the eye and enables light to
enter the eyeball. The cornea accomplishes about four-fifths of the refractive work needed
for clear vision, bending light rays into a point. The crystalline lens, located behind
the cornea, further refines the refractive work begun by the cornea and directs the point
of light toward a precise location on the retina, known as the fovea. If light is not
focused into a fine point on the fovea, the image that reaches the retina cannot be
clearly transmitted to the brain and a blurred image is perceived.
When astigmatism is present, the surface of the
cornea is distorted instead of spherical. It is unable to focus light rays entering the
eye into the fine point needed for clear vision. At any time, only a small proportion of
the rays are focused and the remainder are not, so that the image formed is always
blurred. Usually, astigmatism causes blurred vision at all distances.
Who develops astigmatism?
Astigmatism is very common. Some experts believe that almost everyone has some degree of
astigmatism, often from birth, which may remain the same throughout life.
Of interest to parents and those who work with
children, astigmatism may contribute to poor schoolwork but is often not detected during
routine eye screening in schools.
How is it diagnosed?
Astigmatism is diagnosed in the course of a thorough eye examination.
How is it treated?
If the degree of astigmatism is slight and no other problems of refraction, such as
nearsightedness or farsightedness, are present, corrective lenses may not be needed. If
the degree of astigmatism is great enough to cause eyestrain, headache, or distortion of
vision, prescription lenses will be needed for clear and comfortable vision.
The corrective lenses needed when astigmatism is
present are called "Toric" lenses and have an additional power element called a
cylinder. They have greater light-bending power in one axis or direction than in the
others. Precise tests will be made during your eye examination to determine the ideal lens
prescription.
Astigmatism may increase slowly over time. Regular
eye examinations can help to ensure that proper vision is maintained.
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Farsightedness
(hyperopia)
If you can see objects at a distance clearly but have trouble focusing well on objects
close up, you may be farsighted.
Farsightedness or long-sightedness is often referred
to by its medical names, hypermetropia or hyperopia. Hyperopia causes the eyes to exert
extra effort to see close up. After viewing near objects for an extended period, you may
experience blurred vision, headaches and eyestrain. Children who are farsighted may find
reading difficult.
Hyperopia is not a disease, nor does it mean that
you have "bad eyes." It simply means that you have a variation in the shape of
your eyeball. The degree of variation will determine whether or not you will need
corrective lenses.
What causes farsightedness?
Hyperopia most commonly occurs because the eyeball is too short; that is, shorter from
front to back than is normal. In some cases, hyperopia may be caused by the cornea having
too little curvature. Exactly why eyeball shape varies is not known, but the tendency for
farsightedness is inherited. Other factors may be involved too, but to a lesser degree
than heredity.
How does farsightedness affect sight?
Our ability to "see" starts when light enters the eye through the cornea. The
shape of the cornea, lens and eyeball help bend (refract) light rays in such a manner that
light is focused into a point precisely on the retina.
If, as in farsightedness, the eyeball is too short,
the "point of light" focuses on a location behind the retina, instead of
on the correct area of the retina, known as the fovea. As a result, at the point on the
retina where a fine point of light should be focused, there is a disk-shaped area of
light. Since light is not focused when it hits the retina, vision is blurred. Convex
lenses are prescribed to bend light rays more sharply and bring them to focus on the
retina.
How is it diagnosed and treated?
Hyperopia is seldom diagnosed in school eye-screening tests, which typically test only the
ability to see objects at a distance. A comprehensive eye examination that checks both
near and far vision is necessary to diagnose farsightedness. In some cases it may be
necessary for the practitioner to use drops during the examination to relax the eye
muscles and ensure that the full degree of hyperopia is detected. This is necessary
because the muscles which focus the eye are so accustomed to being used to compensate for
the hyperopia that the muscles go into "spasm" and cannot relax without being
forced to do so.
Corrective convex lenses (positive powers) are
usually prescribed. They bend light rays more sharply and bring them to focus on the
retina. If you do not have other vision problems such as astigmatism, you may only need
glasses for reading or other tasks performed at a close range.
To determine the best avenue of treatment, questions
about your lifestyle, occupation, daily activities and general health status may be asked.
For instance, you may be asked whether or not you frequently need near vision. Providing
candid, considered answers to the questions will help assure that your corrective lenses
contribute to clear sight and general comfort.
A comprehensive eye examination at the recommended
intervals will ensure that minor changes in vision are diagnosed and treated so that your
vision will remain as clear and comfortable as possible.
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Nearsightedness
(myopia)
If you can see objects nearby with no problem, but reading road signs or making out the
writing on the board at school is more difficult, you may be near- or shortsighted.
This condition is known as myopia, a term that comes
from a Greek word meaning "closed eyes." Myopia is not a disease, nor does it
mean that you have "bad eyes." It simply refers to a variation in the shape of
your eyeball. The degree of variation determines whether or not you will need corrective
eyewear.
What causes nearsightedness?
Myopia most often occurs because the eyeball is too long, rather than the normal, more
rounded shape. Another less frequent cause of myopia is that the cornea, the eye's clear
outer window, is too curved. There is some evidence that nearsightedness may also be
caused by too much close vision work.
How does myopia affect sight?
Our ability to "see" starts when light enters the eye through the cornea. The
shape of the cornea, lens and eyeball help bend (refract) light rays in such a manner that
light is focused into a point precisely on the retina.
In contrast, if you are nearsighted, the light rays
from a distant point are focused at a place in front of the retina. As the light
will only be focused in that one place, by the time it reaches the retina it will have
"defocused" again, forming a blurred image.
Myopia usually occurs between the ages of 8 to 12
years. Since the eyes continue to grow during childhood, nearsightedness almost always
occurs before the age of 20. Often the degree of myopia increases as the body grows
rapidly, then levels off in adulthood. During the years of rapid growth, frequent changes
in prescription eyewear may be needed to maintain clear vision. It is important to bear in
mind that the frequent changes in prescription are not making the eyes "weaker".
During the growth period that occurs during the teen years the eye is also growing rapidly
and hence the degree of blur is also increasing. As the growth cycle slows the
prescription changes slow correspondingly.
How is myopia diagnosed and treated?
Myopia is often suspected when a teacher notices a child squinting to see a blackboard or
a child performs poorly during a routine eye screening. Further examination will reveal
the degree of the problem.
A comprehensive eye examination will detect myopia.
Periodic examinations should follow after myopia has been discovered to determine whether
the condition is changing, and whether a change in prescriptive eyewear is needed. Eye
exams also help to ensure that vision impairments do not interfere with daily activities.
Corrective concave (minus) lenses are prescribed to
help focus light more precisely on the retina, where a clear image will be formed.
Depending on the degree of myopia, glasses or
contact lenses may be needed all of the time for clear vision. If the degree of impairment
is slight, corrective lenses may be needed only for activities that require distance
vision, such as driving, watching TV or in sports requiring fine vision.
Nearsightedness in children:
School age children may have vision problems ranging from mild to severe. When problems
are suspected, it is important that the child have a comprehensive eye health examination
to determine the nature of the problem and to rule out serious eye diseases. When vision
conditions are treated properly, the child will enjoy the best possible sight.
To help a child cope with nearsightedness:
- Avoid referring to the child's eyes as "bad
eyes;" instead tell the child that his or her eyes just bend light differently and
corrective lenses are needed to help focus light rays.
- Ensure that they understand that nearsightedness
rarely disappears and that wearing spectacles may be necessary in the long-term, but that
this is not a disease.
- Use illustrations and simple explanations to help the
child understand how a differently-shaped eyeball may result in his or her being
nearsighted.
- Make the occasion of selecting new frames for lenses
a fun time.
- Consider contact lenses as an option.
- Do not restrict the child's activities because of
poor vision.
- Include the child in discussions about his or her
eyesight. Encourage the child to verbalize concerns about the adjustment to rapidly
changing vision.
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Presbyopia
Hold the book up close and the words appear blurred. Push the book farther away, and the
words snap back into sharp focus.
That's how most of us first recognize a condition
called presbyopia, a name derived from Greek words meaning "old eye." Eye
fatigue or headaches when doing close work, such as sewing, knitting or painting, are also
common symptoms. Because it is associated with aging, presbyopia is often met with a groan
-- and the realization that reading glasses or bifocals are inevitable
What causes presbyopia?
As we age, body tissues normally lose their elasticity. As skin ages, it becomes less
elastic and we develop wrinkles. Similarly, as the lenses in our eyes lose some of their
elasticity, they lose some of their ability to change focus for different distances. The
loss is gradual. Long before we become aware that seeing close up is becoming more
difficult, the lenses in our eyes have begun losing their ability to flatten and thicken.
Only when the loss of elasticity impairs our vision to a noticeable degree do we recognize
the change.
Recent research suggests that presbyopia occurs when
the lens keeps growing as people get older and the ligaments become too slack for the
muscles to work properly. This finding contrasts with the traditional view that aging
cause the focusing muscles to become weaker and the lens to become more inflexible.
How does the loss of elasticity affect sight?
The crystalline lens plays a key role in focusing light on the retina. When we are young,
the lens is flexible. With the help of tiny ciliary muscles, it changes shape, or
accommodates, for both near and distant objects by bending or flattening out to help focus
light rays. As we age, the lens becomes stiffer. Changing shape becomes more difficult.
Not only does focusing on near objects become more difficult, the eye is also unable to
adjust as quickly to rapid changes in focus on near and distant objects.
The flexibility of the lens begins to decrease in
youth. The age at which presbyopia is first noticed varies, but it usually begins to
interfere with near vision in the early 40's. Presbyopia affects everyone and there is no
known prevention for it.
How is the problem diagnosed and treated?
An accurate, thorough description of symptoms and a comprehensive eye health examination,
including a testing of the quality of your near vision, are necessary to diagnose
presbyopia.
Usually, the treatment for presbyopia is
prescription eyeglasses to help the eye accommodate for close-up work. Prescription lenses
(reading glasses) help refract light rays more effectively to compensate for the loss of
near vision.
If you do not have other vision problems, such as
nearsightedness or astigmatism, you may only need glasses for reading or other tasks
performed at a close range. If you have other refractive errors, such as nearsightedness,
bifocal or progressive addition lenses (in which the power of the lens changes gradually
towards the bottom to allow reading, without the reading portion of the bifocal lens being
obviously visible) are often prescribed.
Can I still wear contact lenses?
Yes, you have three options with contact lenses: Bifocal contact lenses, monovision, and
normal distance contact lenses with reading glasses. Generally, bifocal contact lenses are
not as successful as the normal "single vision" ones.
What lens option will work best for me?
You will be asked a number of questions about your usual lifestyle or daily activities -
to help determine the solution most suited to your needs. For instance, if you are a
librarian, your needs will be significantly different from those of a truck driver or
office worker.
Presbyopia is a gradual change, happening over a
number of years so your prescription will need to be updated periodically. Changes are
best made at your regular eye examination rather than after the need for change starts to
cause you difficulties.
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Double
Vision
If you see two of whatever you are looking at, you may have a condition known as double
vision, also referred to as diplopia. Double and blurred vision are often thought to be
the same, but they are not. In blurred vision, a single image appears unclear. In double
vision, two images are seen at the same time, creating understandable confusion for anyone
who has it.
What causes double vision?
There are two possible causes.
- Failure of both eyes to point at the object being
viewed, a condition referred to as "strabismus" or "squint". In
normal vision, both eyes look at the same object. The images seen by the two eyes are
fused into a single picture by the brain. If the eyes do not point at the same object, the
image seen by each eye is different and cannot be fused. The result is double vision. Why
might eyes not point in the same direction? Possibly because of a defect in the muscles
which control the movement of the eyes or in the control of these muscles through the
nerves and brain.
- Refractive. Light from an object is split into
two images by a defect in the eye's optical system. Cataracts may cause such a defect.
Strabismus is a more common cause of double vision
than is refractive defect.
What are its implications?
Double vision can be extremely troubling. The brain acts to alleviate the discomfort by
suppressing, or blanking out, one of the images. In young children, if this suppression
persists over a continued length of time, it can lead to an impairment of the development
of the visual system. The suppressed eye may get to the point where it is unable to see
well, no matter how good the spectacle or contact lens correction. Doctors call this
condition "amblyopia". Since it is a result of a defect in the interpretive
mechanisms of the eye and brain, it is more difficult to treat than a refractive condition
(one having to do with the eye's ability to bend light).
How is it treated?
Treatment of double vision consists of eye exercises, surgical straightening of the eye or
a combination of the two. Therapy is aimed at re-aligning the squinting eye where possible
without surgery and re-stimulating the part of the visual pathway to the brain that is not
working correctly.
If the double vision is due to the presence of
cataracts, referral for possible cataract surgery will be undertaken.
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Spots
& Floaters
Do you occasionally see specks or threadlike strands drifting across your field of vision?
Then, when you try to look at them, do they seem to dart away? If so, you're seeing what
eye care practitioners call spots or floaters.
While almost everyone sees a few spots at one time
or another, they can occur more frequently and become more noticeable as you grow older.
If you notice a sudden change in the number or size of spots, you should contact us right
away so you can be sure they are not the result of a more serious problem.
What are spots or floaters?
Spots are small, semi-transparent or cloudy specks or particles within the eye that become
noticeable when they fall within the line of sight. They may also appear with flashes of
light.
The inner part of your eye is made up of a clear,
jelly-like fluid known as the vitreous. As time passes the jelly-like fluid gradually
becomes more liquid in nature and cells and structural fibres detach and float around in
this jelly, resulting in the floaters that we commonly observe.
When flashes of light occur causing spots to become
noticeable, it can be a result of the jelly-like vitreous shrinking and pulling on the
retina. This tugging action stimulates the retinal receptor cells to "fire,"
causing the perception of light flashes.
Can these spots cause blindness?
Most spots are normal and rarely cause blindness. But spots can indicate more serious
problems. If you notice a change in the number and size of spots, a comprehensive eye
examination is in order to determine the cause.
On rare occasions, vitreous detachment can cause
small tears or holes in the retina. The damaged part of the retina subsequently does not
work properly and a blind or blurred spot in vision results. If untreated, retinal tears
or holes can continue to worsen and severe vision loss can result if the retina becomes
detached.
How are spots diagnosed?
In a comprehensive eye examination, your eyes will be evaluated with special instruments
that allow an examination of the health of the inside of your eyes and possible
observation of the spots.
This is often done after special drops are put in
your eyes to make the pupils larger (called dilation) to allow a larger view of the inside
of your eyes. These procedures provide the relevant information to detect spots.
How are spots treated?
While flashes and floaters are normally not serious or treatable, they can be symptoms or
signs of either vitreous or retinal detachment. In either of these cases, treatment with
lasers and/or surgical intervention may be necessary to preserve your vision. If you
notice a sudden increase or change in the number and type of spots and floaters, contact
us immediately.
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Cataracts
While a comprehensive eye examination can determine for certain if you have a cataract
forming, there are a number of signs and symptoms that may indicate a cataract. Among them
are:
- Gradual blurring or hazy vision where colors may seem
yellowed;
- The appearance of dark spots or shadows that seem to
move when the eye moves;
- A tendency to become more nearsighted because of
increasing density of the lens;
- Double vision in one eye only;
- A gradual loss of color vision;
- A stage where it is easier to see without glasses;
- The feeling of having a film over the eyes; and
- An increased sensitivity to glare, especially at
night.
What is a cataract?
A cataract is a clouding of the normally clear crystalline lens of the eye. This prevents
the lens from properly focusing light on the retina at the back of the eye, resulting in a
loss of vision. A cataract is not a film that grows over the surface of the eye, as
is often commonly thought.
Why are they called cataracts?
Sometimes cataracts can be seen as a milkiness on the normally black pupil. In ancient
times, it was believed this cloudiness was caused by a waterfall - or cataract - behind
the eye.
Who gets cataracts?
Cataracts are most often found in persons over the age of 55, but they are also
occasionally found in younger people, including newborns.
What causes cataracts?
It is known that a chemical change within the eye causes the lens to become cloudy. The
change may be due to advancing age or it may be the result of heredity, an injury or a
disease.
Excessive exposure to ultraviolet or infrared
radiation present in sunlight or from furnaces, cigarette smoking and/or the use of
certain medications are also cataract risk factors. Cataracts usually develop in both
eyes, often at different rates.
Can cataracts be prevented and treated?
Currently, there is no proven method to prevent cataracts from forming.
If your cataract develops to a point that daily
activities are affected, you will be referred to an eye surgeon who may recommend the
surgical removal of the cataract.
Prescription changes in your eyewear will help you
see more clearly until surgery is necessary, but surgery is the only proven means of
effectively treating cataracts. The surgery is relatively uncomplicated and has a very
high success rate
When will I need to have cataracts removed?
Cataracts may develop slowly over many years or they may form rapidly in a matter of
months. Some cataracts never progress to the point that they need to be removed. Usually,
you will be ready to have the cataract removed when it is having a significant adverse
effect on your lifestyle.
Our office will arrange a consultation with a
surgeon who will decide on the appropriate time for removal. Most people wait until the
cataracts interfere with daily activities before having them removed.
What happens after cataract surgery?
You, along with your doctors, will decide on the type of post-cataract vision correction
that you will use. Intraocular lens implants, inserted in your eye at the time of surgery,
serve as a "new lens" and are the most frequent form of visual correction. In
some cases, however, eyeglasses or contact lenses may also be needed to provide the most
effective post-cataract vision.
Cataract surgery has now developed to the point
where most procedures are completed in a day and overnight stays in hospital are
unnecessary. The results are usually excellent and patients are often able to appreciate a
significant improvement in vision almost immediately following surgery.
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Keratoconus (Conical Cornea)
Poor vision that cannot be corrected fully with glasses may indicate a condition known as
conical cornea or keratoconus. A rare condition, keratoconus primarily affects people in
their early 20's.
With keratoconus, the cornea, the "clear
window" at the front of the eye, may become thin and bow outwards. It is this
irregular distortion of the cornea that makes vision correction with glasses less than
optimal. For this reason other means of correcting vision are often necessary.
Vision correction with rigid gas permeable
lenses.
Mild to moderate keratoconus is best corrected with rigid gas permeable contact lenses,
which provide a smooth surface in front of the cornea, making clear vision possible.
Because the lens is rigid, the tears between the lens and the cornea form a 'liquid lens,'
which smoothes the irregularities of the cornea and makes clear vision possible again.
Soft lenses, which 'wrap' onto the cornea and take up its shape much more closely than
rigid lenses, are less successful at correcting keratoconus.
Corneal replacement surgery may be necessary.
As keratoconus progresses, some scarring of the cornea can occur. Eventually, contact
lenses may no longer be a successful treatment. Instead, the cornea may need to be
replaced surgically with a cornea of more regular shape. The prognosis for corneal
replacement surgery is generally very good.
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EYE DISEASES
Dry Eye
If your eyes sting, itch or burn, you may be experiencing the common signs of "dry
eye." A feeling of something foreign within the eye or general discomfort may also
signal dry eye.
What is dry eye?
Dry eye describes eyes that do not produce enough tears. The natural tears that your eyes
produce are composed of three layers:
- The outer oily layer, which prevents or slows
evaporation of the tear film;
- The middle watery layer; which moisturizes and
nourishes the front surface of the eye;
- The inner mucus layer, which helps maintain a stable
tear film.
Dry eye may occur because the volume of tears
produced is inadequate (we all produce fewer tears as we get older, and in some cases this
can lead to dry eye symptoms). It may result because the composition of the tears has
changed so that they are unstable and evaporate more quickly.
What causes dry eye?
Dry eye symptoms can result from the normal aging process. Exposure to environmental
conditions, as well as medications, such as antihistamines, oral contraceptives or
anti-depressants, can contribute to the symptoms of dry eye. Or, dry eye can result from
chemical or thermal burns to the eye. Dry eye may also be symptomatic of general health
problems or other diseases. For example, people with arthritis are more prone to dry eye.
Will dry eye harm my eyes?
If untreated, it can. Excessive dry eye can damage tissue and possibly scar the cornea at
the front of your eye, impairing vision. Dry eye can make contact lens wear more difficult
since tears may be inadequate to keep the lenses wet and lubricated. This can lead to
irritation and a greater chance of eye infection. Therefore, it is important to follow the
recommended treatment plan.
How is it diagnosed?
During the examination, you will be asked about your general health, use of medications,
and work and home environments to determine factors, which may be contributing to dry eye
symptoms. This information will help decide whether to perform specific dry eye tests.
To test for dry eye, diagnostic instruments that
allow a highly magnified view of your eyes or small strips of paper or thread and special
dyes to assess the quantity and quality of the tears may also be used.
How is it treated?
Dry eye cannot be cured, but your eyes' sensitivity can be lessened and measures taken so
your eyes remain healthy. The most frequent method of treatment is the use of artificial
tears or tear substitutes. For more severe dry eye, ointment can be used, especially at
bedtime. In some cases, small plugs may be inserted in the corner of the eyelids to slow
drainage and loss of tears.
To keep dry eye symptoms in check, you and your
optometrist need to work together. If you have increased dryness or redness that is not
relieved by the prescribed treatment, let us know as soon as possible.
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Conjunctivitis
Red, watery eyes, inflamed lids, blurred vision and a sandy or scratchy feeling in the
eyes may indicate that you have conjunctivitis. Pus-like or watery discharge around the
eyelids may indicate an infectious form of the disease, commonly known as "pink
eye."
Conjunctivitis is an inflammation or infection of
the conjunctiva, a thin, transparent layer covering the surface of the inner eyelid and
the front of the eye. It affects people of all ages.
What causes conjunctivitis?
The three main types of conjunctivitis are infectious, allergic and chemical. The
infectious form, commonly known as "pink eye," is caused by a contagious virus
or bacteria. Your body's allergies to pollen, cosmetics, animals or fabrics often bring on
allergic conjunctivitis. Irritants like air pollution, noxious fumes and chlorine in
swimming pools may produce the chemical form.
It is important to prevent spreading
conjunctivitis.
If contagious, measures can be taken to prevent spreading conjunctivitis to others.
- Keep your hands away from your eyes;
- Thoroughly wash hands before and after applying eye
medications;
- Do not share towels, washcloths, cosmetics or
eyedrops with others;
- Seek treatment promptly.
Small children, who may forget these precautions,
should be kept away from school, camp and the swimming pool until the condition is cured.
Certain forms of conjunctivitis can develop into a
serious condition that may harm your vision. Therefore, it is important to have
conjunctivitis diagnosed and treated quickly.
How is infectious conjunctivitis treated?
Infectious conjunctivitis, caused by bacteria, is usually treated with antibiotic eye
drops and/or ointment. Other infectious forms, caused by viruses, can't be treated with
antibiotics and must be fought off by your body's immune system. On occasions antibiotics
may be prescribed to prevent secondary bacterial infections from developing.
How are the allergic and chemical forms of
conjunctivitis treated?
The ideal treatment for both forms is to remove the cause of the allergy or irritation.
For instance, avoid contact with any animal if it causes an allergic reaction. Wear
swimming goggles if chlorinated water irritates your eyes. In cases where these measures
won't work, prescription and over-the-counter eye drops are available to help relieve the
discomfort.
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Blepharitis
If your eyelid rims are red and irritated, if they burn and itch or if you've noticed an
oily discharge or scaly skin around them, you may have an inflammatory problem called
"blepharitis". Some people describe it as "psoriasis of the eyelids".
Blepharitis may be either of two main types or a
combination of them.
Seborrheic blepharitis
Characterized by an excessive discharge of oil/grease from the skin around the eyelids. It
is usually accompanied by similarly greasy hair and skin.
Staphylococcal blepharitis
A bacterial infection. It is more likely to result in infective eyelid conditions, such as
styes.
What are the treatments?
To treat seborrheic blepharitis, keep the lid edges and surrounding skin clean by
regularly scrubbing the area with a mild soap. Medicated pads specifically designed for
this are also available. For staphylococcal blepharitis, ointments containing antibiotics
and sulfonamides should be applied to the edges of the eyelids with a cotton ball.
While over-the-counter treatments for blepharitis
are available, it is advisable to seek professional help the first time you experience the
condition. If you have had blepharitis before and had experience with its treatment, using
the over-the-counter ointments may be adequate. But, whether you have had the condition
before or not, if the blepharitis is infectious, you should get appropriate treatment as
soon as possible to reduce the risk of having the infection spread and cause more serious
conditions.
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Glaucoma
The most scary thing about glaucoma is that it can steal your vision gradually and without
your noticing. The best defense against glaucoma is a regular eye examination. Glaucoma
most often strikes people over age 50. But it is recommended that during adult life
everyone be tested at least every two years.
Some people with glaucoma do experience symptoms,
but symptoms vary depending on the type of glaucoma.
Primary open-angle glaucoma
By far the most common type, primary open-angle glaucoma develops gradually and
painlessly. Since there are no early warning signs, it can slowly destroy your vision
without your knowing it. The first indication may only occur after some considerable
vision loss.
Acute angle-closure glaucoma
This results from a sudden blockage of the drainage channels within your eye, causes a
rapid build-up of pressure inside your eye accompanied by blurred vision, the appearance
of colored rings around lights and sometimes extreme pain or redness in the eyes.
What is glaucoma?
The build-up of pressure inside your eye leads to glaucoma. Aqueous fluid, which fills the
space at the front of the eye just behind the cornea, is made behind the iris (the colored
part of the eye) in the ciliary body. It flows through the pupil (the dark hole in the
center of the iris), and drains from the 'anterior chamber angle,' which is the junction
between the edge of the iris and the cornea. If this outflow of liquid is impaired at all,
there is a build-up of pressure inside the eye that damages the optic nerve, which carries
visual images to the brain. The result is a loss of peripheral vision. Thus, while
glaucoma sufferers may be able to read the smallest line on the vision test, they may find
it difficult to move around without bumping into things or to see moving objects to the
side.
What causes glaucoma?
Some causes are known, others are not. Causes differ depending on the type of glaucoma.
The exact cause of open-angle glaucoma, where the drainage channels for the aqueous appear
to be open and clear, is not known. Closed-angle glaucoma can occur when the pupil dilates
or gets bigger and bunches the iris up around its edge, blocking the drainage channel. An
injury, infection or tumor in or around the eye can also cause internal eye pressure to
rise either by blocking drainage or displacing tissues and liquid within the eye. A mature
cataract also can push the iris forward to block the drainage 'angle' between the iris and
the cornea. Glaucoma can occur secondarily to a number of other conditions, such as
diabetes, or as a result of some medications for other conditions.
Who gets glaucoma?
Glaucoma most frequently occurs after age 40, but can occur at any age.
If you're of African heritage, you are more likely
to develop open-angle glaucoma -- and at an earlier age -- than if you're Caucasian.
Asians are more likely to develop narrow-angle glaucoma.
You have a higher risk of developing glaucoma if a
close family member has it or if you have high blood pressure or high blood sugar
(diabetes). There is also a greater tendency for glaucoma to develop in individuals who
are nearsighted. Those at heightened risk for glaucoma should have their eyes checked at
least once a year.
Why is glaucoma harmful to vision?
The optic nerve, located at the back of the eye, carries visual information to the brain.
As the fibers that make up the optic nerve are damaged by glaucoma, the amount and quality
of information sent to the brain decreases and a loss of vision occurs.
Will I go blind from glaucoma?
If diagnosed at an early stage, glaucoma can be controlled and little or no further vision
loss should occur. If left untreated, side awareness (peripheral vision) and central
vision will be destroyed and blindness may occur.
How is glaucoma detected?
Tests for glaucoma are part of a comprehensive eye examination. A simple and painless
procedure called tonometry measures the internal pressure of your eye. Ophthalmoscopy
examines the back of the eye to observe the health of the optic nerve. A visual field
test, a very sensitive test that checks for the development of abnormal blind spots, may
also be completed.
How is glaucoma treated?
Glaucoma is usually treated with prescription eye drops and medicines. In some cases,
surgery may be required to improve drainage. The goal of the treatment is to prevent loss
of vision by lowering the pressure in the eye.
Will my vision be restored after treatment?
Unfortunately, any vision loss as a result of glaucoma is permanent and cannot be
restored. This is why regular eye examinations are important.
Glaucoma cannot be prevented, but early detection
and treatment can control glaucoma and reduce the chances of damage to the eye and a loss
of sight.
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Age
Related Macular Degeneration (ARMD)
Age related macular degeneration or ARMD is the most common cause of irreversible vision
loss for people over the age of 60. It is estimated that 2.5 million people in developed
countries will suffer visual loss from this disorder and that there are approximately
200,000 new cases diagnosed every year.
Macular degeneration is most common in people over
the age of 65 but there have been some cases affecting people as young as their 40s and
50s. Symptoms include blurry or fuzzy vision, straight lines like telephone poles and
sides of buildings appear wavy and a dark or empty area may appear in the center of
vision.
What is the Macula?
The macula is the small portion of the retina located at the center of this light
sensitive lining at the back of the eye. Light rays from objects that we are looking at
come to a focus on the retina and are converted into electrical impulses that are then
sent to the brain. The macula is responsible for sharp straight-ahead vision necessary for
functions such as reading, driving a car and recognizing faces.
The effect of this disease can range from mild
vision loss to central blindness. That is, blindness "straight ahead" but with
normal peripheral vision from the non-macular part of the retina which is undamaged by the
disease.
Two types of Macular Degeneration
Ninety percent of ARMD is of the "atrophic" or "dry" variety. It is
characterized by a thinning of the macular tissue and the development of small deposits on
the retina called drusen. Dry ARMD develops slowly and usually causes mild visual loss.
The main symptom is often a dimming of vision when reading.
The second form of ARMD is called
"exudative" or "wet" because of the abnormal growth of new blood
vessels under the macula where they leak and eventually create a large blind spot in the
central vision. This form of the disease is of much greater threat to vision than the more
common dry type.
What are the causes of ARMD?
Unfortunately, the cause of this eye condition is not fully understood but it is
associated with the aging process. As we age, we become more susceptible to numerous
degenerative processes like arthritis, heart conditions, cancer, cataracts and macular
degeneration. These conditions may be caused by the body's overproduction of free
radicals.
During the metabolic process, oxygen atoms with an
extra electron are released. These extra electrons are quite destructive and cause
cellular damage, alter DNA, and are thought to be at least partially responsible for many
of the degenerative diseases mentioned above. The production of these free radicals is
normal during metabolism but the body produces its own "anti-oxidants" to
neutralize them.
Some of the vitamins in the food we eat also have
anti-oxidant properties. These are vitamins A, C, E and beta-carotene. Unfortunately,
smoking, poor nutrition and other lifestyle factors result in the body producing too many
free radicals. For this reason, lifestyle factors may contribute to the risk of ARMD.
There is some evidence to suggest that ARMD has a
genetic basis, as the condition tends to run in families. The exact nature of this
familial tendency, however, has not been clarified. It has been suggested from twin
studies that there is a defect in the genes responsible for the integrity and health of
the retina.
Exposure to certain types of light may also play a
role. Studies performed on fishermen in the Chesapeake Bay suggest that long-term exposure
to ultraviolet light from the sun may increase the risk of ARMD and other eye conditions
such as the development of cataracts
It has also been hypothesized that hyperopia or
farsightedness may also play a role in the development of the disease. It is thought that
the shortening of the eye in hyperopia may cause changes in the membrane below the macula
and in its blood vessels.
In the dry form of the disease, some form of
inflammation may also be a factor although what causes the inflammation is not known.
How is it treated?
Although researchers are spending a great deal of time investigating the cause and
treatment of ARMD, there is no real cure available. The goal of current treatment efforts
is to attempt to stabilize the condition.
For the more severe wet form of the disease, doctors
have tried laser photocoagulation. This treatment, however, is not without dangers and is
only beneficial in the very early stages of the condition, which is why early detection is
so important. This technique involves directing a beam of laser light at the abnormal
blood vessels in order to destroy them and prevent their leaking. Provided that the blood
vessels have not grown under the macula, this treatment can be helpful in arresting the
progress of the disease. If the blood vessels are already under the macula, the laser may
cause scarring and permanent vision loss.
Several new treatments are under development and
scientific evaluation.
A new type of treatment called photodynamic shows
promise. A drug, injected into the arm travels to the affected eye and is then exposed to
a non-thermal red light. This light activates the drug to close and seal off the abnormal
blood vessels. The entire treatment only takes about 30 minutes and requires no
anesthetic.
Treatment using proton beams, which release power at
predetermined target site and depth, has also been experimentally tested for treatment of
wet-ARMD.
Are Vitamins and Nutrition Useful?
No treatment exists for the dry form but many doctors are convinced that a combination of
specific vitamins and minerals helps slow the progression of the disease. This has yet to
be confirmed scientifically but there are valid reasons for attempting this therapy.
Anti-oxidant vitamins may help to neutralize the free radicals that are associated with
this degenerative process. Zinc, one of the most common trace minerals in our body, is
highly concentrated in the retina and surrounding tissues and is a requirement for
chemical reactions in the retina.
Fat-soluble anti-oxidant vitamins like vitamin A and
vitamin E are stored in the body and can increase to toxic levels if over used and zinc
may interfere with other trace minerals like copper. Caution should therefore be exercised
in the use of vitamins and minerals.
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Styes
(hordeolum)
A small area of redness and pain on the margin of your eyelid may indicate that you have a
stye, known in medical terms as an external hordeolum. A stye is a blocked gland at the
edge of the lid that has become infected by bacteria, usually Staphylococcus aureus.
The area of redness and pain will eventually form a
'point'. Until this occurs, warm compresses should be applied to the area for 15 minutes
three-to-four times a day. The compresses should be followed by the application of
sulphonamide or antibiotic ointment to the stye, available by prescription. Check with
your eye care practitioner.
Once the stye has 'pointed', it can usually be
expressed (squeezed gently to empty its contents), after which the lids should be cleaned.
Treatment with the ointment should be continued until symptoms have cleared. Sometimes it
is necessary for the stye to be lanced to assist with expression.
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Diabetes
and the Eyes
Diabetes, a disease that prevents your body from making or using insulin to break down
sugar in your bloodstream, can affect your eyes and your vision.
Fluctuating or blurring of vision, intermittent
double vision, loss of peripheral vision and flashes and floaters within the eyes may be
symptoms related to diabetes. Sometimes the early signs of diabetes are detected during a
thorough eye examination.
Diabetes can cause changes in nearsightedness and
farsightedness and lead to premature presbyopia (the inability to focus on close objects).
It can result in cataracts, glaucoma, a lack of eye muscle coordination (strabismus) and
decreased corneal sensitivity. The most serious eye problem associated with diabetes is
diabetic retinopathy, which, if not controlled, can lead to blindness.
What is retinopathy?
Diabetic retinopathy occurs when there is a weakening or swelling of the tiny blood
vessels in the retina of your eye, resulting in blood leakage, the growth of new blood
vessels and other changes
Can vision loss from diabetes be prevented?
Yes, in a routine eye examination, your eye care practitioner can diagnose potential
vision-threatening changes in your eyes that may be treated to prevent blindness. However,
once damage has occurred, the effects are usually permanent. It is important to control
your diabetes as much as possible to minimize the risk of developing retinopathy.
How is diabetic retinopathy treated?
In the early stages, diabetic retinopathy can be treated with laser therapy. A bright beam
of light is focused on the retina, causing a burn that seals off leaking blood vessels. In
other cases, surgery inside the eye may be necessary. Early detection of diabetic
retinopathy is crucial. It is routinely screened for in an eye examination.
Are there risk factors for developing
retinopathy?
Several factors that increase the risk of developing retinopathy include smoking, high
blood pressure, excessive alcohol intake and pregnancy.
How can diabetes-related eye problems be
prevented?
Diabetes-related eye problems can be prevented by monitoring and maintaining control of
your diabetes. See your physician regularly and follow instructions about diet, exercise
and medication. A thorough eye examination when first diagnosed as a diabetic, at least
annually thereafter, is recommended.
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CONTACT LENSES
Are
Contacts For You?
The vast majority of people requiring vision correction can wear contact lenses without
any problems. New materials and lens care technologies have made today's contacts more
comfortable, safer and easier to wear. Consider the questions and answers below to help
assess whether they're a choice you should consider.
Contact lens wear may be difficult if:
- Your eyes are severely irritated by allergies;
- You work in an environment with lots of dust and
chemicals;
- You have an overactive thyroid, uncontrolled
diabetes, or severe arthritis in your hands; or
- Your eyes are overly dry due to pregnancy or
medications you are taking.
After a thorough eye examination, your suitability
for contact lenses and the specific contact lens option that best meets your requirements
will be determined.
What are the advantages of wearing contact
lenses?
- Many wearers feel that contact lenses show their eyes
in a better light or don't like the appearance of eyeglasses.
- Better vision correction due to the reduced
obstruction from eyeglass frames.
- They provide excellent peripheral vision.
- No fogging up in warm rooms.
- No splattering during rain showers.
- Less hassle as they don't get in the way during
sports and other recreational activities.
What are the disadvantages?
- Contact lenses require getting used to. New soft lens
wearers typically adjust to their lenses within a week. Rigid lenses generally require a
somewhat longer adjustment period.
- Except for some disposable varieties, almost all
lenses require regular cleaning and disinfection, a process that, although requiring only
a few minutes, is more than some people want to undertake.
- Some types of lenses increase your eyes' sensitivity
to light.
What lifestyle do you lead? What kind of work do
you do?
For those involved in sports and recreational activities, contact lenses offer a number of
advantages. In addition to providing good peripheral vision, eliminating the problem of
fogged or rain splattered lenses, and freeing you from worries about broken glasses,
contact lenses also mean you can wear non-prescription protective eye wear. Looking
sideways through the lenses of glasses leads to prismatic effects because you are not
looking through their centers. Your eyes have to coordinate differently to cope with this.
This does not happen with contact lenses because you always look through the centers of
the lenses as they move with your eye movements.
Your occupation and work environment should also be
taken into consideration. People whose work requires good peripheral vision may want to
consider contacts. Those who work in dusty environments or where chemicals are in heavy
use are likely to find spectacles more comfortable.
Do you like wearing glasses?
Do you like the way glasses feel? Do you like how you look in them? No longer is it really
necessary to choose between either contacts or glasses. Some of today's contacts are so
easy to wear that you can use them intermittently -- for special occasions, while
participating in sports or to match your fashions.
New single-use, one-day disposable lenses are
comfortable and do not require cleaning. They may be easily interchanged with glasses.
How Contact Lenses Correct Vision
Contact lenses are designed to rest on the cornea, the clear outer surface of the eye.
They are held in place mainly by adhering to the tear film that covers the front of the
eye and, to a lesser extent, by pressure from the eyelids.
As the eyelid blinks, it glides over the surface of
the contact lens and causes it to move slightly. This movement allows the tears to provide
necessary lubrication to the cornea and helps flush away debris between the cornea and the
contact lens.
Contact lenses are optical medical devices,
primarily used to correct nearsightedness, farsightedness, astigmatism and presbyopia. In
these conditions, light is not focused properly on the retina, the layer of nerve endings
in the back of the eye that converts light to electrochemical impulses. When light is not
focused properly on the retina, the result is blurred or imperfect vision.
When in place on the cornea, the contact lens
functions as the initial optical element of the eye. The optics of the contact lens
combine with the optics of the eye to properly focus light on the retina. The result is
clear vision.
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Types
of Contacts
Confused about contacts? Advances in contact lens technologies have created many options
in addition to hard and soft lenses. Today, contact lenses are likely to be described in
one or several of the following ways.
By their prescribed wearing period: The time that
the lenses are left in the eyes.
- Daily Wear (Up to 18 hours)
- Extended Wear (For overnight use, up to seven days)
By their replacement schedule: The time interval for
replacing lenses.
- Planned - (Frequent replacement: 1 month, 1-2 weeks;
daily disposable)
- Unplanned, or Conventional Replacement - (No specific
time schedule before lenses are replaced)
By the type of vision correction for which they are
designed:
- Spherical (For near- or farsightedness -- myopia or
hypermetropia)
- Toric (For astigmatism)
- Bifocals (For presbyopia)
By the type of tint they have:
- Tinted to improve handling only
- Tinted to enhance your eye color (For light-color
eyes)
- Tinted to change your eye color (Opaque tints for
light or dark eyes)
- Clear - without tints
Of course, contact lenses are also still described
by the basic type of material of which they are made.
- Soft (hydrophilic)
- Rigid Gas Permeable
By Wearing Period
Daily Wear: Lenses prescribed for daily wear are to be worn only during waking
hours, usually up to a maximum of 18 hours. Daily wear lenses are removed at night and
cleaned and disinfected after each removal.
Extended Wear: Extended wear lenses may be
worn on an overnight basis for up to seven consecutive days (six nights). You should wear
your lenses on an extended wear basis only on the advice of your optometrist.
Extended wear lenses generally have a higher water
content or thinner center thickness than other lenses and permit more oxygen to reach the
eye. However, their use has been linked to a higher incidence of eye problems. Extended
wear lenses need to be cleaned and disinfected at recommended intervals or discarded after
use.
By Replacement Period
Contact lens are often prescribed with a specific replacement schedule suitable to your
specific needs. Planned (or Frequent) Replacement contacts are disposed of and replaced
with a new pair according to a planned schedule. Unplanned replacement lenses (often
called conventional lenses) are not replaced according to a pre-determined schedule. They
are typically used for as long as they remain undamaged, usually around 12 months for soft
lenses.
Why replace lenses frequently?
Almost immediately after they are inserted, contact lenses begin attracting deposits of
proteins and lipids. Accumulated deposits, even with routine lens care, begin to erode the
performance of your contacts and create a situation that presents a greater risk to your
eye health.
A specific replacement schedule helps to prevent
problems before they might occur. Contact lens wearers, in turn, enjoy the added comfort,
convenience and health benefits of a planned replacement program. Planned replacement
lenses are generally a thinner design or are made of different, more fragile materials
with a higher water content than unplanned replacement or conventional contact lenses.
Based on a complete assessment of your needs, a
prescription for planned replacement lenses may call for replacement:
- Quarterly,
- Monthly
- Every 1-2 weeks
- Daily
Except for daily disposables, planned replacement
lenses require cleaning and disinfection after each period of wear unless they are
discarded immediately upon removal. Planned replacement lenses can be worn as daily wear
-- removed before sleep -- or as extended wear, if recommended by your practitioner.
By Type of Vision Correction Required
Contact lenses may be identified by the type of refractive error they are designed to
correct.
- Spherical contact lenses for nearsightedness (myopia)
and farsightedness (hypermetropia);
- Toric contact lenses for astigmatism;
- Bifocal lenses for presbyopia, the loss of ability to
focus on reading or close-up activities.
As an alternative to special bifocal contact lenses,
many practitioners use a system called monovision where one eye is fitted with a distance
lens and the other with a reading lens. Approximately two-thirds of patients adapt to this
type of contact lens wear.
By Type of Tint
Contact lenses may be described as clear or tinted. Tints are used to make lenses more
visible during handling, or for therapeutic or cosmetic reasons. Tints can enhance eye
color, or change it altogether.
Three categories of tinted contact lenses are
available.
- Cosmetic enhancement tints are translucent and are
designed to enhance your natural eye color. They are best for light-colored eyes (blues,
greens, light hazel or grays). When wearing these tints, the color of your eye is a blend
of the lens tint and your natural eye color and iris pattern.
- Opaque or "cosmetic" tints change the color
of your eyes whether they are dark or light. The pattern on the lens, which is colored,
overlies the colored part of your eye, res
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