Fast Facts Farsightedness or hyperopia occurs when the eyeball is too short for the focusing power of the lens and cornea. This causes light rays to focus behind the retina. As a result, the eye sees distant objects more clearly while near objects appear blurred. In essence, the eye is underpowered. To correct hyperopia, a "plus" lens containing additional optical power is needed to permit sharp vision of near objects.
Nearsightedness or Myopia occurs when the eyeball is too long for the focusing power of the lens and cornea. The result is an overpowered eye that causes images to focus in front of the retina. A myopic eye sees near objects within a certain range very clearly while distance vision appears blurry at all times. An estimated 70 million people in the U.S. suffer from myopia. To correct myopia, a 'minus' lens is required to push the image to the back to the retina permitting sharp distance vision.
Astigmatism is a common visual distortion caused by an irregularly shaped cornea. The surface of the cornea is toric, oblong in shape like the side of a football, instead of perfectly spherical like a basketball. One surface of the football is long with a shallow curve while the other surface is short with a steep curve. Light rays passing through an oblong cornea bend unequally, causing two focusing points. The result is blurred vision at most distances. Astigmatism is typically present at birth. Over time the condition may slowly increase but generally it remains relatively stable over a lifetime. Forty-five percent of people who require vision correction have some degree of astigmatism. Symptoms include squinting, occasional headaches and eye strain. Astigmatism often accompanies myopia and hyperopia.
Presbyopia, Greek for "aging eye," is caused by a combination
of natural aging, the hardening of the eye's crystalline lens, a transparent
body in the front of the eye that serves to focus light rays on the
retina, and a weakening of the focusing muscles. As people reach
their 40s, the crystalline lens grows thicker and begins to lose its
elasticity. Gradually, the eye muscle control diminishes and
people find it increasingly difficult to focus on near objects.
To compensate for the reduced focusing ability the tendency is to
hold reading material further away. Eventually the arms become
too short resulting in blurred vision and eye strain.
Dry eye syndrome is a chronic lack
of sufficient lubrication and moisture in the eye. Consequences
extend from subtle but constant irritation to ocular inflammation
of the front of the eye. It is particularly bothersome for wearers
of contact lenses, the elderly, certain lifestyles, medications, and
visual demands.
Dry eye syndrome has several causes. It occurs as a part of
the natural aging process, especially during menopause; as a side
effect of such medications as antihistamines, antidepressants and
birth control pills; the use of cigarettes, marijuana, or because
you live in a dry, dusty or windy climate. Dry eyes are also
a symptom of systemic diseases such as lupus, rheumatoid arthritis
or Sjogren's syndrome (a triad of dry eyes, dry mouth, and rheumatoid
arthritis or lupus). Age Related Macular Degeneration
Age related macular degeneration or AMD 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
vision loss from this disorder and that there are approximately 200,000
new cases diagnosed every year. The second form of AMD 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. 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 appearing wavy and a dark or empty area appearing in the center of vision. There currently is no treatment of macular degeneration. Results of a large multi-factorial study found that the ingestion of certain vitamins high in antioxidants help slow the progression of the dry form of macular degeneration. Several new treatments show promise in not only slowing but may also reverse the degeneration for the wet form. Glaucoma can steal your vision gradually and without you noticing, yet glaucoma is a serious disease that can result in severe loss of sight. Glaucoma is considered a 20 year disease in that it can very slowly lead to the loss of vision. The best defense against glaucoma is regular eye examinations. Glaucoma most often strikes people over age 50, but it is recommended that during adult life everyone be tested at least every two years.
Glaucoma is defined as the gradual deterioration of the optic nerve
that is located at the back of the eye and 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. The result
is the gradual loss of functional 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, such as cars. The
leading theory as to the cause of glaucoma is that a build-up of pressure
inside the eye gradually leading to the destruction of retinal cells.
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. Glaucoma most frequently occurs after age 40, but can occur at any age. African Americans are more likely to develop open-angle glaucoma and at an earlier age than Caucasians. 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. If diagnosed at an early stage, glaucoma can be slowed so that little or no further vision loss should occur. If left untreated however, side awareness (peripheral vision) and central vision will be destroyed and blindness may ultimately occur.
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