Myopia is the medical term for nearsightedness. It means that the eye sees distant images as blurred or fuzzy. For some people that distance may be only a foot or two.

Myopia is caused by light being focused in front of instead of on the retina of the eye. The cornea (the clear front part - or window - of the eyeball) is the eye's major focusing part. Corneal curve determines its focusing power. The steeper, or more curved, the cornea, the greater the focusing power.

Most times in myopia, the cornea is so curved that it has too much focusing power. If this curve is lessened or made flatter, then light is no longer focused as far forward in the eye but rather nearer the retina.

It is generally believed that there is a genetic predisposition to myopia. The condition may begin anytime from early childhood until the late teens, but it usually stabilizes in the early twenties.

Figure 1: The nearsighted eye

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Hyperopia (Farsightedness)

Hyperopia, or farsightedness, is a condition that causes a point in space to focus behind the retina. Often, farsighted people can see distant objects clearly but have difficulty reading. As a hyperopic person ages, he or she can also lose distance vision, because the eye loses its ability to change as easily. Therefore, when a person is farsighted, her or she often needs corrective lenses for both distance and near vision.

Hyperopia is caused when the eye is too short from front to back, or when there is a weakness in the focusing power of the lens or cornea. The focal point of parallel lines in a farsighted person is behind the retina.

Hyperopia generally is present from birth and usually is diagnosed in early childhood. Hyperopia tends to run in families, and it gets worse with age.

Figure 1: The farsighted eye

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Astigmatism

Distorted vision, medically known as astigmatism, is a condition in which vertical lines might be in focus, but not horizontal lines, or vice versa. Diagonal lines might also be out of focus. Distant points in space become a blur on the retina.

Astigmatism is caused by uneven curvature of the cornea. It results when one axis is stronger than the other, causing a blurring on the retina. In other words, one axis focuses differently than the other. High astigmatism can cause double or ghost images.

A person can have a little or a lot of astigmatism. Sometimes it occurs in conjunction with nearsightedness or farsightedness. Astigmatism usually is present from birth, and it may change with age.

Figure 1: The astigmatic eye

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Cataracts

Many people think a cataract is a skin growth over the eyes or something outside of the eye that blocks vision. Actually, a cataract is cloudiness or opacity in the lens inside the eye that gradually blurs sight. One of the most noticeable differences is that after cataracts have formed, colors seem less brilliant, almost muted.

The complete biochemical cause of cataracts is not known. While most cataracts develop gradually during aging, some occur after eye trauma or inflammation. Cataracts can also be associated with diabetes, gout, and other diseases. Less frequently, cataracts can be congenital, affecting babies or young people.

A recent study identified the first clear link between exposure to a particular kind of ultraviolet light (sunlight - UVB) and the formation of cortical cataracts, a faster growing type of cataract that accounts for about one-third of the cataract operations performed each year.

Blurred vision, the key symptom of cataracts, gradually worsens over a period of months or even years. Colors become less distinct, and often vision fades, especially in dim light. Night driving may be greatly impaired. Cataracts usually develop bilaterally, but progress at different rates so vision in one eye may be better than in the other.

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One-stitch, no-patch cataract implant surgery
Phaecoemulsification
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Glaucoma

Glaucoma, an eye disease that is fairly common in adults over age 35, is one of the leading causes of blindness in the United States.

Glaucoma is a condition in which fluid in the eye is blocked, causing increased pressure that can impair the functioning of the retina and optic nerve, both vital to good vision.

Prompt diagnosis and treatment have proved to be effective in minimizing loss of vision due to glaucoma. If treated too late or not at all, glaucoma can eventually lead to blindness.

Trabeculectomy

Diabetic retinopathy

Individuals who have diabetes mellitus already understand that their bodies do not use and store sugar properly. High blood-sugar levels can damage blood vessels in the retina; that damage is referred to as diabetic retinopathy.

There are two types of diabetic retinopathy: nonproliferative (NPDR) and proliferative (PDR). Nonproliferative (NPDR) is an early stage of diabetic retinopathy, in which tiny blood vessels leak blood or fluid, causing the retina to swell or form deposits called exudates. Many people with diabetes have mild NPDR, which usually does not affect their vision. When it is affected, it is the result of macular edema and/or macular ischemia.

Macular edema is swelling or thickening of the macula (a small area in the center of the retina that allows one to see fine details clearly) caused by fluid leaking from retinal blood vessels. It is the most common cause of visual loss in diabetes. Macular ischemia occurs when small blood vessels (capillaries) close. Vision blurs because the macula no longer receives sufficient blood supply to work properly.

PDR is present when abnormal new vessels begin growing on the surface of the retina or optic nerve. The main cause of PDR is widespread closure of retinal blood vessels, preventing adequate blood flow. The retina responds by growing new blood vessels in an attempt to supply blood to the area where the original vessels closed.

Unfortunately, the new, abnormal blood vessels do not re-supply the retina with normal blood flow. The new vessels are often accompanied by scar tissue that may cause wrinkling or detachment of the retina.

PDR may cause more severe vision loss than NPDR because it can affect both central and peripheral vision.

A medical eye examination is the only way to find changes inside your eye. An ophthalmologist can often diagnose and treat serious retinopathy before you are aware of any vision problems. If the doctor finds diabetic retinopathy, he or she may order color photographs of the retina or a special test called fluorescein angiography to find out if you need treatment. In this test, a dye is injected in your arm and photos of your eye are taken to detect where fluid is leaking.

Laser surgery
Vitrectomy

Macular degeneration

The macula, a very small area in the center of the retina, is the point on which light rays meet as they are focused by the cornea and lens of the eye. Like the film in a camera, the retina receives images that come through the "camera-like" lens. If the macula is damaged, the central part of the images is blocked, as if a blurred area had been placed in the center of the picture. The images around the blurred area may be clearly visible.

Macular degeneration is damage to or breakdown of the macula. The eye still sees objects to the side, since peripheral (side) vision is not usually affected. Fortunately, for this reason, macular degeneration, by itself, does not result in total blindness. However, it can make reading or close work difficult or impossible without the use of special low-vision optical aids.

Although macular degeneration most often occurs in older people, aging alone does not always result in central vision loss. Nevertheless, macular degeneration is the leading cause of impairment of reading and close-up vision in the United States.

The most common form of macular degeneration is called involutional macular degeneration. It accounts for 70% of all cases, and is associated with aging. It is caused by a breakdown or thinning of the tissues of the macula.

About 10% of macular degeneration is known as exudative macular degeneration. In this case, very fine blood vessels that nourish the back of the eye break or leak and cause scar tissue to form. This often leads to the growth of new abnormal blood vessels in the scar tissue. Because these newly formed vessels are especially fragile, they rupture easily and may leak. Blood and leaking fluid destroy the macula and cause further scarring. Vision becomes distorted and blurred, and dense scar tissue severely blocks out central vision.

Other types of macular degeneration are inherited, may occur in juveniles, and are not associated with the aging process. Occasionally, injury, infection, or inflammation may also damage the delicate tissue of the macula.

If only one eye is affected, macular degeneration is hardly noticeable in the early stages, especially if the other eye is normal. This condition often involves one eye at a time, so it may be quite a while before a person notices visual problems.

Early detection is important since people may not realize their vision is impaired. Periodic eye examinations by an ophthalmologist are appropriate if there is a family history of retinal problems. Early diagnosis may prevent further damage or aid the individual in making a visual adjustment with low-vision aids.

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Zinc

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