The eye is an extraordinary and intricate organ. Each eye contains more than twenty parts. Its function is highly specialized. There are numerous disorders and diseases of the eye, some common, some rare. Many vision problems can be corrected with eyeglasses, others cannot. Following is information on some of the more common eye conditions.
Age-Related Macular Degeneration (AMD):
The macula is in the center of the retina, located at the back of the eye. It allows perception of fine detail. AMD destroys sharp central vision, such as that needed for reading and driving.
AMD is the leading cause of vision loss in people over the age of 60. It is painless, and can cause a slow or rapid decrease in vision. Risk factors include age, smoking history, obesity, race (most common in Caucasians), and gender (more common in women).
There are two types of AMD: wet and dry. In wet AMD, abnormal blood vessels behind the retina grow under the macula and leak fluid. The first sign is often straight lines appearing crooked. It can develop rapidly. In dry AMD, light-sensitive cells in the macula break down, and blurred vision is usually the first sign. It develops more slowly. More than 85% of AMD cases are the dry form.
There is no current medical treatment for dry AMD; use of aids, such as (prescription eyeglasses) that magnify print, can be helpful. Wet AMD can sometimes be treated with laser therapy, a process known as photodynamic therapy (PDT).
Posterior Vitreous Degeneration (PVD):
The vitreous is the clear jelly-like substance that fills the eye between the lens and the retina. It is 99 percent water, 1 percent collagen. The vitreous is attached to the retina.
As people age, the vitreous changes shape and begins to pull away from the retina. When it does, people notice floaters—dots, circles, cobwebs, or lines—or flashing lights. The flashing occurs as the vitreous pulls on light-sensitive areas of the retina, sending the brain a signal it interprets as light.
There is no treatment for PVD; eventually the brain adapts to the floaters and people adjust to them. It does not cause permanent sight loss, though it can lead to retinal detachment if the vitreous pulls hard enough to tear the retina. Retinal detachment is treated separately from PVD (see below).
The optic nerve is attached to the back of the eye near the macula, the center of the retina. It is responsible for sending electrical impulses to the brain to form images when light enters the retina.
In order for the eye to retain its shape, it needs to maintain a certain amount of pressure. As people age, pressure changes can occur and/or the optic nerve can weaken. When the optic nerve is damaged at the point where it leaves the eye, glaucoma occurs.
There are four types of glaucoma: chronic, acute, secondary, and developmental. Chronic glaucoma is the slow rising of eye pressure with gradual loss of vision. Acute glaucoma is sudden blockage of the flow of aqueous fluid in the eye with rapid loss of vision. Secondary glaucoma occurs when the rise in eye pressure is related to another disease or disorder in the body. Developmental glaucoma is a serious congenital condition in babies, related to the malformation of the eye.
Treatment for glaucoma consists of reducing the pressure in the eye and increasing blood supply to the optic nerve. Eye drops are commonly used, and may be followed by laser therapy, or trabeculectomy. Treatment cannot restore vision loss that has already occurred, but can slow down or prevent further loss of sight.
The retina is the thin layer of nerve tissue that lines the back of the eye. It focuses light that enters the eye through the lens and sends impulses along the optic nerve to the brain, where images are formed.
When the retina weakens or is damaged, such as from glaucoma or trauma, a hole or tear can develop. Fluid leaks through the tear and the retina begins to detach from the rear of the eye. Because a segment of retina peels away, it leaves a blind spot where light can no longer be focused.
The first sign of retinal detachment is the development of a shadow spreading across the vision field of one eye, similar to a shade being pulled down. There may also be flashes of light or floaters in the visual field.
If mild, retinal detachment is repaired by laser treatment under local anesthetic, and by surgical repair of the retinal tear if more severe.
The crystalline lens of the eye is a clear capsule-like bag that hangs behind the iris. It focuses light on the retina, so the retina can transmit visual images to the brain.
As people age, the crystalline lens can cloud, similar to frost on glass, making vision blurred and less sharp. Color may seem washed out, and bright lights, such as headlights, may seem blinding. Cataracts can also occur in younger people with diabetes. Corrective glasses are not helpful because of the lens clouding.
Cataracts can be removed with surgery, a quick, painless procedure accomplished under local anesthetic. The clouded lens is removed and replaced with a small plastic lens. Follow-up treatment includes a series of eye drops to facilitate healing.
The uvea is the inner layer, between the sclera (at the front of the eye) and retina (at the back of the eye), comprised of the iris, the choroid, and the ciliary body. The uvea supplies blood to the retina.
Uveitis is an inflammatory condition of the uvea. If not treated, the resultant scarring from uveitis can cause vision loss.
There are different types of uveitis, occurring in different parts of the uvea: iritis (or Anterior Uveitis) involves the iris or ciliary body; choroiditis (or Posterior Uveitis) involves the choroid; and chorioretinitis (or Intermediate Uveitis) involves the retina.
Uveitis can be caused by many things: a viral infection, a fungal infection, a parasite, trauma to the eye, or it can be related to an autoimmune condition such as rheumatoid arthritis or ankylosing spondylitis.
Treatment varies depending on the cause and other underlying conditions, but includes corticosteroids, eye drops, pain relief, treatment of disease, and prevention of vision loss. While the infection is treated, it is best to wear (eye glasses) rather than contact lenses.