Disorders of the eye

Two-thirds of all the sensory receptors that your body requires are in your eyes. Those photoreceptors do more than detect light. They also allow you to see the world in a rainbow of colors. Your eyes are the single most important source of information about the outside world.

Injuries, disease, inherited abnormalities, and advancing age can disrupt functions of the eyes. The consequences range from relatively harmless conditions, such as near sightedness, to total blindness. Each year, many millions of people must deal with such consequences.

Age-Related Problems Cataracts, a gradual clouding of the lens, is a problem associated with aging, although it also may arise through injury or diabetes. Possibly the condition arises when the transparent proteins making up the lens undergo structural changes. The clouding may skew the trajectory of incoming light rays. If the lens becomes totally opaque, light cannot enter the eye at all.

Eye Diseases. The structure of the eye and its functions are vulnerable to infection and disease. Especially in the southeastern United States, for example, a fungal infection of the lungs (histoplasmosis) can lead to retinal damage. This complication can cause partial or total loss of vision. As another example, Herpes simplex, a virus that causes skin sores, also can infect the cornea and cause it to ulcerate.

Trachoma is a highly contagious disease that has blinded millions, mostly in North Africa and the Middle East. The culprit is a bacterium that also is responsible for the sexually transmitted disease Chlamydia. The eyeball and the lining of the eyelids (conjunctiva) become damaged. The damaged tissues are entry points for bacteria that can cause secondary infections. In time the cornea can become so scarred that blindness follows.

Eye injuries Retinal detachment is the eye injury we read about most often. It may follow a physical blow to the head or an illness hat tears the retina. As the jellylike vitreous body oozes through the torn region, the retina becomes lifted from the underlying choroids. In time it may peel away entirely, leaving its blood supply behind. Early symptoms of the damage include blurred vision, flashes of light that occur in the absence of outside stimulation, and loss of peripheral vision. Without medical intervention, the person may become totally blind in the damaged eye.

Focusing problems. Other heritable abnormalities arise from misshapen features of the eye that affect the focusing of light. Astigmatism, for example, results from corneas with an uneven curvature; they cannot bend incoming light rays to the same focal point.

Nearsightedness (myopia) commonly occurs when the horizontal axis of the eyeball is longer than the vertical axis. It also occurs when the ciliary muscle responsible for adjustments in the lens contracts too strongly. The outcome is that images of distant objects are focused in front of the retina instead of on it.