General Medical Information

Pathologically Decreased Vision

Gradual Loss of Vision

In evaluating reduced vision in pathologic terms, best corrected visual acuity must be considered to eliminate the physiologic abnormalities. The three most common causes of gradual loss of vision are cataract, senile macular degeneration, and glaucoma.

Cataract formation, the loss of transparency of the crystalline lens, is common. Increased density of the lens fibers and changes in protein content occur almost without exception to some degree in every person with increasing age; however, many times the loss of transparency is so marked that visual function is seriously hampered. The term cataract usually is reserved for the latter situation. Cataract formation usually is evolutional, but it occasionally has a specific cause, such as galactosemia, galactokinase deficiency, diabetic ketoacidosis, or trauma. If one of these metabolic abnormalities can be corrected early in the course of cataract formation, the lens opacity can be reversed; however, often there is no known way to prevent or reverse lens changes due to cataract. Treatment is surgical removal of the cataract. The need for surgery usually depends on the patient’s visual requirements and desires. In rare instances, the cataract damages the eye because of high pressure from rapid swelling and may have to be removed for other than optical reasons.

The operation usually is performed by means of opening the anterior capsule and extracting the lens material. The posterior capsule is left intact (extracapsular technique or phacoemulsification). After a person is aphakic, the optical power of the lens must be replaced to provide focusing ability. The patient can be fitted with spectacles or contact lenses after the eye has healed or can have an intraocular lens implanted during the surgical procedure. It is comforting to inform patients that cataract surgery is one of the most successful operations performed.

A second common cause of gradual progressive decrease in vision among older persons is senile macular degeneration. The cause of this condition is unknown, but it may be related to a decrease in the blood supply to the macular area associated with hardening of the arteries in the back of the eye, which begins as a pigmentary disturbance in the macula and usually progresses slowly but steadily with increased scarring and often hemorrhage into the tissues. The disease is bilateral but usually asymmetric. There is no effective treatment, and normal use of the eyes, as for sewing and reading, does not accelerate the process. Patients should be assured that macular degeneration is not a blinding disease because the peripheral vision is not disturbed. Patients with this condition always are able to move around unaided, even though their useful reading vision may be markedly decreased. Unlike the two aforementioned visually disabling conditions, glaucoma characteristically produces a decrease in peripheral visual ability, but good reading vision is maintained until late in the disease.