Many of the conditions affecting vision are progressive; however, early diagnosis and treatment may prevent or slow deterioration. Some conditions are difficult to recognize early in their course, but when possible, early diagnosis and treatment are often of great benefit. The presence of one condition in your eye does not mean that another, entirely different problem cannot occur in the same eye. If
you have visual impairment, regardless of the degree, you should have periodic examinations.

Certain signs and symptoms are danger signals that indicate an urgent need for an examination by an ophthalmologist. They are:

flashes of light
halos around lights
a curtain or veil blocking vision
sudden loss of vision
double vision
dimming of vision that comes and goes
sudden onset of floating spots in front of eye
crossed eye
pain in the eye
redness of eye or surrounding area
discharge or crusting of the eyelids
difference in the size of the two pupils
swelling of the eyes
protrusion of one or both eyes
persistent irritation, watering or dryness

The chief causes of blindness in the United States are glaucoma, diabetic retinopathy, and macular degeneration. These and other conditions commonly seen in people with impaired vision are described in the following sections. May help you understand these conditions.