Color Blindness Night Blindness

The retina of the eye is lined with millions of rods and cones. The cones permit us to distinguish shapes and colors in bright light. Millions of shades, hues, and tints of colors can be differentiated. In some individuals, however, the cones (and other color-perception apparatus, including the brain connections) fail to distinguishcertain colors; most commonly, they fail to sort out reds and greens. This creates the condition of colorblindness. So far as is known, color blindness is a hereditary defect and there is no treatment for the condition.

The ability to see in dim light and to dis­tinguish movement depends on the rods in the retina. Since the rods are less plentiful at the dead center than on the sides of the ret­ina, vision at night is usually improved by looking obliquely rather than directly at the objects to be seen.

To see in dim light, the rods must contain a chemical substance known as visual purple. The elaboration of this pigment, which goes on constantly, requires the presence of vita­min A. In the presence of light, the visual purple disappears rapidly and must be re­formed. If it is not. owing to a deficiency of vitamin A or other cause, ability to see at night and in twilight is seriously and in some instances, such as piloting an automobile or an airplane, dangerously curtailed. Night blindness can usually be prevented and alle­viated by a diet rich in vitamin A, provided no disease process exists.

Prevention of Blindness

Total blindness in both eyes is a human calamity of top magnitude; few people can rise above it, and they are to be honored. But any degree of blindness is a physical handi­cap that can be economically and emotion­ally crippling.

It is estimated that there are something over 260.000 "legally" or "industrially" blind persons in the United States and that perhaps half of these cases were readily preventable. The leading causes of blindness are infectious and degenerative diseases and accidents.