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 distinguish certain colors; most commonly, they fail to sort out reds and greens. This creates the condition of color blindness. 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.

The critical distance for seeing is the distance between the light source and the observed object. Where close work such as read­ing, writing, or sewing is to be done, the light falling on the book or paper or threads should be of an intensity of about 15 or 30 foot-candles, or more.

The major source of light on the printed page or other close work should come from behind. Direct glare of light into the eyes should always be avoided. Lamps should be well shaded, and bulbs should be frosted. It is better to work in a room that is reasonably well lighted throughout than to depend on "pinpoint" lighting on the work itself. In this respect modern, indirect lighting is an advan­tage. Position while reading for example, reading in bed-makes little difference provided that the proper conditions of illumina­tion are maintained. The book should be about 14 inches in front of the eyes.

You are the best judge of the amount of light you need to read or do other work. If there is not enough light, you will start to squint and frown and become uncomfortable. If there is too much light and glare, you will begin blinking and turn away from the light source.

Glare requires eye muscles to make con­stant and extensive readjustments, resulting in eyestrain and in an extreme case, under special conditions, "snow blindness." Use of tinted glasses, optically correct, can be a help in avoiding undue glare. Too many people, however, wear sunglasses solely for costume effect.

When to Wear Sunglasses

You can buy sunglasses for anywhere from 25 cents to $2750 (diamond-studded frames) a pair. For a good acceptable pair of sunglasses you will have to pay anywhere from about $6 to $20. An "acceptable" pair of sunglasses transmits from about 15% to 30% of visible light (i.e. it cuts out from about 70% to 80%) and also offers adequate protection against infrared and ultraviolet rays of the sun. neutral colors gray, green and tan, in that or der are preferable.

Sunglasses should be worn for the purpose for which they are primarily manufactured: to protect your eyes from discomforting expo­sure to the sun's rays. They should not be worn for night driving that is, to protect the driver from the glare of oncoming headlights.

Fashion has made dark glasses a more popular item of feminine beauty accessories than is physiologically warranted. Too many young women, perhaps, have gotten into the habit of concealing the natural beauty of the eyes and distorting the natural and appealing contours of their faces by hiding themselves behind dark glasses when this is not really necessary. One observer has said of light-tint sunglasses (those that transmit more than 30% of visible light) "They are a cosmetic, a decoration a palliative for neurotics."