Physiologically the eye is a mechanism, much like a camera, which brings the rays of light to focus upon light-sensitive nerve endings in the retina. These, in turn, transmit a stimulus to the brain where the visual image is perceived. In the lowest types of seeing animals the eye consists merely of-a few pigmented cells, sensitive to light, at or near the surface of the body, and connected with some simple nerve structure. In the higher forms of life these structures become more complex and connected with the brain. In addition to these more highly developed eyes, insects and worms retain some of the simple, supernumerary eyes. Most spiders, for example, have eight, and some worms four or more such eyes.
The simplest type of eye can perceive only light, but as one proceeds up the biological scale the visual apparatus becomes, more complex and begins to perceive size, shape, distance, and color. Since acute vision is an asset in the struggle for existence, the animals with the most efficient eyes tend to rise in the biological scale.
Until recently, biologically speaking, man lived out of doors and used his eyes chiefly for distance vision. Some change of focus was necessary, but the demands made upon the visual apparatus were but a fraction of what they have been since he changed his mode of living. Several million years of reading the printed page may bring about a better adaptation of these outdoor eyes to the manner in which we now live.
The Cause and Prevention of Blindness
One of the greatest calamities that can befall one is blindness. The occasional genius, such as Milton or Helen Keller, can rise above this calamity, but most persons are crushed by it. It has been estimated that there are 100,000 blind persons in the United States and that in at least 50 per cent of these cases the blindness was due to causes which could have been prevented. Of these causes, the most important are injuries, infections, poisons, and degenerative diseases.
Injuries constitute an important cause of blindness. Some of these for all practical purposes can hardly be called preventable, but the vast majority could be avoided with reasonable precaution. Children can be taught that they should not use sharp instruments and that certain toys and games are hazardous; industry can safeguard the vision of employees; and individuals can learn to take necessary precautions.
Most industrial eye injuries occur in such occupations as machine operating, chipping, grinding and polishing, mining and quarrying, riveting, welding and cutting, glass making, sand blasting, and woodworking operations. In these and other occupations in which fragments of metal, wood, or stone may be thrown about, goggles or masks should be worn. The Chicago Division of the American Steel and Wire Company reports that eye injuries resulting in total loss of vision were reduced from 1 per 643 employees to 1 per 2,700 employees and that the reduction in partial loss of vision was from 1 per 750 employees in last decade. This reduction was the result of the use of goggles and the adoption of other protective devices. Injuries on the farm and in many other areas could likewise be greatly reduced by reasonable care and the use of protective goggles.
First Aid in Eye injuries
Cleanliness is of the greatest importance in the care of eye injuries. A slight scratch on the surface of the eye may become so seriously infected that the eyesight is lost. The tissues of the eye are extremely delicate. For this reason expert medical attention should be secured whenever there is an injury to the eye.
Cinders in the Eye
Dust, Cinders, and other small particles of foreign material frequently lodge on the surface of the eyeball. The irritation thus produced results in a flood of tears which usually wash the offending particle away. Occasionally, however, such particles become lodged under a lid and for this or some other reason refuse to be dislodged. In such cases closing both eyes for a few moments without moving the eyeball leads to the accumulation of tears so that with the opening of the eyes the particle may be flushed out. Rubbing of the eyes irritates the tissues and embeds the particle.
Cosmetics Dangerous to Eyes
Among the cosmetics offered for the enhancement of beauty are dyes for eyebrows and eye lashes. Some of these contain chemicals which are injurious to the delicate structure of the eye; hence, their use is distinctly hazardous.
Mild infections of the eye, such as those which are frequently accompany common colds; usually clear up with simple treatments. The more severe infections, on the other hand require medical attention. These may be acute and self limited or they may be due to serious disease, such as trachoma or gonorrheal ophthalmic, which, if not properly treated, will result in blindness.