Tamara Missler, age 12, of San Diego, Calif, for the questions
How do glasses correct vision?
Sensible people guard their eyes from strain and have them tested to see that they are in proper working order. Eyes that do not see perfectly are not necessarily sick but they may need the help of glasses to get a clear picture of the world. We visit an ophthalmologist or an optometrist. The ophthalmologist is an eye doctor who may also be called an oculist. This expert is a medical man, trained to test your eyes and prescribe whatever is necessary to put them right, including medication. The optometrist may only test the eyes and fit corrective glasses.
The oculist may prescribe glasses and send you to an optician with a prescription. The optician is an expert in making lenses and fitting the frames to your face. If you wish to keep the fact that you wear glasses a secret, the optician can also make contact lenses which is a very delicate and quite expensive fob of work.
The eye looks out at the world through a lens and a cornea. The cornea is a bulge in front of the eyeball and the lens is a clear window pane behind it. The two work together to bend and angle the light rays so that they focus in a clear picture on the retina, which is the picture screen on the inside wall at the back of the eyeball.
Light rays from the outside world strike the curved surface of the cornea and pass through the lens. The rays are angled to form a clear little picture .Ol inch wide. When the angles are just right, the picture falls directly on the retina and the picture is in sharp, clear focus. To get these angles gust right, the lens is ,Fitted with a little muscle which squeezes it thick for close up viewing and relaxes it flat for distant viewing perfect vision,
In perfect vision, the eye can focus a clear picture on the retina from objects both near and far.
Nearsighted people see close ups well, but distance is blurred. This is because the light rays are angled to form a clear picture before they reach the retinas Concave lenses made by the optician fan out the rays slightly before they reach the eye. The eye can then taper these rays td form a clear picture further back, where it focuses directly on the retina. '
Farsighted people see distance well, but close ups are blurred. Here the light rays strike the retina before the picture is clearly focused. Convex lenses taper the rays before they reach the eye. The eye can then angle them to form a picture in a shorter distance where it focuses directly on the retina. Other vision defects are corrected with still different lenses. All the prescribed lenses help the eye to angle the light rays so that they focus clearly on the retina.