Common Eyesight Problems and Lenses

Common eyesight problems and how lenses correct them:

The image formed should be projected on the retina of the eye. Eyesight problems result if the image is not formed on the retina.

Eyesight Problems:

1. Myopia

Medical term for nearsightedness.

People suffering from this visual problem can see close objects clearly, but distant objects are blurry. A myopic eye forms image of a distant object in front of the retina because the eyeball is longer than the normal or is too curved.

Can be corrected by using diverging lens or a concave lens that causes the light to bend slightly before entering the eye so that the image will be formed exactly at the retina.

2. Hyperopia

Medical term for farsightedness.

Can see distant objects but cannot focus clearly on nearby objects. In this case, the eyeball is too short and the image of a close object is formed behind the retina.

A converging lens or a convex lens can correct this problem by the focal length of a converging lens being computed correctly for farsightedness.

3. Presbyopia

Also called aging eyes or old eyes in as much as it is a normal consequences of growing old and cannot be prevented.

People aged 40 and above experiences this. As we grow old, the crystalline lens hardens and the ciliary muscles become less flexible, making accommodation not as easy as before. As a result of this, distant objects can be seen clearly, but nearby objects are not.

A bifocal lens is prescribed. The upper half of a bifocal lens is for normal viewing while the lower half is for reading purposes. It produces the so-called split image effect.

4.Astigmatism

A person suffering from astigmatism cannot focus simultaneously on horizontal and vertical lines. This condition is caused by the cornea’s unequal curvature in various direction.

In an astigmatism eye, the light entering the cornea is not focused on a single point, resulting in a blurry image.

The cylindrical lens is used to correct astigmatism.