Defects of Vision in Human Eye and their Correction The human eye is a most wonderful object. However, the eye can still be thought of as simply a lens. The lens in our eyes that focuses light to form an image sometimes has defects. These defects create problems in seeing objects clearly and are corrected with glasses. Opticians realized this a long time ago. They were invented in Pisa around 1290 and were found to correct vision. Since then, we have come to know and understand defects better and how to correct them. Here are the major eye defects and how they are corrected:
Defects of Vision – Myopia
This is also known as nearsightedness. When it happens, the image is formed not on the retina but in front of it. The retina is somewhat like the screen where images should be formed. A person with myopia can therefore not see objects farther away. However, seeing objects nearby is unaffected. Technically, myopia happens when the focal length of the crystalline lens in the eye decreases. This, in turn, may happen because of too much curvature in the cornea. It can also happen due to elongation of the eyeball. To correct myopia, opticians use the concave lens. These are diverging lenses. It reduces the power of the combined lens. This helps bring back the image on the retina.To correct myopia, opticians use the concave lens.
Defects of Vision – Hypermetropia
This defect is also known as farsightedness. If a person has this defect they are not able to see objects close by. Seeing objects that are far away is unaffected. Hypermetropia happens when the focal length of the eye lens decreases. This means that the image is formed behind the retina and is unfocused. This defect usually happens when the focal length of the eye is excessive. If the eyeball is too short, hypermetropia results too. To correct this defect, opticians use convex lenses. These are converging lenses. They increase the power of the combines lens which helps focus the image on the retina.To correct Hypermetropia, opticians use convex lenses.
Defects of Vision – Presbyopia
This vision defect is usually seen in old people. The near point of the eye is the nearest point to which images can be focused. This point, in presbyopia, recedes further and further. It happens because of the gradual weakening of ciliary muscles in the eyes. To correct it, convex lenses are used just like hypermetropia. If a person suffers from hypermetropia and myopia, bifocals are used whose upper part is concave for long-range vision and the lower part is convex for short range vision.To correct Presbyopia, convex lenses are used .
Quick Facts about Eye
- The world’s most common eye colour is brown.
- Eye colour is determined by the amount of melanin in your iris.
- All babies are colour blind at birth.
- The cornea is the only tissue in the human body which doesn’t contain blood vessels.
- The human eye only sees three colours, red, blue and green. All other colours are combination of these.