Function of the eye and terms to know!

emmetropia: Normal focusing hypermetropia: farsightedness : the failure of the lens to bend the light rays enough to bring them to a focal point on the retina. vision closer is clearer, vision at a close range is blurry

myopia: nearsightedness: too strong a lens system for the distance of the retina behind the lens. Light rays are focused before they reach the retina, and by the time they do, they have spread apart again, and cause fuzziness. This person can see objects close to them very clearly. They are unable to focus at a distance.

Astigmatism: This happens when one of the components of the lens system becomes egg shaped rather than spherical. Either the cornea or the crystalline lens becomes elongated in one direction in comparison to the other direction. Because the radius of curvature is greater in the elongated direction than the short direction, the light rays entering the lens along this lengthened curvature are focused in front of the retina.

In other words, the eye is far-sighted for some light rays and near-sighted for the rest. This person is unable to focus ANY object clearly regardless of the object’s distance.

Correction for these problems: Glasses with properly prescribed lenses can be used to correct the abnormalities. Glasses bend the light rays before they enter the eye in an appropriate manner to correct for the excess or deficient refractive power of the eye.

Concave Lens: In the myopia person the light rays normally focus in front of the retina. To prevent this a concave lens is placed in front of the eye. This type of lens bends the light rays outward and therefore, compensates for the excess inward bending of the myoptic person

The hypermetropic eye lens fails to bend the light rays enough. To correct this abnormality, a convex lens is placed in front of the eye so that the light rays will be partially bent even before they reach the eye. With the convergence of the rays the eye can bring the rays to a focal point on the retina.

To correct astigmatism is more complicated, because the corrective lens has to have curvature in more than one direction.

Concave Lenses: A concave lens is thinner in the center than at the edges. As parallel rays of light pass through a concave lens, they are bent away from the center of the lens. Because the light rays never meet, a concave lens can produce only a virtual image.

Convex Lens: is thicker in the center than at the edges. As parallel light rays pass through a convex lens, they are bent toward the center of the lens. The rays meet at the focal point of the lens and then continue on. The more curved the lens, the more it refracts light.

Mixing Colors: It is possible to produce any color by mixing colors of the spectrum in varying amounts. Three colors that can be used to make any other color are called primary colors. Any 2 primary colors combined in equal amounts produce a secondary color.

The primary colors of light are red, green, and blue. When combined in equal amounts, the primary colors produce white light. But if they are combined in varying amounts they can produce any other color.

Examples: red & green --> yellow light (yellow is a secondary color of light because it is produced form 2 primary colors) green + blue --> cyan red+ blue --> magenta

A primary color and a secondary color can combine to make white. Any two colors that combine to form white light are called complementary colors. Yellow and blue are complementary colors, as are cyan and red, and magenta and green.

Pigments are substances that are used to color other materials. Color pigments are opaque substances that reflect particular colors. The color you see is the color that particular pigment reflects.

Mixing colors of pigments is different from mixing colors of light. As pigments are added together, fewer colors of light are reflected and more are absorbed. The more pigments that are combined, the darker the mixture looks.