Lesson 15

A near-sighted eye is one that sees objects better when they are nearer than 20 feet from the eyes. Distant objects are, more or less, blurred. In optics, it is called Myopia. It is an eye that, when relaxed and flattened, has more curvature than needed to focus on the retina. The excess curvature brings the farther light rays to a focus before they reach the retina. The light rays then spread out and reach the retina with an imperfect focus, with a blurred focus. The eye mechanism for near and far vision, being a one-way adjustment, is unable to reduce the curvature. The eye must accept blurred vision for distance.

If the size of the eye is exactly one inch and the curvature of the eye, when fully relaxed or flattened, is 41 optical diopters, it would have 1.00d. too much. It would be a 1.00d. near-sighted eye. If the eye is larger or smaller, it would make no difference. If the eye has 1.00d. more curvature than is required for the right focus, it will be 1.00d. near-sighted, if it has 2.00d. more curvature, it will be 2.00d. near-sighted, if it has 10.00d. excess ucrvature, it will be 10.00d. near-sighted.

Minus lenses which have minus curvatures neutralize plus curvatures. If the eye has plus 10.00d. more curvature than is needed, a minus 1.00d. lens will take it away. It will neutralize it. The eye, then, will become a neutral eye and will have 20/20 distant vision the same as a neutral eye. If the eyes have 2.00d. ttoo much curvature, a pair of minus 2.00d. glasses will give them 20/20 vision. If a person has 10.00d. too much curvature, which would make him very near-sighted, a pair of minus 10.00 glasses will make him see distant objects as good or almost as good as a neutral eye.

Near-sighted eyes of lower and medium grades are better suited for near-seeing than neutral, normal or perfect eyes. Neutral eyes have to bend 3.00d. at 13 inches where most of near seeing is done. A near-sighted person of 1.00d. at 13 inches, has to bend his eyes only 2.00d. which is 1.00d. less than neutral, normal or perfect eyes. A near-sighted person of 2.00d. bends his eyes only 1.00d. or 2.00d. less than neutral or perfect eyes.

It is advisable for near-sighted eyes of less than 2.00d., especially children, not to use minus glasses for proloonged reading or other sustained near work.

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