REFRACTIVE ERRORS

in #health • 9 years ago (edited)

Refractive error is a condition when the light rays do not intersecting in the focus, i.e. the place of the clearest point on the retina. (fovea- responsible for sharp vision)

There are few refraction errors

NEARSIGHTEDNESS (Myopia)

Light rays are intersecting in focal point in front of the retina.
Nearsighted person cannot see far objects clearly, but can see near objects.
Even small nearsightedness is problem sometimes.

It is "fixed" with concave (minus) lenses.

FARSIGHTEDNESS (Hyperopia)

Light rays are intersecting in focal point behind the retina.
Farsighted person can see far object very good (although can have latent hyperopia), but cannot see near objects (Presbyopia).
Presbyopia - you may heard the term short hands. Those are the persons who entered 40's and their ocular lens doesn't have elasticity and power as used to.

It is "fixed" with convex (plus) lenses.

ASTIGMATISM

Light rays doesn't intersecting in one focal point but into multiple focal points.
Therefore the person gets unclear distorted image.

It is "fixed" with cylinder lenses.

refractiveErrors.jpg

Source of the image:
http://www.hendersoneyesite.com/refractive-errors/

#eyes #glasses #vision #sight
9 years ago in #health by
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     9 years ago 

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       9 years ago 

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