REFRACTIVE ERRORS: MYOPIA, HYPEROPIA, & ASTIGMATISMJanuary 15, 2014

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According to the National Eye Institute, about ½ of the adults in US have refractive error.

Myopia

Common name: Causes: Diagram:

Myopia Common name: near-sightedness Causes: long eyeball or overly curved cornea Diagram:

Why can myopic individuals see close objects better? Because light from close objects diverges more / needs more refraction or greater distance to properly hit the retina

Myopia Correction:

Concave corrective lenses / contacts magnify the image (make the light diverge

more), before it enters the eye Lasik surgery to flatten cornea makes the light focus less so it can properly reach the retina.

Hyperopia

Common name: Causes: Diagram:

Hyperopia Common name: farsightedness Causes: short eyeball or a lens that does not bulge

enough Diagram:

Why can hyperopic individuals see distant objects better? Because light from distant objects is parallel, requiring less refraction or less distance to properly hit the retina

Hyperopia Correction:

Convex corrective lenses / contacts Cornea surgery to make the cornea more

rounded Both focus the light more so that it properly

reaches retina

Astigmatism A-stigma = not a point (light focuses

unevenly on retina) Causes: Diagram:

Astigmatism A-stigma = not a point (light focuses

unevenly on retina) Causes: Irregularly shaped cornea or lens Diagram:

Astigmatism Signs of astigmatism:

Fine details are blurry – whether near or far “Halo”effects or glare from lights

Astigmatism Correction

Corrective lenses or contacts Shape of lens /contact varies across the surface to

counteract irregular shape of the eye Contact lenses are often weighted so that they

align properly with the eye Ortho-K / cornea surgery

Reshape cornea with special contact lenses worn at night or with laser surgery

Quick Review

Show with fingers – 1) Myopia, concave lens2) Myopia, convex lens3) Hyperopia, concave lens4) Hyperopia, convex lens5) Astigmatism, uneven lens

Quick Review

Show with fingers – 1) Myopia, corrected with concave lens2) Myopia, corrected with convex lens3) Hyperopia, corrected with concave lens4) Hyperopia, corrected with convex lens5) Astigmatism, corrected with uneven lens

Why? What does hyperopia look like?Astigmatism?