January 15, 2014 Watch me! According to the National Eye Institute, about ½ of the adults in US have refractive error.

 Common name:  Causes:  Diagram:

 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

 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.

 Common name:  Causes:  Diagram:

 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

 Correction:  Convex corrective lenses / contacts  Cornea surgery to make the cornea more rounded  Both focus the light more so that it properly reaches retina

 A-stigma = not a point ( light focuses unevenly on retina)  Causes:  Diagram:

 A-stigma = not a point ( light focuses unevenly on retina)  Causes: Irregularly shaped cornea or lens  Diagram:

 Signs of astigmatism:  Fine details are blurry – whether near or far  “Halo”effects or glare from lights

 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

Show with fingers – 1) Myopia, concave lens 2) Myopia, convex lens 3) Hyperopia, concave lens 4) Hyperopia, convex lens 5) Astigmatism, uneven lens

Show with fingers – 1) Myopia, corrected with concave lens 2) Myopia, corrected with convex lens 3) Hyperopia, corrected with concave lens 4) Hyperopia, corrected with convex lens 5) Astigmatism, corrected with uneven lens Why? What does hyperopia look like? Astigmatism?