1. Refractive ERRORS: Myopia, Hyperopia, & astigmatism
December 5-6, 2018
According to the National Eye Institute, about ½ of the adults in US have refractive error.
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2. Myopia
Common name:
Causes:
Diagram:

3. 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

4. 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.

5. Hyperopia
Common name:
Causes:
Diagram:

6. 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

7. 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

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

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

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

11. 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

12. Quick Review Show with fingers – Myopia, concave lens
Myopia, convex lens
Hyperopia, concave lens
Hyperopia, convex lens
Astigmatism, uneven lens

13. Quick Review Show with fingers – Myopia, corrected with concave lens
Myopia, corrected with convex lens
Hyperopia, corrected with concave lens
Hyperopia, corrected with convex lens
Astigmatism, corrected with uneven lens
Why?
What does hyperopia look like?
Astigmatism?