Light that enters your eyes is focused to form an image on your retina. The optics of your visual system have a total power of about +60 D about +20 D from the lens in your eye and +40 D from the curved shape of your cornea. Surgical procedures to correct vision generally do not work on the lens; they work to reshape the cornea. In the most common procedures, a laser is used to remove tissue from the center of the cornea, reducing its curvature. This change in shape can correct certain kinds of vision problems.

Part A

For which condition would flattening the cornea be a good solution?

Nearsightedness
Farsightedness

Either nearsightedness or farsightedness

Part B

Suppose a woman has a far point of 50 cm. How much should the focusing power of her cornea be changed to correct her vision?
-2.0 D
-1.0 D
+1.0 D
+2.0 D

Part C

A cataract is a clouding or opacity that develops in the eye's lens, often in older people. In extreme cases, the lens of the eye may need to be removed. What effect would this have on someone?
He would become nearsighted.
He would become farsighted.
He would become neither nearsighted nor farsighted.

Part D

The length of your eye decreases slightly as you age, making the lens a bit closer to the retina. Suppose a man had his vision surgically corrected at age 30. At age 70, once his eyes had decreased slightly in length, what condition would he have?

Nearsightedness
Farsightedness
Neither nearsightedness nor farsightedness