1.                    We do not see an image until the nerve impulse gets to our ____________________.

2.                   The eye is protected in several ways; by ____________________ sockets, eyelids and _______________, which keep the surface, clean.

3.                   The casing of the eye (the sclera) becomes transparent over the front of the eye.  This clear area is called the __________________.

4.                   The iris, a circular muscle, controls the ________________ of the pupil.

5.                   Only a ___________ part of the light from a source actually enters the eye.

6.                   The lens changes _____________ to focus on different distances.  It is ______________ for close up objects; ________________ for distant ones.

7.                   Someone who is _________________ has an eyeball that is too long.  This causes the lens to focus the light ahead of the retina.

8.                   On the retina, the _______________ cells are concentrated in the center.  Rod cells found further out, is sensitive at (low, high) light levels because they have several cells connected to one nerves.

9.                   A condition called _______________ retina will lead to blindness if not treated by a laser.

10.                Glaucoma is caused by the (buildup, draining) of eye fluids.

11.                 Sound waves cause the eardrum to vibrate, which causes 3 bones (hammer, _____________, stirrup) to vibrate.  They (amplify, reduce) the sound level by 22 times.

12.                The vibration of fluid in the _________________ stimulates hairs, which trigger nerve impulses to the brain.  (Higher, lower) sounds are heard in the first portion; (higher, lower) sounds in the rest.

13.                Damage to the bones can sometimes be repaired with _______ % of cases having some hearing improvement.