Physio: Optics and Retina

Question 1

What is a converging lens?

Answer 1

Convex lens usued to decrease the focal length and increase the diopters in vision.

Question 2

What is a diverging lens?

Answer 2

Concave lens that scatters light and increases the focal length, decreasing the diopters in vision.

Question 3

With a convex lens, how do you increase diopters?

Answer 3

Increase the curvature of the lens. (increase the thickness of the lens)

Question 4

Where does most of the refractive power of the eye come from?

Answer 4

The cornea

Question 5

How can people adjust the focal length of the images entering the eye?

Answer 5

Adjust the thickness and curvature of the lens with the cililar body.

Question 6

How does the ciliary muscle adjust the lens for near and far sight?

Answer 6

The ciliary muscle is like a sphincter muscle. When it contracts the suspensory ligaments holding the lens relax and the lens gets thicker = near sightedness

When the ciliar muscle relaxes the suspensory ligaments tighten and the lens becomes flat = far sightedness

Question 7

What is presbyopia?

Answer 7

Loss of elasticity of the lens and diminishing ability to accomodate. Usually occurs with age.

Question 8

What kinds of lenses are required to fix:

1. Narrow eyes in relation to normal cornea and lens size (hyperopia)
2. Wide eyes with normal cornea and lens size (Myopia)

Answer 8

1. Convex lens to decrease the focal length

2. Concave lens to increase the focal length

Question 9

What are cataracts?

Answer 9

Increasing opacity of the lens.

Question 10

Site in the retina with the highest visual acuity.

Answer 10

Fovea Centralis

Question 11

Form of vitamin A that is bound to opsin.

Answer 11

11-cis-retinal (aldehyde form of Vitamin A)

Question 12

How does light begin the signal cascade into an electrical depolarization signal to the brain?

Answer 12

1. Light isomerizes 11-cis-retinal into all trans retinal
2. All trans retinal detaches from opsin and is converted to retinol
3. Retinol starts the G-protein coupled receptor cascade and activates a phosphodiesterase that decreases cGMP and decreases NT release.

Question 13

What do light signals do the levels of cGMP in signal transduction?

Answer 13

Decreases the levels and prevents NT release from photoreceptor cells. This actually stimulates a signal cascade in neurons to interpret vision.

Question 14

What are the functions of horizontal and amacrine cells?

Answer 14

These are interneurons that have lateral inhibitory or excitatory capabilities to adjacent bipolar ganglion cells.

Horizontal Cells are alway inhibitory

Amacrine cells help analyze visual info before leaving the retina.