Part III: Vision

Question 1

In order for the eye to properly focus on a nearby object, two main structures are active to
ensure that the light rays from the object fall upon the proper location of the retina

Answer 1

: )

Question 2

When the eye “focuses,” what really is happening is that the light rays from an object
entering the eye are bent (______________) so that they come together
(________________) on a small pit on the retina.

Answer 2

Refracted; converge

Question 3

What two main structures are responsible for bending the light rays in this manner?
Which of these is the most important in this role?

Answer 3

Cornea, lens. The cornea is the most important for refraction and convergence of light
rays. The cornea has a refractive power of 42 diopters compared to a refractive power of
12 diopters for the lens

Question 4

The small pit in the retina that light rays must fall on, the _______________, is
surrounded by a yellow area known as the _____________________.

Answer 4

Fovea; macula lutea

Question 5

What change in shape occurs to the lens when the eye focuses on a nearby object?

Answer 5

The lens takes on a rounder shape.

Question 6

What causes this shape change in the lens?

Answer 6

Contraction of the ciliary muscles (which are connected to the lens by suspensory
ligaments).

Question 7

The changes in the eye that occur for near vision are called ___________________
and are caused by ___________________.

Answer 7

Accommodation; the oculomotor nerve.

Question 8

Besides the change in lens shape, what else happens when the eye focuses for near
vision (during accommodation)?

Answer 8

Constriction of the pupil and inward rotation of the eyes (which is also called convergence
of the eyes).

Question 9

What three important aspects of vision are the cones in the retina responsible for?

Answer 9

Vision in bright light, color vision, visual acuity (a sharply focused image)

Question 10

What two important aspects of vision are the rods in the retina responsible for?

Answer 10

Vision in dim light; black and white vision

Question 11

What happens to rhodopsin, the photopigment found in rods, when it is exposed to bright
light?

Answer 11

It stops sending action potentials to the brain—it “turns off.” Bright light causes it to break
apart into its two components (retinal and opsin) and lose its purple color. This is known
as bleaching.

Question 12

Why does it take a few seconds for you to be able to see when you leave a bright room
and walk out into the night?

Answer 12

Since you have been in bright light, your rhodopsin is inactive, literally broken in half. It
takes a few seconds for it to be remade–So that the rods can produce action potentials in
dim light, allowing you to see

Question 13

What is the focal distance of the eye? How is focal distance connected to eye shape?

Answer 13

Focal distance is the distance it takes light rays to focus after entering the eye.
This means the distance at which the light rays come together (converge into a point) on
the fovea.
(The cornea and lens are what determine the focal distance. The human eye has a focal
distance on average of 22 mm.)
Assuming the cornea has the “perfect” shape/curvature, causing the focal distance to be
22 mm, the human eye needs to be the “perfect” size for vision to be sharp/crisp.

Question 14

What is the clinical term for nearsightedness? How can eyeball shape cause this
problem?
Where is the image focused?

Answer 14

Myopia (“squint-eye vision”)= The eyeball is too long, causing light rays to focus in front
of the fovea. The normal focal distance (22 mm) is too short to reach the fovea and needs to be
increased.

Question 15

What type of lens is used to correct nearsightedness? How does the shape of the
lens correct the problem?

Answer 15

A concave lens, or one that is relatively flat on both sides.
A concave lens causes light rays that pass through it to diverge, or spread out.

The concave lens increases the focal distance–allows the light rays to travel farther
before they focus—so that they reach the fovea.

Question 16

What causes hyperopia? Where is the image focused?

Answer 16

Hyperopia= Farsightedness. The eyeball is too short. This causes the light rays to
focus behind the fovea. The normal focal distance (22 mm) is too long and needs to be
shortened.
FYI: Hyperopia means “excessive measure vision”—the idea that the
light rays go too far, past the fovea.

Question 17

What kind of corrective lens is used to correct hyperopia?

Answer 17

A convex lens, one that is round.

Question 18

How is presbyopia, which is age-related farsightedness, different from hyperopia, or
regular farsightedness?

Answer 18

Presbyopia (“old man vision”) begins to develop in the mid-40s because the lens loses its
elasticity. As we age, the lens becomes less flexible because more crystallines are added
to it. This means it can no longer take on the round shape it needs (during
accommodation) to properly focus for near vision.

Question 19

What two eye disorders can be caused by diabetes?

Answer 19

Cataracts and retinal detachment (degeneration).

Question 20

Astigmatism occurs with myopia or hyperopia. It results in blurring of an image either
vertically or horizontally. What causes this?

Answer 20

A cornea that is aspheric or asymmetric. This means it may be flattened on one side or
that its overall curvature is more oval than round.