Week 2 Lecture 3: Optics of the Eye

Question 1

What is the lens and what ligament is it suspended by?

Answer 1

The lens is a transparent disk that focuses light suspended by ligaments called zonules

Question 2

What are the two chambers of the eye and how is the eye divided? (3)

Answer 2

• The eye is divided into two chamber by the lens.
• The anterior chamber is in front of the lens and is filled with aqueous humour (plasma-like fluid).
• The vitreous chamber is behind the lens and is filled with vitreous body (clear jelly that helps maintain the eyeball’s shape

Question 3

Which structure of the eye does light enter through?

Answer 3

The cornea, a transparent bulge in the front of the eye

Question 4

What is the cornea continuous with?

Answer 4

The sclera, the white outer wall of the eyeball

Question 5

What does the cornea and the lens focus light on?

Answer 5

The retina, the inner lining of the eye than contains photoreceptors

Question 6

How does light pass through the cornea?

Answer 6

Through a hole in the iris called the pupil

Question 7

What is the function of the pupil?

Answer 7

The pupil helps to focus light and controls depth of field

Question 8

How does the pupil change size?

Answer 8

In bright light, parasympathetic signals from the brain causes the pupil constricts via (ring-shaped) pupillary constrictor muscles and in the dark sympathetic signals from the brain dilates the pupil via radial pupillary dilator muscles

Question 9

Why does the pupil constrict?

Answer 9

A small pupil ensures that each point on the retina receives light from one direction is space, focus

Question 10

What is depth of field?

Answer 10

When the pupil is tightly constricted, we have full depth of field, everything we see is equally in focus and when the pupil is dilated, we have shallow depth of field, only objects at specific distances are in focus

Question 11

Is the pupils sufficient to focus light?

Answer 11

No, with pupil (pin-hole) focusing alone, the retinal image is dim when the pupil is constricted because the pupil doesn’t let in much light and blurry when the pupil is dilated because the retinal imaging is not focused, refraction is required

Question 12

What is refraction and refractive indices?

Answer 12

The bending of light as it passes through different medium. The refractive index is the number associated with the refraction of different mediums

Question 13

Where is light refracted in the eye?

Answer 13

In both the cornea (2/3 of refraction) and the lens (1/3 of refraction)

Question 14

What is the lens composed of?

Answer 14

• Long cells without nuclei and crystallin, a clear protein, that are zippered together in layers that provide flexibility

Question 15

Is the lens convex or concave?

Answer 15

The lens is convex (fat in the middle, thin at the edges) and allows light rays to converge at a focal point

Question 16

What is an angle of incidence?

Answer 16

The angle at which light ray hits the surface of the lens and depends on the shape of the pen and the direction of the light ray

Question 17

What is dependent on the angle of incidence?

Answer 17

Refraction

Question 18

What is accommodation?

Answer 18

Changing a lens to alter the amount of refraction

Question 19

What does a rounder lens do and what happens as a result?

Answer 19

A rounder lens bend more light and for that reason the focal point is closer

Question 20

What is required for clear vision?

Answer 20

The focal point falling directly on the retina

Question 21

If an item comes closer and the lens stay flat, what happens to the focal point?

Answer 21

The focal point falls behind the retina, blurry image

Question 22

What happens to the lens to bring a close object into focus?

Answer 22

The lens becomes rounder (accommodation) via parasympathetic nerve signals that contract smooth ciliary muscle which reduces tension in the zonules. Sympathetic signals relax the ciliary muscles and makes the lens flatter for far vision

Question 23

What is the near point of accommodation?

Answer 23

The closest point a person can focus

Question 24

What is the stiffening of the lens associate with advanced age that hinders accommodation
called?

Answer 24

Presbyopia

Question 25

What is hyperopia?

Answer 25

Far-sightedness, the focal point falls behind the retina, cannot see objects that are up close, solve with convex lens (reading glasses)

Question 26

What is myopia?