2. Digital Images and the Eye

Question 1

What is the Cornea

Answer 1

Transparent covering protecting the front of the eye

Question 2

What is the iris

Answer 2

It controls the pupil size and brightness accommodation

Question 3

What is the Lens

Answer 3

Focusses image on retina by ciliary muscles

Question 4

What is the retina

Answer 4

Light sensitive tissue on the inner layer of the eye

Question 5

What is the fovea

Answer 5

Central pit in macula with high density of cones for central vision

Question 6

What is the blind spot

Answer 6

A lack of rods and cones on the optic disc

Question 7

Are rods scioptic or photoptic?

Answer 7

Scioptic (they see dim light)

Question 8

Are cones scioptic or photoptic?

Answer 8

Photoptic (bright light)

Question 9

How many rods are in the fovea?

Answer 9

0/ Very few

Question 10

How many cones are in the fovea

Answer 10

About 200,000 per mm^-2

Question 11

Why do cones have higher visual acuity?

Answer 11

They each have their own nerve end, so can distinguish finer detail

Question 12

What kinds of vision are rods responsible for?

Answer 12

Night, sensitive motion detection, peripheral

Question 13

Why does the eye move continuously?

Answer 13

To keep the light from the object of interest falling on the fovea

Question 14

How many types of rods are there?

Answer 14

1

Question 15

What are the 3 types of cone?

Answer 15

Red, Green, and Blue.

Question 16

What is the focal length?

Answer 16

The distance from the centre of the lens to the retina

Question 17

How is refractive power calculated?

Answer 17

1 / focal length

Question 18

When is refractive power lowest?

Answer 18

When focusing on objects further than 3m away

Question 19

When is the focal length longest?

Answer 19

17mm

Question 20

Why is the focal length longest at 17mm?

Answer 20

The relaxed muscle flattens the length

Question 21

For distant objects, do we want a small or a long focal length?

Answer 21

Small, as we do not want to ben the light much

Question 22

Does a small refractive power have long or short focal length?

Answer 22

Long

Question 23

How is a long distance image formed? (4 steps)

Answer 23

1. Ciliary muscles relax
2. Stretches and makes lense thinner
3. Focal length is made longer
4. Refractive power is less

Question 24

How is a short distance image formed? (4 steps)

Answer 24

1. Ciliary muscles contract
2. Lens becomes thicker in the middle
3. Focal length becomes shorter
4. Refractive power is greater