Chapter 2 - Light and the Eye

Question 1

Describe light.

Answer 1

• it is a particle and a wave
• it is electromagnetic energy
• 400-700nm visible to humans

Question 2

What is a wavelength?

Answer 2

the distance between two peaks = colour

Question 3

What is amplitude?

Answer 3

Distance between peak and trough = brightness

this describes the number of photons entering the eye (more=brighter)

Question 4

What is the duality principle?

Answer 4

Light acts as both a particle and as a wave

Question 5

What is reflectance?

Answer 5

to redirect something that strikes a surface (like a mirror)

Question 6

what is transmission?

Answer 6

to convey from one place to another

Question 7

what is absorption?

Answer 7

to take up light and not transmit it at all

Question 8

what is refraction?

Answer 8

to alter the course of a wave of energy that passes into something from another medium, as water does to light entering it from air
- refraction also occurs when light enters the eye

Question 9

What is a field of view?

Answer 9

the proportion of a surrounding space you can see when your eyes are in a given position in their sockets

Question 10

Name the three pairs of muscles that control eye movement

Answer 10

superior and inferior rectus (up and down)
medial and lateral rectus (side to side)
superior oblique and inferior oblique (stabilizing movements of the head)

Question 11

What is the length of the average human eye?

Answer 11

24mm

Question 12

Name some parts of the eye and their functions.

Answer 12

1. sclera: outer membrane of eye; protective layer
2. cornea: transparent membrane at the front of the eye
3. anterior chamber: space between the cornea and the crystalline lens; filled with aqueous humor
4. crystalline lens: structure near the front of the eye that refracts the light coming from the pupil
5. vitreous chamber: the main interior portion of the eye; filled with vitreous humor

Question 13

Which structures in the eye contribute the most to refracting the light?

Answer 13

the cornea, aqueous humor and vitreous humor (their refractive power is fixed)

Question 14

How can the lens refract light?

Answer 14

It can change its refractive power due to the thickening or thinning of the lens

Question 15

How does the iris work?

Answer 15

It contracts to shrink the pupil, letting less light in (this helps to focus the light, like an aperture on a camera)

Question 16

Describe how the eye can work like a camera in terms of focal length

Answer 16

The point at which the photons emitted from a source come into focus will vary based on the distance of the object

Question 17

How is accommodation in the eye accomplished?

Answer 17

accomplished by the relaxation and contraction of the ciliary muscles

Question 18

What are the ciliary muscles attached to?

Answer 18

to the crystalline lens (attached by the zonules of zinn)

Question 19

What occurs in the eye when objects are distant?

Answer 19

• ciliary muscles are relaxed
• zonules are stretched
• lens is relaxed (thin)

Question 20

What occurs in the eye when objects are close?

Answer 20

• the ciliary muscles contract
• reduces tension in the zonules
• lens contracts (thickens)

Question 21

In what unit do we measure refractive power?

Answer 21

In diopters

• unit of reciprocal length
• 1/focal length (in meters)
• the greater the power of the lens, the shorter the focal length (ex. a lens of 2 diopters will have a focal length of 0.5 meters; a lens of 41 diopters will have a focal length of 0.024 meters)

Question 22

What happens when the refractive power of the cornea, aqueous, lens and vitreous are matched to the length of the eye?

Answer 22

Individuals will be able to accommodate successfully

Question 23

What is emmetropia?

Answer 23

good vision

Question 24

What happens as we age?

Answer 24

• our lens becomes sclerotic (harder) and loses accommodative power

Question 25

What is presbyopia?

Answer 25

aka “old eye” - the loss of near vision because of insufficient accommodation (lens can’t get thick enough to accommodate to near objects)

Question 26

What is nearsightedness?

Answer 26

myopia

Question 27

Why would myopes develop old eye much later than the rest of the population?

Answer 27

Because the lens of the myope is more dense

Question 28

What is hyperopia?

Answer 28

Farsightedness

Question 29

What is astigmatism?

Answer 29

a visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye (usually the cornea)