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AQA A2 Physics Unit 5B - Medical > Physics of the Eye > Flashcards

Physics of the Eye Flashcards

1
Q

What is the function of the cornea?

A

Protect the eye and focus light onto retina via refraction. (most refraction is done here)

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2
Q

What is the function of the iris?

A

To control the amount of light that can enter the eye by changing the diameter of the pupil.

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3
Q

What is the function of the pupil?

A

To allow light to enter the eye.

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4
Q

What is the function of the lens?

A

To focus light onto the retina via refraction.

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5
Q

What is the function of the ciliary muscles?

A

To change the thickness of the lens to focus on objects of differing length from the lens.

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6
Q

What is the function of the retina?

A

To form a real image when light rays from an object hit the photosensitive cells.

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7
Q

What is the function of the optic nerve?

A

To carry nerve impulses from the retina to the brain.

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8
Q

What is the blind spot?

A

The point where the optic nerve connects to the retina. There are no photosensitive cells, so no image will be formed.

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9
Q

What is the function of the suspensory ligaments?

A

To support and hold the eyeball in its place.

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10
Q

What is the sclera?

A

The protective outer layer of the eyeball containing collagen and elastic fibre.

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11
Q

What is the vitreous humour?

A

The clear gel that fills the space between the retina and the lens. It holds the shape of the eyeball.

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12
Q

What is the aqueous humour?

A

The clear gel that fills the space between the lens and the cornea. It maintains pressure and provides nutrition to eye tissue.

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13
Q

What humour is constantly refreshed?

A

Aqueous humour.

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14
Q

What humour is there from birth?

A

Vitreous humour.

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15
Q

What is the fovea?

A

The small highly concentrated area of cones on the back of the eyeball.

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16
Q

What is the fovea responsible for?

A

Sharp central vision.

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17
Q

What is the choroid?

A

The layer that lies between the retina and the sclera.

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18
Q

What is the bulbar conjunctiva?

A

The fine membrane that encases the eyeball.

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19
Q

When does refraction occur?

A

When light moves between two mediums that each have a different density.

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20
Q

When does light bend towards the normal?

A

When moving from a lower to higher density, it also slows down.

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21
Q

When does light slow down?

A

When moving from a lower to higher density, it also bends towards the normal.

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22
Q

When does light bend away from the normal?

A

When moving from a higher to a lower density.

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23
Q

When does light speed up?

A

When moving from a higher to a lower density, it also bends away from the normal.

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24
Q

How much of the refraction occurs in the cornea?

A

60%

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25
Q

What is the refractive index when moving from A to B?

A

refractive index = speed of light in A / speed of light in B

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26
Q

What is a converging lens?

A

A convex lens.

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27
Q

What is a diverging lens?

A

A concave lens.

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28
Q

What do the rays do when a converging lens is used?

A

Converge on focal point.

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29
Q

What do the rays do when a diverging lens is used?

A

Diverge from the focal point?

30
Q

What is myopia?

A

Short sighted-ness. The image is focused before the retina.

31
Q

What is hypermetropia?

A

Long sighted-ness. The image is focuses beyond the retina.

32
Q

What is the focal length?

A

The distance between the centre of the lens and the focal point.

33
Q

What lenses are used to correct myopia? How?

A

Diverging lenses. Spreads light out which pushes focal point back.

34
Q

What lenses are used to correct hypermetropia? How?

A

Converging lenses. Bends light inwards which brings focal point forward.

35
Q

What is the lens power equation?

A

P = 1/f

36
Q

What sign is used for the power of a diverging lens?

A

-

37
Q

What sign is used for the power of a converging lens?

A

+

38
Q

What is the unit for power?

A

Diopters (D)

39
Q

In what case is a real image formed using a converging lens?

A

If the object is further away than the principal focus.

40
Q

In what case is a virtual image formed by a converging lens?

A

If the object is closer than the principal focus.

41
Q

What lens always forms virtual images?

A

Diverging lens.

42
Q

What image is larger than the object?

A

Virtual.

43
Q

What image is smaller than the object?

A

Real.

44
Q

What is the lens formula?

A

1/f = 1/u + 1/v

f = focal length
u = object distance
v = image distance
45
Q

What is the magnification produced by a lens?

A

m = v/u

m = magnification
v = image distance
u = object distance
46
Q

What are the two types of photoreceptors in the retina?

A

Rod and Cones.

47
Q

What are the rods responsible for?

A

Vision at low light levels. (Scoptic vision)

48
Q

What are the cones responsible for?

A

Vision at high light levels (Photopic vision) and all high resolution vision.

49
Q

Which photoreceptors are responsible for colour vision?

A

Cones.

50
Q

What are the three types of cone and what are they responsible for?

A 
Short wavelength (S-cone) - blue light
Medium wavelength (M-cone) - green light
Long wavelength (L-cone) - red light
51
Q

What is the light level at which both rods and cones are being used?

A

Mesopic.

52
Q

Which photoreceptors are most sensitive?

A

Rods.

53
Q

Which photoreceptors detect the most detail?

A

Cones.

54
Q

How many rods are in the retina?

A

120 million

55
Q

How many cones are in the retina?

A

6-7 million

56
Q

Where are cones most concentrated?

A

The central fovea (0.3mm)

57
Q

What colour cones are most concentrated in the central fovea?

A

Red and green.

58
Q

What cones are the most sensitive?

A

Blue cones.

59
Q

Where are blue cones mostly found?

A

Outside the fovea.

60
Q

Which of the three cones are the least in numbers in the retina?

A

Blue.

61
Q

What is colour blindness?

A

When one or more coloured cones are missing from the retina.

62
Q

What is protanopia?

A

No red cones.

63
Q

What is deuteranopia?

A

No green cones.

64
Q

What is tritanopia?

A

No blue cones.

65
Q

What is monochromacy?

A

Missing two types of cones.

66
Q

What is achromatopsia?

A

All colour cones missing or defective.

67
Q

Where are rods more predominant?

A

In the peripheral vision.

68
Q

What sensitive photopigment is used in the rods?

A

Rhodopsin.

69
Q

What is spatial resolution?

A

The eye’s ability to see detail. It is dependant on the spacing of rods and cones in the retina.

70
Q

What is the persistence of vision?

A

Flicker fusion. When a cone detects light, the signal takes 50-80 milliseconds and when a rod detects light the signal takes 300 milliseconds.

71
Q

What is astigmatism?

A

A condition where the cornea curvature is large or irregular. The image on the retina is unevenly focused.

72
Q

What lens is used to correct astigmatism?

A

Cylindrical lens.

AQA A2 Physics Unit 5B - Medical (5 decks)

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