The Optics of the Eye Flashcards

1
Q

What is accommodation of the eye?

A

When your eye focuses the lens system in the eye.

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2
Q

What does accommodation of the eye involve?

A

the change in the shape of the lens.

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3
Q

Why does accommodation of the eye occur?

A

In order to see close objects.

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4
Q

What does it mean when lens become taut?

A

The lens flattens and its refractive power decreases.

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5
Q

What occurs when in accommodating for distant vision?

A

Ciliary muscles relax and the zonule of Zinn becomes taut.

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6
Q

What occurs when accommodating for near vision?

A

ciliary muscles contract and Zonule fibers relax.

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7
Q

What occurs when Zonule fibers relax?

A

it causes the lens curvature to increases > leading to refractive power increasing.

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8
Q

Parasympathetic activation stimulates the contraction of what causing what?

A

of the ciliary muscles causing the relaxation of the Zonule of Zinn.

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9
Q

When lens become more convex and increases its refractive power what just occurred?

A

The Zonule of Zinn is relaxed.

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10
Q

What is presbyopia?

A

The inability of the lens to change its shape during accommodation.

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11
Q

What reduces with age?

A

The capability or power of accommodation.

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12
Q

Why does the capability of accommodation reduce with age?

A

lens become thicker, larger, and less elastic due to denaturation of lens proteins.

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13
Q

In children the refractive power of the lens can do what?

A

increase voluntarily by 14 diopters.

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14
Q

By age 45-50 the accommodation capabilities do what and by how much?

A

Reduce from 14 to 2 diopters.

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15
Q

A middle aged person has a refractive lens power of what?

A

2 diopters.

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16
Q

By age 70 accommodation capabilities is what?

A

0

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17
Q

Eyes are permanently focused at a constant distance at what age and what do they need?

A

age 70 and they need bifocals.

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18
Q

What is the function of the iris?

A

The iris regulates the amount of light entering the eye.

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19
Q

What occurs in darkness what happens to the iris?

A

more light enters.

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20
Q

What occurs in a bright environment to the iris?

A

the less light enters the eye.

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21
Q

What are pigmented in the iris?

A

The stroma and epithelial cells.

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22
Q

What forms the boundary of the pupil?

A

The medial or inner aspect of the iris.

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23
Q

Define the pupillary zone?

A

The medial or inner aspect of the iris forms the boundary of the pupil.

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24
Q

The lateral or outer segment of the iris is attached to the what?

A

The ciliary body and sclera.

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25
Q

What does the pupillary region contain?

A

The sphincter muscles of the iris.

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26
Q

What does the ciliary region contain?

A

The radial muscles of the iris.

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27
Q

What is the sphincter muscle also known as?

A

pupillary sphincter, pupillary constrictor, or circular muscle of iris.

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28
Q

What is the radial muscle of the iris is also known as?

A

pupil dilator muscle or pupillary dilator.

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29
Q

What type of muscles are the sphincter and radial muscles?

A

Smooth muscles that regulate the size of the pupil.

30
Q

What is the area called between the pupillary and ciliary zones of the iris known as?

A

Collarette region of the iris.

31
Q

The amount of light entering the eye is proportional to what?

A

The area of the pupil.

32
Q

The human pupil can become as narrow or as wide as what?

A

1.5 mm or as wide as 8mm

33
Q

When pupil is narrowing or widening the amount of light entering the eye can change by how much?

A

30 folds due to the changes in pupillary diameter.

34
Q

What muscle exhibits the parasympathetic effect?

A

The sphincter muscles

35
Q

What muscle exhibits the sympathetic effect?

A

radial muscles of the iris.

36
Q

What two muscles regulate the pupillary diameter?

A

the radial and sphincter muscles.

37
Q

What occurs to pupillary diameter in low light?

A

the radial muscles contract while the sphincter muscles relax to widen pupil.

38
Q

What occurs to the pupil when the radial muscles contract while the sphincter muscles relax?

A

the pupil will widen.

39
Q

What occurs to pupillary diameter in high light?

A

The radial muscles will rely while sphincter muscles contract to narrow pupil.

40
Q

What occurs to the pupil when radial muscles relax and sphincter contracts?

A

the pupil will become narrow.

41
Q

What is emmetropia?

A

Normal vision

42
Q

What is hyperopia?

A

farsightedness

43
Q

What is hyperopia also known as?

A

hypermetropia

44
Q

In hyperopia, light is focused behind the retina this error is caused primarily by what?

A

a short eye ball.

45
Q

In hyperopia, light is focused behind the retina this error is caused secondarily by what?

A

by a lens with weak refractive power.

46
Q

In hyperopia the light rays aren’t bent sufficiently by a weak lens this is why?

A

light rays are focused behind the retina of a short eye ball.

47
Q

When hyperopia’s error occurs, who compensates it?

A

accommodation will try to wherever its possible.

48
Q

In older subjects why isn’t accommodation can’t compensate hyperopia?

A

they are presbyopic subjects. Lenses can’t accommodate.

49
Q

In myopia where is light focused on?

A

In front of the retina.

50
Q

What is myopia is also known as?

A

nearsightedness.

51
Q

What causes the error of myopia?

A

usually caused by a long eye ball o by lens with too much refractive power.

52
Q

In myopia light rays are bent strongly resulting in what?

A

focusing light infront of the retina of a long eyeball.

53
Q

Which condition of the eye cannot compensate for the action of the lens?

A

Myopia

54
Q

Which condition of the eye can compensate for the action of the lens?

A

Hyperopia

55
Q

What kind of lenses used to correct myopia?

A

concave lenses

56
Q

Why are concave lenses used to correct myopia?

A

they disperse light entering the eye.

57
Q

What kind of lenses are used to correct hyperopia?

A

Convex lenses

58
Q

Why are convex lenses used to correct hyperopia?

A

They converge light entering the eye.

59
Q

What is astigmatism?

A

an optical defect caused by refractive error due to eye unable to focus.

60
Q

In astigmatism what occurs to images in planes that are right angles to each other?

A

focused at different distances cause the image to be blurred with lack of fine detail.

61
Q

Where are the focal points of the astigmatic eye?

A

focal points are in different planes.

62
Q

What causes astigmatism?

A

differences in the degrees of curvature of the cornea and of the lens.

63
Q

Astigmatism is usually do to what?

A

too great a curvature of the cornea.

64
Q

How can astigmatism be corrected?

A

cylindrical lens with different radii of curvature in different planes.

65
Q

What is visual acuity?

A

clearness of vision.

66
Q

How is visual acuity determined by?

A

the sharpness of focus of image on retina and the sensitivity of brain interpretative system.

67
Q

How is visual acuity assessed?

A

the ability to recognize different sizes of letters or symbols at a standard distance.

68
Q

The visual acuity symbolizes what?

A

The smallest details the eye can see

69
Q

What does visual acuity not measure?

A

the total quality of vision.

70
Q

What chart is used to measure visual acuity?

A

The Snellen Eye Chart.

71
Q

Predator animas have eyes in the front of their head meaning what?

A

The are primarily binocular vision.

72
Q

What is binocular vision necessary for?

A

perception of depth.