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Physical & Geometric Optics > Module 5 > Flashcards

Module 5 Flashcards

1
Q

What is an abnormal refractive condition of the eye in which images fail to focus on the retina?

A

Ametropia

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2
Q

What are the 3 types of ametropia?

A

Hyperopia
Myopia
Astigmatism

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3
Q

What is myopia?

A

Nearsightedness
A condition in which parallel rays of light come to focus at a point just in front of the retina in the unaccomodated eye

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4
Q

What are the 3 types of myopia?

A

Axial - eyeball too long
Curvature - shorter than avg radius of curvature of cornea, more than avg power to retina
Index - caused by diabetes (lens swells) and cataract forms

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5
Q

What is hyperopia?

A

A condition of ametropia in which sharp image forms posterior to the fovea, indicating presence of inadequate positive vergence (+ power) and requiring plus lenses for correction

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6
Q

What are the types of hyperopia?

A

Axial- eyeball is too short

Curvature - greater than avg radius of curvature of cornea, less than avg power to retina

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7
Q

What is a refractive error that prevents the light rays from coming to a single focus on the retina because of different degrees of refraction in the various meridians of the eye?

A

Astigmatism

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8
Q

What are the types of astigmatism?

A 
Simple hyperopic 
Compound hyperopic
Simple myopic
Compound hyperopic
Mixed
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9
Q

What happens in simple hyperopic astigmatism?

A

Vertical rays are focused on the retina

Horizontal rays are focused behind the retina

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10
Q

What happens in compound hyperopic astigmatism?

A

Both focal points fall behind the retina

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11
Q

What happens in simple myopic astigmatism?

A

Vertical rays are focused on the retina

Horizontal rays are focused in front of the retina

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12
Q

What happens in compound myopic astigmatism?

A

Both focal points lie in front of the retina

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13
Q

What happens in mixed astigmatism?

A

Vertical rays come to a focus behind the retina

Horizontal rays focus in front of the retina

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14
Q

What does clarity of retinal image depend upon?

A

Refractive surface and media (tear film, aqueous, lens, vitreous)

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15
Q

What does cornea contribute in the accommodation process?

A

About 43 D

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16
Q

What does the lens contribute in the accommodation process?

A

About 15 D

17
Q

What is the total power of the eye?

A

60 D

18
Q

What is the change in the focusing power of the crystalline lens?

A

Accommodation effort

Accommodation response

19
Q

What is accommodation effort?

A

Ciliary muscles relax
Zonules relax and
Crystalline lens changes shape

20
Q

What is accommodation response?

A

Increase in the focusing power of the crystalline lens due to an increase in convexity of the anterior surface of the crystalline lens to create sharp images

21
Q

What is the accommodation process for viewing a distance object?

A

Ciliary muscles relax
Zonules are stretched
Lens thins

22
Q

What is the accommodation process for viewing near objects?

A

Ciliary muscles contract
Zonules relax
Lens thicken

23
Q

What is a loss of the amplitude of accommodation?

A

Presbyopia

24
Q

What happens with presbyopia?

A

Lens hardens
Atrophy of ciliary muscles
Loss of muscle tone

25
Q

What is maximum accommodation?

A

+14 D age 8

26
Q

What is accommodation loss scale?

A

Between 8 and 40 1 D every 4 years
Between 40 and 48 1.5 D every 4 years
Between 48 and 72 0.5 D every 4 years

27
Q

What are simple refractive errors determined by?

A

Refractive power of cornea and lens

Length of eyeball

28
Q

What are pathological errors determined by?

A

Degenerative changes in the choroid and retina

Excessive growth of the eyeball in all dimensions

29
Q

What is a normal eye in which all of the rays of light from a distant fixed object are imaged sharply on the retina without the necessity of any accommodative effort.

A

Emmetropia

Physical & Geometric Optics (4 decks)

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