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OPTM 5032 - Ocular Physiology > Accommodation and Presbyopia > Flashcards

Accommodation and Presbyopia Flashcards

1
Q

What is accommodation?

A

A dynamic change in the power of the eye

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2
Q

What does accommodation provide the eye?

A

The ability to change the point of focus of the eye from distant to near objects

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3
Q

Does the optical power of the lens increase of decrease with accommodation

A

Increase

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4
Q

What unit is accommodation measured in?

A

Diopteres

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5
Q

What is a diopter and how is it measured?

A

a reciprocal meter

measure of the vergence of light

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6
Q

How is accomodation mediated?

A

◦Contraction of the ciliary muscle
◦Release of zonular tension at the equator
◦“Rounding up” of the lens (force exerted by capsule)

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7
Q

How is the increased optical power in accommodation achieved?

A

Through the increased anterior and posterior lens surface curvatures and increased thickness of the lens

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8
Q

Myopes can focus clearly on objects _____ than optical infinity with accommodation

A

closer

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9
Q

Hyperopes can focues clearly on objects at ____ ___ only through an accommodative increase or with + lens

A

optical infinity

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10
Q

What is the refractive index of the cornea?

A

About 1.376

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11
Q

The refractive index of the aqueous humor is about?

A

1.336

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12
Q

Because the refractive indexes of the aqueous humor and cornea are so close the optical affective is?

A

relatively little

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13
Q

The optical power of the cornea comes from?

A

The change in refractive index and positive radius of curvature

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14
Q

the anterior and posterior surface of the lens add or subtract to the optical power of the eye

A

add

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15
Q

The posterior lens surface increases or decreases in curvature and moves backward or forward with accommodation?

A

Increases

Backward

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16
Q

What is the depth of field?

A

The range over which a target can be moved toward or away from the eye without a perceptible change in blur or focus of the image

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17
Q

What is the depth of focus?

A

Depth of focus is the focusing error that can be tolerated without an appreciable decrease in acuity or change in blur or focus of the image on the retina

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18
Q

Depth of focus is dependent on?

A

Pupil size

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19
Q

What does a small pupil say about depth of focus? large pupil?

A

Small - larger depth of focus

Larger - smaller depth of focus

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20
Q

Does the pupil size increase or decrease with accommodation?

A

Decreases (increasing depth of focus)

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21
Q

Does pupil size increase ot decrease with aging? What is this referred to?

A

Decreases

Senile Miosis

(decreased need for add in presbyopic correction- increased depth of focus)

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22
Q

When the eye is at rest focused on distance the resting tension on the zonular fibers spanning the anterior zonule applies what?

A

An outward directed tension on the lens squator throgh the lens capsule

(holds lens in relatively flattened and unaccommodated state)

23
Q

At rest, the eyes have some residual or resting level of accommodation amounting to approx. _____ D. What is this called?

A

1.5 D

tonic accommodation (residual)

24
Q

What is the accommodative triad?

A

◦1. the pupil constricts
◦2. the eyes converge
◦3. the eyes accommodate

25
Q

An accommodative stimulus presented ______ results in a binocular accommodation and convergence response.

A

Monocularly

26
Q

A convergence stimulus in one eye results in ____ _____, _______, and ______ in both eyes.

A

Pupil Constriction

Convergence

Accommodation

27
Q

If a myopic blur is presented to one or both eyes which lens will cause the eyes to accommodate to overcome the imposed defocus?

A

negative lens

28
Q

If a base-out prism is placed in front of the eye will vergence increase or decrease?

A

Increase

29
Q

What can accommodation be induced through?

A

Pharmacologic stimulation

(muscarinic cholinergic agostists)

(pupil constriction ill also occur but no convergence)

30
Q

Accommodative esotropia most often occurs in?

A

Uncorrected persons with hyperopia as a consequence of a need to accommodate even to see distance objects in focus

31
Q

What can block accommodation?

A

Cycloplegia

induced byt topical application of muscarinic antagosists

32
Q

The push-up method in accommodation requires the patient to report?

A

When a near letter chart can no longer be maintained in sharp focus as the chart is gradually brought closer to the eye

33
Q

What is the minus lens to blur method?

A

◦Placing negatively powered trial lenses in front of one or both eyes to blur a distant letter chart stimulating accommodation
◦
◦Letter size is minified - problem

34
Q

What are surgical options for persons with presbyopia?

A

◦Corneal refractive surgery
◦Cataract surgery
◦Accommodative IOLs

35
Q

As we age, there is a (loss/gain) of muscle fibers and (increase/decrease) in connective tissue?

A

Loss

Increase

36
Q

In aging, the contractive force does not (increase/decrease); it (increases/decreases) and is at its max at the age presbyopia manifests

A

Decrease

Increases

37
Q

Where does the inner apex of the unaccommodated ciliary muscle reside in the aging eye?

A

Further forward and inward toward the anteroposterior axis

38
Q

What is presbyopia?

A

The age-related loss in accommodative ability; results in nearly complete loss in accommodative ability by age 50

39
Q

How much of accommodative amplitude is lost between ages 15-35?

A

2/3

40
Q

What is the thickness of the lens capsule at birth and at age 60?

A

11 um at birth

20 um at age 60 (decrease slightly thereafter)

41
Q

Force transmitted per unit of thickness by ____ at age 60

A

half

42
Q

What does increased thickness of the lens compensate for?

A

The loss of elasticity

43
Q

Does the equatorial diameter of the lens increase?

A

Yes

44
Q

When young lenses are removed from the eye they (do/do not) accommate?

A

Do

45
Q

When older lenses are removed from the eye they (do/ do not) change in shape

A

do not

46
Q

How much does the hardness of the lens increase of the life span?

A

four-fold (doesnt stop at age 50)

47
Q

The lens substance must remain suffiecintly pliable so the capsular foces can act on it to ____ it (______) and ______ it (______)

A

Flatten it (unaccommodative)

Curve it (accommodative)

48
Q

Lenticular sclerosis

A

Most commonly articulated explanation for presbyopia

lens becomes harder with increasing age

49
Q

Where are the anterior zonular connections in the young lens?

A

Near the lens equator and exert strong influence on the curvature of the lens

50
Q

Where are the anterior zonular connections in the aged lens?

A

Farther forward than equator, not effective relaxation of the force with ciliary muscle contraction

51
Q

What does the disaccommodation theory suggest?

A

Not caused by a failure of the lens to accommodate but instead a gradual failure of the lens to be held in the unaccommodated form at rest

52
Q

What is the multifactorial theory?

A

Presbyopia results not from any single causal factor, but through global deterioration of accommodative function

Presbyopia is not an end point, but a time point in a gradual, progressive continuum of deterioration of the accommodative structures

53
Q

Optical compensation for presbyopes is achieved with?

A

◦Spectacle lenses
◦Contact lenses
◦Corneal refractive surgical procedures
◦Or artificial intraocular lenses (IOLs).

OPTM 5032 - Ocular Physiology (9 decks)

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