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Methods BLOCK 3 > Accommodation (prob 9 Qs) > Flashcards

Accommodation (prob 9 Qs) Flashcards

1
Q

Why is accommodation important?

A

It’s a dynamic process to produce and maintain a focused retinal image

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2
Q

What changes in accommodation to maintain the image?

A

The power of the lens

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3
Q

What about the lens changes to accommodate?

A
  • lens curvature
  • lens power
  • focusing
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4
Q

What does the change in lens shape allow in accommodation?

A

Objects are various distances to be focused on the retina

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5
Q

What is the only active element of accommodation?

A

The ciliary muscle

All other parts are passive

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6
Q

Biomechanics of accommodation

A
  • innervation of the ciliary muscle
  • ciliary muscle contracts
  • ciliary muscle moves inward an anteriorly/forward
  • ciliary ring advances appx 0.5mm along with the ciliary muscle
  • choroid and posterior zonules stretch appx 0.5mm
  • anterior zonular tension decreases, and the zonules relax
  • lens capsule molds the lens, becomes more spherical
  • lens power increases, focal length decreases
  • eye changes focus from distance to near
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7
Q

Changes to the lens

A
  • equatorial diameter decreases from 10 to 9.6mm
  • the anterior lens surface moves anteriorly while posterior surface moves posteriorly
  • central anterior radius of curvature changes from 11 to 5.5mm (becomes more steep)
  • central posterior radius of curvature decreases from 5.18 to 5.08mm
  • central thickness increases by 0.36 to 0.58mm (at the nucleus)
  • lens sinks 0.3mm as a result of gravity (denser, heavier)
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8
Q

What causes the lens to change shape in accommodation?

A

Ciliary muscle

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9
Q

What happens to equatorial diameter of lens during accommodation?

A

Decreases from 10 to 9.6mm

Shortens to become more round

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10
Q

What happens to the anterior lens surface during accommodation?

A

Moves anteriorly

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11
Q

What happens to the posterior surface of the lens during accommodation?

A

Moves posteriorly

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12
Q

What happens to the central anterior radius of curvature of lens during accommodation?

A

Becomes steeper

11 to 5.5mm

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13
Q

What happens to the central posterior radius of curvature of the lens during accommodation?

A

Decreases (5.18 to 5.05mm)

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14
Q

What happens to the central thickness of the lens during accommodation?

A

Increases at nucleus (0.36 to 0.58mm)

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15
Q

What happens to the lens in terms of gravity during accommodation?

A

The lens sinks 0.3mm (denser, Heavier)

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16
Q

What kind of innervation does the ciliary muscle have?

A

Parasympathetic

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17
Q

During accommodation, what is the general thing that happens to the ciliary muscle??

A

The ciliary muscle in the ciliary body contracts and moves forward

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18
Q

What does the contraction of the ciliary muscles cause on other parts of the eye?

A

Releases the resting tensions on the zonules around the lens equator

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19
Q

What molds the lens?

A

The lens capsule, to become more spherical

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20
Q

Parasympathetic pathways to ciliary muscle

A
  • unfocused image on retina
  • blur signals transmitted to visual cortex
  • cortical cell produce sensory blur signals
  • signal goes to Edinger-Westphalia nucleus (parasympathetic pathway starts here)
  • oculomoter nerve (CN3)—ciliary ganglion—short ciliary nerve
  • ciliary muscle contraction
  • crystalline lens deforms to produce an in-focus retinal image

This pathway is coupled with pupillary function

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21
Q

Where do blur signals go?

A

Visual cortex

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22
Q

What produce sensory blur signals?

A

Cortical cells

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23
Q

Where does the blur signal go to?

A

Edinger-Westphal nucleus

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24
Q

Edinger-Westphal nucleus

A

Parasympathetic pathways starts here

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25
Q

What is the motor command transmitted to ciliary muscle?

A

Oculomotor nerve (CN3)—ciliary ganglion—short ciliary nerve

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26
Q

What is accommodation coupled with?

A

Pupillary function

-also need to converge eyes to accommodate

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27
Q

The lens during no accommodation

A
  • taught and flat
  • ciliary muscle relaxed
  • convergence demand is 0
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28
Q

When an object is closer than infinity

A
  • object has divergent rays that focus behind the eye
  • lead to unfocused image on the retina
  • optical power of the eye has to increase to add positive convergent rays
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29
Q

In the accommodative eye, the image is in focus because…

A

Of the accommodating lens

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30
Q

How to calculate the accommodative demand

A

50cm
Divide 100 by the distance (100/50)…2D of accommodation is used
-make sure you use cm!

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31
Q

How many diopter needed for 40cm?

A

2.5D

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32
Q

Accommodation triad/near reflex

A
  • eye accommodation
  • pupil restriction
  • eyes converge
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33
Q

What is the accommodation triad /near reflex coupled with?

A

Parasympathetic innervation from the EW nucleus

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34
Q

What happens if accommodative stimulus is presented to one eye?

A

The convergence, accommodation, and pupil contrisction occur in both eyes

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35
Q

Change in pupil size in accommodation

A
  • controls light
  • modifies depth of focus
  • varies any optical aberration
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36
Q

The triad: distance fixation

A
  • no accommodation

- absence of the triad

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37
Q

The triad: near fixation

A
  • accommodation (the red reflex change show change in power, dimmer because the lens changed shape)
  • eyes converge (the corneal reflex more temporally shows convergence
  • pupil constriction
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38
Q

Components of accommodation

A
  • reflex accommodation
  • vergence accommodation
  • tonic accommodation
  • proximal accommodation
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39
Q

Reflex accommodation

A

-automatic adjustment of the refractive state to maintain a focused retinal image

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40
Q

When does reflex accommodation occur?

A
  • responding to blur

- reduction in contrast

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41
Q

What is reflex accommodation important for?

A

Small scanning eye movements or micro saccades

42
Q

Vergence accommodation

A

Change in accommodation induced during fusional Vergence

-leads to the convergence accommodation/convergence ratio (CA/C)

43
Q

PRoximal accommodation

A

Refocusing that occurs due to the apparent (or perceived) nearness (proximity) of a target

44
Q

What is proximal accommodation activated by?

A

Perceptual cues

  • phoropter coming closer to face
  • stimulated by targets located within 3m (within optical infinity)
45
Q

Tonic accommodation

A
  • lead of accommodation (first start of accommodation)

- residual/resting level of accommodation due to baseline stable innervation input from the midbrain

46
Q

What is accommodation at rest?

A

0.5D to 1.5D

47
Q

When is tonic accommodation present?

A
  • present even in the absence of blue, disparity and proximal cues
  • even if nothing else is happening
48
Q

When does tonic accommodation reduce?

A

With age

Kids have a ton of it

49
Q

Factors that affect accommodation

A
  • blur
  • Convergence
  • proximal issues (close to me)
  • pharmacology (meds)
  • minus lens
  • diseases
50
Q

What type of lens will help EVERYONE accommodate?

A

Minus lens

51
Q

Retinal image factors that affect accommodation

A
  • contrast
  • spatial frequency
  • retinal image motion
52
Q

non retinal factors that affect accommodation

A
  • mood
  • voluntary efffort
  • target luminance
  • training
53
Q

Optical cues that affect accommodation

A

Offer information about directionality (of image on the retina), astigmatism, aberrations

54
Q

Non optical cues that affect accommodation

A
  • size
  • proximity
  • apparent distance
  • depth cues
55
Q

When do accommodative errors increase significantly?

A

With changes in eccentricity and retinal image velocity

56
Q

Retinal eccentricity

A

Not on fovea, due to strabismus

57
Q

Are all these factors that affect accommodation happening in isolation?

A

No

Accommodation has a very robust and healthy way of detecting optimally and discriminating fine details

58
Q

Aberrations

A

(On optical cues)

-occur when the peripheral rays don’t coincide with the central and on axis rays

59
Q

Depth of focus

A

Variation/small range in the image distance that is tolerable without a profound defocus
-this influences accommodation as it increases

60
Q

What is accommodation stimulated by in the CNS?

A

Parasympathetic system

61
Q

What is accommodation best antagonized with?

A

Muscarinic blockers

-they block acetylcholine from binding

62
Q

What are some common muscarinic blockers used in practice?

A
  • tropicamide (mydriacly)

- cyclopentolate

63
Q

Trpicamide

A
  • muscarinic antagonist

- very short half life and should not be used to determine the cycloplegic refraction

64
Q

Cyclopentolate

A
  • muscarinic antagonists

- effective with sufficient half life, used frequently in peds

65
Q

What are some other muscarinics?

A
  • atropine
  • homatropine
  • scopolamine

Produce mydriasis and loss of accommodation

66
Q

Atropine

A
  • muscarinic antagonist

- used for Iritis

67
Q

Iritis

A
  • jolted iris
  • inflamed
  • light sensitivity due to focusing back and forth
68
Q

Phenylephrine

A
  • adrenaline
  • sympathomimetic
  • causes mydriasis but has not significant effect on accommodation
  • not muscarinic
69
Q

Other drugs that affect accommodation

A
  • alcohol
  • ganglion blockers
  • phenothiazides and antidepressants
  • CNS stimulants
  • marijuana
  • carbonic anhydrase inhibitors
  • antihistamines
  • morphine
70
Q

Some conditions that affect accommodation

A
  • DM
  • TBI
  • MS
  • myasthenia gravis
  • botulism
  • down syndrome
  • glaucoma
  • iritis
  • iris tear
  • eye trauma
  • aides tonic pupil
  • syphilis
  • neuro-ophthalmic lesions
71
Q

Presbyopia

A

Gradual age-related irreversible loss of accommodative amplitude

72
Q

When is presbyopia typically reported

A

40-45 years old

Some are earlier like little kids who accommodate so much, they will grow up to report presbyopia earlier

73
Q

When do you typically have complete loss of accommodation?

A

50-55 years old

74
Q

How much accommodation do you lose per year in presbyopia?

A

2.5D

75
Q

Complaints of presbyopia

A
  • receded near point of accommodation
  • blurred vision
  • discomfort and asthenopia at near
76
Q

Contributing factors and biochemical changes that lead to the decrease of accommodation

A
  • lens thinkens and size increases
  • springiness of capsule decreases (thickness)
  • anterior surface curvature increases
  • stiffer lens (cataracts)
  • ciliary muscle remains stable
  • cortex stiffens
  • zonules become less dense (number of them, cant relax them enough)
77
Q

What factors do not change in presbyopia?

A
  • zonules still have they elasticity
  • ciliary muscle still functions
  • motor neuronal pathway still functions
78
Q

Treatment of presbyopia

A
  • plus lenses
  • in form of bifocals, reading glasses, mono vision or bifocal CL or even surgical correction

Take into consideration what distance they like to work at

79
Q

Accommodative excess

A
  • treated with proper distance correction and VT
  • adults and children
  • result of medication, illness or even an accommodative anomaly
80
Q

Accommodative infacility

A
  • adult and children
  • result of medication, illness, or even an accommodative anomaly
  • proper correction and vision therapy is treatment
  • have it, don’t know how to use it
81
Q

Accommodative insufficiency

A
  • adult and children
  • proper distance correction and plus lenses
  • result of medication, illness or even an accommodative anomaly
82
Q

AC/A

A

Accommodative convergence/accommodation ratio

The amount of convergence induced by a change in accommodation

83
Q

Change in accommodation is accompanied by…

A

Change in vergence

84
Q

What permits clear, stable single binocular vision across a range of viewing distances?

A

Accommodation and vergence

85
Q

With accommodation there is…

A

Convergence

86
Q

With no accommodation, there is…

A

Divergence

87
Q

Abnormal AC/A ratios cause what

A

Binocular problems

88
Q

What are 2 ways of measuring the AC/A ratio?

A
  • gradient determination

- near-far (or calculated) determination

89
Q

Gradient determination of AC/A ratio

A

Phoria is measured at the same near distance (40cm) but with different lenses to change the accommodative demand

Induce accommodation and measure phoria

90
Q

What is the advantage of gradient determination of AC/C ratio?

A

At the same distance, the proximal accommodation is controlled

91
Q

How can gradient determination of AC/A ratio be done?

A

In phoropter or with modified thorington, through the subjective refraction
-with prisms in phoropter to dissociate to provide a open loops so accommodation is no influenced by any other stimulus

92
Q

What to tell patient when doing gradient determination of AC/A ratio

A

Remind the patient to keep the near point target clear to maintain accommodation. Have patient read the letters, measure the phoria
-measure phoria again through -1.00D lenses added to refraction

93
Q

What is the change in convergence in gradient determination of AC/A ratio

A

The difference in prism diopter between the phoria with the subjective and the phoria with the -1.00D lens

-This is how convergence responds to the accommodative stimulus

94
Q

AC/A=

A

(Phoria with plus or minus lenses-baseline phoria)/(absolute power of additional minus or plus lenses)

95
Q

Expected AC/A

A

3/1 or 5/1 (3:1 To 5:1)

Some state 4:1 with SD+/- 2

96
Q

If the near phoria is 2EP’ through subjective and then 7EP’ through -1.00D lens, what is the AC/A ratio?

A

(7-2)/1

5/1

97
Q

If near phoria is 2XP’ through subjective and then 7EP’ through -1.00D, what is AC/A?

A

(7-(-2))/1
9/1

Absolute change in the phoria

98
Q

Near-far/calculated AC/A ratio

A

AC/A=PD(cm) + NFD(P’near-Pdist)

PD=pupillary distance (cm)
NFD=near fixation distance in meter
P’near=near phoria (eso is plus and exo is minus)
Pdist=distance phoria

99
Q

What is the AC/A ratio if the PD=60mm, 2XP at distance, 10XP’ at near (40cm)

A

AC/A=6+0.4(-10-(-2))

=2.8

100
Q

What does a high AC/A ratio mean?

A

There is excess convergence with accommodation

101
Q

What does a low AC/A ratio mean?

A

There is low convergence with accommodation

Methods BLOCK 3 (6 decks)

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