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B3 Methods > Accomodation > Flashcards

Accomodation Flashcards

1
Q

Why is accommodation important?

A

A dynamic process to produce and maintain a focused retinal image

The power of the lens changes to maintain the image.

The lens curvature changes, the lens power changes and focusing changes.

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2
Q

The Accommodative Process

A

There is a change in the shape which leads to a change in the power of the lens

This allows objects at various distance to be focused at the retina.

The only active element is the ciliary muscle, while other parts are passive

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3
Q

What is the only active element of Accommodation?

A

The ciliary muscle, the rest are passive

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4
Q

What allows objects at various distances to be focused on the retina?

A

Change in shape that leads to a change in power of the lens

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5
Q

Smooth muscle with parasympathetic innervation

A

Ciliary muscle

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6
Q

In accommodation, the ciliary muscle does what?

A

The ciliary body contracts and moves forward

The contraction releases the resting tension on the zone less around the lens equator

The lens capsule is able to mold the lens to become more spherical

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7
Q

Function of the lens capsule

A

To mold the lens to become more spherical

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8
Q

Biomechanics of the accommodative process

A

Innervation to the ciliary muscle

Ciliary muscle contracts

Ciliary muscles moves inward and forward

Ciliary ring advances along the ciliary muscle

Choroid and posterior zone lens stretch

Anterior zonular tension decreases, and the zonules relax

Lens capsule mold the crystalline lens, lens becomes more spherical

Lens power increases and focal length decreases

Eye changes focus from distance to near

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9
Q

Accommodation occurs when:

A

The overall power of the lens increases.

Process:

  • Equatorial diameter decreases
  • anterior lens surface moves forward while posterior surface moves backward
  • central anterior radius of curvature becomes more steep
  • central posterior radius of curvature decreases
  • central thickness increases
  • lens sinks 0.3mm due to gravity
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10
Q

Parasympathetic pathway to ciliary muscle

A

Unfocused image on the retina
Blur signals transmitted to visual cortex
Cortical cell produce sensory blur signals
Signal goes to midbrain/oculomotor nucleus/Edinger-Westphal nucleus
Motor command transmitted to ciliary muscle
Ciliary muscle contraction
Crystalline lens deforms to produce an in focus retinal image

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11
Q

Where does the parasympathetic pathway start for the ciliary muscle?

A

Midbrain/oculomotor nucleus/Edinger-Westphal nucleus

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12
Q

How is the motor command transmitted to the ciliary muscle?

A

Oculomotor nerve (CN3) -> ciliary ganglion -> short ciliary nerve -> ciliary muscle

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13
Q

Parasympathetic pathway to the ciliary muscle is coupled with..

A

Pupillary function

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14
Q

When there is no accomodation, the anterior and posterior capsule is..

A

Taught and flat

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15
Q

When there is no accommodation, the ciliary muscle is..

A

Relaxed

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16
Q

What type of eye focuses on a distant target with no need for accommodation? What is the convergence?

A

Unaccommodated Emmetropic eye

Zero

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17
Q

With a near object, the object has _________ rays, leading to an unfocused image on the retina.

The optical power in the eye has to ________ to add positive convergent rays.

A

Diverging

Increase

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18
Q

In the accommodative eye, the image is in focus because of the:

A

Accommodating lens

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19
Q

When an eye accommodates from infinity to a target at 1m (100cm) from the eye, it requires ____ of accommodation (100/100)

A

1D

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20
Q

Accommodation is measured in:

A

Diopters

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21
Q

3 physiological changes in accomodation

A
  1. Eye accommodation
  2. Pupil constriction
  3. Eye converge

AKA Near Reflex

Coupled with parasympathetic innervation from EW nucleus

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22
Q

Convergence, accommodation and pupil constriction occur in..

A

Both eyes.

Even if stimulus is in one eye

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23
Q

Reasons for change in pupil size

A
  1. Controls light
  2. Modifies depth of focus
  3. Varies any optical aberration
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24
Q

Corneal reflex in distance in near fixation

A

Reflex is nasally in distance fixation

Reflex is temporally in near fixation due to convergence

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25
Q

Components of Accommodation

A

Reflex accommodation
Vergence accommodation
Tonic accommodation
Proximal accommodation

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26
Q

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

A

Reflex accommodation

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27
Q

When does reflex accommodation occur?

A

When responding to blur, or reduction in contrast.

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28
Q

When and why is reflex accommodation important?

A

Important for small scanning eye movements/micro saccades

Very important because it makes the fine change under binocular and monocular condition

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29
Q

The change in accommodation induced during fusion all vergences

A

Vergence accomodation

Leads to convergence accommodation/convergence ratio (CA/C)

30
Q

The refocusing that occurs due to apparent nearness (or perceived proximity) of a target

A

Proximal accommodation

Activated by perceptual cues

Stimulated by targets within 3 m of individual

31
Q

“Lead of accomodation”

The residual/resting level of accommodation

Due to baseline stable innervation input from the midbrain

A

Tonic accomodation

Accommodation at rest (0.5 to 1.5 D)

Present even in absence of blur, disparity, and proximal cues

Reduces with age

32
Q

Factors that affect accommodation

A 
Blur
Convergence
Proximal issues
Pharmacology
Minus lens
Diseases
33
Q

Retinal image factors to accommodation

A

Contrast

Spatial frequency

Retinal image motion

34
Q

Nonretinal factors to accommodation

A

Mood

Voluntary effort

Target luminance

Training

35
Q

Type of medication sued best for antagonizing accommodation

A

Muscarinic blockers

36
Q

Prevent acetylcholine from binding

A

Muscarinic blockers

37
Q

Common used muscarinic blockers

A

Tropicamide and cyclopentolate

38
Q

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

A

Tropicamide

39
Q

Effective with sufficient half-life, commonly used in kids

A

Cyclopentolate

40
Q

Other muscarinic blockers used that produce mydriasis and loss of accomodation

A

Atropine (iritis)
Homatropine
Scopolamine

41
Q

A sympathomimetic that causes mydriasis but has no significant effect on accomodation

A

Phenylephrine (adrenaline)

42
Q

Other drugs that affect accomodation

A 
Alcohol
Ganglion blockers
Antidepressants
Stimulants 
Marijuana
Carbonic Anhydrase Inhibitors
Antihistamine
Morphine
43
Q

Conditions that affect accommodation

A 
Diabetes 
Traumatic Brain Injury (TBI) 
Multiple Sclerosis 
Myasthenia Gravis 
Botulism 
Down syndrome 
Glaucoma
Iritis 
Iris Sphincter tear 
Eye trauma 
Adie’s tonic pupil 
Encephalitis 
Syphilis 
Neuro-ophthalmic lesions
44
Q

Gradual age-related irreversible loss of accommodative amplitude

A

Presbyopia

45
Q

When is presbyopia usually reported?

A

40-45 years of age

46
Q

Complete loss of accommodate, due to presbyopia, usually by

A

50-55 years

47
Q

There’s about a _____ loss of accommodation per year due to presbyopia

A

2.5 D

48
Q

Complaints related to presbyopia

A

receded near point of accommodation

blurred vision

discomfort and asthenopia at near.

49
Q

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

A

lens thickness and size increases

springiness of capsule decreases (thickens)

anterior surface curvature increases

stiffer lens

ciliary muscle remains stable

cortex stiffens

zonules become less dense (number of them)

50
Q

Factors that do not change in presbyopia:

A

Zonules still have their elasticity

Ciliary muscle still functions

Motor neuronal pathway still functions

51
Q

How do you treat presbyopia?

A

Plus lenses

52
Q

Forms of treating presbyopia

A

Bifocals, reading glasses, mono vision or bifocal contact lenses, or surgical correction

53
Q

Typical add powers based on age:

A

Early 40s - +1.00 to+1.25

45 - +1.50

50 - +2.00

55 - +2.25

60 and above - +2.50

54
Q

Other accommodative conditions

A

Accommodative excess

Accommodative infacility

Accommodative insufficiency

55
Q

Result of other accommodative conditions

A

Result of medication, illness, or accommodative anomaly

56
Q

Treated with proper distance correction and VT

A

Accommodative excess

57
Q

treated with Proper correction and VT

A

Accommodative infacility

58
Q

Treated with proper distance correction and additional plus lenses

A

Accommodative insufficiency

59
Q

Amount of convergence induced by a change in accommodation

A

AC/A

Accommodation convergence/Accommodation Ratio

60
Q

A change in accommodation is accompanied by a change in:

A

Vergence

61
Q

In accommodation there is:

A

Convergence

62
Q

With no accommodation there is:

A

Divergence

63
Q

Abnormal AC/A ratios are seen in:

A

Binocular problems

64
Q

2 ways of measuring AC/A ratio

A

Gradient determination

Near-far (calculated) determination

65
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

This can be done in the phoropter or with Modified Thorington, through the subjective refraction

Remind the patient to keep the near point target clear to maintain accommodation. Have the patient read the letters

Measure the phoria

Then measure the phoria again through -1.00D lenses added to the refraction

The difference in prism diopters between the phoria with the subjective and the phoria with the -1.00 is the change in convergence

That is – this is how convergence responses to the accommodative stimulus

66
Q

Gradient determination of AC/A calculation

A

(Phoria with minus lens power - baseline Phoria)/absolute power of addition minus lens

67
Q

What is the expected gradient determination of AC/A

A

3/1 to 5/1

Or 4:1 with SD +/- 2

68
Q

Near-far/calculated AC/A ratio

A

PD(cm) + NFD (P’near -Pdistance)

PD = interpupillary distance in cm

NFD = near fixation distance in meter

P’near = near Phoria (eso is plus and exo is minus)

Pdistance= distance Phoria

69
Q

Calculated near-far AC/A is usually ________ than the gradient AC/A because of:

A

Larger

Due to the proximal vergences that influence the near phoria

70
Q

A high AC/A ratio means:

A low AC/a ratio means:

A

Excess convergence with accommodation

Low convergence with accommodation

B3 Methods (2 decks)

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