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1 Strab > Theory 1 > Flashcards

Theory 1 Flashcards

1
Q

What tells us about how the person is habitually calculating space

A

Phoria. When the eye is covered, the eye moves out of alignment and when uncovered, alignment is quickly restored at blink or within 10 seconds.

Distorted perception?` will calculate space incorrectly. Ex: Swing too early.

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2
Q

How did Kraskin define amblyopia?

A

Binocular dysfunction manifesting as amblyopia.
2 eyed problem, both channels are not working properly.
“There is no vision in an eye”

The channels may work together. One channel seems to take the lead for “what” activities and the other for “where” activities.

Amblyope channel gives more info about the periphery using M cells.

Non amblyope channel gives more info about the center channel using P cells.

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3
Q

Amblyopia prevalence in military, preschool, and patients seeking vision care

A
  1. 6% military
  2. 8% pre school
  3. 3% patients
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4
Q

Eccentric fixation

A

Looking with the line of sight away from the fovea in an otherwise healthy eye. Pt not using fovea when viewing the world.

Can be:

  • steady: harder to break. Fovea remains in same location relative to axis of fixation.
  • or unsteady: easier to break. Fovea will appear to move relative to axis of fixation.
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5
Q

Eccentric fixation location and corresponding degrees

A 
Foveal center- 0 
Foveal off center 0 to 1 
Parafoveal 1 to 3
Paramacular 3 to 5
Peripheral greater than 5
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6
Q

VA as a function of eccentricity

degrees off foveal center compared to VA

A 
1/2, 20/25 
1, 20/30 
2, 20/40 
3, 30/50 
4, 20/60 
5, 20/70 
10, 20/100 
20, 20/200
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7
Q

Pts VA is 20/100 and eccentric fixation is 3 degrees. What does this mean?

A

EF makes acuity at least 20/50. The other part of acuity loss is due to a sensory component such as suppression.

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8
Q

Eccentric viewing

A

The person uses a point near the fovea to look with due to LOSS of vision. The loss can be optical, retinal, or neuro.

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9
Q

Difference between EF and EV

A

EF: Not using fovea in a healthy eye
EV: Not using fovea due to loss of foveal vision due to optical, retinal, or neuro.

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10
Q

Pleoptics

A

A method of treating amblyopia due to pt using eccentric fixation. Dazzle the eccentric location with high illumination while protecting the fovea. The fovea will then be more responsive to the fixation stimuli.

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11
Q

Prevalence of amblyopia and or strabismus

A

4-6%

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12
Q

Eso compared to exo deviations

A

eso : exo is 3: 1

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13
Q

Prevalence of eso or exo deviations in infantile onset cases

A

This is birth to 6 months.

85% are isotopes with a mean deviation of 40pd.

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14
Q

Definition of amblyopia

A

20/40 or worse or 2 line difference between eyes.

Abnormal best corrected monocular spatial vision associated with a history of abnormal visual experience

**Must have abnormal life experience or else you won’t develop amblyopia

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15
Q

If it turns early…..

A

Usually going to be ET, high (40pd), and unilateral. Likely not due to hyperopia since accommodative ET comes later

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16
Q

___% develop normal binocularity. __% develop strab/amblyopia

A

95%

5%

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17
Q

Optometric suppression vs neural suppression

A

Optometric: Conflicting or confusing visual info is suppressed as part of the normal mechanism of seeing. Inner geniculate leaflets. Purpose is intermittent central suppression.

Neural: Deep suppression becomes habitual and these behavior patterns become the norm. Seen in amblyopia or strabismus. occurs in V1 due to locus ceruleous.

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18
Q

How does strab/amblyopia preserve binocularity

A

Makes it easier to rely on the central flow through one visual channel. Suppresses the central vision to preserve the peripheral. Spatial perception is still good.

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19
Q

White noise concept of behavior

A

Infant is constantly trying different ways of using their hardware.

Younger the infant- more array of behavior. All tropics and refractive conditions.

The infant seeks stimulation!

Has to do with Hebbian synapses. At first, everything connects to everything. Experiences strengthen beneficial connections. Increases the potential to detect JND.
40% of brain tissue is removed in first couple of years.

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20
Q

Why does V1 send signals back to LGN

A

Attention mechanism. Part of seeing what is important.

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21
Q

The binding problem

A

62 brain centers. Memory about an object is not in 1 location, it is stored all around the brain. Connected by locus ceruleous and has to do with gathering/filtering information coming in. This allows for JND.

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22
Q

When do purposeful bilateral movements begin to emerge?

A

first few months. Earlier, just reflexive.

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23
Q

Accommodation after birth

A

Birth -3 months: 5D of accommodation. 20cm target.

3-6 months: Child begins to control accommodation.

6 months: Full control

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24
Q

Do asymmetries in binocularity cause development of asymmetries in bilateral use of the body?

A

Rarely. Usually the other way around.

Could be due to trauma or disease of the eye.

25
Q

How common is congenital strab?

A

Very low

26
Q

Chaos theory vs butterfly

A

Belief that there must have been a big problem in development to cause a big problem in visual field when in fact it is due to the butterfly effect- tiniest thing could go wrong and cause something big to happen to visual system. Do good case history but parents may not know the cause.

27
Q

Development of strabismus at different ages

A

3-6 months: 40-45pd ET with deep amblyopia
6-18 months: 40-45pd ET without amblyopia
18-30 months: Moderate ET (18-25pd blind spot), XT, or refractive amblyopia
3-5 years: Accommodative ET with high plus (+4 to +7) and no amblyopia.

^^Hyperopia is a risk factor. But only 5% with that Rx will develop accommodative ET

28
Q

ET occurs in 3 amounts

A

small (5-8pd) Usually with anomalous projection and or EF. Use 4 BO test.

Medium: 18-25pd. Blind spot. Usually no amblyopia.

Large: 40-45pd. Uses nose as occluder.

29
Q

XT

  • Onset is usually when?
  • What is it associated with
A

Onset before age 2. Between 2-6 years.
Associated with alternating deviation, hypoxia at birth, delayed developmental milestones and neuro involvement.

56% of constant XT and 19% of intermittent XT present with neuro or ocular pathology.

30
Q

__% of constant XT and __% of intermittent XT present with neuro or ocular pathology

A

56% constant and 19% IXT

31
Q

When would you see amblyopia with XT?

A

When surgery caused it. Consecutive XT

32
Q

Prevalence of XT

A

Intermittent- 76%
Constant- 25%

Basic- 56%
CI type- 21%
DE type- 21%

*most are I and basic

33
Q

Most common systemic and ocular condition with XT

A

Brain injury or ADD and ROP or nystagmus

34
Q

Non comitant. Prognosis is better if

A

they have not had surgery (due to scar tissue)

35
Q

3 P’s

A

Paralysis- Loss or impairment of muscle function/feeling.
Paresis- partial paralysis
Palsy in optometry- Specific paresis
Palsy in medicine- has to do with tremor. Paralysis affecting 1 muscle.

36
Q

__% of people older than 19 that have strabismus bc of paresis. Most due to which nerve? Due to which top 3 causes?

A

90%
Most due to 6th nerve

26% due to undetermined reason
20% head trauma
17% vascular

37
Q

Frequency of A and V syndrome

A

V Eso- 41%
A Eso- 25%
V Exo- 23%
A Exo- 11%

38
Q

Other names for Double hypers

A

Dissocisated vertical diplopia (DVD)
Dissociated vertical deviation (DVD)
Alternating cisumduction

39
Q

Common cause of DVD

A

Secondary to surgery or trauma. They do not appear strabismic. Not a barrier to successful VT

40
Q

When does DVD come out?

A

When the total amount of visual field that they use is restricted. Mid periph and peripheral help lock the 2 channels together

41
Q

105 ET were followed over a 10 year period. __% had a DVD

A

92%

42
Q

How can a weakening of the muscle be achieved

A

Recession. Or short term by injecting botulin toxin into the muscle- short term paresis of an EOM to allow ipsilateral antagonist to gain an advantage for cortical fusion.

43
Q

How long does botulinum toxin last

A

dose peaks 5-7 days after injection. Lasts 3-8 months. Mean near 4.

Could be used for strab, migraines, blepharospasm and lid retraction

44
Q

__% of the population has IXT yet __% of cases of strab surgeons

A

1%

25%

45
Q

On IXT, how many US OMDs only do surgery compared to international groups

A

US OMD: 50% do surgery first
International OMD: 14% do surgery first.

Other % try other options first

46
Q

Avg number of operations

A

2.8 to 3.4 surgeries to get a person within +/- 10pd of orthophoria.

47
Q

How do ear aches cause ET at young age

A

CN 6 travels near the mastoid. Infection may cause temporary decrease in nerve conduction to the muscle causing an underaction. If brain cannot correct this with signals, the pt will turn their head towards the problem, allowing the eye to slip in so rectus muscle doesn’t have to work as hard. Newly formed ET.

Could either: Turn fact, send out more signal until maxed, suppress the eye, or let the eye turn in.

48
Q

When are ear aches more significant - when are the critical times

A

Birth to 6 months when pt is in prone posture a lot

Age 6-18 months beginning to be in upright posture.

**Different orientation of the semi circular canals

49
Q

Torticollis

  • What is it
  • Usually develop what deviations
  • how many develop strab if left untreated
A

Frozen head tilt
Vertical deviations
2/3 if left untreated.

50
Q

How many tibia torsion patients will develop strab

A

2/3 to 3/4

Restricted movements in lower part of body sets the stage for learning how to move symmetrically.

51
Q

What asymmetries in the body can cause visual asymmetries

**main point: Look for functional cues before prism!

A
  • Torticollis 2/3
  • Tibia torsion 2/3 to 3/4
  • Cerebral palsy. First demonstration if you want to get something to move in one direction, move it in the opposite direction to start.
  • Hip dysplasia
  • Functional leg length difference (ex, hips rotate when walking.) Refer to therapist!
  • Actual leg length difference. Refer to orthoptics
  • VOR: If VOR is not triggered
52
Q

Diplopia

A

The conscious awareness of seeing 2 images of a single object which appear in 2 different areas of space at the same time

See 2 of the same images- 2 stars

53
Q

Confusion

A

Each eye is directed towards a different object. Confusion occurs when the images of the 2 objects compete to be represented on the internal representation of reality for the same location in space at the same time.

More devastating that diplopia, which we have all the time. Drives person to make a change- converge more, diverge more, unilateral blur (refractive or amblyopic) to make one eye more dominant.

See 3 images, 2 objects.
+, circle, overlapping + and circle

54
Q

The need to resolve ___ drives the process of adaptation

A

Confusion

55
Q

Suppression occurs where

A

Foveal or parafoveal. 3-4 degrees of high spatial frequencies.

Much of the visual info from the periphery is used

Strab and amblyopia is developed to preserve binocularity, not give it up.

Avoiding confusion by suppressing the center 3-4 degrees. Then can use the rest of the eye!

56
Q

5 ways to resolve confusion

A
  1. Tune out one channel by suppression of central 3-4 degrees. This occurs early in neurology and costs a good deal of energy to shut down flow.
  2. Physically cover an eye
  3. Blur 1 channel with single sided refractive condition.
  4. Shift relative position of 2 images by making an eye turn more or less. AXT (flax hypothesis) or ET (micro, medium, or large)
  5. Reprogram the directional sense of one eye using anomalous retinal correspondence (ARC) or anomalous projection (AP). Cheap energy solution to rewire the eye !
57
Q

Flax hypothesis

A

resolve confusion by shifting position of two images- May develop AXT to have 2 areas of space that can perceptually be used.

58
Q

Pt has a vertical. Observe their

A

Gait/walk/posture,

1 Strab (2 decks)

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