7-8. Strabismus III+IV

Question 1

What are the 6 sensory aspects of strabismus?

Answer 1

• Visual Acuity;
• Fixation;
• Suppression;
• Stereopsis;
• Motor fusion;
• Anomalous correspondence

Question 2

Fixation is always at the ... and is always ... in patients with .... In amblyopia, fixation is always ... and ..., but always .... Occsaionally, the macula of the deviating/ amblyopic eye .... Then the fixation is ... but ..., this is called ... and is a ... phenomenon. The cause of this is .... Deviation is typically ... degrees and so cannot be seen with .... We should worry about this when ... or ....

Answer 2

Fixation is always at the central/ macula and is always steady in patients with normal acuity. In amblyopia, fixation is always central and unsteady, but always around the macula. Occsaionally, the macula of the deviating/ amblyopic eye does not have motor superiority. Then the fixation is steady but eccentric, this is called eccentric fixation and is a monocular phenomenon. The cause of this is unknown. Deviation is typically 1-3 degrees and so cannot be seen with casual observation or a cover test. We should worry about this when VA is bad or there is anisometropia >4DS.

Question 3

How can eccentric fixation be diagnosed?

Answer 3

Using a visuoscope on a direct ophthalmoscope. Patient should be dilated and done with other eye covered, because this is a monocular phenomenon. Ask px to look at the circle, move the circle little by little. Assess how much deviation there is coompared to the foveal reflex. Compare dominant eye fixation with amblyopic eye. Can also use Haidenger’s Brushes, but this is not used anymore. OCT can also be used to assess eccentric fixation.

Question 4

Can eccentric fixation be treated?

Answer 4

No, eccentric fixation cannot be fixed. Treatments options available currently doesn’t improve VA, therefore there is no point of treating.

Question 5

What are the 3 causes of monocular double vision?

Answer 5

• Uncorrected astigmatism;
• Cataract;
• Tear film abnormalities

Question 6

What is true diplopia? What is the cause of binocular double vision (diplopia)?

Answer 6

True diplopia can be resolved by closure of one or other eye. This strongly suggests misalignement and is sometimes a result of retinal surgery.

Question 7

Diplopia in strabismus usually does not occur if .... However, in ..., diplopia always occurs. Diplopia occurs for ... after the age of ... . This is the age of .... This is often caused by ... or ... palsy. Diplopia should always ... and we should always suspect .... This should also be differentially diagnosed from ....

Answer 7

Diplopia in strabismus usually does not occur if the onset is before visual maturity. However, in Duane's syndrome, diplopia always occurs. Diplopia occurs for acquired starbismus after the age of 7 . This is the age of visual maturity. This is often caused by CN6 or CN4 palsy. Diplopia should always be investigated and we should always suspect intracranial pathology. This should also be differentially diagnosed from monocular double vision.

Question 8

When an esotropic px is viewing binocularly, will they notice their eye turn? What about when they are viewing monocularly?

Answer 8

No, px will be unaware of their eye turn due to adaptations, including reorganisation of the fovea and retina along the posterior pole. Px will only recognise that their eye is turned when looking in a mirror. When monocular with the turned eye, the eye will pick up fixation.

Question 9

In RET esotropia, px may see double, where one image forms at the ... and the other at the ... part of the ... of the ... eye that corresponds to the ... of the good eye. The second image is projected into the brain incorrectly and tends to have ... as it is not at the .... The other image will be seen to the ... of the clearer image.This is therefore ... diplopia.
In exotropia, the ... is stimulated on the strabismic eye, therefore the other image will be seen on the .... This is therefore called ... diplopia.

Answer 9

In RET esotropia, px may see double, where one image forms at the fovea of the good eye and the other at the nasal part of the retina of the strabismic eye that corresponds to the fovea of the good eye. The second image is projected into the brain incorrectly and tends to have reduced resolution as it is not at the macula. The other image will be seen to the right of the clearer image.This is therefore uncrossed diplopia.
In exotropia, the temporal retina is stimulated on the strabismic eye, therefore the other image will be seen on the left. This is therefore called crossed diplopia.

Question 10

What is confusion in BV? What is it caused by?

Answer 10

Confusion is when different objects are seen in the same direction. This is caused by both macula seeing different objects but both perceiving them as being straight ahead in position. This is rarely seen in clinic. Px will tend to develop suppression scotoma at least as large as the angle of deviation.

Question 11

Suppression is a ... phenomenon and is thought to arise from .... Suppression can be tested with 4 different tests: ..., ..., ... and using ....

Answer 11

Suppression is a binocular phenomenon and is thought to arise from binocular rivalry. Suppression can be tested with 4 different tests: Worth Four Dot Test, Polarised letters or targets, Bagolini Red Filter Ladder and using Synoptophore.

Question 12

Suppression scotoma is the ... of the eye. It emcompasses the fovea to ... (...), which is the ... mapped onto the retina. The primary function of the suppression scotoma is to .... Suppression can exists with ..., but ... cannot exist without suppression. The ... of the scotoma may be similar in most px, but the ... will vary.

Answer 12

Suppression scotoma is the suppressed area of the eye. It emcompasses the fovea to point Z (zero measure point), which is the angular deviation mapped onto the retina. The primary function of the suppression scotoma is to remove diplopia and confusion. Suppression can exists with amblyopia, but amblyopia cannot exist without suppression. The size of the scotoma may be similar in most px, but the depth will vary.

Question 13

What are the associations between alternating ET and suppression?

Answer 13

Alternating ET indicates that the px has alternating suppression. Suppression can be unilateral, alternating and differing based on focal distance.

Question 14

The Worth Four Dot Test uses a special torth viewed with .... The red lens allows px to see ..., whereas the green lens allows px to see .... Given that the px has red lens over the right eye and that the px sees 3 dots, this px has ....

Answer 14

The Worth Four Dot Test uses a special torth viewed with red-green glasses. The red lens allows px to see two dots, whereas the green lens allows px to see three dots. Given that the px has red lens over the right eye and that the px sees 3 dots, this px has suppression on their right eye.

Question 15

How does suppression scotoma correlate with retinal image?

Answer 15

The depth of the suppression scotoma is related to the size of the retinal image. The closer the W4dot torch, the larger the retinal image and more dense the suppression. Suppression is refraction independent.

Question 16

What would a strabismic and an amblyopic px see with Worth Four Dot Test at 20cm?

Answer 16

They will both see 4 dots at 20cm

Question 17

Suppression Scotoma size with Worth 4 Dot Test:
* 33cm = ...º
* 1m = ...º
* 2m = ...º
Size and depth of scotoma can affect ...:
* 6-3º of scotoma allows ... = ...
* 3-1º of scotoma allows ... = ...
* <1º allows foveal fusion = ...

Answer 17

Suppression Scotoma size with Worth 4 Dot Test:
* 33cm = 6.4º
* 1m = 2.3º
* 2m = 1º
Size and depth of scotoma can affect stereopsis:
* 6-3º of scotoma allows peripheral fusion = fly or worse
* 3-1º of scotoma allows macula fusion = animals
* <1º allows foveal fusion = wirt circles

Question 18

What are the approximate VA associated with 40 seconds of arc and 20 seconds of arc of stereopsis?

Answer 18

40 seconds of arc = 6/12
20 seconds of arc = 6/6

Question 19

Physiological considerations of Titmus Fly test:
* Titmus Fly - px with ET up to ...pd can have fly stereo
* Animals - px with ET up to ...pd can have ... animals; if have ... seconds of arc, there is no chance of deterioration
* Wirt Circles - circles can appear ...

Answer 19

Physiological considerations of Titmus Fly test:
* Titmus Fly - px with ET up to 15pd can have fly stereo
* Animals - px with ET up to 8pd can have 2-3 animals; if have 200 seconds of arc, there is no chance of deterioration
* Wirt Circles - circles can appear up or displaced towards the suppressed eye

Question 20

Contour stereopsis is a ... phenomenon like .... ... gets gradually larger towards the .... This allows slight ... and ....

Answer 20

Contour stereopsis is a graded phenomenon like visual acuity. Receptive fields gets gradually larger towards the periphery. This allows slight misalignment and peripheral stereopsis.

Question 21

Which stereopsis test is highly specific for esotropia but will often miss exotropia and cannot find refractive amblyopia?

Answer 21

Titmus Randot test - can find intermittent ET and alternating ET. Can be performed at age 3. Tend to be more yes/no than contour stereopsis.

Question 22

What are the stereopsis passing norms for 3 year olds with Fly and Randot?

Answer 22

All children aged 3 yo and older can pass the Fly tetst if physiologically capable
90% of 3 yo and essentially all 4 yo pass the large forms of Randot

Question 23

What are the paed norms with the Animals on Titmus Fly and Randot?

Answer 23

By the age of 4, most children should pass all 3 plates on the animal subtest of Fly and Randot, which are not significantly different.

Question 24

What are the paed norms with the Wirt Circles?

Answer 24

• All children older than age of 6yo should achieve 40 seconds of arc
• 4yo = at least 4 circles = 140 seconds
• 5yo = at least 6 circles = 80 seconds
• 6yo = at least 9 circles = 40 seconds

Question 25

How does depth perception differ from stereopsis?

Answer 25

Depth perception is a result of monocular cues and binocular cues. No stereopsis does not result in no depth perception, but it does result in reduced depth perception.

Question 26

Motor fusion should only be conducted when there is ... and .... This mostly used on ..., mostly XT. Using a pen torch, ... should be assessed with .... Some sensory fusion is needed, therefore should use ..., or ....

Answer 26

Motor fusion should only be conducted when there is good VA and sufficient stereopsis. This mostly used on intermittent tropic px, mostly XT. Using a pen torch, Hirschberg reflex should be assessed with loose prisms. Some sensory fusion is needed, therefore should use 2 or 3 animals, or Worth 4 Dot at 3 metres.

Question 27

Anomalous Correspondence is a ... that occurs in most strabismics. This is a ... phenomenon that occurs in the ... of the brain. This is when there is rearrangement of the ... of the strabismic eye, so that it .... This occurs in the .... This is usually tested with .... With time, anomalous correspondence can become ..., therefore px may experience ... after strabimus surgery. This can be predicted with ... or with ... of the strabismus.

Answer 27

Anomalous Correspondence is a spatial adaptation that occurs in most strabismics. This is a binocular phenomenon that occurs in the cortex of the brain. This is when there is rearrangement of the correspondence of the receptors of the strabismic eye, so that it matches that of the fixating eye. This occurs in the periphery with central (macula) suppression. This is usually tested with Bagolini lenses. With time, anomalous correspondence can become central, therefore px may experience diplopia after strabimus surgery. This can be predicted with Worth 4 Dot or with prism neutralisation of the strabismus.

Question 28

What are Bagolini Glasses?

Answer 28

Bagolini glasses are like a pair of Maddox rods that are clear and orientated 45º and 135º

Question 29

How is anomalous correspondence assessed with Bagolini glasses? What will the px report if they are:
1. Normal (not strabismic), with normal correspondence
2. Px with ET, diplopia and normal correspondence
3. Left ET, abnormal correspondence and left suppression

Answer 29

Px is asked to look at a pen torch while wearing Bagolini glasses.
1. Px with normal correspondence and no strabismus will see a even cross with a dot in the middle of the cross. The left eye sees the line going from top left to bottom right and right eye sees the other.
2. Px with esotropia, diplopia and normal correspondence will still see a cross but the lines will cross near the bottom end of the cross and px will see two dots on either lines.
3. Px with left esotropia, abnormal correspondence and left suppression will see an even cross with a centre dot, but the left line will appear to be disconnected around the dot. This is the most common scenario.

Question 30

Amblyopia stands for ... or ... in Greek. This is the reduction in ..., including ... & ... of one or both eyes that is not improved by ... and occurs in the absence of ocular or ... pathology. Amblyopia must also occur with ... and/ or .... In rare incidence, it may also occur with occlusion from ..., ... or ....

Answer 30

Amblyopia stands for dull vision or lazy eye in Greek. This is the reduction in visual capacity, including VA & quality of one or both eyes that is not improved by refractive correction and occurs in the absence of ocular or visual pathway pathology. Amblyopia must also occur with misalignment and/ or anisometropia. In rare incidence, it may also occur with occlusion from cataract, corneal dystrophy or ptosis.

Question 31

Why should amblyopia be treated? (4)

Answer 31

• Amblyopia reduces binocularity, which reduces hand-eye coordination in px, espeically for playing high level small ball sports
• A number of vocations require adequate vision in each eye e.g. pilot, police, army, heavy vehicle
• Provides a spare eye for the px in case of diseases/ low vision
• Amblyopia treatment is an essential part of treatment for strabismus

Question 32

How common is amblyopia in developed countries?

Answer 32

Around 2 to 6% prevalence in developed countries.

Question 33

Is amblyopia development genetic?

Answer 33

No, amblyopia develops during the post-natal stage where visual experience is a huge factor. The post-natal refining processs includes competition for cortical space between projection from each eye. Ocular dominance is determined depending on visual input from each eye.

Question 34

The post-natal refining process relies on ... during the .... Clinical evidence have shown that this period remains until the age of ... yo.
This was demonstrated in kittens and .... Amblyopia can be triggered by:
* ... such as ..., ..., ...
* ...
* or both.

Answer 34

The post-natal refining process relies on visual input during the sensitive period/ critical period. Clinical evidence have shown that this period remains until the age of 11 or 12 yo.
This was demonstrated in kittens and macaque. Amblyopia can be triggered by:
* Deprivation of form vision such as cataract, ptosis, unequal hyperopia
* Abnormal binocular interaction
* or both.

Question 35

How does deprivation amblyopia arise?

Answer 35

Clarity of the retinal image on one eye is not matched, therefore it doesn’t compete with the other eye. Axons of the eye with clearer image take over the binocular cells through ocular dominance .This occurs in cataracts or high unilateral refractive error.

Question 36

How does anisometropic amblyopia arise?

Answer 36

Refractive blur in one eye causes the neural signals from that eye to be weaker than the neural signals from the other eye. Neural signals depend on contrast, not absolute light levels.

Question 37

How does strabismic amblyopia arise?

Answer 37

This occurs due to abnormal binocular interaction. This occurs if there is different images at corresponding points due to strabismus, causing diplopia. Diplopia drives the development of suppression, therefore leading to amblyopia.

Question 38

The depth of amblyopia to achieve suppression of diplopia in strabismus is ... to .... This is ... of the ... of strabismus.
The depth of amblyopia in ... is related to the amount of ..., same with the severity of ....

Answer 38

The depth of amblyopia to achieve suppression of diplopia in strabismus is 6/30 to 6/60. This is independent of the angle of strabismus.
The depth of amblyopia in anisometropia is related to the amount of anisometropia, same with the severity of cataracts.

Question 39

What is an amblyogenic factor?

Answer 39

An amblyogenic factor is a condition that will cause amblyopia if present during the sensitive period.

Question 40

Rank the amblyogenic factors from highest prevalence to lowest.

Answer 40

Anisometropia > Strabismus > Visual deprivation > Organic (morphological or dietary insufficiencies) > Secondary to nystagmus

Question 41

How can nystagmus be detected?

Answer 41

Using ophthalmoscopy, specifically visuoscopy. Track movement of gaze while looking at a specific blood vessel on px’s fundus.

Question 42

How do younger children with amblypia respond to treatment compared to older children?

Answer 42

Younger children respond:
* Quicker - faster VA improvement
* Better - better final acuity
* Happier - better compliance
* More complete - better binocular function

Question 43

What are the sensory impacts of amblyopia?

Answer 43

• Reduced contrast sensitivity + Loss of high spatial frequency info
• VA reduction both D & N
• Spatial localisation impaired
• Reduced binocularity - bino summation, sensory fusion, stereopsis
• Visual processing speed reduced

5 impacts

Question 44

What are the motor impacts of amblyopia?

4 impacts

Answer 44

• Poor fixation
• Poor eye movements - inaccurate saccades, jerky pursuits
• Poor motor fusion: strabismus > Poor accommodation/ vergence
• Poor accommodative function - increased lag, remote NPA, reduced facility monocularly

Question 45

What are the 3 steps of amblyopia management?

Answer 45

1. Spectacle correction to provide the clearest retinal image possible to the amblyopic eye - as high plus as possible and must give exact Rx for full time wear
2. Occlusion/ Patching - force fixation with amblyopia eye and to decrease strength of neural signals coming from dominant eye. In mild amblyopia, translucent patch, atropine or change Rx on good eye may be sufficient.
3. Assess strabismus - treat any strabismus, may req glasses, surgery, vision therapy or prisms

Question 46

In esotropia:
* Spectacles are helpful in ...% of cases
* Spectacles are curative in ...% of cases
In exotropia:
* Spectacles are helpful in ...% of cases
* Spectacles are curative in ...% of cases

Answer 46

In esotropia:
* Spectacles are helpful in 90% of cases
* Spectacles are curative in 70% of cases
In exotropia:
* Spectacles are helpful in 70% of cases
* Spectacles are curative in 50% of cases

Question 47

Surgery should be considered for strabismus that is ... and considered .... The aim is for a better ... and readjust ... for the ... the success rate is ...% over the first two years and ...% in the long term. There is 10% chance that px may also improve .... Surgery is the only option for ....

Answer 47

Surgery should be considered for strabismus that is constant and considered uncosmetic. The aim is for a better appearance and readjust muscles for the distorted innervational pattern the success rate is 90% over the first two years and 60-70% in the long term. There is 10% chance that px may also improve stereopsis. Surgery is the only option for infantile esotropia.

Question 48

Which patients will benefit from vision therapy?

Answer 48

Px with intermittent strabismus of phoria, usually with XT.
Px has to be older than 8yo so that they understand what is required.
Px needs to have at least 200 seconds of arc of stereopsis (3 animals).