Sensory adaptations

Question 1

What is meant by sensory

Answer 1

relating to the sense of vision

what the eyes see, as opposed to motor which relates to the movement of the eyes.

Question 2

What is meant by adaptation

Answer 2

the process of adapting to environmental conditions or the quality of stimulation

Question 3

Example 1 of sensory

Answer 3

a strabismus surgery result may be described by the change in the strabismus angle, 50 XT pre-op to 5 XT post-op (motor outcome) or by the change in vision, diplopia pre-op and BSV post-op (sensory outcome).

Question 4

Example 2 of sensory

Answer 4

a sensory adaptation can occur following a change in the quality of visual stimulation received by the visual system

Question 5

Is it possible for BSV to develop in the presence of infantile ET?

Answer 5

Surgical alignment of infantile ET in a young child gives the best chance of BSV developing, but despite good alignment stereoacuity is likely to be subnormal.

Question 6

What would be the consequence if the infantile ET was untreated?

Answer 6

Successful surgical alignment of early onset ET in adulthood can result in BSV, but this is likely to be very gross BSV. If BSV can be achieved in adulthood, what would you expect the clinical scenario to be?
Animal evidence supports that some binocular visual experience is necessary if recovery of any binocular vision is to be achieved.

Question 7

What would be the consequence of an untreated unilateral cataract?

Answer 7

In an older child with a mild unilateral cataract, observation may be indicated rather than early surgery. For example: if they wore occlusion well and maintained an acceptable level of vision in their amblyopic eye. They may have a small angle secondary XT and no BSV.

Question 8

Types of correspondence

Answer 8

Harmonious ARC
Unharmonious ARC
Paradoxical

Question 9

Note about infantile cataract

Answer 9

Would you correct the refractive error of the amblyopic eye even if they did not have BSV?
Why not leave the affected eye uncorrected?
What would this child gain from wearing refractive correction in their amblyopic eye?

Question 10

What is harmonious ARC

Answer 10

the angle of anomaly is equal to the objective angle of deviation (objective angle > subjective angle & subjective angle = 0)

Question 11

What is unharmonious ARC

Answer 11

the angle of anomaly is less than the angle of deviation (objective angle > subjective angle & subjective angle > 0)

Question 12

What is paradoxical ARC

Answer 12

If the localization of the subjective and objective angles is crossed or uncrossed it is called

Question 13

What is the angle of anomaly

Answer 13

difference between the objective angle of deviation and the subjective angle of deviation

Question 14

What is incongruous diplopia

Answer 14

separation of the diplopic images (when assessed subjectively) does not correspond with the objective angle of deviation, occurs in unharmonious abnormal correspondence. This may occur when a patient with abnormal correspondence requires less prism than expected to join diplopia.

Question 15

What is an example of incongruous diplopia

Answer 15

For example: 5∆ ET with abnormal correspondence as a child, ET angle increases over time, patient with a 20∆ ET reports homonymous diplopia, PCT measures 20∆ ET but shows BSV responses with 15∆ BO prism.

Question 16

What is an example of paradoxical diplopia

Answer 16

For example: 8∆ET with abnormal correspondence as a child, ET angle increases over time, surgery to reduce ET as an adult, small 4∆ET post-operatively but the patient complains of heteronymous diplopia

Question 16

What is paradoxical diplopia

Answer 16

diplopia occurs on the opposite side to that expected by the deviation, example: heteronymous diplopia (crossed) occurs in an ET or homonymous diplopia occurs in an XT. This may occur when a patient with harmonious abnormal correspondence has surgery to reduce a deviation, but the abnormal correspondence remains.

Question 17

What is microtropia

Answer 17

Microtropia involves a tiny deviation (under 5 degrees), often with anomalous retinal correspondence (ARC) or suppression, mild amblyopia, and significantly reduced stereoacuity. Diplopia is rare, and surgery is usually not beneficial due to adaptation mechanisms.

Question 18

What is a small angle strabismus

Answer 18

Small-angle strabismus with abnormal BSV has a slightly larger deviation (5-10 degrees), no ARC, and can cause intermittent diplopia. Stereoacuity is moderately reduced, amblyopia may or may not be present, and surgery is often more effective.

Question 19

Where does abnormal correspondence happen?

Answer 19

Abnormal retinal correspondence (ARC) occurs when the brain adapts to eye misalignment by pairing the fovea of the straight eye with a non-foveal point in the deviating eye, helping to avoid double vision but reducing normal binocular vision and depth perception.

Question 20

Does the size of strabismus cause abnormal BSV to develop

Answer 20

Yes, smaller strabismus angles are more likely to cause the brain to adapt with abnormal BSV (like ARC or suppression), while larger angles often lead to diplopia or suppression without adaptation.

Question 21

How does the neuroanatomical evidence support small angle strabismus being more likely to develop abnormal correspondence?

Answer 21

The neuroanatomical evidence supports small angle strabismus being more likely to develop abnormal correspondence due to the adaptations in the oculomotor control systems, the cerebellum, the visual cortex, and the parietal lobe, as well as the plastic changes that occur in response to the constant misalignment of the visual axes.

These adaptations can lead to suppression of input from one eye, favoring the other, and result in abnormal correspondence and potential amblyopia.

Question 22

How to treat microtropia

Answer 22

Surgical Treatments
Double Recession of the Medial Rectus Muscles: This involves weakening the muscles that pull the eyes inward to correct the misalignment.

Combined Recession and Resection: This technique involves both weakening and strengthening the muscles to achieve better alignment.

Single Muscle Surgery: In some cases, a single muscle can be adjusted (either recession or resection) to correct the microtropia.

Minimally Invasive Surgery: Modern techniques use smaller incisions to reduce tissue damage and improve surgical outcomes. This includes the use of microscopes to enhance precision and reduce complications.

Non-Surgical Treatments

Glasses and Contact Lenses: Correcting any underlying refractive errors (such as myopia, hyperopia, or astigmatism) can sometimes help in managing microtropia.

Prism Lenses: These can be used to correct small-angle deviations and reduce symptoms like double vision.

Vision Therapy: This includes exercises to improve eye coordination and strengthen the eye muscles. It can be particularly effective in children and when combined with other treatments.

Botulinum Toxin (Botox) Injections: This can be used to temporarily weaken overactive muscles, allowing the eyes to align correctly. It is often used in cases where surgery is not suitable or as a temporary measure before surgery.

Question 23

What are the consideration of microtropia treatment

Answer 23

Age and Severity: The choice of treatment can depend on the age of the patient and the severity of the condition. Early intervention is generally more effective, especially in children.

Comprehensive Evaluation: A thorough evaluation by an ophthalmologist is essential to determine the best course of treatment, which may include a combination of surgical and non-surgical method

Question 24

Considerations

Answer 24

In an adult patient with strabismus and no potential BSV, what would be the aim of management? Example: 50 XT
Consider what the patient has to ‘gain’ from surgery. Does the patient feel the strabismus negatively affects their quality of life? Could surgery improve their life?

Question 25

Could surgery change their vision?

Answer 25

Peripheral vision (field of vision measured with both eyes open, or a binocular field of vision) may be expanded in some patients, typically patients with an ET. Even in the absence of BSV patients can appreciate their ‘monocular temporal crescent’.

Question 26

What is panoramic vision

Answer 26

Patients with an XT may describe ‘panoramic vision’, where they don’t see diplopia or confusion, but they are aware of the image from their strabismic eye at the same time as the image from their fixing eye. Some patients with XT may dislike losing their panoramic vision if they have surgery to align their eyes.

Question 27

More on panoramic vision

Answer 27

Some patients with XT would prefer to have aligned eyes and lose their panoramic vision, as they are aware their panoramic vision occurs when they have an XT.

Question 28

Why should panoramic vision be discussed

Answer 28

In patients with an XT, panoramic vision and the change expected in their vision after surgery should be part of the discussion about surgery and their expectations of surgery.

Question 29

Are any other visual changes possible after strabismus surgery?

Answer 29

Unexpected BSV has been reported after strabismus surgery. Yet, it also raises the question how well is potential BSV investigated pre-operatively, if at all?

Question 30

What is binocular summation

Answer 30

the improved performance of a visual task with both eyes open (binocularly) compared to monocularly using the better eye

Question 31

What is binocular inhibition

Answer 31

the improved performance of a visual task monocularly compared to both eyes open.

Question 32

Use of binocular summation/ inhibition

Answer 32

Binocular summation / inhibition has been measured using low contrast visual acuity charts in dim lighting. These measures are thought by some to represent a more realistic every day visual task compared to a high contrast VA measurement.

Question 33

What can decreased binocular summation or causing binocular inhibition suggest

Answer 33

suggested as reasons why a patient may close one eye to perform a visual task, despite not experiencing diplopia.

Question 34

Evidence of binocular summation

Answer 34

Some evidence reports that binocular summation may improve after strabismus surgery, yet more evidence is required to establish what factors affect binocular summation and whether binocular summation improves following all types of strabismus surgery.