Incomitancy

Question 1

What is incomitancy?

Answer 1

A condition where the angle of deviation changes depending on gaze direction

Unlike comitant deviations where it remains constant.

Question 2

What is the key diagnostic feature of incomitancy?

Answer 2

Secondary angle > primary angle

Primary angle → measured with normal (fixing) eye; Secondary angle → measured when affected eye fixates.

Question 3

Why is the secondary angle larger in incomitancy?

Answer 3

Due to extra innervation required for the weak/affected muscle → overaction in the fellow eye

This is explained by Hering’s law.

Question 4

What is secondary concomitance?

Answer 4

In chronic cases, the deviation becomes equal in all gazes, masking the original incomitancy

This can complicate diagnosis.

Question 5

What does the mnemonic “RAD SIN” represent?

Answer 5

• Recti ADduct → rectus muscles act more in adduction
• Superiors INtort → superior muscles cause intorsion

This helps determine which muscle is being tested in different gaze positions.

Question 6

Why is RAD SIN clinically useful?

Answer 6

Helps determine which muscle is being tested in different gaze positions

This aids in diagnosing muscle function.

Question 7

How do eye muscle actions differ between distance and near?

Answer 7

• Distance → elevation and divergence more active
• Near → depression and convergence more active

Understanding this is crucial for assessing muscle function.

Question 8

What are A and V patterns?

Answer 8

• A pattern → more eso in upgaze / more exo in downgaze
• V pattern → more exo in upgaze / more eso in downgaze

These patterns indicate changes in horizontal deviation.

Question 9

Why are A/V patterns tested?

Answer 9

To detect incomitancy related to muscle overaction or underaction

This is important for accurate diagnosis.

Question 10

What are the main tests used to assess incomitancy?

Answer 10

• Associated Broad H (screening)
• Dissociated Broad H
• Cover test in all gaze positions
• Hess screen
• Lancaster screen

These tests help evaluate muscle function and deviation.

Question 11

What does the Hess/Lancaster test show?

Answer 11

Maps underaction and overaction of muscles, showing deviation pattern across gaze

This is crucial for understanding muscle dynamics.

Question 12

How is ocular motility testing performed?

Answer 12

Hold light ~50 cm from patient, move slowly through all gaze directions, observe corneal reflections

This ensures comprehensive assessment of eye movements.

Question 13

What must be ensured during motility testing?

Answer 13

• Patient can see the target with both eyes
• No obstruction (nose/brow blocking view)
• Smooth tracking

These factors are essential for accurate results.

Question 14

What symptoms should you ask about during testing?

Answer 14

• Diplopia
• Pain

Both are important clues for pathology.

Question 15

How should testing be adapted if the patient has suppression or reduced vision?

Answer 15

• Use both objective and subjective tests
• Use an accommodative target

This ensures reliable fixation and more accurate results.

Question 16

Why should you NOT rely only on corneal reflections?

Answer 16

Because small deviations can be missed: 1 mm shift ≈ 15 prism diopters

Even small errors can have large clinical significance.

Question 17

What is the preferred method for detecting small deviations?

Answer 17

Cover testing in all positions of gaze

This method is more sensitive to changes.

Question 18

What are you assessing during cover testing in different gazes?

Answer 18

• Change in magnitude of deviation
• Change in direction of deviation

This identifies incomitancy and muscle involvement.

Question 19

How do you identify the affected muscle using cover test findings?

Answer 19

The deviation increases in the direction of action of the weak/affected muscle

This helps pinpoint the specific muscle issue.

Question 20

When should you escalate to more advanced testing (Hess/Lancaster)?

Answer 20

• New onset diplopia
• History of strabismus surgery
• Large deviation in primary gaze
• Restriction on motility testing

These factors indicate the need for further evaluation.

Question 21

When is the Hess screen appropriate to use?

Answer 21

Only when the patient has normal retinal correspondence (NRC)

This is crucial for accurate interpretation of results.

Question 22

What does the center point on the Hess screen represent?

Answer 22

Deviation in primary gaze

This serves as a reference point for analysis.

Question 23

How do you identify the affected eye on a Hess screen?

Answer 23

The eye with the smaller field is the affected eye

This indicates which eye has the muscle issue.

Question 24

What does a “squashed” Hess pattern indicate?

Answer 24

Mechanical restriction (e.g. orbital restriction, muscle entrapment)

This suggests a physical limitation affecting muscle function.

Question 25

How do **underacting and overacting muscles** appear on Hess?

Answer 25

* Underacting muscle → pulls points inward (toward centre) * Overacting muscle → pushes points outward ## Footnote This visual representation aids in diagnosis.

Question 26

What are the **three main causes** of ocular motility disorders?

Answer 26

* Neurological → nerve palsies (CN III, IV, VI) * Mechanical → restriction (e.g. Duane’s, Brown’s) * Myogenic → muscle disease (e.g. thyroid eye disease, myasthenia gravis) ## Footnote These categories help in diagnosing the underlying issues affecting eye movement.

Question 27

What happens to **muscle activity** in a nerve palsy? (Hering’s law)

Answer 27

* Weak muscle → brain increases innervation * Contralateral synergist → overacts * Ipsilateral antagonist → appears overacting (unopposed) * Contralateral antagonist → underacts ## Footnote This describes the compensatory mechanisms in response to muscle weakness.

Question 28

Why does the **contralateral synergist** overact?

Answer 28

Due to equal innervation (Hering’s law) → increased signal to both eyes. ## Footnote This results in an imbalance in muscle activity.

Question 29

How does **primary gaze** differ in neurological vs mechanical causes?

Answer 29

* Neurological → large deviation in primary gaze * Mechanical → may look normal in primary gaze ## Footnote This distinction aids in identifying the type of disorder present.

Question 30

How do **ductions vs versions** differ?

Answer 30

* Neurological → ductions better than versions * Mechanical → ductions = versions (both limited) ## Footnote This reflects the functional capacity of eye movements in different conditions.

Question 31

Why are **ductions better** in neurological cases?

Answer 31

Because the muscle can still be moved passively (no restriction). ## Footnote This indicates the presence of neurological function despite weakness.

Question 32

What type of **movement limitation** is seen in mechanical problems?

Answer 32

Abrupt stop in movement ## Footnote This suggests physical restriction affecting eye movement.

Question 33

How does **muscle sequelae** differ?

Answer 33

* Neurological → full muscle sequelae pattern * Mechanical → only contralateral synergist overacts ## Footnote This highlights the differences in muscle response based on the underlying cause.

Question 34

What special sign may be seen in **mechanical conditions**?

Answer 34

Globe retraction (e.g. Duane’s syndrome) ## Footnote This is a characteristic finding in certain mechanical disorders.

Question 35

How does **pain** differ between the two?

Answer 35

* Mechanical → may have pain (especially on movement) * Neurological → usually no pain ## Footnote This symptom can help differentiate between mechanical and neurological issues.

Question 36

What is the **forced duction test** and what does it show?

Answer 36

* Mechanical → positive (resistance felt) * Neurological → negative (eye moves freely) ## Footnote This test assesses the presence of mechanical restrictions in eye movement.

Question 37

How does **intraocular pressure (IOP)** differ?

Answer 37

* Neurological → no change * Mechanical → increases when looking toward restriction ## Footnote This change in IOP can indicate the presence of mechanical issues affecting eye movement.

Question 38

How do **longstanding** and **recent-onset motility problems** differ in symptoms?

Answer 38

* Longstanding: often no diplopia, found incidentally * Recent: clear diplopia, patient knows onset ## Footnote Understanding the differences in symptoms can aid in diagnosis and treatment.

Question 39

How does **head posture** differ between longstanding and recent-onset motility problems?

Answer 39

* Longstanding: patient unaware of abnormal head posture * Recent: patient actively adopts head posture to avoid diplopia ## Footnote This reflects the adaptation of patients to their visual challenges.

Question 40

How do **muscle sequelae** differ in longstanding versus recent-onset motility problems?

Answer 40

* Longstanding: full muscle sequelae present * Recent: mainly contralateral synergist overaction ## Footnote The muscle responses can indicate the duration of the condition.

Question 41

How do **vertical fusional amplitudes** differ between longstanding and recent-onset motility problems?

Answer 41

* Longstanding: large (adapted) * Recent: normal (no adaptation yet) ## Footnote This indicates how the visual system adapts over time.

Question 42

How does **torsion** differ in longstanding versus recent-onset motility problems?

Answer 42

* Longstanding: rare/minimal torsion * Recent: torsion common (e.g. acquired CN IV palsy) ## Footnote Torsion can be a significant indicator of the underlying condition.

Question 43

What is the key **adaptation** in longstanding motility problems?

Answer 43

The visual system develops sensory and motor adaptations → suppresses symptoms. ## Footnote This adaptation can complicate diagnosis.

Question 44

What is the main goal in managing **incomitant deviations**?

Answer 44

Improve alignment in primary gaze (straight ahead). ## Footnote Achieving proper alignment is crucial for visual function.

Question 45

What are the main **treatment options** for incomitant deviations?

Answer 45

* Prism (for primary gaze alignment) * Surgery (if needed) ## Footnote Treatment options vary based on the severity and type of deviation.

Question 46

Why are **incomitant deviations** more difficult to manage?

Answer 46

Because deviation changes with gaze, so correction may only work in certain positions. ## Footnote This variability complicates treatment strategies.

Question 47

When should you **refer** incomitant deviations?

Answer 47

If unsure whether the condition is longstanding or recent, or if complex → refer for specialist care. ## Footnote Early referral can lead to better outcomes.

Question 48

What is **Park’s 3-step test** used for?

Answer 48

To identify the paretic muscle in vertical diplopia. ## Footnote This test is a crucial diagnostic tool in ophthalmology.

Question 49

What are the **3 steps** of Park’s 3-step test?

Answer 49

* Which eye is higher in primary gaze? * Is deviation worse in left or right gaze? * Is deviation worse with head tilt left or right (Bielschowsky test)? ## Footnote Each step helps narrow down the cause of diplopia.

Question 50

What is the **Bielschowsky head tilt test**?

Answer 50

Tilting the head to each side to see which position worsens vertical deviation, helping identify the weak muscle. ## Footnote This test is often used in conjunction with Park’s 3-step test.

Question 51

When should Park’s 3-step test **NOT** be used?

Answer 51

* Bilateral deviations * Horizontal deviations * Multiple muscle involvement * Mechanical or myogenic causes * Post-strabismus surgery ## Footnote These conditions may lead to inaccurate results.

Question 52

What additional signs should be checked in **motility exams**?

Answer 52

* Lid changes (ptosis, retraction) * Pupil abnormalities * Globe position (proptosis/retraction) * Cogan’s lid twitch (myasthenia gravis) ## Footnote These signs can provide important diagnostic information.