Investigations and management of incomitant deviations

Front: What is incomitant strabismus?

Back: Incomitant strabismus is an eye misalignment where the degree of deviation varies depending on the direction of gaze or which eye is used for fixation.

Front: How does the treatment plan for incomitant strabismus vary?

Back: The treatment plan varies depending on the cause (neurogenic, myogenic, or mechanical) and the severity of the deviation.

What are the short-term management options for incomitant strabismus?

• Prisms can be used to eliminate or reduce diplopia

• Occlusion therapy may be necessary for patients who cannot tolerate diplopia

What are the long-term management options for incomitant strabismus?

• Surgery may be considered for persistent and significant deviations

• Botulinum toxin injections may be used for specific muscle palsies

Front: How would you assess BSV in a patient with Lateral Rectus (LR) palsy?

• Use a Frisby test in the position of minimum deviation

• Measure primary and secondary deviations using prism cover test (PCT) in all gaze positions

• Document diplopia in both horizontal and vertical planes and use prisms to assess whether the diplopia can be separated or eliminated

What are some advanced diagnostic tools used in assessing incomitant strabismus?

• Tensilon Test for myasthenia gravis (MG)

• Imaging (CT/MRI) for suspected lesions or tumors

• Electromyography (EMG) for muscle function tests

• Exophthalmometer to assess for globe protrusion (e.g., in thyroid eye disease, TED)

What conservative treatment options are available before considering surgery for incomitant strabismus?

• Observation: Monitoring the condition over time

• Orthoptic exercises: Exercises to improve eye muscle control and coordination

• Occlusion: Patching one eye to prevent double vision and encourage the other eye's function

• Spectacles: Correcting refractive errors to improve alignment

• Prisms: Using prisms in glasses to help with diplopia (double vision)

• Botulinum toxin A (BTA): Temporarily weakens overactive muscles to improve alignment or assess the risk of post-operative diplopia

What are the three main types of surgical interventions for strabismus?

Strabismus surgery aims to either weaken, strengthen, or transpose the extraocular muscles to achieve proper alignment.

What are some weakening procedures in strabismus surgery?

• Recession: Moves the muscle's insertion point backward, reducing its pull and creating slack

• Myectomy: Partial or complete removal of the muscle to weaken it

• Fadenisation (Posterior Fixation): A suture is placed posteriorly to limit a muscle's rotational force when the eye moves into specific positions of gaze

What are some strengthening procedures in strabismus surgery?

• Resection: The muscle is cut and reattached, shortening it and increasing its pull

• Tuck: The muscle is folded or pleated to shorten it without full resection

• Plication: An alternative to resection where the muscle is sutured to the sclera without cutting the muscle itself

What are transposition procedures in strabismus surgery?

Transposition surgeries involve moving a muscle to a different position to take over the action of a weakened or paralyzed muscle. Types include:

• Whole Muscle Transposition: Entire muscle is repositioned

• Part Muscle Transposition: Part of the muscle is moved, as in the Hummelsheim or Jensen procedures

What are the key surgical principles in strabismus surgery?

• Matching the defect: The amount of muscle correction is calculated based on the severity of deviation

• Consideration for both eyes: Surgery often involves operating on both eyes to ensure balanced eye movement and proper alignment

• Muscle-specific principles: Different muscles have different effects on near and distance deviations

What is the general guide for muscle movement correction in strabismus surgery?

A general guide is that 1 mm of muscle movement equals approximately 3 prism diopters (PD) of correction.

: What are some special muscle surgeries in strabismus treatment

 

• Inferior Oblique (IO) Weakening: Techniques include disinsertion, recession, and myectomy

• Superior Oblique (SO) Tuck: Used in cases of SO palsy or overaction

• Superior Oblique Expander: A silicone spacer used to weaken the muscle without inducing excyclotorsion

Front: What is adjustable surgery in strabismus treatment?

Back: Adjustable sutures allow for fine-tuning the position of the muscles after surgery while the patient is awake and able to fixate on a target. This method improves accuracy, reducing the risk of residual misalignment.

Front: What are the potential complications of strabismus surgery?

Pre-operative: Errors in diagnosis or surgical planning

Peri-operative: Bleeding, loss of muscle, globe perforation

Post-operative:

• Endophthalmitis: A rare but serious infection of the eye

• Intractable diplopia: Persistent double vision

• Lid abnormalities: Eyelid positioning issues

How is Botulinum Toxin A (BTA) used in strabismus treatment?

Back: BTA is used in cases where temporary paralysis of a muscle can provide therapeutic benefit, either by reducing the angle of the squint or by helping assess the potential for post-operative diplopia. It's commonly used in acute nerve palsies or to aid in post-operative alignment.

Front: What are the main goals of surgical management in incomitant strabismus?

Back: The goals are to achieve orthotropia (straight eyes), restore binocular function, and reduce symptoms, all while minimizing risks and preserving normal ocular motility.