Acute superior oblique palsy in monkeys: I. Changes in static eye alignment

Area of Science:

• Ophthalmology
• Neuroscience
• Ocular Motor Function

Background:

• Superior oblique palsy (SOP) is a common cause of vertical and torsional strabismus.
• Understanding the adaptive changes in ocular alignment following acute SOP is crucial for clinical management.

Purpose of the Study:

• To investigate immediate and long-term changes in static ocular alignment in a primate model of acute acquired superior oblique palsy (SOP).
• To characterize the ocular motor signature of superior oblique muscle denervation.

Main Methods:

• Acute superior oblique palsy was induced by intracranial trochlear nerve transection in two rhesus monkeys.
• Ocular alignment was assessed using binocular, dual search coils to measure three-axis eye movements (horizontal, vertical, torsional).
• Measurements were taken before lesion and at various time points post-lesion, including assessments with +/-30 degrees head tilt.

Main Results:

• Induced SOP resulted in significant vertical (10-12 degrees in adduction) and torsional (10-12 degrees in abduction) misalignment.
• Vertical deviation (VD) showed changes with head tilt (2-6 degrees difference between left and right tilts).
• VD and comitance worsened with binocular viewing compared to monocular viewing during the early post-lesion period.

Conclusions:

• Rhesus monkeys with induced SOP exhibit a distinct pattern of misalignment, defining the ocular motor signature of acute superior oblique muscle denervation.
• The study highlights dynamic changes in vertical misalignment and its comitance over time, dependent on viewing conditions (monocular vs. binocular).
• Findings suggest proprioception plays a role in adapting to misalignment, particularly with habitual monocular viewing.