Abstract
Purpose :
To compare vertical fusion amplitude and vertical vergence amplitude at different horizontal directions of gaze in normal non-human primates.
Methods :
Scleral search coils were used to record movements of both eyes as two normal non-human primates performed a vertical vergence task. Using a frame-sequential presentation technique, a 50° x 50° stimulus which comprised a central fixation cross (4° x 4°) and sparse pattern of random dots (1° each) elsewhere was presented at a distance 57cm from the animal. Shutter goggles synched with stimulus frames achieved dichoptic viewing conditions. Vertical disparity was introduced by displacing the stimulus for one eye vertically (upward or downward) in small steps of 0.05° continuously. The maximum target disparity at which the animal could no longer maintain fixation was adjudged as the vertical fusional amplitude and the difference between the left and right vertical eye positions at this disparity was quantified as vertical vergence amplitude. Measurements were taken at three horizontal direction of gaze (-10°, 0° and 10°) with multiple repetitions for each eye moving in either direction.
Results :
During left-over-right vergence in monkey M1, the right eye moving down condition showed a significantly smaller vertical fusional amplitude in the adducted position (5.18°±0.44) compared to primary (5.52°±0.44) and abducted (5.57°±0.52) positions whereas the left eye moving up condition showed a smaller fusional amplitude in the abducted position (4.98°±0.48) than primary (5.26°±0.44) and adducted (5.25°±0.41) positions. Although vertical fusional amplitude ranges showed differences, the vertical vergence response (motor response) in the primary (4.18°±0.60), abducted (4.00°±0.54) and adducted (3.85°±0.50) positions did not significantly differ. During right-over-left vergence (right eye moving up and left eye moving down), neither fusional amplitudes nor vergence responses showed gaze position differences. Data acquisition and analysis from the second animal is ongoing.
Conclusions :
Vertical fusion capability differ slightly for different horizontal gaze direction and hence eye position in the orbit. Examination of vertical fusion amplitude from this subject suggest the recti muscles predominantly mediates vertical vergence in the right eye and the oblique muscles in the left eye. However such indications were not corroborated by the associated vertical vergence response.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.