Abstract
Purpose: :
So far, the effect of strabismus surgery in patients with trochlear nerve palsy (TNP) has been investigated using subjective methods. This study objectively evaluated the follow up of different strabismus surgery options in the horizontal, vertical and torsional gaze component. To find the most likely cause of the preoperative observed strabismus pattern, this data was used for modeling.
Material and Methods: :
Ten patients with unilateral TNP were measured before, at 1.5 months (5 patients), and at 3 months after strabismus surgery (7 ipsilateral anteropositions of the inferior oblique muscle, 2 ipsilateral superior oblique muscle tucks and 1 contralateral inferior rectus muscle recession). To evaluate the mean deviation angle and the degree of incomitance, nine different gaze positions (straight ahead, +/– 20° components up and down, left and right) were recorded binocularly and 3–dimensionally (torsional, vertical, horizontal) with search coils. We used SEE++ for the preoperative data, a computer based 3–dimensional model of the oculomotor plant.
Results: :
Three months post–operatively, mean vertical deviation (8.6° to 4.7°; p=0.006; dependent t–test) and vertical incomitance (3.7° to 2.8°; p=0.04) were reduced significantly. Mean horizontal deviation and torsional incomitance also decreased. Horizontal incomitance was unchanged (1.9° to 2.1°). Gaze field area of the paretic eye decreased in proportion to the non–paretic eye (1.03 to 0.91; p= 0.02). Before the surgery, the amount of the vertical deviation at gaze straight ahead could not be solely explained by the lack of force of the palsied superior oblique muscle, but rather in combination with an overaction of the contralateral inferior rectus muscle.
Conclusions: :
In patients with trochlear nerve palsy, the search coil technique showed that strabismus surgery reduces vertical incomitance while decreasing mean vertical deviation. However, the area of the vertical/horizontal gaze field of the paretic eye decreased by about 12% due to the surgery. The applied model confirmed that the overaction of the inferior rectus muscle of the fellow eye could be corrected by weakening this muscle or by weakening the torsional antagonist of the superior oblique muscle of the palsied eye.
Keywords: eye movements: recording techniques • strabismus: treatment • ocular motor control