Abnormal Slant Perception About the Horizontal Axis Induced by Cyclo–Deviation in Patients With Superior Oblique Palsy

Abstract

Purpose: : Patients with superior oblique (SO) palsy sometimes compensate for their residual cyclo–deviation (<10 degrees) with powerful sensory fusion and achieve binocular single vision. This study investigated whether such a cyclo–deviation influences three–dimensional spatial localization.

Methods: : Eight patients with congenital and acquired SO palsy who showed stable binocular single vision at near distances (age range: 33–76 years) and 9 normal controls were recruited. On a video–monitor 33cm in front of the subject’s eyes, a vertical bar (height: 8 degrees) was presented separately to each eye by the anaglyph method. In the first experiment, the subjects were asked to adjust the cyclodisparity of the vertical bar with a computer–mouse so that they perceived that the bar was exactly in a front–parallel plane, and the cyclodisparities were recorded and compared with subjectively measured cyclo–deviations. In the second experiment, while the vertical bar with a different amount of cyclodisparity (cyclodisparity individually recorded using the method described above +/–0, 2, 4 and 6 degrees) was presented in random succession, a perceived slant angle of the bar about horizontal axis was evaluated using a rotational inspection stick under a visual–feedback open–loop condition (tactile matching task).

Results: : All of the patients perceived that the vertical bar slanted toward top–forward direction about the horizontal axis when the cyclodisparity was zero degree. The cyclodisparities when the patients perceived that the bar was in the front–parallel plane ranged from 2.5 to 12.3 degrees (excyclo–disparity), whereas those for normal controls remained within +/–1.4 degrees. The cyclodisparities correlated with the subjectively measured cyclo–deviations (R²=0.77, p<0.01). The mean (+/–SD) gradient of perceived slant angles to given cyclodisparities for the patients and the normal controls was 3.9 +/–2.0 and 3.3+/–0.7(degrees/degrees), respectively, and there was no significant difference between the two values.

Conclusions: : Conclusion: Patients with SO palsy have abnormal slant perception about the horizontal axis, or distorted three–dimensional spatial localization, derived from their residual cyclo–deviation when they achieve binocular single vision, at least partially or intermittently.

Keywords: binocular vision/stereopsis • strabismus • space and scene perception