Optometry & Visual Performance 126 Volume 14 | Issue 2 | June 2026 Figure 1. Standard fundus photography of the right eye (OD) and left eye (OS). Note the increased excyclotorsion OD (-11.0°) compared to the normal ocular torsion OS (-4.0°). This is consistent with a right trochlear nerve palsy. Figure 2. Optical coherence tomography (OCT) of the patient in this case using Cirrus OCT (Cirrus 5000, Carl Zeiss Meditec, Dublin, California, USA) macular thickness scans of the right eye (OD) and left eye (OS). The standard measuring tool on the Cirrus OCT was used to measure the linear distance (microns) from the center of the optic nerves to the fovea (red line with red arrow) and the horizontal meridian (red line with black arrow). These two distances were used to estimate the disc-to-fovea angle with the cosine trigonometric calculations below each respective photo (-11.4° OD, -6.6° OS). The excessive excyclotorsion of the OD is consistent with a right trochlear nerve palsy.
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