Abstract
Purpose :
Missing or aberrant connections in the brainstem cause a range of abnormal eye movements in subjects with hypoplasia of the cerebellum and vermis. This study quantified dynamic torsional, vertical, and horizontal eye movements in such subjects acquired by a scanning laser ophthalmoscope (SLO) during OCT imaging.
Methods :
8 subjects with Joubert Syndrome (JS), 1 with COACH syndrome, and 1 with hypoplasia of the cerebellum and vermis but without a molar tooth sign were selected for retrospective study (mean age = 12 years; range 4-19). Imaging was performed by a Spectralis SLO/OCT while subjects viewed a central target. Published SLO videos from 2 subjects with JS were also analyzed (Papanagnu et al., 2014). Fundus tracking of SLO videos (or serial still images) were analyzed by software using the OpenCV library (SURF feature detector; homography with RANSAC outlier removal, and additional criteria). The software can measure torsion while compensating for image shear and scale during gaze shifts and saccades. Relative torsion of the fundus was compared to an image in which the fovea was approximately 7 degrees below the optic disc. Accuracy of the tracking software was compared to manual scoring of fovea and optic disc fiducials . Video-oculography (2-D VOG) recording was available in 8 subjects.
Results :
All subjects had severe abnormalities in all 2D conjugate eye movements (saccades, smooth pursuit, OKN). Seven subjects with JS had large torsional eye movements that ranged from 25 - 60 degrees. The torsion waveform (rotation across time) varied between subjects. Many of these subjects had a bias towards excyclotorsion over incyclotorsion of the recorded eye. Despite variable nystagmus, subjects showed they could intermittently foveate the target even with retinal degeneration. There was no consistent relationship between torsion and distance from the fixation targets (either abduction, adduction, elevation or depression). The amplitude of torsion was unrelated to logMAR visual acuity (r = -0.07). Two subjects (1 with JS, 1 with hypoplasia of the cerebellum and vermis but without a molar tooth sign) had torsional amplitudes < 15 degrees .
Conclusions :
Ocular torsion is an important diagnostic feature of Joubert syndrome. The torsional component does not rely upon horizontal or vertical eye deviation from a fixation target. This study highlights objective methods to measure dynamic torsional movements in these subjects.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.