Abnormal Saccadic Behaviour in Patients with Albinism but without Nystagmus

Abstract

Abstract: : Purpose: Bilateral involuntary nystagmus is not always a feature of albinism. We therefore investigated fixation behaviour and saccadic eye movements in order to characterise gaze holding and shifting in patients with albinism but without nystagmus Methods: All 3 subjects were diagnosed as albinos on the basis of ophthalmic and electrophysiological tests. Binocular horizontal eye movements were measured with an infrared limbus tracker. Fixation was evaluated on primary and secondary gaze. Saccadic eye movements to random targets were measured over a range of +/- 15 degrees. Results: The 3 subjects exhibited frequent saccadic instabilities (1 per second) on primary and secondary gaze. The square wave jerks had variable amplitude (0.5 - 5 degrees). Two patterns of saccadic abnormality were found. The saccades were either hypometric (often multiple) or showed a slow centri-petal drift, often with a following corrective saccade. These abnormalities were clearest with the +/- 15 amplitude degree saccades. For two of the 3 subjects every 15 degree saccade was abnormal. Conclusion: Our albino subjects did not show stable fixation, and gaze shifting behaviour was abnormal. These patterns of fixation represent a less marked instability than that found in albinos with nystagmus, but are similar to those reported in carriers of blue-cone monochromatism or family members of patients with dominant or X-linked congenital nystagmus.

Keywords: eye movements: saccades and pursuits • neuro-ophthalmology: diagnosis • nystagmus