Purpose: To study eye movements in 3D space - saccades, vergence and combined eye movements - in a subject with Manifest Latent Nystagmus (MLN).
Methods: A 13-year-old girl diagnosed with MLN participated in this study. Saccades, pure vergence along the median plane and combined saccade-vergence movements were recorded under both binocular and monocular viewing. Horizontal eye movements from both eyes were recorded simultaneously with a photoelectric device (Bouis Oculometer).
Results: The recordings of saccades, vergence or both components of combined movements show that such movements have a staircase trajectory. The consequence of this staircase behavior is that the time for approaching the target is prolonged. The latency of all types of eye movements is extended when the subject is viewing binocularly, while latency values are normal when viewing monocularly; the difference between the viewing conditions is significant for vergence.
Conclusion: The normal latency values under monocular viewing are attributed to facilitation of eye movement initiation by the increased nystagmus.