Development of Optokinetic and Smooth Pursuit Eye Movements in Infant Monkeys

Abstract

Purpose:: Optokinetic and smooth pursuit eye movements were recorded longitudinally in infant monkeys to evaluate the development of conjugate eye movements in a non-human primate model.

Methods:: 13 infant pigtail macaque monkeys (2 days to 3 months in age) were evaluated with constant velocity (15-45 deg/s), full field, optokinetic stimuli (0.5 cycles per degree, sine-wave modulated vertical and horizontal gratings) and/or pursuit stimuli (sinusoidal motion, +/-10 deg amplitude, 10-30 deg/s peak velocity). All stimuli were back-projected on a 3' x 5' screen. Eye movements were recorded non-invasively with 2D video-oculography while the infants sat with, and were manually restrained by, an investigator. These data were compared with data collected previously in human infants using the same paradigm.

Results:: Optokinetic stimuli produced variable gain optokinetic nystagmus OKN and short duration (Tc = 3-5 s) optokinetic after nystagmus (OKAN) at the youngest test ages. The duration of individual epochs of OKN increased with age, as did the average gain and duration of OKAN. Smooth pursuit stimuli produced smooth eye movement in the direction of target motion at all ages, with lower gain and more catch-up saccades at higher stimulus velocities. The gain and duration of the epochs of smooth eye movement increased with age.

Conclusions:: Infant pigtailed macaques show similarities to human infants in the general sequence of development of OKN and smooth pursuit. The development of conjugate eye movements is accelerated in this species, but these studies suggest that it should be a good animal model for studying the development of the neural mechanisms of eye movement control.

Keywords: development • eye movements: conjugate • ocular motor control