Oculomotor control in children who were born very prematurely

Preterm infants are at increased risk of a variety of cerebral lesions, involving the white matter, cortex, cerebellum, thalamus, and caudate nucleus, many of which could compromise the control of eye movement. Visual problems and disorders of binocularity and alignment have been reported, but little if any quantitative assessment of oculomotor control has been undertaken. The purpose of this study was to extend the initial pilot study and quantitatively examine the control of saccades, smooth pursuit, and antisaccades in children who were born very prematurely.

A group of preterm (PT) children aged 8 to 11 years (<32 weeks' gestation), who had normal IQ (>or=85) and were free of major disabilities (cerebral palsy, blindness, or deafness), and full-term (FT) control subjects of similar age were recruited from a geographically defined cohort. Antisaccades were examined in 36 preterm and 33 full-term subjects and smooth pursuit and saccades in 21 preterm and 19 full-term subjects, by using infrared oculography. Saccade and antisaccade targets were presented at an amplitude of 5 degrees according to a standard synchronous paradigm, and pursuit was assessed by using a step-ramp paradigm with a target velocity of 14 deg/s.

There were no statistically significant differences between the preterm and the full-term subjects in relation to saccade gain, latency, duration, peak velocity, or the proportion of express saccades. Smooth-pursuit latencies tended to be slightly longer in the preterm subjects (leftward: P = 0.17, rightward: P = 0.02), but there were no significant differences between them and the full-term subjects in pursuit acceleration, open-loop velocity, or peak slow-eye velocity. The main area of deficit in the preterm children occurred in the voluntary control of saccades, with significantly higher antisaccade directional error rates (PT: 73.3% +/- 18.1%, FT: 54.2% +/- 16.9%, mean +/- SD; P < 0.001). The latency of the antisaccade error tended to be shorter in preterm subjects (P = 0.065), with a greater proportion of errors with latency in the express range (P = 0.08).

Despite the increased risk of cerebral lesions, the control of saccades and pursuit was largely normal in the preterm children, suggesting that pathways at the level of the brain stem were principally intact. However, the preterm children had difficulties with the voluntary control of saccades, particularly in the area of inhibition, which may be indicative of a deficit in the region of the dorsolateral prefrontal cortex. This finding is consistent with other reports in preterm children in whom executive function has been found to be compromised, and both these aspects of behavior are likely to share similar areas of cortical control.