Research Article: Development of smooth pursuit eye movements in very preterm infants: 1. General aspects

Date Published: July , 2011

Publisher: Blackwell Publishing Ltd

Author(s): Katarina Strand-Brodd, Uwe Ewald, Helena Grönqvist, Gerd Holmström, Bo Strömberg, Erik Grönqvist, Claes von Hofsten, Kerstin Rosander.

http://doi.org/10.1111/j.1651-2227.2011.02218.x

Abstract

To investigate early oculo-motor development in a population-based cohort of very preterm infants.

Early oculo-motor development was prospectively studied by measuring smooth pursuit eye movements at 2 and 4 months corrected age in a population of very preterm infants born in Uppsala County 2004–2007. Eighty-one preterm infants were studied, and 32 healthy term infants constituted the control group.

The study group consisted of infants with a mean gestational age of 28 + 5 weeks. At 2 and 4 months corrected age, infants born very preterm showed lower gain (p < 0.001) and proportion of smooth pursuit eye movements (p < 0.001) compared to the control group. The boys showed higher gain of smooth pursuit eye movements at both 2 and 4 months corrected age, compared to girls. Oculo-motor development measured by smooth pursuit eye movements is delayed in very preterm infants at 2 and 4 months corrected age. This might be a risk factor or early indicator of later perceptual and behavioural impairment.

Partial Text

During the recent decades, the incidence of infants born very preterm [i.e. born before 32 gestational weeks (GW)] has increased, and today, infants born before 27 GW have a survival rate that is approaching 70–80% (1).

The aim of the present study was to evaluate early visuomotor development in a population-based cohort of infants born before 32 GW. Infants’ visuomotor capacity regarding smooth pursuit at 2 and 4 months corrected age (CA) was measured and compared to healthy term infants at the same ages. In addition, background clinical data including major neonatal complications are recorded for the cohort.

The LOVIS project is a multidisciplinary population-based follow-up study involving the Departments of Women’s and Children’s Health, Psychology and Neuroscience at Uppsala University.

In the present study, infants born very preterm (<32GW) showed lower Gain as well as propSP at 2 and 4 months CA compared to infants born at term. Both Gain and propSP are proportional measures where Gain measures smooth pursuit relative to the object motion and propSP measures smooth pursuit relative to the total eye movement. If the eye movements correspond to the object motion, then the two measures give the same results. If the head contributes substantially to the tracking, the Gain measure tends to underestimate the contribution of smooth pursuit in relation to the total eye movement. This is because head tracking is also smooth but it does not enter into the Gain equation. On the other hand, if the tracking is incomplete and the eyes fail to stabilize on the object, the propSP will overestimate the contribution of smooth pursuit in relation to the object motion. In this study, both measures are needed because very preterm and full-term infants may employ different amounts of head movements and eye movements in the attempt to stabilize gaze on the object. Although starting at a much lower level, as a group, the very preterm infants did not improve more than the full-term infants. Nevertheless, the number of very preterm infants who had reached the full-term infants’ level of Gain at 4 months CA had increased compared to 2 months CA while this was not the case for propSP. This result could be an effect on the fact that the very preterm group employed very small amount of raw eye movements at 2 months CA. In addition, the very preterm density curves became more dispersed at 4 months CA compared to 2 months CA. A plausible explanation for these findings is that some of the infants in the very preterm group caught up whereas some did not develop at all.   Source: http://doi.org/10.1111/j.1651-2227.2011.02218.x

 

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