Development of smooth pursuit eye movements in very prematurely born infants: 2. The low-risk subgroup.

Aim: To investigate the impact of premature birth on visual tracking in a group of 37 infants, born before the 32nd gestational weeks (mean 29 + 6 weeks) and diagnosed as being without major neonatal complications. This paper is a part of the LOVIS study (Strand Brodd, Ewald, Grönqvist, Holmström, Strömberg, Von Hofsten, et al. Acta Pediatrica, 2011).

Methods: At 2 and 4 months corrected age, eye and head movements were measured when the infant tracked a moving object. The eye movements were analysed in terms of smooth pursuit and saccades (Vision Res, 37, 1997, 1799; Exp Brain Res, 146, 2002, 257). Accuracy of gaze, proportion of smooth pursuit, head movements and saccades were calculated.

Results:   Between 2 and 4 months of age, all infants improved their ability to smoothly pursue a moving object. However, at both occasions, the preterm infants had less proportion smooth pursuit than the full-term infants. The groups did not differ with respect to gaze and head movements, but the saccade frequency was higher for the very preterms in some of the conditions.

Conclusion: The development of smooth pursuit in the low-risk preterm infant group was strongly delayed compared to typically developed infants. Thus, the 2 months or more extra visual experience did not have a distinguishable positive effect on visuo-motor development as expressed in smooth pursuit.