Visual and visuocognitive development in children born very prematurely

Preterm birth is a risk factor for deficits of neurological and cognitive development. Four cohort studies are reported investigating the effects of very premature birth (<32 weeks gestation) on visual, visuocognitive and visuomotor function between birth and 6-7 years of age. The first study used two measures of early visual cortical function, orientation reversal visual event-related potentials (OR-VERP) and fixation shifts under competition. Both these functional measures of visual development correlated with the severity of brain abnormality observed on structural MRI at and before term, and were sensitive predictors of neurodevelopmental outcome at 2 years. The second study compared VERP measures for orientation-reversal and direction-reversal (DR) stimuli, from 2 to 5 months post-term age, in healthy very premature infants compared to infants born at term. The groups did not differ on the development of OR-VERP responses, but the development of the DR-VERP motion responses was delayed in the premature group despite the absence of any brain damage visible on ultrasound, consistent with the developmental vulnerability we have identified in the dorsal cortical stream. The third study used the Atkinson Battery of Child Development for Examining Functional Vision (ABCDEFV) to assess sensory, perceptual, cognitive and spatial visual functions, together with preschool tests of attention and executive function. The premature group showed delays on these tests in line with severity of observed perinatal brain damage on structural MRI at term age. Deficits on certain spatial tasks (e.g. block-construction copying) and executive function tests (e.g. the detour box task) were apparent even in children with minimal damage apparent on MRI. The fourth study tested a large cohort of 6- to 7-year old children born before 32 weeks gestation, across a wide range of cognitive domains, including new tests of spatial cognition and memory. The premature group as a whole showed significant deficits on both auditory and visual tests of attention and attentional control from the TEA-Ch battery, on tests of location memory, block construction and on many visuocognitive and visuomotor tests. Development was generally relatively normal on language tests and on WPPSI scores. Factor analysis showed that while general cognitive ability accounted for the largest part of the variance, significant deficits, and a relationship to MRI results, were primarily in spatial, motor, attention and executive function tests. A model is proposed suggesting that the cluster of deficits seen in children born prematurely may be related to networks involving the cortical dorsal stream and its connections to parietal, frontal and hippocampal areas.