Early Visual Marker Tasks Indicating Abnormal Visual Development in Very Premature Infants

Abstract

Abstract: : Purpose:Significant prematurity is associated with poor visual and cognitive outcome, particularly in infants with periventricular leukomalacia (PVL). We have found that very low birth weight premature infants, normal on ultrasound and neurological examination, show normal onset of visual cortical function, indicated by significant VEP responses to orientation-reversal. With abnormalities on ultrasound there are delays or absence of cortical responses(Atkinson et al 1990,91,94,2002). Here we study visual development in a large cohort (N=43) of very premature infants (mean gestational age 29 weeks) from birth to 6 years, who are at risk of perinatal insults. They are divided by neonatal structural MRI into those with cystic PVL, other abnormalities on MRI, and apparently normal. MRI. Methods:We measure visual development using orientation reversal VEPs and attention fixation shifts as cortical indicators, a standardized battery (ABCDEFV) for sensory, optical, perceptual, visuocognitive and spatial development, and newly devised tests of attention and executive frontal lobe function. Results:The cystic PVL group show high failure rates on core vision tests, OR-VEP, fixation shift, and later visuocognitive testing. Failure rates are lower in the subgroup with other MRI abnormalities and lower still in the group with apparently normal scans. Almost all the latter group show normal acuity, orthoptic results, fields, accommodation, and OKN in the first year, compared to 0% and 50% in the other two groups. However, half or more of each group fail the visual cortical tests (OR-VEP and fixation shifts) and the executive function tests which may be sensitive indicators of later, more subtle problems. Conclusions: We find a good correlation between failures on early vision tests and damage indicated on neonatal MRI. We discuss the relatively normal development as indicated by early core vision tests and contrast these measures with those gauging function of visuocognitive attentional mechanisms (involving extrastriate visual, parietal and frontal areas)in the light of models of subcortical-cortical interactions and the ‘dorsal stream vulnerability' hypothesis. References: http://www.psychol.ucl.ac.uk/vdu/publications.html

Keywords: visual development: infancy and childhood • visual cortex • neuro-ophthalmology: cortical function/rehabil