In this study, the pupillary size and light reflex was examined in premature infants using infrared video-pupillography and stimuli of red and blue light. Only eyes of infants without retinopathy of prematurity were included in the study. Pupillary light reflexes were obtained in response to 470nm blue and 635nm red stimuli with varying intensities. Red stimuli did not evoke a pupillary response in premature infants. Blue stimuli did produce a pupillary reflex and the extent of the reaction was dependent on the intensity of the stimulus. The results suggest that, in premature infants, the origin of the light reflex may be mediated predominantly by melanopsin-containing retinal ganglion cells. Preterm babies do not have fully functioning retinas. This study suggests that only the primitive non-image-forming system is operational, and the more sophisticated rod / cone system develops during later postnatal periods. 

Pupillary size and light reflex in premature infants.
Ikeda T, Ishikawa H, Shimizu K, et al.
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Claire Howard

Salford Royal NHS Foundation Trust, Salford, UK.

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