Pupillary diameter and reaction to light in preterm

The pupil controls the amount of light entering the eye. We have examined both the time course for the development of the light reflex and pupil diameter before and after this event in 50 neonates. The pupillary light reflex was absent in ali neonates of less than 30 weeks' gestational age, it graduafly developed from this age and by 35 weeks it was present in all. Several possible mechanisms that may explain the onset of this reflex are considered. Before the onset of the pupil reflex mean horizontal pupillary diameter was 3-46 mm compared with 3-02 mm after the reflex development. We have estimated the amount of light reaching the retina (retinal irradiance) for preterm neonates and although it is less than that known to cause retinal damage in animals, further research is necessary to determine whether early light exposure has an adverse or beneficial effecton the immature visual system. Department of Ophthalmology, University of Birmingham, Birmingham and Midland Eye Hospital J Robinson A R Fielder Correspondence to: Miss J Robinson, Department of Ophthalmology, University of Birmingham, Birmingham and Midland Eye Hospital, Church Street, Birmingham B3 2NS. Accepted 22 June 1989 The pupil regulates the amount of light entering the eye by reflex dilatation or constriction in response to changes in the illumination. Few studies have been performed that have explored the development of the light reflex in neonates. In 1966 Robinson investigated the development of 20 types of reflexes in an attempt to produce an assessment that would be useful to the paediatrician interested in distinguishing between preterm and small for date neonates.' Of the reflexes examined he found that the presence of the pupillary light reflex was one of five that were highly correlated with gestational age. Finnstrom designed a study to assess the use of reflex testing as part of a gestational age 2 assessment. Babies of less than 29 weeks' gestational age (n=4) had no pupillary response to light, but by 31 weeks' gestational age the reflex appeared to be present, although sluggish in all. When the presence of the pupillary light reflex was examined as a function of gestation, he found a correlation coefficient of only 0-24, although he accepted that this may have been due to the small number (n=6) of infants of less than 32 weeks' gestation in this study. In both of these studies the numbers of babies of less than 29 weeks' gestational age were small and their gestational ages were not given. This indicates the need to examine the pupil of the very immature infant: to date the pupil diameter of the preterm neonate has been mentioned on two occasions only and divergent values of 1-5 mm3 and 2-9 mm4 have been quoted. We therefore decided to study pupillary diameter and light reflex prospectively, and we report, first, the time course of the development of the pupillary light reflex and second,pupil diameter in infants with and without pupillary constriction