The pupils of term and preterm infants.

We studied the pupils of 100 term and preterm infants between 26.5 and 46 weeks' postconceptual age. The mean (+/- S.D.) pupil diameter in a dark environment (less than 10 foot-candles of illumination) was 3.6 mm (+/- 0.9). Anisocoria of 0.5 to 1.0 mm was found in nine infants. The pupils did not consistently respond to 600 foot-candles of light before 32 weeks' postconceptual age, but responded increasingly thereafter. This progressive light response correlated significantly with postconceptual age, weight, Apgar scores, and corneal diameter (P less than .01). In the perinatal period, neurologic or radiologic examination may be warranted if the pupil diameter in a dark environment is less than 1.8 mm or greater than 5.4 mm or if the pupils do not respond to light challenge after 31 weeks' postconceptual age.