The fixed and dilated pupils of premature neonates.

We examined on a weekly basis the pupils of 30 preterm infants. In relative darkness (less than 10 foot-candles [ft.-c.] of illumination), the pupils measured a mean of 4.7 mm in the youngest infants (26 weeks' postconceptional age) when the corneal diameter was 7.0 mm. The pupils became progressively smaller, reaching 3.4 mm at 29 weeks' postconceptional age (P less than .001). The pupils did not constrict to the stimulating light (600 ft.-c.) until a mean of 30.6 weeks' (+/- 1 week) postconceptional age. Mydriasis should not be considered indicative of a central nervous system disorder, and a pupil unresponsive to light should not be considered suggestive of blindness until a preterm infant reaches at least 32 weeks' postconceptional age.