Keratometry measurements in preterm and full term newborn infants

To evaluate the relation between postconceptional age and birth weight with keratometric values in preterm and full term infants.

A prospective cross sectional study was performed. The cohort included 99 infants (198 eyes) admitted to the Neonatal and Neonatal Intensive Care Units at Schneider Children's Medical Center of Israel from February to September 2002. Keratometry in the horizontal and vertical meridians was performed in both eyes of each infant by two ophthalmologists using an autokeratometer. The results were evaluated according to: postconceptual age (<32 weeks, 32-36 weeks, >36 weeks) and birth weight (<1500 g, 1501-2500 g, >2501 g).

Corneal curvature measurements decreased progressively with both postconceptual age and birth weight. At <32 weeks, mean (standard deviation) readings were 63.3 (3.2) diopters (D) for the horizontal meridian and 57.3 (2.6) D for the vertical meridian; corresponding values at >36 weeks were 54.0 (3.0) D and 50.7 (2.4) D. In the <1500 g group, mean (SD) readings were 61.3 (3.9) D for the horizontal meridian and 56.0 (2.9) D for the vertical meridian; corresponding values in the >2501 g group were 51.3 (2.1) D and 48.6 (1.8) D.

There is an inverse relation of horizontal and vertical keratometric values with both postconceptional age and birth weight. Highest readings were noted in the babies with the lowest birth weight and youngest postconceptional age. The decrease in corneal dioptric power to normal values is linear and is apparently part of the normal ocular maturation.