DIURNAL-VARIATIONS IN HUMAN CORNEAL THICKNESS

Aim - To elucidate the diurnal variation in human corneal thickness ov er a 48 hour period. Method - Changes in central corneal thickness wer e monitored in eight healthy subjects (four male, four female) aged be tween 10 and 63 years using an ultrasonic pachymeter. Measurements wer e made over a 48 hour period - immediately before sleep, immediately u pon waking and at 15, 30, 45 minutes, 1, 1.5, 2, 2.5, 3 hours, and at 2 hour intervals thereafter throughout the remainder of each day. Resu lts - The mean corneal thickness for the group (SD) was 546 (14) mu m, with a mean overnight increase of 5.5% (2.9%) (range 1.9-12.6%) and a maximum diurnal increase of 7.2% (2.8%) (range 2.1-14.3%). Individual differences in the extent of diurnal and overnight variation occurred within the group. For three subjects, the first reading taken on waki ng was not the highest and corneal thickness continued to increase. Co nclusion - These data confirm an increase of corneal thickness during sleep, but also reveal considerable variation during waking hours. Thu s, the overnight changes in corneal thickness are not truly representa tive of diurnal variations in human corneal thickness and, in fact, mu ch greater diurnal variation occurs than the 3.0-4.4% previously repor ted.