The Relation of Axial Length and Corneal Thickness Fluctuations in Human Eyes

Abstract

Purpose: : To determine if diurnal fluctuations of axial length (AL) in human eyes are related to daily fluctuations in corneal thickness (CT).

Methods: : 12 subjects (24 eyes), ages 19 to 26 years, underwent serial axial length and corneal thickness measurements using highly precise, non–contact partial coherence interferometry. Both eyes were measured five times at 3–hour intervals, starting at 6:30am and ending at 8:30pm. The significance of fluctuation was tested using analysis of variance (ANOVA) with repeated measurements. Sine curve fitting was performed for eyes with significant fluctuation to determine the peaktime and amplitude of the fluctuation.

Results: : Of 19 eyes with sufficient data for ANOVA, 12 had significant AL fluctuation over the day (ANOVA, p < 0.05). Four subjects had significant AL fluctuation in both eyes. The mean ± SD magnitude of AL fluctuation was 52.0 ± 37.6 µm. Among 5 eyes with significant sine–curve fitting, mean peak time was 1:55 pm. Of 24 eyes with sufficient data for ANOVA, 12 had significant CT fluctuation over the day (ANOVA, p < 0.05). Three subjects had significant CT fluctuation in both eyes. The mean ± SD magnitude of CT fluctuation was 11.5 ± 5.7 µm. Mean peak time from 8 eyes with significant sine–curve fitting was 9:18 am. Of all eyes with measured AL and CT, there was discordance in 6 (4 only had AL fluctuations, 2 only had CT fluctuations). Of the 14 eyes that had either significant AL or CT fluctuations, 8 had both (57.1%). Of these 8 eyes, the mean magnitude of AL fluctuation was ∼37 µm larger (p=0.008) than that of CT.

Conclusions: : Both AL and CT fluctuate over the day. The CT changes do not appear to account for AL changes for three reasons: (1) the peak time differs, (2) the magnitude of fluctuations differs, and (3) both AL and CT fluctuations are not consistently present in an individual eye. Further research is needed to determine physiologic factors that contribute to AL fluctuations.

Keywords: myopia • cornea: clinical science • refractive error development