Diurnal Variation of Axial Length and Intraocular Pressure in Young Adults

Abstract

Abstract: : Purpose: To elucidate the diurnal variation of human axial length with optical coherence biometry. Methods: Changes in axial length and intraocular pressure (IOP) were measured every 2 hours for a period of 24 hours in 18 young adults (average age: 23.3 years old) using IOLMasterTM (Zeiss) and a non-contact tonometer (KT-500, KOWA). Light-Dark conditions were strictly controlled. Subjects were instructed to keep a regular sleep cycle from 23:00 PM to 6:00 AM. To strengthen their circadian synchronization, they were asked to keep their lights off during sleep for 3 days before and during this study. Results: The axial length showed a remarkable diurnal variation throughout 24 hours. A significant difference between the light-wake periods and dark sleep periods of 0.05mm was found (p<0.001). IOP was significantly higher during light-wake periods than dark-sleep periods (p<0.001). Only in the females, corneal curvature and thickness showed a remarkable diurnal variation. Conclusions: Diurnal variation of axial length was significant, approximately 0.05mm in young subjects. The increase of axial length was correlated with the increase of IOP. Diurnal variation of axial length is an important parameter for planning refractive surgery.

Keywords: circadian rhythms • refraction • refractive surgery