Nocturnal dip in the optic nerve head perfusion

Purpose: Many physiological parameters, including blood pressure, show circ adian variations. Diurnal fluctuations of the optic nerve head (ONH) circul ation have not yet been studied. The purpose of the present study was to de termine the pattern of ONH blood flow variations over a 24-hour period in h ealthy subjects. Methods: The subject group comprised 15 healthy volunteers (6 women, 9 men) aged 22 to 43 years (mean +/- SEM: 28.2 +/- 1.3 years). Blood flow in the ONH was measured by laser Doppler flowmetry (LDF) over a 24-hour period at 08:00, 12:00, 16:00, 20:00, 24:00 hours, and at 08:00 hours the following m orning. Results: ONH perfusion varied significantly over time. The mean LDF-flow du ring daytime ranged from 8.2 to 8.9 arbitrary units (AU) and fell at midnig ht to 7.1 AU (P =.0015). The mean LDF-volume during daytime was 0.23 to 0.2 4 AU and decreased at midnight to 0.20 AU (P =.04). The mean LDF-velocity r anged from 0.39 to 0.41 kHz with no significant differences at any time poi nt. Conclusions: Our study in normal subjects reveals small mean changes of ONH perfusion during daytime and a significant reduction at night. The physiol ogical and clinical relevance of the nocturnal dip in the ONH perfusion nee ds to be determined in future studies. Jpn J Ophthalmol 2000;44:128-131 (C) 2000 Japanese Ophthalmological Society.