CIRCADIAN-RHYTHM OF INTRAOCULAR-PRESSURE - A RAT MODEL

The purpose of this study was to examine whether there is a circadian rhythm of intraocular pressure (IOP) in the Lewis rat. Therefore, 20 L ewis rats (40 eyes) were subjected to an alternating 12-hour-light and 12-hour-dark cycle. Using a Tone-Pen 1, IOP was measured every 2 h be tween 6 a.m. and 12 midnight and every 3 h between 12 midnight and 6 a .m. for 2 consecutive days. These measurements in the Lewis rat reveal ed a reproducible circadian rhythm with a peak at 8 p.m. and a trough at 6 a.m. In conclusion, when using the Lewis rat as an animal model i n longitudinal studies that involve the IOP, the IOP should be measure d at the same time each day to correct for diurnal variations. Additio nally, Lewis rats may be a useful model to study the causes of circadi an rhythms of IOP and for pharmacologic studies of new glaucoma medica tions.