The circadian rhythm of the intraocular pressure in the New Zealand White rabbit.

Most physiologic functions in man as well as in animals have been shown to have a circadian (approximately 24 hour) rhythm. It has been found in both the normal and glaucomatous human eye that the intraocular pressure, which is one of these circadian functions, varies considerably over a 24-hour period. Because of the extensive use of the rabbit in glaucoma research, a detailed study of the intraocular pressure over a 24-hour period was undertaken. Using hourly applanation tonometry for 25 consecutive measurements in ten New Zealand White rabbits (20 eyes), a circadian rhythm of the rabbit intraocular pressure was found. The pressures were lowest at night and rose to their highest values during the day. In addition, the data suggest that the maximum intraocular pressure may be biphasic with maximum values occurring between 0800 and 1100 and 1600 and 1900. Therefore, studies involving the New Zealand White rabbit must take into consideration these 24-hour pressure changes when intraocular pressure measurements are made.