Twenty-four-hour pattern of mouse intraocular pressure.

The 24-hr pattern of intraocular pressure in the mouse eye remains poorly characterized. The present study was undertaken to determine the magnitude, dynamic pattern, and synchrony of the 24-hr pattern of intraocular pressure (IOP) in NIH Swiss mice exposed to a 12-hr light/dark cycle or to constant light. IOP was measured every 3 hr using a microneedle method. Mice exposed to a 12-hr light /dark cycle were either measured repeatedly at 1 week interval (group 1) or were only measured once (group 2). A third group was exposed to constant light for 2 weeks prior to IOP measurements. The 24-hr IOP pattern in the first and second groups showed a similar rhythmic pattern that appeared to be sinusoidal. This IOP pattern declined in the morning until 12:00, and then increased in the early evening until 21:00. In contrast, IOP in the third group was asynchronous with some mice exhibiting multiple peaks and troughs during the 24-hr period. These results show that 24-hr IOP pattern in mouse eyes is biphasic and that extended exposure to constant light disrupts this 24-hr IOP pattern.