Effect of light cycle on 24-hour pattern of mouse intraocular pressure.

Purpose: The present study was undertaken to determine the magnitude, dynamic pattern, and synchrony of the 24-hour pattern of intraocular pressure (IOP), and to clarify the effect of light cycle on 24-hour pattern of IOP in ddY albino mice.

Methods: Three groups of ddY albino mice were exposed to a 12-hour light/dark cycle (control group), to constant light and, to constant dark, respectively. Every group was exposed to each condition for 4 weeks before IOP measurements. IOP was measured every 3 hours using a microneedle method. Mice were measured repeatedly at 1-week interval.

Results: The 24-hour IOP pattern of the control group showed a rhythmic pattern that appeared to be sinusoidal. This IOP declined in the morning until 9:00, and then increased in the early evening until 21:00. In contrast, IOP of the constant light and dark groups were asynchronous exhibiting multiple peaks and troughs during the 24-hour period. The mean IOP of the constant light group was almost equal to that of control group. The mean IOP measured at the daytime of the constant dark group (light time of control group), was significantly higher than that of the control group, and was almost equal to the mean IOP measurements at the dark time of the control group.

Conclusion: These results show that 24-hour IOP pattern in mouse eyes is biphasic and that extended exposure to constant light or dark disrupts this 24-hour IOP pattern.