<p> Existence of a daily circadian rhythm of intraocular pressure (IOP) in pigs has not been previously published, and is a necessary first step to investigate if minipigs could be used as an animal model for glaucoma. Study goals were to (1) investigate the presence of a pattern of rhythmicity to minipig IOP under a regular light/dark cycle, effects of reversing light/dark cycles on (2) immune response and (3) IOP, and if the (4) topical application of Timolol Maleate lowers IOP. </p><p> Eight female Sinclair minipigs were exposed to regular light/dark cycles. Four baseline IOP collections were taken at least 10 days apart. Data collections were 24 hours, with IOP taken from both eyes every two hours using a Reichert Tonopen XL. Light/dark cycles were flipped ten days prior to reversed IOP data collection. Timolol was administered twice a day, for seven days prior to another IOP collection. </p><p> Baseline data were analyzed by repeated measures ANOVA. There was a significant effect of time, F(11,77) = 12.56, <i>p</i> &lt; 0.001. Bonferroni post hoc tests revealed a significant difference between hour 0 and 6, 6 and 10 (the peaks), and between 10 and 14, and 14 and 0 (the troughs). This supports the hypothesis that minipigs have an daily rhythmicity to their IOP. </p><p> Reversed light/dark data were analyzed by mixed measures ANOVA. There was a main effect of time, F(11,143) = 7.503, <i>p</i> &le; 0.001, no main effect of condition (reversed vs baseline), F(1,13) = 1.092, <i> p</i> = 0.315, and an interaction effect (time*reversed vs. baseline), F(11,143) = 5.384, <i>p</i> &lt; 0.001. </p><p> Paired samples t-tests were run on the baseline complete blood cell count (CBC) and the samples taken during the light/dark cycle reversal to investigate if there was an immune response to light/dark cycle reversal. There was a significant effect on several CBC factors; however, none of the factors were out of the &ldquo;normal&rdquo; for female Sinclair Minipigs. </p><p> The final hypothesis was that Timolol Maleate would lower IOP. A mixed ANOVA was run and revealed that there was a main effect of time, F(11,143) = 5.146, <i>p</i> &lt; 0.001, a main effect of condition (baseline vs Timolol), F(1,14) = 6.511, and a significant interaction effect (time*baseline vs Timolol), F(11, 154) = 2.703, <i>p</i> = 0.003. Because the minipigs displays two peaks and two troughs, which has never been seen before, and Timolol had no effect on IOP, further research is needed before pigs can be used as an animal model for glaucoma research.</p><p>