NORMAL VARIATION IN, AND EFFECT OF 2-PERCENT PILOCARPINE ON, INTRAOCULAR-PRESSURE AND PUPIL SIZE IN FEMALE HORSES

Objective-To determine normal variation in, and effect of 2% pilocarpi ne hydrochloride on, intraocular pressure (IOP) and pupil size in fema le horses during a specified period. Animals-10 female horses with nor motensive eyes. Procedure-IOP and horizontal and vertical pupil size w ere measured on a single day between 8 AM and 8 PM at hours 0, 0.5, 1, 2, 4, 6, 8, 10, and 12. Measurements were repeated after single- dose application of 2% pilocarpine to both eyes. IOP and pupil size were m easured at 8 AM and noon in a 5-day experiment of twice-daily applicat ion of 2% pilocarpine. Results-Variation in IOP and pupil size was not significant between 8 AM and 8 PM. Change in IOP or pupil size after a single dose of 2% pilocarpine also was not significant. In the multi ple-dose experiment, the IOP at noon on the fifth day was significantl y higher than the IOP in the morning on the first and second days. The IOP in the morning on the fifth day was significantly higher than the IOP in the morning and at noon on the first and second days. The IOP at noon on the fourth day was significantly higher than the morning IO P on the first and second days and at noon on the first day. The decre ase in vertical pupil size was significant. Conclusions-Between 8 AM a nd 8 PM, variation in IOP and pupil size in normotensive eyes of horse s is not significant. Two percent pilocarpine does not significantly c hange IOP between 8 AM and 8 PM in clinically normal horses after a si ngle dose or multiple twice-daily applications. After multiple twice-d aily applications, a trend toward an increase in IOP was seen, and the decrease in vertical pupil size was significant.