Intraocular pressure in Lewis rats.

ABSTRACT

PURPOSE: To perform noninvasive measurements of intraocular pressure (IOP) in rats, the Tono-Pen-1 and Tono-Pen-2 were calibrated against direct manometry. Normal values and the long-term fluctuations of IOP in Lewis rats were established. METHODS: For calibration, 24 eyes were cannulated and connected to a pressure transducer with a chart recorder. IOP was increased from 5 to 40 mm Hg in 5 mm Hg increments, and from 40 to 60 mm Hg in 10 mm Hg increments. After each incremental increase, IOP was measured with a Tono-Pen-1 and a Tono-Pen-2 tonometer. To determine normal IOP in Lewis rats, IOP was measured with a Tono-Pen-1 in 229 eyes of 115 rats, and a histogram of normal IOP was established. To ascertain long-term IOP fluctuations, the pressure in 52 eyes of 26 rats was measured every day between 830 and 930 AM for 7 consecutive days. RESULTS: Plotting the mean Tono-Pen readings for each eye against the transducer IOP produced two regression formulas y = 1.819 + 0.711 x (r2 = 0.92) for Tono-Pen-1, and y = -1.291 + 0.784 x (r2 = 0.97) for Tono-Pen-2. The normal IOP in rats was 17.30 +/- 5.25 mm Hg (90% confidence interval 7.28 and 26.98 mm Hg for the lower and upper limits of normal IOP). There was no long-term fluctuation in IOP (P = 0.55). CONCLUSIONS: IOP can be measured accurately in living rats with the Tono-Pen-1 or the Tono-Pen-2.