INTRAOCULAR-PRESSURE IN LEWIS RATS

Purpose. To perform noninvasive measurements of intraocular pressure ( IOP) in rats, the Tono-Pen-1 and Tono-Pen-2 were calibrated against di rect manometry. Normal values and the long-term fluctuations of IOP in Lewis rats were established. Methods. For calibration, 24 eyes were c annulated 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 Pig increments. After each incremental increa se, 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 establishe d. To ascertain long-term IOP fluctuations, the pressure in 52 eyes of 26 rats was measured every day between 8:30 and 9:30 AM for 7 consecu tive days. Results. Plotting the mean Tone-Pen readings for each eye a gainst the transducer IOP produced two regression formulas: y = 1.819 + 0.711 x (r(2) = 0.92) for Tono-Pen-1, and y = -1.291 + 0.784 x (r(2) = 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 up per 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.