MEASUREMENT OF RABBIT INTRAOCULAR-PRESSURE WITH THE TONO-PEN

A Tono-Pen-1 (TP-1) and a Tone-Pen-2 (TP-2) were calibrated against di rect manometry in the eyes of living rabbits to determine the accuracy of the Tone-Pen. Eighteen normal eyes of 10 rabbits were cannulated a nd connected to a pressure transducer with a chart recorder. Intraocul ar pressure (IOP) was increased from 5 to 40 mm Hg in 5-mm-Hg incremen ts and from 40 to 80 mm Hg in IO-mm-Hg increments. After each incremen tal increase, IOP was measured first with a TP-1 and then with a TP-2. Plotting the mean Tone-Pen readings for each eye against the transduc er pressure produced the following two regression line formulas: y = - 0.613+0.790x (r(2) = 0.97) for TP-I, and y = -1.45+0.824x (r(2) = 0.97 ) for TP-2. Neither regression line was statistically different; p = 0 .2 for the two slopes, and p = 0.24 for the y-axis intersection. The T P-1 and TP-2 can be used to rapidly and accurately measure the IOP in normal rabbit eyes. Tone-Pen readings do, however, significantly under estimate pressures in the range of 5-80 mmHg. A table with 95% confide nce intervals for corrected IOP readings obtained with the TP-I or -2 is provided.