Intraocular pressure in Lewis rats.
OBJECTIVE
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 8:30 and 9:30 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.
Mermoud
A
A
Doheny Eye Institute, Los Angeles, CA 90033.
Baerveldt
G
G
Minckler
D S
DS
Lee
M B
MB
Rao
N A
NA
D000818:Animals; D002138:Calibration; D007429:Intraocular Pressure / Q000502:physiology*; D008137:Longitudinal Studies; D008365:Manometry; D051381:Rats; D011917:Rats, Inbred Lew; D012016:Reference Values; D014065:Tonometry, Ocular / Q000379:methods