Noninvasive measurement of rat intraocular pressure with the Tono-Pen

Invest Ophthalmol Vis Sci. 1993 Feb;34(2):363-9.


Purpose: The purpose of this study was to evaluate the Tono-Pen 2 tonometer for measuring intraocular pressure (IOP) in the living rat eye.

Methods: One eye from each of 20 adult, anesthetized brown Norway rats (group 1) was cannulated and simultaneously connected to a syringe and a pressure transducer with a chart recorder. We increased IOP from 15 to 45 mmHg in 5-mmHg increments and obtained 15 consecutive readings (ignoring instrument-generated averages) at each pressure increment with a Tono-Pen 2 tonometer. To test the tonopen's ability to measure unknown IOP, transducer pressures were varied randomly in 20 additional animals (group 2), and tonopen readings were obtained in masked fashion.

Results: Plotting the mean tonopen readings for each animal against transducer IOP produced a regression formula of y = 4.54 + 0.79x (r = 0.98). Mean group 2 tonopen values plotted against transducer IOP yielded a regression formula of y = 4.75 + 0.78x (r = 0.94). A method comparison analysis showed that the tonopen significantly overestimates pressures at low IOP (< or = 15 mmHg), and it significantly underestimates pressures at high IOP (> or = 30 mmHg). Using two-way analysis of variance, it was determined that the group 2 data did not differ significantly from the group 1 data (P > or = 0.76). Because of this consistency, we generated a correction factor with 95% prediction intervals for Tono-Pen readings.

Conclusions: The Tono-Pen 2 can be used reliably to measure IOP in the normal rat eye.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Disease Models, Animal
  • Evaluation Studies as Topic
  • Intraocular Pressure* / physiology
  • Male
  • Ocular Hypertension / physiopathology
  • Predictive Value of Tests
  • Rats
  • Rats, Inbred BN
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Tonometry, Ocular / instrumentation*
  • Tonometry, Ocular / methods