Intraocular pressure in Lewis rats

Area of Science:

• Ophthalmology
• Veterinary Medicine
• Physiology

Background:

• Intraocular pressure (IOP) is a critical factor in ocular health.
• Accurate IOP measurement in animal models is essential for research.
• Noninvasive methods are preferred for repeated measurements in research settings.

Purpose of the Study:

• To calibrate Tono-Pen-1 and Tono-Pen-2 tonometers against direct manometry for noninvasive IOP measurement in rats.
• To establish normal IOP values in Lewis rats.
• To determine long-term IOP fluctuations in Lewis rats.

Main Methods:

• Calibration involved cannulating rat eyes and connecting them to a pressure transducer, with IOP incrementally increased and measured by tonometers.
• Normal IOP was determined by measuring IOP in 229 eyes of 115 Lewis rats using Tono-Pen-1.
• Long-term fluctuations were assessed by daily IOP measurements over 7 days in 52 eyes of 26 rats.

Main Results:

• Regression formulas were derived for Tono-Pen-1 (y = 1.819 + 0.711x, r2 = 0.92) and Tono-Pen-2 (y = -1.291 + 0.784x, r2 = 0.97).
• Normal IOP in rats was determined to be 17.30 +/- 5.25 mm Hg, with a 90% confidence interval of 7.28 to 26.98 mm Hg.
• No significant long-term fluctuations in IOP were observed (P = 0.55).

Conclusions:

• Tono-Pen-1 and Tono-Pen-2 tonometers provide accurate noninvasive measurements of IOP in living rats.
• The established normal IOP range and lack of fluctuation aid in future rat ocular research.