Evaluation of two applanation tonometers in cats

Area of Science:

• Veterinary Ophthalmology
• Ophthalmology
• Animal Health

Background:

• Intraocular pressure (IOP) measurement is crucial for diagnosing and managing ocular conditions in cats.
• Applanation tonometry is a common method for IOP assessment, but device accuracy can vary.
• The MacKay-Marg and Tono-Pen are widely used tonometers, necessitating a comparison of their performance in feline eyes.

Purpose of the Study:

• To compare the accuracy of the MacKay-Marg and Tono-Pen applanation tonometers in feline eyes.
• To establish correction formulas for IOP measurements obtained from these tonometers in cats.
• To evaluate the influence of tonometer order on IOP readings in vivo.

Main Methods:

• In vitro comparison of MacKay-Marg and Tono-Pen against direct manometry using feline eyes.
• In vivo IOP measurements in clinically normal cats, with varying sequences of tonometer application.
• Statistical analysis to determine significant differences and develop predictive IOP correction formulas.

Main Results:

• Both tonometers significantly underestimated IOP compared to direct manometry (P < 0.001) with high correlation (r2 = 0.99).
• Predictive formulas were derived: Actual IOP = 1.36 x (MacKay-Marg) - 1.67 and Actual IOP = 1.37 x (Tono-Pen) + 0.8.
• In vivo, the Tono-Pen consistently underestimated IOP compared to the MacKay-Marg (P < 0.001), with readings being lower when Tono-Pen followed MacKay-Marg (P < 0.05).

Conclusions:

• The MacKay-Marg and Tono-Pen require IOP correction formulas for accurate assessment in cats.
• The order of tonometer use can influence Tono-Pen readings, suggesting potential for measurement bias.
• These findings provide essential data for improving the clinical accuracy of IOP measurements in feline patients.