Comparison of applanation tonometers in dogs and horses.

The research article is about a comparison of two types of applanation tonometers—Mackay-Marg and Tono-Pen—in measuring intraocular pressure (IOP) in dog and horse eyes at various pressure levels.

Objective of the Study

• This study aimed to determine the level of accuracy in the measurement of intraocular pressure (IOP) by two types of applanation tonometers—Mackay-Marg and Tono-Pen—against a manometer, which was used as the standard measure. The IOP was manipulated over a range of pressures from 0 to 100 millimeters of mercury (mm of Hg) in anesthetized dogs and enucleated horse eyes.

Methods and Study Design

• Four separate tonometers were evaluated (two Mackay-Marg tonometers and two Tono-Pen tonometers) in eyes where the intraocular pressure had been deliberately altered.
• The research used eyes from anesthetized dogs and eyeballs removed from horses (enucleated horse eyes), altering the intraocular pressure using a manometer – a device for measuring the pressure of a fluid.

Key Findings

• The study found that none of the tonometers were accurate throughout the entire range of 0 to 100 mm of Hg when compared to the manometer. This suggests the limitations of these tonometers at higher levels of IOP.
• However, when the pressure ranged from 0 to 30 mm Hg, several of the tonometers provided accurate measurements. This indicates that these devices may have high efficiency and precision within a certain range of pressure levels.
• The researchers also noted significant differences amongst the tonometers themselves, especially at higher IOP levels, demonstrating that not all tonometers perform equally under the same conditions.
• The coefficient of determination (r2) values for a linear model ranged from 0.979 to 0.991 in dogs, and from 0.982 to 0.996 in horse eyes. The r2 value is a statistical measure that shows the proportion of the variance for a dependent variable that’s explained by an independent variable or variables in a regression model. Higher r2 values mean that the model explains more variation, showing that these tonometers were broadly accurate within the above-mentioned range.