Measuring Intraocular Pressure in Horses

The article “Inter‐user and intra‐user variation of two tonometers in horses” was authored by A.C. Lewin; C. Liu; P. Camacho‐Luna; C. Alling; and R.T. Carter.

This randomized, masked, cross‐over trial aimed to determine whether applanation or rebound tonometry has the lowest inter‐ and intra‐user variation when measuring intraocular pressure (IOP) in horses.

Four examiners used rebound (ICare® TonoVet) and applanation (TonoPen®) tonometers to measure the IOP in triplicate in 10 normal horses before and after sedation with xylazine. The order of examiners, eye examined first and instrument used first were determined randomly and varied between horses. Coefficient of variation (CV) values were calculated from the mean of each examiner for each condition combination to determine inter‐user variation. 

For intra‐user variation, CV values were calculated from the individual measurements of each examiner for each condition combination. CV values were also assessed in relation to other variables using ANOVA.

The rebound tonometer was found to have significantly (P<0.01) lower inter‐user (15.4% vs 21.7%) and intra‐user (9.1% vs 16.1%) variation in un-sedated horses and lower intra‐user (8.4% vs 14.7%,) variation in sedated horses than the applanation tonometer. Both instruments had similar inter‐user variation in sedated horses. For the rebound tonometer, sedation did not affect inter‐user or intra‐user variation, but for the applanation tonometer, inter‐user variation was lowest while horses were sedated (16.0% vs 21.7%, P = 0.03). No other variable assessed was found to have an effect on IOP.

Bottom line: Rebound tonometry might be the preferred instrument to minimize intra‐user and inter‐user variation for IOP measurement in un-sedated horses.

You can read or purchase access to this article from Wiley online library here.