Inter-user and intra-user variation of two tonometers in horses.
Authors: Lewin Andrew C, Liu Chin-Chi, Camacho-Luna Pilar, Alling Christopher, Carter Renee T
Journal: Equine veterinary journal
Summary
# Editorial Summary: Inter-user and intra-user variation of two tonometers in horses Accurate intraocular pressure (IOP) measurement is essential for diagnosing and monitoring equine ocular disease, yet the clinical reliability of the two tonometers most commonly used in equine practice—the rebound (ICare TonoVet) and applanation (TonoPen) devices—had not been directly compared for measurement consistency. Four examiners performed triplicate IOP measurements using both instruments on 10 healthy horses in both sedated and unsedated states, with variation quantified using coefficient of variation (CV) values to assess both consistency between different operators (inter-user) and within the same operator (intra-user). The rebound tonometer demonstrated substantially superior consistency in unsedated horses, with inter-user variation of 15.4% versus 21.7% for applanation (P = .01) and intra-user variation of 9.1% versus 16.1% (P < .0001); in sedated horses, the rebound device again showed lower intra-user variation (8.4% vs 14.7%, P < .0001), whilst both devices performed similarly for inter-user consistency. Notably, sedation improved applanation tonometry's inter-user variation significantly (16.0% vs 21.7%, P = .03) but did not affect rebound tonometry performance. For equine practitioners, these findings suggest the rebound tonometer is the more reliable choice for IOP measurement in unsedated horses, and if applanation tonometry is preferred for clinical or practical reasons, sedating the patient will improve measurement reproducibility between operators, though absolute intra-user variation remains higher than with rebound technology.
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Practical Takeaways
- •Use the rebound tonometer (ICare TonoVet) for IOP measurements in unsedated horses to obtain more reliable and consistent readings across different examiners
- •If forced to use the applanation tonometer (TonoPen), sedate the horse first to reduce examiner-to-examiner variation in measurements
- •The rebound tonometer produces more consistent results regardless of whether the horse is sedated, making it more practical for routine clinical use
Key Findings
- •Rebound tonometer demonstrated significantly lower inter-user variation than applanation tonometer in unsedated horses (15.4% vs 21.7%, P=0.01)
- •Rebound tonometer showed lower intra-user variation than applanation tonometer in both unsedated (9.1% vs 16.1%, P<0.0001) and sedated horses (8.4% vs 14.7%, P<0.0001)
- •Sedation reduced inter-user variation for applanation tonometer (21.7% to 16.0%, P=0.03) but did not affect rebound tonometer variation
- •Rebound tonometer is the preferred device to minimize measurement variation for IOP assessment in equine patients