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Equine veterinary journal2020; 52(4); 572-576; doi: 10.1111/evj.13208

Inter-user and intra-user variation of two tonometers in horses.

Abstract: It is currently unknown which of the two devices most commonly used in equine ophthalmology for intraocular pressure (IOP) estimation demonstrates the lowest inter-user and intra-user variation. Objective: To assess the inter-user and intra-user variation of two tonometers in sedated and unsedated horses. Methods: Randomised masked cross-over trial. Methods: Four examiners used the rebound (ICare TonoVet) and applanation (TonoPen ) tonometers to measure the intraocular pressure (IOP) in triplicate in 10 normal horses before and after sedation with xylazine. For inter-user variation, coefficient of variation (CV) values were calculated from the mean of each examiner for each condition combination. 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. Results: The rebound tonometer was found to have lower inter-user (15.4% vs 21.7%, P = .01) and intra-user (9.1% vs 16.1%, P < .0001) variation in unsedated horses and lower intra-user (8.4% vs 14.7%, P < .0001) 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 = .03). No other variable assessed was found to have an effect on IOP. Conclusions: No animals with ocular disease were included in this study. Conclusions: The rebound tonometer may be the preferred instrument to minimise intra-user and inter-user variation for IOP measurement in unsedated horses. The rebound tonometer is also likely to be the preferred instrument to minimise intra-user variation in sedated horses. If the applanation tonometer is used to perform IOP measurement in horses, it is recommended that this is performed while horses are sedated to minimise inter-user variation for this instrument.
© 2019 EVJ Ltd.
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Publication Date: 2020-02-08 PubMed ID: 31721273DOI: 10.1111/evj.13208Google Scholar: Lookup
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  • Journal Article
  • Randomized Controlled Trial
  • Veterinary

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research article compares the performance of two types of tonometers used for estimating intraocular pressure (IOP) in horses, to identify which demonstrates the lowest variability between users and repeat measurements by a single user. The study found the rebound tonometer to be the most reliable instrument, particularly when used on unsedated horses.

Research Methods

  • The researchers conducted a randomised masked cross-over trial involving four examiners and 10 horses with normal ocular conditions.
  • Each examiner used two different tonometers, the rebound (ICare TonoVet) and applanation (TonoPen), to measure intraocular pressure in each horse multiple times both before and after sedation with xylazine.
  • The study then calculated the coefficient of variation (CV) from the mean readings of each examiner (inter-user variation) and from individual measurements by each examiner (intra-user variation).
  • They also used an ANOVA to assess if other variables could be affecting the CV values.

Results

  • The rebound tonometer was found to have lower inter-user and intra-user variation in unsedated horses, along with lower intra-user variation in sedated horses, compared to the applanation tonometer.
  • In sedated horses, inter-user variation was similar for both the rebound and applanation tonometers.
  • For the applanation tonometer, sedation was found to lessen inter-user variation, although it still had a higher variation than the rebound tonometer overall.
  • None of the other evaluated variables were found to have an effect on intraocular pressure.

Conclusions

  • The research concluded that the rebound tonometer may be the preferred instrument due to its lower variation in intra-user and inter-user measurements, particularly when used on unsedated horses.
  • When sedation is involved, the rebound tonometer also consistently performs better in reducing intra-user variation.
  • If using the applanation tonometer, sedating the horses is suggested to help minimize inter-user variation.
  • It should be noted, however, that the study didn’t include any horses with ocular diseases, which might potentially affect the measurements.

Cite This Article

APA
Lewin AC, Liu CC, Camacho-Luna P, Alling C, Carter RT. (2020). Inter-user and intra-user variation of two tonometers in horses. Equine Vet J, 52(4), 572-576. https://doi.org/10.1111/evj.13208

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 52
Issue: 4
Pages: 572-576

Researcher Affiliations

Lewin, Andrew C
  • School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA.
Liu, Chin-Chi
  • School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA.
Camacho-Luna, Pilar
  • School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA.
Alling, Christopher
  • School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA.
Carter, Renee T
  • School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA.

MeSH Terms

  • Anesthesia / veterinary
  • Animals
  • Horses
  • Intraocular Pressure
  • Reproducibility of Results
  • Tonometry, Ocular

Grant Funding

  • Louisiana State University School of Veterinary Medicine

References

This article includes 19 references
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Citations

This article has been cited 3 times.
  1. Hodgson KJ, Harman CD, Bajric S, Cabble A, Anderson AL, Palanivel H, Taylor DA, Komáromy AM. Comparison of three rebound tonometers in normal and glaucomatous dogs. Vet Ophthalmol 2023 Jan;26(1):31-38.
    doi: 10.1111/vop.13043pubmed: 36440595google scholar: lookup
  2. Mustikka MP, Pietilä EM, Mykkänen AK, Grönthal TSC. Comparison of two rebound tonometers in healthy horses. Vet Ophthalmol 2020 Sep;23(5):892-898.
    doi: 10.1111/vop.12819pubmed: 32888242google scholar: lookup
  3. Wang C, Su Y, Shi F, Fu J. Comparison of three rebound tonometers in rabbits. Sci Rep 2025 Dec 29;15(1):44840.
    doi: 10.1038/s41598-025-28990-8pubmed: 41462550google scholar: lookup
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