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Equine veterinary journal2020; 53(3); 612-617; doi: 10.1111/evj.13336

Intraocular pressure following four different intravenous sedation protocols in normal horses.

Abstract: Intravenous sedation is frequently necessary for ophthalmic examination in horses. Common sedation protocols have not been directly compared in terms of relative intraocular pressure (IOP) reduction, duration of IOP reduction and time to maximum IOP reduction. Objective: To compare the effects of standing sedation protocols on IOP. Methods: Randomised cross-over experiment. Methods: Twelve healthy horses received four intravenous sedation protocols with a 48 hours washout: 0.5 mg/kg xylazine and 0.01 mg/kg butorphanol (SED1); 10 µg/kg detomidine and 0.01 mg/kg of butorphanol (SED2); 10 µg/kg detomidine (SED3); 0.5 mg/kg xylazine (SED4). IOP was measured with rebound tonometry before sedation (Tpre) and 5, 10, 15, 30, 45 and 60 minutes post-sedation (Tpost). Post-sedation readings were taken with the head elevated to the Tpre position. Separately, IOP readings were also obtained following sedation with the head not elevated (TpostHeadDown). IOP values were compared using mixed ANOVA and ANCOVA models respectively with significance at P < .05. Results: All protocols decreased IOP compared with baseline with greatest reduction at Tpost5. IOP at Tpre (mean ± SD) was 21.8 ± 4.4 mm Hg. At Tpost5, IOP was 16.3 ± 3.8 mm Hg (SED1), 14.5 ± 2.9 mm Hg (SED2), 17.1 ± 3.8 mm Hg (SED3) and 16.9 ± 4.2 mm Hg (SED4). SED2 Tpost5 IOP was lower than other treatments. Considering all time points following sedation, SED3 IOP readings were higher than other treatments. TpostHeadDown IOPs were higher than readings taken with the head elevated (P < .001). Conclusions: Animals with ocular disease were not studied. No animals received mock sedation or equivalent. Conclusions: A combination of detomidine and butorphanol causes greater IOP reduction 5 minutes following sedation than other commonly used sedation protocols. IOP reduction is less pronounced when detomidine is used alone. Consideration of head height is important when performing IOP measurements in horses.
© 2020 EVJ Ltd.
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Publication Date: 2020-09-19 PubMed ID: 32844457DOI: 10.1111/evj.13336Google Scholar: Lookup
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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.

The study explored the effects of four different sedation methods in horses on intraocular pressure (IOP). The study found that a combination of detomidine and butorphanol caused the greatest reduction of IOP 5 minutes after sedation, in comparison to other common sedation protocols.

Study Purpose and Design

  • This research was designed to compare the effects of four common standing sedation protocols on intraocular pressure (IOP) in horses.
  • The study was a randomized cross-over experiment involving twelve healthy horses.
  • Each horse received four sedation protocols with a 48-hour break (washout) in between: 0.5 mg/kg xylazine and 0.01 mg/kg butorphanol (SED1); 10 μg/kg detomidine and 0.01 mg/kg of butorphanol (SED2); 10 μg/kg detomidine (SED3); 0.5 mg/kg xylazine (SED4).

Methodology

  • IOP was measured with rebound tonometry before sedation (Tpre) and then at 5, 10, 15, 30, 45 and 60 minutes after sedation (Tpost).
  • The post-sedation readings were taken with the horse’s head elevated to the same position as in the pre-sedation measurement.
  • Separate IOP measurements were also taken after sedation with the horse’s head not elevated (TpostHeadDown).
  • The IOP measurements were compared statistically using mixed ANOVA and ANCOVA models, with a significance level set at P < .05.

Results

  • All sedation protocols caused a decrease in IOP compared to the baseline measurements.
  • The greatest reduction of IOP was seen 5 minutes post-sedation, at which point the combination of detomidine and butorphanol (SED2) caused a lower IOP than the other treatment methods.
  • Across all the time-points following sedation, the IOP readings when detomidine was used alone (SED3) were higher than with the other treatments.
  • When the horse’s head was not elevated after sedation (TpostHeadDown), the IOP measurements were higher than when it was (P < .001).

Conclusion

  • No animals with ocular disease were studied in this experiment.
  • The research did not include a mock sedation or equivalent control.
  • The results suggest that a combination of detomidine and butorphanol causes a greater IOP reduction 5 minutes after sedation than other protocols.
  • Less of an IOP reduction occurs when detomidine is used alone.
  • The study underlines the importance of considering the height of the horse’s head when taking IOP measurements.

Cite This Article

APA
Joyner RL, Liu CC, Cremer J, Carter RT, Lewin AC. (2020). Intraocular pressure following four different intravenous sedation protocols in normal horses. Equine Vet J, 53(3), 612-617. https://doi.org/10.1111/evj.13336

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 53
Issue: 3
Pages: 612-617

Researcher Affiliations

Joyner, Rebekah L
  • 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.
Cremer, Jeannette
  • 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.
Lewin, Andrew C
  • School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA.

MeSH Terms

  • Animals
  • Butorphanol
  • Eye Diseases / veterinary
  • Horse Diseases
  • Horses
  • Intraocular Pressure
  • Tonometry, Ocular / veterinary
  • Xylazine / pharmacology

Grant Funding

  • Louisiana State University School of Veterinary Medicine

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This article includes 18 references
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Citations

This article has been cited 3 times.
  1. Allen R, Goodhead AD. A survey of ocular pathology in Warmblood horses in South Africa. Equine Vet J 2025 Jul;57(4):889-897.
    doi: 10.1111/evj.14427pubmed: 39535442google scholar: lookup
  2. Preston JF, Mustikka MP, Priestnall SL, Dunkel B, Fischer MC. Clinical features and outcomes of horses presenting with presumed equine immune mediated keratitis to two veterinary hospitals in the United Kingdom and Finland: 94 cases (2009-2021). Equine Vet J 2025 May;57(3):598-610.
    doi: 10.1111/evj.14213pubmed: 39183684google scholar: lookup
  3. Ignacio C, Del Mar LM, Marta B, Sina Z, Vicent R, Aloma MF. Comparison of two sedation protocols for long electroretinography in horses using the Koijman electrode. BMC Vet Res 2023 Aug 4;19(1):106.
    doi: 10.1186/s12917-023-03654-9pubmed: 37537621google scholar: lookup
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