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Veterinary ophthalmology2026; 29(4); e70188; doi: 10.1111/vop.70188

Short-Term Daily Oral Administration of Cannabidiol Does Not Impact Rebound Tonometry Intraocular Pressure or Schirmer Tear Test Values in Healthy Adult Horses.

Abstract: To assess the effect of orally administered cannabidiol (CBD) on TonoVet measured intraocular pressure (IOP) and Schirmer tear test I (STT) in horses. Methods: Horse. Methods: This was a masked, randomized, balanced cross-over study of six healthy adult horses. Horses were randomly assigned and received 3 mg/kg CBD in sesame oil or volume matched placebo by mouth once daily for three days. Baseline and daily 4-, 12-, and 24-h post treatment IOPs were measured in triplicate without sedation or eyelid akinesia. Baseline and 24-h post final (day 3) treatment STTs were measured without sedation or eyelid akinesia. After a five-week washout period, horses received the alternate treatment, and measurements were repeated as above. Results: Overall, there were no clinically relevant differences in IOP with CBD administration. Irrespective of treatment, IOPs were significantly higher in the second treatment period (p = 0.009). There were no differences in STT with CBD administration. Conclusions: Oral CBD administration in healthy horses does not impact rebound tonometry IOP or STT measurements.
© 2026 The Author(s). Veterinary Ophthalmology published by Wiley Periodicals LLC on behalf of American College of Veterinary Ophthalmologists.
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Publication Date: 2026-05-16 PubMed ID: 42141801DOI: 10.1111/vop.70188Google 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.

Overview

  • This study investigated whether giving healthy adult horses cannabidiol (CBD) by mouth affects their eye pressure or tear production.
  • The researchers found that short-term oral CBD administration did not change intraocular pressure (IOP) or tear test values in these horses.

Study Objective

  • To determine the effect of orally administered cannabidiol (CBD) on intraocular pressure (IOP) measured by rebound tonometry (TonoVet) and Schirmer tear test I (STT) values in healthy adult horses.

Study Design and Methods

  • Type: Masked, randomized, balanced cross-over study.
  • Subjects: Six healthy adult horses.
  • Intervention: Each horse received either 3 mg/kg CBD in sesame oil or a volume-matched placebo orally once daily for three days.
  • Treatment administration was blinded to the observers measuring outcomes.
  • Measurements:
    • Intraocular pressure (IOP) was measured by rebound tonometry at baseline and at 4, 12, and 24 hours post-treatment each day without sedation or eyelid akinesia, performed in triplicate for accuracy.
    • Schirmer tear test (STT) values were taken at baseline and 24 hours after the final dose (day 3), also without sedation or eyelid akinesia.
  • After a five-week washout period, the horses were crossed over to receive the alternate treatment and the measurements were repeated following the same protocol.

Results

  • No clinically significant differences in intraocular pressure (IOP) were observed when horses received oral CBD compared to placebo.
  • IOPs were significantly higher during the second period of treatment regardless of which treatment was administered (p = 0.009), suggesting a possible period effect unrelated to CBD.
  • There were no significant differences in tear production as measured by the Schirmer tear test (STT) with CBD administration compared to placebo.

Conclusions and Implications

  • Oral administration of cannabidiol at 3 mg/kg once daily for three days does not alter intraocular pressure or tear production in healthy adult horses.
  • This suggests that short-term oral CBD use is unlikely to affect these ocular parameters in healthy horses, supporting its safety in terms of eye pressure and tear secretion.
  • The study does not explore longer-term effects, different dosing regimens, or effects in horses with ocular diseases, which could be areas for further research.

Additional Notes

  • The use of a randomized crossover design with a washout period strengthens the validity of results by reducing inter-subject variability.
  • The masking of observers reduces bias in measurement of IOP and STT values.
  • The methods carefully avoided sedation or eyelid akinesia to prevent confounding effects on eye pressure and tear tests.

Cite This Article

APA
Diehl K, Sheridan C, Reed R. (2026). Short-Term Daily Oral Administration of Cannabidiol Does Not Impact Rebound Tonometry Intraocular Pressure or Schirmer Tear Test Values in Healthy Adult Horses. Vet Ophthalmol, 29(4), e70188. https://doi.org/10.1111/vop.70188

Publication

Veterinary ophthalmology
ISSN: 1463-5224
NlmUniqueID: 100887377
Country: England
Language: English
Volume: 29
Issue: 4
Pages: e70188

Researcher Affiliations

Diehl, Kathryn
  • University of Georgia College of Veterinary Medicine, Athens, Georgia, USA.
Sheridan, Colleen
  • University of Georgia College of Veterinary Medicine, Athens, Georgia, USA.
Reed, Rachel
  • University of Georgia College of Veterinary Medicine, Athens, Georgia, USA.

MeSH Terms

  • Animals
  • Horses / physiology
  • Intraocular Pressure / drug effects
  • Tonometry, Ocular / veterinary
  • Administration, Oral
  • Cross-Over Studies
  • Cannabidiol / administration & dosage
  • Cannabidiol / pharmacology
  • Male
  • Female
  • Tears / drug effects

Grant Funding

  • U.S. Department of Agriculture

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