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Equine veterinary journal2017; 49(6); 810-814; doi: 10.1111/evj.12695

Effects of 0.2% brimonidine and 0.2% brimonidine-0.5% timolol on intraocular pressure and pupil size in normal equine eyes.

Abstract: Brimonidine is an α2 -adrenergic agonist that decreases aqueous humour production and may increase uveoscleral outflow. It has not been evaluated in normal or glaucomatous equine eyes. Objective: To evaluate the efficacy and safety of brimonidine in lowering intraocular pressure (IOP), alone and in conjunction with timolol, as a treatment for equine glaucoma by comparing IOP in normal equine eyes treated with brimonidine and brimonidine-timolol, respectively, with IOP in control eyes. Methods: A balanced crossover design with 16 horses receiving one of two treatments, brimonidine and brimonidine-timolol, during each of two 10-day study phases, was used. Four horses were randomly assigned to each of four combinations of treated eye (right or left) and drug order within the two 10-day study phases (brimonidine first or brimonidine-timolol first). Methods: Pupil size and conjunctival hyperaemia were assessed twice per day and IOP was measured three times per day using rebound tonometry in both eyes of 16 normal horses throughout two 10-day study periods (brimonidine and brimonidine-timolol) separated by an 18-day washout period. One eye of each horse was treated with brimonidine or brimonidine-timolol and the opposite eye was treated with balanced salt solution (BSS). Results: There were no adverse effects and no significant changes in pupil size in normal equine eyes treated with brimonidine or brimonidine-timolol. Average IOP in normal equine eyes treated with brimonidine (25.6 mmHg) was statistically higher than in eyes treated with brimonidine-timolol (24.6 mmHg) or BSS (24.5 mmHg). However, IOP differences were of ≤1 mmHg and thus not clinically important. Conclusions: Horses with normal eyes may not be as sensitive to the IOP-lowering effects of treatment as horses with glaucoma. Conclusions: Brimonidine and brimonidine-timolol are well tolerated in normal horses but do not decrease IOP.
© 2017 EVJ Ltd.
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Publication Date: 2017-06-05 PubMed ID: 28470857PubMed Central: PMC5640458DOI: 10.1111/evj.12695Google 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 research focuses on assessing the impact of brimonidine and a combination of brimonidine-timolol on intraocular pressure (IOP) and pupil size in normal horse eyes. The conclusion of the study suggests that these treatments do not lower IOP but are well tolerated in horses.

Objective and Methods

The study aimed to determine the safety and effectiveness of brimonidine, both alone and with timolol, in reducing IOP in horses. This was done in efforts to treat equine glaucoma. The researchers contrasted the IOP in normal horse eyes treated with brimonidine and brimonidine-timolol respectively, to control IOP in untreated eyes.

  • 16 horses, put into a balanced crossover design, received either one of the two treatments during two separate 10-day study phases. The horses were randomly distributed into four groups, each with a different combination of treated eye (right or left) and drug order.
  • Measurement and assessment tools such as rebound tonometry were used to measure IOP and assess pupil size and conjunctival hyperaemia twice a day over two 10-day study periods, namely the brimonidine and the brimonidine-timolol phases.
  • Each study period was separated by an 18-day washout period, which served to remove the residual effects of the drugs before the start of the next phase.
  • One eye of each horse was treated with either brimonidine or brimonidine-timolol, while the opposite eye was treated with a balanced salt solution (BSS) to serve as a control.

Results

Following the treatments, there were no adverse effects observed, nor were there any significant changes in pupil size in the eyes treated with brimonidine or brimonidine-timolol.

  • The average IOP in normal horse eyes treated with brimonidine alone stood at 25.6 mmHg. This was slightly higher than IOP in eyes treated with brimonidine-timolol (24.6 mmHg) or BSS (24.5 mmHg).
  • However, the differences were ≤1 mmHg, rendering them not clinically important.

Conclusion

The study concludes that horses with normal eyes may not be particularly susceptible to the IOP-lowering impacts of the treatment. The treatments, brimonidine and brimonidine-timolol in particular, do not lower IOP in horses but are well tolerated. Thus, they might not be effective in treating horses with glaucoma, a condition characterized by elevated eye pressure.

Cite This Article

APA
Von Zup M, Lassaline M, Kass PH, Miller PE, Thomasy SM. (2017). Effects of 0.2% brimonidine and 0.2% brimonidine-0.5% timolol on intraocular pressure and pupil size in normal equine eyes. Equine Vet J, 49(6), 810-814. https://doi.org/10.1111/evj.12695

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 49
Issue: 6
Pages: 810-814

Researcher Affiliations

Von Zup, M
  • Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California, USA.
Lassaline, M
  • Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California, USA.
Kass, P H
  • Department of Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, Davis, California, USA.
Miller, P E
  • School of Veterinary Medicine, University of Wisconsin Madison, Madison, Wisconsin, USA.
Thomasy, S M
  • Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California, USA.

MeSH Terms

  • Aging
  • Animals
  • Brimonidine Tartrate / administration & dosage
  • Brimonidine Tartrate / pharmacology
  • Brimonidine Tartrate, Timolol Maleate Drug Combination / pharmacology
  • Circadian Rhythm
  • Female
  • Horses / physiology
  • Intraocular Pressure / drug effects
  • Male
  • Pupil / drug effects

Grant Funding

  • K08 EY021142 / NEI NIH HHS

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Citations

This article has been cited 1 times.
  1. 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
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