Effects of action of proparacaine and tetracaine topical ophthalmic formulations on corneal sensitivity in horses

Karen L. Sharrow-Reabe Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48823.

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Wendy M. Townsend Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48823.

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 DVM, MS, DACVO
DOI:
https://doi.org/10.2460/javma.241.12.1645
Volume/Issue:
Volume 241: Issue 12
Online Publication Date:
15 Dec 2012
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Abstract

Objective—To compare the corneal anesthetic effects and duration of action of 2 ophthalmic anesthetic agents in horses.

Design—Prospective, randomized masked crossover study.

Animals—8 clinically normal adult horses.

Procedures—Corneal sensitivity was determined by measuring each eye's corneal touch threshold (CTT) with a Cochet-Bonnet esthesiometer. Each eye's baseline CTT was recorded prior to anesthetic instillation at 0 minutes and every 10 minutes thereafter for 60 minutes. Each eye was randomly assigned to receive 2 of 4 treatments: 0.5% aqueous proparacaine ophthalmic solution (aqueous proparacaine; 8 eyes); 0.5% aqueous tetracaine ophthalmic solution (aqueous tetracaine; 8 eyes); 0.5% viscous tetracaine ophthalmic solution (viscous tetracaine; 8 eyes); and saline (0.9% NaCl) eyewash solution (8 eyes) as a negative control. There was a 48-hour washout period. Every horse received all treatments.

Results—Median baseline CTT of eyes was 4.5 cm (range, 0.5 to 6 cm). Median CTT for saline solution–treated eyes never differed significantly from baseline. The maximum anesthetic effect with the other 3 treatments occurred at 10 minutes. Median CTT of eyes at 10 minutes was 0.5 cm (range, 0 to 2.5 cm) with aqueous proparacaine treatment, 0.25 cm (range, 0 to 2.0 cm) with aqueous tetracaine treatment, and 0 cm (range, 0 to 0.5 cm) with viscous tetracaine treatment. Maximum anesthetic duration was 20 minutes with aqueous proparacaine and aqueous tetracaine treatments and 30 minutes with viscous tetracaine treatments.

Conclusions and Clinical Relevance—Treatment of eyes with viscous tetracaine resulted in the greatest decrease in CTT and the longest duration of action, compared with treatment with aqueous proparacaine or aqueous tetracaine.

Abstract

Objective—To compare the corneal anesthetic effects and duration of action of 2 ophthalmic anesthetic agents in horses.

Design—Prospective, randomized masked crossover study.

Animals—8 clinically normal adult horses.

Procedures—Corneal sensitivity was determined by measuring each eye's corneal touch threshold (CTT) with a Cochet-Bonnet esthesiometer. Each eye's baseline CTT was recorded prior to anesthetic instillation at 0 minutes and every 10 minutes thereafter for 60 minutes. Each eye was randomly assigned to receive 2 of 4 treatments: 0.5% aqueous proparacaine ophthalmic solution (aqueous proparacaine; 8 eyes); 0.5% aqueous tetracaine ophthalmic solution (aqueous tetracaine; 8 eyes); 0.5% viscous tetracaine ophthalmic solution (viscous tetracaine; 8 eyes); and saline (0.9% NaCl) eyewash solution (8 eyes) as a negative control. There was a 48-hour washout period. Every horse received all treatments.

Results—Median baseline CTT of eyes was 4.5 cm (range, 0.5 to 6 cm). Median CTT for saline solution–treated eyes never differed significantly from baseline. The maximum anesthetic effect with the other 3 treatments occurred at 10 minutes. Median CTT of eyes at 10 minutes was 0.5 cm (range, 0 to 2.5 cm) with aqueous proparacaine treatment, 0.25 cm (range, 0 to 2.0 cm) with aqueous tetracaine treatment, and 0 cm (range, 0 to 0.5 cm) with viscous tetracaine treatment. Maximum anesthetic duration was 20 minutes with aqueous proparacaine and aqueous tetracaine treatments and 30 minutes with viscous tetracaine treatments.

Conclusions and Clinical Relevance—Treatment of eyes with viscous tetracaine resulted in the greatest decrease in CTT and the longest duration of action, compared with treatment with aqueous proparacaine or aqueous tetracaine.

Contributor Notes

Dr. Sharrow-Reabe's present address is Bay Area Pet Hospital, 844 Front St, Traverse City, MI 49686.

Dr. Townsend's present address is Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN 47906.

Presented in part at the 40th Annual Conference of the American College of Veterinary Ophthalmologists, Chicago, November 2009.

Address correspondence to Dr. Townsend (Townsenw@purdue.edu).
Cover Journal of the American Veterinary Medical Association
Journal of the American Veterinary Medical Association
Publication Date:
15 Dec 2012

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