Latanoprost and pilocarpine are effective ocular hypotensive drugs for dogs and humans. Latanoprost, a prostaglandin analog, reduces IOP in humans and other primates by initial relaxation of the ciliary muscle and remodeling of the extracellular matrix between the muscle bundles over time, thus facilitating uveoscleral outflow.1,2 Pilocarpine, a cholinergic receptor agonist, contracts the ciliary muscle bundles to pull on the scleral spur, thus opening fluid channels in the trabecular meshwork and increasing trabecular outflow.3 Despite the antagonistic mechanism of action on the ciliary muscle status, additive effects of latanoprost with pilocarpine have been suggested in human clinical studies.2,4,5 Slightly greater reductions in IOP, although not significantly different, were also detected after a combination of latanoprost and pilocarpine was administered to dogs.6
In contrast to effects in humans and other primates, prostaglandin-mediated miosis is commonly described in dogs, cats, and horses.7 Among the prostaglandins, prostaglandin F2α is the most potent for contracting the iris sphincter muscle of dogs.8 Miosis has been regarded as an important effect6,7; however, it has been suggesteda that latanoprost-induced miosis could play an important role in rapid reduction of IOP by resolving the pupillary block (contact of the pupillary margins with the lens) in dogs with primary closed-angle glaucoma. In addition, cholinergic miotics have been used for the long-term treatment of dogs with open-angle glaucoma.7 During cholinergic-mediated miosis, the iris reportedly pulls the inner leaflet of the ciliary body rostrally and centrally, which results in widening of the CC.9 However, few studies have been conducted to investigate differences between prostaglandin-mediated and cholinergic-mediated miosis.
The purpose of the study reported here was to investigate differences in morphology of the CC region between prostaglandin-mediated and cholinergic-mediated miosis in dogs. We hypothesized that there would be structural differences associated with their pharmacological action on ciliary muscle contractility. Ultrasonographic biomicroscopy was used to describe the dynamic morphology of the anterior ocular segment in vivo. Furthermore, we sought to identify possible additive effects of pilocarpine and latanoprost in dogs and the relationship between those effects and structural alterations.
Supported by the BK 21 PLUS Program for Creative Veterinary Science Research and the Research Institute for Veterinary Science (RIVS) of Seoul National University, Seoul, Republic of Korea.
Presented in part as an abstract at the Annual Meeting of the European College of Veterinary Ophthalmologists, Estoril, Portugal, May 2017.
Angle opening distance
Ciliary cleft area
Ciliary cleft length
Ciliary cleft width
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SL-D7, Topcon Corp, Tokyo, Japan.
Vantage plus, Keeler, Windsor, England.
TonoVet, iCare, Helsinki, Finland.
Xalatan, Pfizer Inc, New York, NY.
Isopto carpine, Alcon Korea, Seoul, Republic of Korea.
Lacure, Samil Pharm Co Ltd, Seoul, Republic of Korea.
Alcaine, Alcon Korea, Seoul, Republic of Korea.
MD-320W, MEDA Co Ltd, Tianjin, People's Republic of China.
SPSS, version 21, SPSS Inc, Chicago, Ill.
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