title: Pharmacologically stimulated pupil and accommodative changes in Guinea pigs.
abstract: OBJECTIVE
  The guinea pig is being used increasingly as a model of human myopia. As accommodation may influence the effects of manipulations used in experimental myopia models, understanding the accommodative ability of guinea pigs is important. Here, nonselective muscarinic agonists were used as pharmacological tools to study guinea pig accommodation.
  
  
  METHODS
  Measurements were made on 15 pigmented guinea pigs. For in vivo testing, animals were anesthetized and, following baseline measurements, 2% pilocarpine was applied topically. Measurements included A-scan ultrasonography, optical coherence tomography (OCT) imaging, corneal topography, and refraction. In vitro lens scanning experiments were performed using anterior segment preparations, with measurements before and during exposure to carbachol. Anterior segment structures were examined histologically and immunohistochemistry was done to characterize the muscarinic receptor subtypes present.
  
  
  RESULTS
  In vivo, pilocarpine induced a myopic shift in refractive error coupled to a small, but consistent decrease in anterior chamber depth (ACD), a smaller and more variable increase in lens thickness, and a decrease in pupil size. Lens thickness increases were short-lived (10 minutes), while ACD and pupil size decreased over 20 minutes. Corneal curvature was not significantly affected. Carbachol tested on anterior segment preparations in vitro was without effect on lens back vertex distance, but did stimulate pupil constriction. Immunohistochemistry indicated the presence of muscarinic receptor subtypes 1 to 5 in the iris and ciliary body.
  
  
  CONCLUSIONS
  The observed pilocarpine-induced changes in ACD, lens thickness, and refraction are consistent with active accommodation in the guinea pig, through cholinergic muscarinic stimulation.
authors.affiliation: University of Houston College of Optometry, Houston, Texas, United States.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Ostrin
authors.affiliation: University of California Berkeley School of Optometry, Berkeley, California, United States.
authors.forename: Mariana B
authors.initials: MB
authors.lastname: Garcia
authors.affiliation: University of Waterloo Optometry and Vision Science, Waterloo, Ontario, Canada.
authors.forename: Vivian
authors.initials: V
authors.lastname: Choh
authors.affiliation: University of California Berkeley School of Optometry, Berkeley, California, United States.
authors.forename: Christine F
authors.initials: CF
authors.lastname: Wildsoet
mesh_terms: D000065:Accommodation, Ocular / Q000187:drug effects*; D000818:Animals; D000867:Anterior Chamber / Q000187:drug effects; D019781:Corneal Topography; D004195:Disease Models, Animal; D006168:Guinea Pigs; D007908:Lens, Crystalline / Q000187:drug effects; D018721:Muscarinic Agonists / Q000494:pharmacology*; D010862:Pilocarpine / Q000494:pharmacology*; D011680:Pupil / Q000187:drug effects*; D012029:Refraction, Ocular / Q000187:drug effects; D041623:Tomography, Optical Coherence
chemical_list: D018721:Muscarinic Agonists; D010862:Pilocarpine
keywords: accommodation; anterior segment; guinea pig; muscarinic agonists; pupil size
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