title: The M1 muscarinic antagonist pirenzepine reduces myopia and eye enlargement in the tree shrew.
abstract: OBJECTIVE
  To determine the efficacy of the M1-selective muscarinic antagonist, pirenzepine, in preventing experimentally induced myopia in a mammalian model, the tree shrew.
  
  
  METHODS
  Tree shrews were monocularly deprived (MD) using translucent goggles or negative lenses for a period of 12 days. In two of the MD groups, tree shrews received daily subconjunctival administration of either pirenzepine (17.7 mumol; n = 9) or vehicle control (n = 6). Control groups (n = 6) were used to assess the effects of MD, injection regimen, and drug effects.
  
  
  RESULTS
  In sham-injected and saline-injected MD tree shrews, 12 days of MD produced-13.2 D +/- 0.8 D and -14.1 D +/- 0.5 D of axial myopia, respectively. In pirenzepine-injected MD tree shrews, 12 days of MD induced an axial myopia of only -2.1 D +/- 1.4 D. The significant reduction in myopia in pirenzepine-injected MD tree shrews was caused by significantly less vitreous chamber elongation of the deprived eye (0.05 mm +/- 0.04 mm) relative to the contralateral control eye when compared to sham-injected and saline-injected MD tree shrews (0.24 mm +/- 0.02 mm and 0.29 mm +/- 0.01 mm). Mean equatorial enlargement and increased eye weight were prevented in pirenzepine-injected MD tree shrews (P < 0.01). Pirenzepine also was found to reduce myopia and ocular enlargement in lens defocus-induced myopia. Control experiments demonstrated that pirenzepine did not cause a significant reduction in amplitude of carbachol-induced accommodation.
  
  
  CONCLUSIONS
  Findings demonstrate that chronic administration of the M1-selective muscarinic antagonist, pirenzepine, prevents experimentally induced myopia in this mammalian model by a nonaccommodative mechanism.
authors.affiliation: Department of Optometry and Vision Sciences, University of Wales, Cardiff, United Kingdom.
authors.forename: C L
authors.initials: CL
authors.lastname: Cottriall
authors.forename: N A
authors.initials: NA
authors.lastname: McBrien
mesh_terms: D000065:Accommodation, Ocular; D000818:Animals; D003228:Conjunctiva; D004195:Disease Models, Animal; D005123:Eye / Q000187:drug effects / Q000473:pathology*; D006984:Hypertrophy / Q000209:etiology / Q000473:pathology / Q000517:prevention & control; D007267:Injections; D018727:Muscarinic Antagonists / Q000008:administration & dosage / Q000627:therapeutic use*; D009216:Myopia / Q000209:etiology / Q000473:pathology / Q000517:prevention & control*; D010890:Pirenzepine / Q000008:administration & dosage / Q000627:therapeutic use*; D012029:Refraction, Ocular; D012160:Retina / Q000187:drug effects / Q000473:pathology; D012590:Sclera / Q000187:drug effects / Q000473:pathology; D012683:Sensory Deprivation; D014418:Tupaiidae
chemical_list: D018727:Muscarinic Antagonists; D010890:Pirenzepine