title: Opposing effects of atropine and timolol on the color and luminance emmetropization mechanisms in chicks.
abstract: This study analyzed the luminance and color emmetropization response in chicks treated with the nonselective parasympathetic antagonist atropine and the sympathetic β-receptor blocker timolol. Chicks were binocularly exposed (8h/day) for 4days to one of three illumination conditions: 2Hz sinusoidal luminance flicker, 2Hz sinusoidal blue/yellow color flicker, or steady light (mean 680lux). Atropine experiments involved monocular daily injections of either 20μl of atropine (18nmol) or 20μl of phosphate-buffered saline. Timolol experiments involved monocular daily applications of 2 drops of 0.5% timolol or 2 drops of distilled H2O. Changes in the experimental eye were compared with those in the fellow eye after correction for the effects of saline/water treatments. Atropine caused a reduction in axial length with both luminance flicker (-0.078±0.021mm) and color flicker (-0.054±0.017mm), and a reduction in vitreous chamber depth with luminance flicker (-0.095±0.023mm), evoking a hyperopic shift in refraction (3.40±1.77D). Timolol produced an increase in axial length with luminance flicker (0.045±0.030mm) and a myopic shift in refraction (-4.07±0.92D), while color flicker caused a significant decrease in axial length (-0.046±0.017mm) that was associated with choroidal thinning (-0.046±0.015mm). The opposing effects on growth and refraction seen with atropine and timolol suggest a balancing mechanism between the parasympathetic and β-receptor mediated sympathetic system through stimulation of the retina with luminance and color contrast.
authors.affiliation: New England College of Optometry, 424 Beacon Street, Boston, MA 02115, United States. Electronic address: goldbela30@gmail.com.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Goldberg
authors.affiliation: New England College of Optometry, 424 Beacon Street, Boston, MA 02115, United States.
authors.forename: Frances J
authors.initials: FJ
authors.lastname: Rucker
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D058452:Axial Length, Eye / Q000187:drug effects; D002645:Chickens; D002829:Choroid / Q000187:drug effects; D055253:Color Vision / Q000187:drug effects*; D015350:Contrast Sensitivity / Q000187:drug effects; D058453:Emmetropia / Q000187:drug effects*; D007908:Lens, Crystalline / Q000187:drug effects; D008029:Lighting; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009184:Mydriatics / Q000494:pharmacology*; D010275:Parasympathetic Nervous System / Q000187:drug effects; D012029:Refraction, Ocular / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects; D013999:Timolol / Q000494:pharmacology*
chemical_list: D000319:Adrenergic beta-Antagonists; D018727:Muscarinic Antagonists; D009184:Mydriatics; D001285:Atropine; D013999:Timolol
keywords: Atropine; Color; Emmetropization; Luminance; Myopia; Timolol