Beta-adrenergic receptor antagonism in myopia.
A previous study has demonstrated that timolol maleate (0.5%), a non-selective beta-adrenergic antagonist, produces in emmetropes a significant reduction in accommodative convergence (AC) during the initial four minutes of a near-vision task. The present study has examined the effect of timolol on AC for three refractive groups (each comprising N = 20): emmetropes, early-onset myopes (EOMs), i.e. myopia onset prior to 15 years of age and late-onset myopes (LOMs), i.e. myopia onset after 15 years. A double-blind protocol was adopted between timolol and a saline control. AC was derived from accommodation stimuli of 3.3, 4.1 and 4.8 D with changes in heterophoria being assessed using a Maddox rod and tangent scale. The relationship between the ocular hypotensive effect of timolol and anterior corneal curvature was also investigated using a Goldmann applanation tonometer and a two-position keratometer (Haag-Streit). Timolol produced a significant reduction in AC in emmetropes but did not induce significant changes in AC in LOMs or EOMs. The timolol-induced reduction in IOP did not result in any changes in anterior corneal curvature.