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JC Chen, KL Schmid, B Brown, MH Edwards, JK F Lew, BS Y Yu; The Effect of Timolol Induced Beta-adrenergic Antagonism on Accommodative Adaptation in Hong Kong Children . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1513.
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Purpose:Nearwork-induced adaptation effects have been suggested as a possible risk factor for myopia development. The prevalence of myopia in Hong Kong children is particularly high (55-58%), it is not known if this is due to the effects of nearwork. The purpose of this study was to measure accommodative adaptation following nearwork and assess the effect of beta-adrenergic antagonism on accommodative adaptation in Hong Kong children. We predicted that timolol would produce increased accommodative adaptation in stable myopes, who presumably have normal sympathetic innervation to the ciliary muscle, but not in progressing myopes. Methods:Thirty children (10 emmetropes, 5 stable and 15 progressing myopes (progression rate ≷ -0.25 D per year)) aged between 8 and 12 years were tested. Tonic accommodation (TA) was measured using the Shin-Nippon SRW-5000 autorefractor, both before and after 5 minutes of video game playing. Twenty readings measured at 2-second intervals were averaged to give the pre- and post-task TA levels. Measurements were repeated 30 minutes after the instillation of timolol maleate (0.5%, 20µl). Results: Mean refractive errors for the emmetropes, stable and progressing myopes were -0.060.41 D, -2.521.24 D, and -4.601.39 D respectively. Progressing myopes showed the largest accommodative adaptation effects (0.160.43 D), while stable myopes showed counter-adaptive changes (-0.440.74 D). Emmetropes were not susceptible to such nearwork-induced adaptation (0.030.36 D). Timolol increased the magnitude of the adaptation effects in the stable myopes (0.530.77 D), had no effect in the progressing myopes and counter-adaptive effects (-0.14 0.38 D) in the emmetropes. The response profiles following timolol instillation were significantly different (3 factor split-plot ANOVA, F2,28 = 3.792, p = 0.035). Conclusion:Nearwork-induced accommodative changes are a characteristic of Hong Kong children with progressing myopia. Our results support the prediction that sympathetic innervation to the ciliary muscle in stable and progressing myopia differs.
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