AC/A ratios in myopic and emmetropic Hong Kong children and the effect of timolol
Chen, Jennifer C., Schmid, Katrina L., Brown, Brian, Edwards, Marion H., Yu, Bibianna S.Y., & Lew, John K.F. (2003) AC/A ratios in myopic and emmetropic Hong Kong children and the effect of timolol. Clinical and Experimental Optometry, 86(5), pp. 323-330.
Caucasian children with myopia have elevated response accommodative vergence to accommodation (AC/A) ratios. The purpose of this study was twofold: to determine if response AC/A ratios vary with refractive error and with myopic progression rate in Hong Kong Chinese children, and to determine the effect of beta-adrenergic antagonism with topical timolol application on AC/A ratios. METHODS: Thirty children aged eight to 12 years participated in the study. All refractive errors were corrected with spectacle lenses. Accommodative responses were measured using a Shin-Nippon autorefractor and concurrent changes in vergence were assessed using a vertical prism and a Howell-Dwyer card at three metres and 0.33 metre. Accommodative demand was altered using plus or minus two dioptre lenses and lens- and distance-induced response AC/A ratios were calculated. Measurements were repeated 30 minutes after the instillation of topical timolol maleate (0.5 per cent). RESULTS: AC/A ratios appeared higher in progressing myopic children but the difference was not statistically significant. Timolol application reduced accommodative convergence (AC) in the stable myopes (reduction = -3 ± 1.14 prism dioptres) but not in the emmetropes (0.69 ± 0.96 prism dioptres) or progressing myopes (0.16 ± 0.43 prism dioptres) and this difference between refractive groups was statistically significant (F2, 27 = 3.766; P = 0.036). However, timolol did not produce a significant change in the accommodative response to positive or negative lenses or response AC/A ratios. CONCLUSIONS: We did not find that AC/A ratios in myopic Chinese children were elevated and therefore, it is unlikely that elevated AC/A ratios are responsible for the high levels of myopia that occur in Hong Kong. The finding that timolol reduced AC in the stable myopes suggests that the autonomic control of accommodative convergence in these children may be different from that in emmetropic children and those with progressing myopia.
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|Item Type:||Journal Article|
|Subjects:||Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300)|
|Divisions:||Current > QUT Faculties and Divisions > Faculty of Health|
|Copyright Owner:||Copyright 2003 Optometrists Association Australia|
|Copyright Statement:||Reproduced in accordance with the copyright policy of the publisher: Issues published between 1998-2005 are available free online - use hypertext link above.|
|Deposited On:||11 Oct 2005|
|Last Modified:||29 Feb 2012 13:00|
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