|Author:||Chat, Wing-shan Sandy|
|Title:||Accuracy and reliability of the Shin-Nippon SRW-5000 open-field autorefractor, and tonic accommodation and accommodative lag in Hong Kong children from 4 to 8 years of age|
|Subject:||Eye -- Accommodation and refraction|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Optometry and Radiography|
|Pages:||xxiv, 223 leaves : ill. ; 30 cm|
|Abstract:||Introduction The Shin-Nippon SRW-5000 autorefractor is a new open-field autorefractor which allows refraction to be measured at different fixation distances, making it suitable for the investigation of aspects of accommodation. The goals of this study were to evaluate the accuracy and reliability of this new autorefractor, and to examine tonic accommodation and accommodative lag in Hong Kong children from 4 to 8 years of age. Results were analysed in terms of the dioptric power matrix, coordinate vector h. This analytical approach overcomes the problems associated with the reduction of the three-dimensional sphero-cylinder to any of the one-dimensional expressions commonly used to quantify refractive error, all of which result in loss of information. The spherical equivalent refractive error was also used in statistical analysis to permit comparison with other studies. Methods Subjects were children from 4 to 8 years of age. Autoreftaction measures taken in the normal accommodative state (n=53) and under cycloplegic conditions (n=44) were compared with cycloplegic refraction, as well as measures taken from a closed-field autorefractor (the Canon RK5). The reliability of the distance autorefraction was characterized by the 95 % limits of agreement between two sets of measurement taken by one observer (repeatability) and two observers (reproducibility). Tonic accommodation (TA), the accommodation when the eye is in its resting state, was determined by measuring refractive error in 56 children in total darkness. Ocular accommodative lag, the difference between the accommodative stimulus and its response, was determined in 33 children, with a target placed at 40 cm. Three stimulus conditions were investigated, namely, white letters on a dark background in dim light, white letters on a dark background in normal room lighting and black letters on a light background in normal room lighting. Results The overall accuracy of the SRW-5000 was high, and similar to that reported for the Canon R-1 open-field autorefractor. As would be expected, the agreement between cycloplegic open-field autorefraction and cyclopelgic refraction was better than between non-cyclopelgic open-field autorefraction and cyclopelgic refraction. Autorefraction taken under both conditions tended to produce results which were more myopic than cycloplegic refraction. Non-cyclopelgic SRW-5000 autorefiaction produced slightly more myopic results than closed-field autoreftaction using the RK5, and the difference was mainly for hyperopes. Reliability was considerably better for cycloplegic than non-cycloplegic autorefraction, and slightly better for one compared with two observers. Repeatability results from the SRW-5000 autorefractor, both with and without cycloplegia, were similar to those reported for the Canon R-1. The mean tonic accommodation for all the children was 1.07 DS/-0.05 DC x 138 and 1.09 DS/-0.04 DCx68 for children under 6 years of age. There was no relationship between tonic accommodation and age for the age range tested. Hyperopes exhibited the highest TA, followed by emmetropes and then myopes. The 95% limits of agreement between two spherical equivalent measures was 0.83 D. Accommodative lag was greatest for white letters on a dark background in dim light (condition DD), followed by white letters on a dark background in normal room lighting (condition LD) and black letters on a light background in normal room lighting (condition LL). Myopes tended to exhibit higher ocular accommodative lag than hyperopes. The 95 % limits of agreement obtained from three conditions were similar and was around 0.55 D in spherical equivalent. Conclusions This is the first report of tonic accommodation and accommodative lag presented in terms of vector h. Tonic accommodation values in children younger than six years of age were also presented for the first time. Tonic accommodation was found to be lower in myopes than in other refractive groups and, in agreement with the suggestions of other workers, this may reflect an overall reduction in autonomic innervation. Accommodative response tended to be lower in myopes but the results were equivocal. It is still possible that the hyperopic retinal defocus resulting from greater lag may cause myopia development in children. Target presentation could be improved for the measurement of distance autorefraction and near accommodative response and it is suggested that measurement of tonic accommodation would be improved by use of a difference of Gaussian target in semi-darkness.|
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