Screening for refractive errors in children: accuracy of the hand held refractor Retinomax to screen for astigmatism

Aims-To assess the reliability of the hand held automated refractor Retinom ax in measuring astigmatism in non-cycloplegic conditions. To assess the ac curacy of Retinomax in diagnosing abnormal astigmatism in non-cycloplegic r efractive screening of children between 9 and 36 months. Methods-Among 1205 children undergoing a non-cycloplegic refractive screeni ng with Retinomax, 299 (25%) had repeated non-cycloplegic measurements, 302 (25%) were refracted under cycloplegia using the same refractor, and 88 (7 %) using retinoscopy or an automated on table refractor. The reproducibilit y of non-cycloplegic cylinder measurement was assessed by comparing the cyl indrical power and axis values in the 299 repeated measurements without cyc loplegia. The influence of the quick mode on cylinder measurement was analy sed by comparing the cylinder and axis value in 93 repeated measurements wi thout cycloplegia where normal mode was used in one measurement and quick m ode in the other. Predictive values of the refractive screening were calcul ated for three different thresholds of manifest astigmatism (greater than o r equal to 1.5, greater than or equal to 1.75, and greater than or equal to 2 D) considering as a true positive case an astigmatism greater than or eq ual to 2 D under cycloplegic condition (measured by retinoscopy, on table, or hand held refractor). Results-The 95% limits of agreement between two repeated manifest cylinder measurements with Retinomax attained levels slightly less than plus or minu s 1 D. The 95% limits of agreement for the axis were plus or minus 46 degre es. The comparison of non-cycloplegic measurements in the quick and normal mode showed no significant difference and 95% limits of agreement plus or m inus 0.75 D. The mean difference between non-cycloplegic and cycloplegic cy linder values measured by Retinomax reached 0.17 D and was statistically si gnificant. Manifest thresholds of greater than or equal to 1.5 D, greater t han or equal to 1.75 D, 22 D cylinder value diagnosed 2 D of astigmatism un der cycloplegia respectively with 71-84%, 59-80%, 51-54% of sensitivity (ri ght eye-left eye) and 90-92%, 95%, 98% of specificity. Conclusion-Without cycloplegia, Retinomax is able to measure cylinder power with the same reproducibility as cycloplegic retinoscopy, No significant d ifference was found in the cylinder values obtained with the quick and the normal modes. Therefore, the quick mode of measurement is recommended as it is more feasible in children. No difference, which is significant from a s creening point of view, exists between the non-cycloplegic and the cyclople gic cylinder value (<0.25 D). Retinomax diagnoses abnormal astigmatism (gre ater than or equal to 2 D) in a non-cycloplegic refractive screening at pre school ages with 51-84% sensitivity rates and 98-90% specificity rates, dep ending on the chosen threshold of manifest astigmatism. If 2 D of manifest astigmatism is chosen as a positive test, the positive predictive value of the screening reaches 81-84% and the negative predictive value 91-90% (righ t eye-left eye).