Comparison of Forward Light Scatter Measurements Between the Optical Quality Analysis SystemTM and the C-QuantTM Retinal Stray Light Meter

Abstract

Purpose: : The Optical Quality Analysis System^TM (OQAS, Visiometrics, Terrassa, Spain) and the C-Quant^TM retinal straylight meter (Oculus, Lynnwood, WA) both measure intraocular forward light scatter. In this study we determined the repeatability of, and the association between, the objective scatter index (OSI), measured by the OQAS^TM, and the stray light parameter, measured by the C-Quant^TM, in eyes with high and low scattering characteristics.

Methods: : Ninety-two eyes of 49 subjects were examined by using both the OQAS^TM and the C-Quant^TM. The sample included 38 normal eyes, 26 pseudophakic but otherwise healthy eyes, 13 pseudophakic eyes after Descemet’s stripping with endothelial keratoplasty (DSEK), 7 pseudophakic eyes with Fuchs’ dystrophy, and 8 cataractous eyes with or without Fuchs’ dystrophy. The OQAS^TM measures the retinal point-spread function from a double-pass through the ocular media, and the OSI is an objective measure calculated from the brightness of the point-spread function in a defined band from the center and presumably originates from forward scatter. The C-Quant^TM measures forward light scatter by using the compensation comparison method, which is a psychometric test. Variability of measurements was assessed by calculating the coefficient of variation (CV, standard deviation/mean) of 5 measurements from each of 10 eyes (5 eyes with high and 5 with low scattering characteristics) and the CVs were compared by using paired tests. The association between the OSI and the stray light parameter was assessed by the Pearson correlation coefficient. Generalized estimating equation models were used to account for possible correlation between data from fellow eyes of the same subject.

Results: : The average CV for the OSI (12 ± 7 %, mean ± standard deviation) was higher than the average CV for the stray light parameter (7 ± 5 %, p=0.01, n=10). For all included eyes, the OSI correlated with the retinal stray light parameter (r=0.54, p<0.001, n=92).

Conclusions: : Repeated measures of the OSI by the OQAS^TM vary more than repeated measures of the stray light parameter by the C-Quant^TM for high and low scattering eyes. Although the OSI correlates with the stray light parameter, they are not predictive of each other (r²=0.25), possibly because factors other than forward scatter contribute to the OSI.

Keywords: optical properties • transplantation • cornea: clinical science