Repeatability of measurements with a double-pass system.

PURPOSE To evaluate the repeatability of measurements with a double-pass system. SETTING Rothschild Foundation, Paris, France. METHODS Eyes were separated into 2 control groups (<30 years old and >40 years), a post-refractive surgery group, and a cataract group. Measurements were performed using the Optical Quality Analysis System. The main outcome measures were the objective scattering index (OSI), the cutoff frequency of the modulation transfer function (MTF), and the Strehl ratio. The repeatability limit was obtained from the individual standard deviations. RESULTS Forty-two eyes were evaluated. The mean OSI value was 0.47 +/- 0.11 (SD) in the younger control group, 1.73 +/- 0.26 in the older control group, 1.34 +/- 0.16 in the post-refractive surgery group, and 6.15 +/- 0.50 in the cataract group. The mean cutoff MTF value was 39.44 +/- 3.93 cycles per degree (cpd), 26.07 +/- 3.89 cpd, 28.34 +/- 2.84 cpd, and 13.3 +/- 1.69 cpd, respectively, and the mean Strehl ratio, 0.234 +/- 0.023, 0.146 +/- 0.021, 0.169 +/- 0.023, and 0.098 +/- 0.010, respectively. The repeatability limit for the whole population was 0.841 (33.5%) for the OSI, 8.499 (31.1%) for the cutoff MTF, and 0.051 (31%) for the Strehl ratio. CONCLUSIONS The repeatability limit was good and equivalent for the OSI, the MTF, and the Strehl ratio values. There was a wide interval between the normal and pathologic threshold for OSI measurements, indicating that the reliability of the double-pass device complies with the requirements for quantitative assessment of scattering. FINANCIAL DISCLOSURE No author has a financial or proprietary interest in any material or method mentioned.