Polychromatic refractive error from monochromatic wavefront aberrometry.

PURPOSE

To determine if measurement of monochromatic wavefront aberrations in near-infrared light can accurately and precisely predict subjective refractive error for polychromatic light. Our approach requires knowledge of the monochromatic wavelength-in-focus (WiF) when polychromatic light is well focused, for which new empirical measurements are reported.

METHODS

With accommodation paralyzed, subjective refractive error was measured as a function of wavelength using a Badal optometer by optimally focusing a letter chart illuminated with monochromatic or white light (color temperature, 4575 K). Wavelength-in-focus was determined by interpolation as that wavelength for which monochromatic refractive error matches white light refractive error. The population-based mean value of WiF, used in conjunction with the Indiana Eye model of chromatic aberration, corrected for monochromatic (842 nm) estimates of refractive error obtained from wavefront aberration measurements, predicts the absolute refractive error of individual eye for polychromatic light for comparison with empirical measurements.

RESULTS

Average WiF for eight subjects was 569 nm (SE = 3.6 nm) for a 3-mm pupil and 575 nm (SE = 3.0 nm) for an 8-mm pupil. For small (3 mm) pupils, the mean (±SD) error in predicting refractive error for white light was 0.20 (±0.05) diopters (D) (range, +0.70 to -0.46 D), and for large (>8 mm) pupils, the mean (±SD) prediction error was 0.004 (±0.12) D (range, +0.56 to -0.52 D). The population mean of prediction errors was statistically not different from zero for large pupils but was slightly hyperopic for small pupils.

CONCLUSIONS

Subjective refractive error for white light can be accurately and precisely predicted objectively from monochromatic wavefront aberrations obtained for near-infrared light, but intersubject variability limits accuracy for individual subjects.