Wavelength dependence of the ocular straylight.

PURPOSE

Ocular straylight is the combined effect of light scattering in the optical media and the diffuse reflectance from the various fundus layers. The aim of this work was to employ an optical technique to measure straylight at different wavelengths and to identify the optimal conditions for visually relevant optical measurements of straylight.

METHODS

The instrument, based on the double-pass (DP) principle, used a series of uniform disks that were projected onto the retina, allowing the recording of the wide-angle point spread function (PSF) from its peak and up to 7.3° of visual angle. A liquid crystal wavelength tunable filter was used to select six different wavelengths ranging from 500 to 650 nm. The measurements were performed in nine healthy Caucasian subjects. The straylight parameter was analyzed for small (0.5°) and large (6°) angles.

RESULTS

For small angles, the wavelength dependence of straylight matches the transmittance spectrum of hemoglobin, which suggests that diffuse light from the fundus contributes significantly to the total straylight for wavelengths longer than 600 nm. Eyes with lighter pigmentation exhibited higher straylight at all wavelengths. For larger angles, straylight was less dependent on wavelength and eye pigmentation.

CONCLUSIONS

Small-angle straylight in the eye is affected by the wavelength-dependent properties of the fundus. At those small angles, measurements using wavelengths near the peak of the spectral sensitivity of the eye might be better correlated with the visual aspects of straylight. However, the impact of fundus reflectance on the values of the straylight parameter at larger angles did not depend on the measuring wavelength.