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Wavelength Dependence Of Intraocular Scatter Assessed With An Optical Method


Purpose: : Intraocular light scattering depends on the wavelength due to the physical properties of different inhomogeneities in the ocular media. This could in principle be used to the early diagnosis of underlying pathologies. Toward a practical application of this concept, a baseline characterization of the scatter wavelength dependence in normal young healthy eyes was performed with an optical method.

Methods: : The instrument is a modification of the double-pass principle allowing to record wide angle point-spread function (PSF) for different wavelengths. A liquid-crystal wavelength tunable filter was used to select three different wavelengths: 500, 600 and 650 nm (FWHM = ± 50 nm). Series of uniformly illuminated disks with increasing angular size up to 9.1 degrees in radius were sequentially projected onto the retina. The disk’s double-pass retinal images were recorded by a cooled electron-multiplied CCD camera. The derivative of intensity at the center of each disk’s retinal image with respect to its radius provides an estimation of the amount of light below the eye’s wide-angle double-pass PSF. The wavelength dependence of the ocular scattering was estimated by calculating a scatter parameter. The complete series of measurements were performed in 8 healthy eye subjects (age range: 26-40 yo, mean=34).

Results: : The wide-angle PSFs differ from the shorter to the longer wavelength. The PSF at 500 nm presents a 30% more intense light scatter in the angular range between 5 and 9 degrees than the two longer wavelengths tested (600 and 650 nm) which showed indiscernible results at this angular domain. However, between 0 and 2 degrees, the PSF showed statistically significant (p<0.05) 60% increase of scattered light when using 650 instead of 600 nm wavelength. This finding for longer wavelengths may be attributed to light diffusion at the fundus.

Conclusions: : An optical estimation of intraocular scattering shows a statistically significant decreasing for increasing wavelengths. This result may help to understand the nature of the sources and typical amount of scattering in the young healthy eye. This could be used as a reference for the early detection of ocular pathologies originated from changes in the optical homogeneity of the ocular media.

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