![]() ![]() This technique (Santamaria, Artal et al., 1987) is based on projecting a point source on the retina and recording the reflected image after double pass through the eye with a camera conjugated with the retina. Since the PSF contains all the relevant information from both aberrations and scatter, it has been a long history trying to directly record it in the living eye (Campbell & Gubisch, 1966 Flamant, 1955) using the ophthalmoscopic or double-pass approach. In general, scattered light reduces retinal image quality due to a decrease in the contrast of the retinal images. An example of such a condition is the visual environment during night driving. In particular, light scattering may have a significant impact on retinal image contrast when the eye is observing scenes in which bright light sources are present. It was also shown that is also possible that scatter and aberration may interact to produce an improved retinal image (Perez, Manzanera, & Artal, 2009). Although aberrations and scatter are often treated separately due to their different origin, under particular experimental conditions or depending on the visual task, they contribute in combination to the retinal image deterioration. This effect is described by statistical terms (e.g., intensity and angular distribution) rather than by a calculation based on the geometrical characteristics of the eye that can describe quite accurately the aberrations (Tabernero, Berrio, & Artal, 2011). Light scattering is a phenomenon originated from localized (particle-like) irregularities of the refractive index within the ocular media and leads to the spread of the light at larger angles over the retina. The homogeneity of the ocular structures affects the retinal images, although this fact is not usually taken into account when describing the optical quality only in terms of aberrations (Diaz-Douton, Benito et al., 2006). The image of a point source projected onto the retina, the ocular point spread function (PSF), is affected by diffraction in the pupil, aberrations, and scatter. Wavefront sensors provide information on the overall optical quality of the eye through the aberrations. ![]() The study of the eye in terms of its optical quality is approached by analyzing both the geometrical characteristics of the ocular surfaces and the intrinsic properties of the media with which the light interacts when passing through the eye. ![]() The optical quality of the retinal image (Artal, Guirao, Berrio, & Williams, 2001) is the first physical factor influencing visual performance. This procedure allows the direct, accurate, and in vivo measurement of the effect of intraocular scattering and may be a step toward the comprehensive optical evaluation of the optics of the living human eye. Examples of application of the technique in real eyes with different amount of scatter artificially induced are presented. The methodology consists of projecting disks of uniform radiance on the retina, recording the images after reflection and double pass through the eye's optics and performing a proper analysis of the images. We report here a new optical method for the accurate reconstruction of the wide-angle PSF in the living human eye up to 8 degrees. However, the more peripheral areas of the PSF in the living human eye, ranging from about 1 to 10 degrees of eccentricity, have been investigated only psychophysically. The impact of the spatial characteristics of this central part of the PSF on the retinal image quality and visual function has been extensively analyzed and documented both by optical and psychophysical methods. There is a plethora of optical methods for the direct and indirect measurements of the central part of the PSF as a result of monochromatic and polychromatic aberrations. The point spread function (PSF) of the human eye spans over a wide angular distribution where the central part is associated mostly to optical aberrations while the peripheral zones are associated to light scattering.
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