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. 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 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. 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. 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. 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. Examples of application of the technique in real eyes with different amount of scatter artificially induced are presented. 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.

*I*

_{o}and subtends on the retina a visual angle equal to

*ϑ*(radius), the intensity at the center of the disk as recorded at the camera plane is given by the following equation:

*I*

_{c}(

*ϑ*) is the intensity at the center of the disk (which depends on the radius of the projected disk) and PSF

_{dp}(

*ϕ*) is the double-pass PSF of the eye. With reference to Figure 1, this value is also equal to the surface integral of the PSF within a circle of radius

*ϑ*. Assuming that the integral of the PSF (either single pass or double pass) for

*ϑ*=

*π*/2 is equal to unity, it can be shown that the central intensity of an infinite disk is equal to

*I*

_{o}. Qualitatively, this means that while for a small patch the central intensity is attenuated by light scattering this intensity is increased as peripheral annuli are added to the patch and scattered light from the annuli is complemented to the center of the patch.

*I*

_{c}can be normalized in respect to the largest available disk. This assumption is supported by existing models of the PSF in the human eye (van den Berg, Hwan et al., 1993; Vos & van den Berg, 1999).

*I*

_{c}(

*ϑ*) denotes the normalized intensity in respect to the central intensity of the largest disk. Of course,

*I*

_{c}in this case takes values between 0 and 1.

*ϑ*ranging from 0.18 to 8.1 degrees is projected onto the retina. If

*I*

_{c}is known experimentally, then the PSF can be retrieved from Equation 2 by taking its derivative in respect to

*ϑ*:

^{−1}denote 2-dimensional Fourier and inverse Fourier transforms, respectively.

*I*

_{c}(or the radial integral of the PSF). A straightforward method is to approximate the derivative in Equation 3 with finite differences:

*ϑ*

_{ i }are the radii of the consecutive disks, and

*ϑ*

_{ n }= (

*ϑ*

_{ i+1}+

*ϑ*

_{ i })/2.

*I*

_{c}and the derivative can then be evaluated analytically. An appropriate function for

*I*

_{c}can be found by using one of the known models (IJspeert, van den Berg, & Spekreijse, 1993) for glare and by using Equation 2.

_{dl}is the diffraction-limited PSF (calculated based on the apertures of the system and radially normalized to 1),

*a*is a coefficient of scatter,

*ϑ*

_{o}is an arbitrary small angle (to avoid the singularity at

*ϑ*= 0),

*n*is approximately 2, and

*b*is a normalization coefficient so that the scattering law is radially normalized (

*a*,

*n*, and

*ϑ*

_{o}, this formula produces—practically—identical numerical values with other functions in the literature for the range of angles assessed with our method (0–9 degrees).

*I*

_{c}(

*ϑ*) (as in Equation 2). The derivative of this intensity with respect to the disk radius was numerically estimated by fitting a linear function to two regions of angles (0.5–2 and 2.5–8 degrees) and applying Equation 7. The particular values of the computed double-pass PSF at 1.25 and 5.25 degrees are reported as parameters to quantify the amount of intraocular scatter.

*μ*W/cm

^{2}. A bite bar mounted on a three-axis positioning stage was used to stabilize the subject's head during measurements.

*μ*m in their RGP material. The CLs have no refractive power. Their scattering properties have been measured in a separate experiment both optically (Bueno et al., 2007) and psychophysically (by means of the commercially available instrument C-Quant) and were found to contribute with amounts of scatter consistent with normal or mildly scattering eyes (0 to 0.6 log units increase of the straylight parameter as in Franssen et al., 2006). Figure 3 shows a dark field photograph of the CLs used here, where differences in the scattering produced can be observed.