the eye, i.e. the distance between the lens and fovea, is 17.1 mm. From these values, one can calculate the average angle of view of a single sensor (cone cell), which is approximately arc seconds. The following is a table of pixel densities required at various distances so that there is one pixel per 31.5 arc seconds: Peak cone density varies highly between individuals, such that peak values below 100,000 cones/mm and above 324,000 cones/mm are not uncommon. Assuming average focal lengths, this suggests that individuals with both high cone densities and perfect optics may resolve pixels with an angular size of arc seconds, requiring PPI values at least times those shown above in order for images not to appear pixelated. It is worth noting that individuals with 20/20 (6/6 m) vision, defined as the ability to discern a 5x5 pixel letter that has an angular size of 5 arc minutes, cannot see pixels smaller than 60 arc seconds. In order to resolve a pixel the size of 31.5 and 21.2 arc seconds, an individual would need 20/10.5 (6/3.1 m) and 20/7.1 (6/2.1 m) vision, respectively. To find the PPI values discernible at 20/20, simply divide the values in the above table by the visual acuity ratio (e.g. 96 PPI / (20/10.5 vision) = 50.4 PPI for 20/20 vision). Entoptic effects in the fovea The presence of the pigment in the radially arranged axons of the Henle fiber layer causes it to be dichroic and birefringent to blue light. This effect is visible through the Haidinger's brush when the fovea is pointed to a polarized light source. The combined effects of the macular pigment and the distribution of short wavelength cones results in the fovea having a lower sensitivity to blue light (blue light scotoma). Though this is not visible under normal circumstances due to "filling in" of information by the brain, under certain patterns of blue light illumination, a dark spot is visible at the point of focus. Also, if mixture of red and blue light is viewed (by viewing white light through a dichroic filter), the point of foveal focus will have a central red spot surrounded by a few red fringes. This is called the Maxwell's spot after James Clerk Maxwell who discovered it. Bifoveal fixation In binocular vision, the two eyes converge to enable bifoveal fixation, which is necessary for achieving high stereoacuity. In contrast, in