http://arapaho.nsuok.edu/~salmonto/vs3_materials/Lecture6.pdf [Broken] In this website (and in many more) in page 5, it’s written that photoreceptors are more densely packed in nasal areas of retina than temporal. That's one of the explanations why empirical horopter (that's the unit of all points in visual field, that are seen in the same position monocularly) deviates from theoretical. In page 6, in graphs we see that the same segment in visual field has longer arc in nasal retina than temporal (binocular vision). I don’t see how these two things agree: density of photoreceptors in nasal and temporal retinas and the magnitude of arcs. If compensation would be the case, then I think it should be reverse situation. Given there are less amount of photoreceptors in temporal area, arc should be longer than that of nasal - so that the quantity of photoreceptors in both areas would be the same. Does anybody have an idea?