Thus, the rays that leave each visible point of an object, in order to converge exactly at as many points on the retina, undergo three refractions, which all tend toward the axis the first upon entering the aqueous humor, for the refraction they undergo upon entering and leaving the cornea should not be counted; the second upon entering the crystalline lens; and the third upon leaving the crystalline lens; and this last refraction, it seems to me, must also be rather great due to the great convexity of the crystalline lens on the side touching the vitreous humor.