Show now biow eyes ey are lewd tile the theory of the optically perfect eye is that parallel rays of light en cn bering v it ore are brought to a focus on its retina any deviation from this condition constitutes an error of refraction fmc tion and requires for its correction an artificial variation of the luminous rays the generally adopted method of determining 0 the refraction of the eye is to use test types placed a distance that the rays of light emanating emanatian from froin them may bo be regarded in practice as parallel ind and the deviation from par allela nl necessary to correct a ro fracci ve error is effected by placing a lens in front of the eye thero there aro are many other methods s of changing 1 tho the course of luminous rays raya coming from a test ob object eject and of those these all the single convex leus is the simplest and most often med iii in optometry new york telegram |