In order to determine the relation of congenital defective vision without squint, to defective vision with squint, I have taken those cases where congenital defective vision without squint was observed, together with the cases of squint, from the diaries of my private practice for the last ten years. I have personally investigated every case, and the observations on each were carefully examined before being included in the statistics; all cases with myopia of six or more dioptres, all cases of double nystagmus, and, finally, all those cases where the previous existence of squint might be suspected, were excluded, as above stated. I must also remark that before the last ten years I had not begun to collect these cases. In order to find monocular congenital defective vision one must seek for it, as patients usually come under treatment for quite different disorders, and in the consulting-room there is not always time carefully to investigate what possesses interest for us but none for the patient. In cases of squint the opportunity for investigating the power of vision does not escape us so easily, and yet the same list, which contains among 629 patients 177 cases of squint with a visual acuteness of 1/8 to less than 1/36, furnished at the same time 98 cases with undoubted congenital defective vision of the same high degree without squint, which I place together in the following review. Cases of congenital amblyopia with visual acuteness of 1/7 are so frequent, that I have not drawn up special statistics of them. I was not anxious to collect a large number of cases but only material for evidence. I have therefore divided the 98 cases I observed into 3 groups. (1) Cases with visual acuteness of less than 1/7 to V. 1/12; (2) V. less than 1/12 to V. 1/36; (3) visual acuteness less than 1/36. The limits between these groups are of course not very sharply defined, for what is designated as "measurement" of visual acuteness contains, even if we accept the statements of patients as trustworthy, not an inconsiderable number of sources of error; and we often find a remarkable absence of conformity in the analysed causes of congenital amblyopia, according as we seek to determine the visual acuteness by means of single test-letters or by reading printed matter. In a case of visual acuteness of 1/12 No. 0·75 with convex 6 was the smallest type that could be read, and that with difficulty, larger type was usually required; and in one case where at first only single words of No. 2·25 were read with difficulty--this test was on that account repeated in myosis by eserine--No. 1·75 was finally the smallest print which could with the same difficulty be deciphered. In the division of the groups here arranged the best visual acuteness ascertained in the various examinations was always used as the basis. A. Vision less than 1/7 to V. 1/12 38 cases. The examination of the better eye showed: