1. BLACK, G. W. (1943). Trans. ophthal. Soc. U.K., 62, 304.
2. CARTER, R. B. (1874). Trans. clin. Soc., 7, 60.
3. " Text-book of Ophthalmology ". Vol. 3;DUKE-ELDER, S.;British Journal of Ophthalmology,1940
4. GIFFORD, S. (1918). Arch. Ophthal., Chicago, 47, 241.
5. KNAPP, H. (1879). Ibid., 8, 82.