1. ASHTON, N. (1949). British Journal of Ophthalmology, 33, 407.
2. ASHTON, N. (1951). Ibid., 35, 189.
3. BALLANTYNE, A. J., and LOEWENSTEIN, A. (1943). Trans. ophthal. Soc. U.K., 63, 95. DoBREE, J. H. (1950). British Journal of Ophthalmology, 34, 720.
4. Text-book of Ophthalmology,;DUKE-ELDER, S.,1940
5. MADDOX, K. (1933). British Journal of Ophthalmology, 17, 393.