1. Text-book of Ophthalmology;DUKE-ELDER, S.,1932
2. HARTRIDGE, H., and OWEN, H. B. (1922). Brit. J. Ophthal., 6, 543.
3. HIGGINS, G. C., and STULTZ, K. (1948). J. opt. Soc. Amer., 38, 756.
4. JONES, L. A., and HIGGINS, G. C. (1947). Ibid., 37, 217. O'BRIEN, B. (1950). Ibid., 40, 796.
5. JONES, L. A., and HIGGINS, G. C. (1951). Ibid., 41, 882.