1. BALLANTYNE, A. J. (1938). Trans. ophthal. Soc. U.K., 58, 207. B6CK, J. (1938). Z. Augenheilk., 95, 1.
2. COLLINS, E. TREACHER (1923). Trans. ophthal. Soc. U.K., 43, 273.
3. DOYNE, R. W. (1889). Ibid., 9, 128.
4. GUENTHER, E. (1946). Acta med. scand., 123, 482.
5. HAGEDOORN, A. (1939). Arch. Ophthal. (Chicago), 21, 746.