1. CRIGLER, L. W. (1913) J. Amer. med. Ass., 6o, 1297
2. Text-Book of Ophthalmology;DUKE-ELDER, S.;vol. VI,1954
3. Amer;JOHNSON, F.B.; ZIMMERMAN, L.E.;J. clin. Path,1965
4. LOWELL, H. (1913) J. Amer. med. Ass., 6i, 2303
5. Brit;NELSON, C.;J. Ophthal,1970