1. Epstein, D. L., and Paton, D. (1968). New England Journal of Medicine, 279, 396.
2. Hilsdorf, C., and Zenklusen, G. (1973). Klinische Monatsbldtter fur Augenheilkunde, 162, 525.
3. Willis, W. E., and Laibson, P. R. (1970). Canadian Journal of Ophthalmology, 5, 239.