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2. Brit;DEUTMAN, A.F.; JANSEN, L.M.A.A.;J. Ophthal,1970
3. DONDERS, F. C. (1855) v. Graefes Arch. Ophthal., I, abt. 2, p. io6
4. (I 940) "Textbook of Ophthalmology";DUKE-ELDER, S.
5. GASS, J. D. M. (1967) Ibid., 63, 573