The eyes of three species of animals, rats, mice, and guinea pigs, reared in a bacteria-free environment, have been examined histologically at selected ages and compared with eyes of conventionally reared animals of the same age. At birth the quantity of leukocytes in the conjunctiva and the size of the fornix follicles are about equal in the germ free and conventional. Thereafter, the number of leukocytes in the germ free may increase slightly or decrease depending upon the species. By contrast the number of leukocytes in the conjunctiva of the conventional become much more numerous with time. The size of the fornix follicles also remains smaller in the germ free than in the conventional.
McMaster PRB, Aronson SB, Bedford MJ. Mechanisms of the Host Response in the Eye IV. The Anterior Eye in Germ-Free Animals. Arch Ophthalmol. 1967;77(3):392-399. doi:10.1001/archopht.1967.00980020394019