The earliest lesions in ophthalmia of rats resulting from a deficiency of vitamine A consist in focal inflammatory lesions in the conjunctivæ of the lids and nictitating membrane. The involvement of the cornea, which constitutes the most conspicuous feature of the well developed ophthalmia, is a secondary phenomenon. The characteristic corneal plaque consists of keratinized epithelium beneath which the deeper layers of epithelium are generally found intact.
Pathologically, the ocular manifestations of a deficiency of vitamine A are referable to a low grade inflammatory process, originating in the palpebral conjunctiva and spreading to the cornea.
The rapidity of development and the degree of destruction probably depend in large part on the type of bacterial infection. The specific changes which lead to the establishment of such an infection have not been determined. It is conceivable that they may be either physiological or anatomical. There is some evidence in favor of a general disturbance of antibody formation in animals on deficient diets. The possibility of a disturbed function in the paraocular glands must be considered.