Besides its action as a bactericide, astringent and mild anesthetic, the alkaloid quinine passes through the epithelium into the underlying tissues when applied locally to the mucous membrane. It is a protoplasmic poison which acts on the nutrition of almost all forms of protoplasm, at first augmenting and later depressing the activity of the protoplasm and finally causing the death of cells. Roth1 and others showed that it destroys leukocytes and lymphocytes in and out of blood vessels. These properties explain the rationale of the treatment of certain diseases of the conjunctiva and cornea by the local application of quinine.
In two papers2 dealing with the subject of local quinine therapy for trachoma, active interstitial keratitis and old corneal opacities, I reported that experiments on animals showed that the normal conjunctiva and cornea as well as the traumatized cornea show no ill effects from the daily
SELINGER E. LOCAL QUININE THERAPY FOR SOME DISEASES OF THE CONJUNCTIVA AND CORNEA. Arch Ophthalmol. 1936;15(1):31–35. doi:10.1001/archopht.1936.00840130041003