The skin presents obvious obstacles to a satisfactory study of the detailed changes which occur in the vascular responses involved in specific and nonspecific wheal formation. The accessibility of the ophthalmic mucosa, with its visible blood supply, suggested the conjunctiva as an ideal site for the study of vascular reactions resulting from excitation with immunologic and nonspecific agents. With the aid of the slit lamp miscroscope, studies were undertaken to compare the characteristics of the specific and of the nonspecific reactions.
The ability of certain substances, antigenic and nonantigenic, to produce a conjunctival reaction is well known. Pollen extracts and other allergens almost regularly produce ophthalmic reactions in persons sensitive to them. Histamine and ethylmorphine, because of their ability to induce dilatation of the conjunctival vessels and even edema, are examples of nonspecific substances capable of eliciting a conjunctival reaction. Ethylmorphine, a derivative of morphine, is a vasodilator and lymphagogue.