Due to its vascularisation and system of lymphatic drainage, the eye is privileged territory for development of immunological phenomena. The tears, because of lactoferrin, lysozymes, mucins, different immunoglobulins: IgA (CALT), IgG and IgM, are the first line of defence against physical, chemical, infectious and extra-ocular antigenic attack. ACAID, "Anterior Chamber Associated Immune Deviation", by its type of defence against intra-ocular aggressors, assures some protection of the eye and explains the development of some intra-ocular tumours and tolerance to corneal grafts.