According to the immunological mechanism responsible for the final clinical picture, Leonardi et al have classified ocular allergic conditions into three main categories:[109] IgE-mediated reactions, including seasonal allergic conjunctivitis (SAC) and perennial allergic conjunctivitis (PAC); combined IgE and non-IgE-mediated reactions, including VKC and AKC; and non-IgE-mediated reactions, including giant papillary conjunctivitis (GPC) and contact dermatoconjunctivitis (CDC) (Figure 5). The gene discussed is IGHE; the disease is atopic conjunctivitis.