The anatomic distribution of ocular mast cells and their localization to distinct ocular tissues (varying between species) supports the hypothesis that mast cells serve a variety of unique and specialized biological functions in the normal eye. Our understanding of the role of the mast cell in ocular disease is still limited, however, and remains an emerging area of research. Conjunctival mast cells have long been accepted as an effective target for evaluating potential pharmaceutical interventions in ocular allergic diseases, and animal models have been critical to this process. The improvement in prognosis and symptoms that has been achieved using certain mast cell stabilizing drugs has traditionally been attributed to abrogation of histamine release. However, current research supports the notion that mast cell cytokines, chemokines, and surface receptors also play a critical role in both acute allergic and chronic inflammation, especially because the mast cell is one of the earliest responders to antigen challenge (Figs. 2 and 3). Recent research also challenges the classic concept that the role of ocular mast cells is primarily allergic. It has become apparent that a number of nonallergic diseases of the eye are associated with increased mast cell numbers in certain tissues, as well as changes in mast cell activation and protein expression (Table 4). Nevertheless, it is becoming increasingly evident that the lack of knowledge among the scientific community concerning ocular mast cell biology far outweighs our current understanding. The recent development of techniques to isolate conjunctival and choroidal mast cells and to further purify conjunctival mast cells should lead to a better understanding of mast cell biology. This will allow characterization of cytokine and chemokine profiles, surface-receptor expression, and patterns of upregulation. It will also facilitate examination of cell-to-cell interactions, which are critical to the progression of chronic and sight-threatening ocular diseases. Research goals in the area of ocular disease should take into consideration that a better understanding of these processes and development of in vitro models to evaluate them is essential to basic knowledge of ocular disease mechanisms and development of novel therapeutic interventions.
