Many diseases may give rise to cystoid macular oedema (CMO), which suggests that this condition is not a disease but a final common pathway of many diseases. It is not exclusively associated with retinal vascular disturbance, but may be secondary to choroidal vascular changes and alterations of the retinal pigment epithelium. In some forms of CMO, generalized ocular involvement is present and results in vascular leakage of the iris and possibly other ocular structures. Experimental pathological models suggest that leakage of the retinal vasculature and/or retinal pigment epithelium alone may not give rise to CMO. Ischaemia resulting in microinfarction may be one of the important factors in the production of CMO.