The pathogenesis and clinical presentation of macular edema in inflammatory diseases

Cystoid macular edema (CME) is a classical complication of ocular inflammation. This syndrome was already described by Irvine in 1953 but the pathogenesis of this condition remains unclear. Cystoid macular edema can result either from a rupture of the inner or from the outer blood ocular barrier. Clinical CME that is responsible for a low visual acuity must be differentiated from angiographic CME that can be present even without any decrease in visual acuity. Fluid progressively accumulates into the outer plexiform layer of the retina and pools into cystic spaces. Fluid accumulation can now be better seen with optical coherence tomography (OCT). In chronic CME fluid accumulation is associated with thinning of the retina and fibrosis. At this stage irreversible lesions are present and CME does not respond to medical therapies. Inflammatory CME must be differentiated from CME resulting from irreversible vascular damage such as in diabetic CME or due to vein occlusions. Experimental research on cystoid macular edema has been hampered by the lack of animal model: most of laboratory animals have no macula, monkeys appear to be highly resistant to macular edema. Five major causes have been suspected to be at the origin of CME: (1) photic retinopathy, (2) trauma of ocular tissue, (3) secondary irritation of the ciliary body, (4) vitreous traction and (5) pharmaceutically induced CME. Clinical experience has shown that pseudophakic CME usually responds well to local therapy of steroids and non-steroidal antiinflammatory drugs (NSAIDs) and/or in association with systemic acetazolamide. Acetazolamide is increasing fluid resorption through the retinal pigment epithelium. Postoperative CME rarely needs additional posterior subtenon's injections to resolve. But in CME occurring secondary to uveitis additional posterior sub-Tenon's steroid injections or systemic steroids may be necessary to decrease the constant release of inflammatory mediators.