Microcystic macular edema: clinical significance and pathogenetic mechanisms

Microcystic macular edema represents a specific type of intraretinal cystic changes, localizing predominantly in the inner nuclear layer and detectable using the optical coherence tomography. Contrary to the classic concepts on the macular edema as a result of vascular permeability, microcystic macular edema is not accompanied by exudation and it is perceived as the manifestation of neuroglial dysfunction, often associated with the damaging of the optic nerve. Initially described in patients with multiple sclerosis, microcystic macular edema was subsequently detected in the wide spectrum of diseases, including glaucoma, neuromyelitis optica spectrum disorders, diabetic retinopathy, occlusion of the retinal veins, senile macular degeneration and epiretinal membranes. The key pathogenetic mechanisms are considered the retrograde transsynaptic degeneration of the ganglionic cells in the retina and the functional/structural damage of the Muller’s cells, in particular, the impaired operation of the AQP4 aquaporin channels. The morphological features of the microcystic macular edema, its location and clinical significance vary depending on the main disease and in a number of cases can act as the early biomarker of the neurodegenerative process. The article contains the pathophysiological models, the clinical correlates and the modern methods of the diagnostics of microcystic macular edema with special emphasis on the role of multimodal visualization and artificial intelligence technologies. Taking into consideration the rates of accidental detection and the potential relation to the systemic diseases, microcystic macular edema should be considered not as an isolated ophthalmology condition, but as the component of wider neuroretinal disorder requiring interdisciplinary approach to the diagnostics and follow-up.