The aim of this paper was to report the cases of 3 consecutive patients with mitogen-activated protein kinase kinase inhibitor (MEKi)-associated retinopathy with characteristic multiple serous retinal detachments (SRDs). A functional analysis of the retinal pigment epithelium was performed in 2 patients by electro-oculography (EOG). In all 3 patients, SRD lesions were observed in the posterior pole including the fovea of both eyes. Interestingly, neither obvious leakage in fluorescein/indocyanine angiography nor abnormal fundus autofluorescence was associated. SRDs and associated cystoid macular edema in one case rapidly resolved with the cessation of MEKi but recurred quickly after treatment resumption. In EOG tests, three of four eyes with multiple SRDs showed a marked decrease in the light-peak-to-dark-trough ratio (LP:DT ratio). The LP:DT ratio in EOG reflects the transepithelial potential of the retinal pigment epithelium, suggesting the involvement of disrupted tight junctions and impaired active transport of fluid/ions in MEKi-associated retinopathy. The latter may be the major cause of SRDs as we observed that fluid leakage in angiography was absent in the areas of the patients' SRDs.
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