A 38-year-old Type-A male marketing executive on oral prednisolone for contact dermatitis presents with sudden micropsia, positive scotoma, and metamorphopsia in the right eye. Best-corrected visual acuity is 6/9, improving to 6/6 with a +1.0 D hyperopic shift. Amsler grid shows central distortion. Dilated fundus examination reveals a round, well-circumscribed, shallow elevation of the neurosensory retina at the fovea with absent foveal reflex. OCT confirms sub-retinal fluid between the ellipsoid zone and RPE without intra-retinal fluid; choroidal thickness is increased to 480 µm. The structure marked **A** in the diagram represents the serous neurosensory retinal detachment. Which of the following is the PRIMARY PATHOPHYSIOLOGICAL MECHANISM underlying this finding in this patient?