A 55-year-old non-diabetic man presents with bilateral blurred central vision and metamorphopsia for one year. Visual acuity is 6/12 OU. Dilated fundoscopy reveals the finding marked **A** in the diagram—subtle loss of retinal transparency temporal to the fovea—along with fine crystalline deposits, blunted right-angle venules, and small pigment plaques. Fluorescein angiography shows early parafoveal telangiectasia in the deep capillary plexus with late staining. OCT demonstrates hyporeflective inner retinal cavities and ellipsoid zone disruption. Which of the following BEST explains the pathophysiological basis of the finding marked **A** in this condition?
A. Hyperglycemia-induced pericyte loss and basement membrane thickening in diabetic retinopathy
B. Unilateral aneurysmal dilation of parafoveal capillaries with exudative leakage in Coats disease
C. Obliterative capillary disease with neuro-systemic involvement in MacTel Type 3
D. Loss of Müller cell support and parafoveal capillary remodeling in a neurodegenerative-vascular disease
Explanation
Why "Loss of Müller cell support and parafoveal capillary remodeling in a neurodegenerative-vascular disease" is right
The parafoveal greying (subtle loss of retinal transparency) marked A is a hallmark of idiopathic macular telangiectasia Type 2 (MacTel 2). The clinical anchor explicitly states that pathogenesis involves Müller cell loss and capillary remodeling, which directly explains the retinal greying. This is a bilateral, symmetric, slowly progressive neurodegenerative-vascular disease of the parafoveal capillaries—not a metabolic or aneurysmal process. The absence of diabetes, the bilateral symmetric presentation, the late staining (not cystoid leakage), and the deep capillary plexus involvement all confirm MacTel 2, where Müller cell dysfunction is the key pathophysiological driver of the greying appearance.
Why each distractor is wrong
Hyperglycemia-induced pericyte loss and basement membrane thickening in diabetic retinopathy: The patient is explicitly non-diabetic with no hard exudates. Diabetic retinopathy produces a different pattern of retinal changes and cystoid macular edema on FA, not the late staining seen here. This is a common distractor because both conditions affect retinal vasculature, but the clinical context rules it out entirely.
Unilateral aneurysmal dilation of parafoveal capillaries with exudative leakage in Coats disease: This describes MacTel Type 1 (Yannuzzi/Gass classification), which is unilateral, aneurysmal, and predominantly affects men. The patient's presentation is bilateral and symmetric, and there is no mention of unilateral aneurysmal dilation. Type 1 is treated like Coats disease; this patient does not fit that phenotype.
Obliterative capillary disease with neuro-systemic involvement in MacTel Type 3: MacTel Type 3 is very rare and characterized by obliterative capillary disease with neuro-systemic features. The patient's OCT-A shows telangiectatic capillaries in the deep capillary plexus—the opposite of obliteration—and there is no mention of systemic neurological disease. This is a distractor for students who confuse the MacTel subtypes.
High-YieldNEET PG
MacTel 2 is bilateral, symmetric, non-diabetic, and driven by Müller cell loss; MacTel 1 is unilateral, aneurysmal, and male-predominant; MacTel 3 is rare and obliterative with systemic neuro involvement.
AAO BCSC: Retina and Vitreous; MacTel 2 pathophysiology and classification
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