In Stargardt disease (ABCA4 mutations), the characteristic 'silent choroid' on fluorescein angiography occurs because:

• A Choroidal atrophy reduces choroidal vascular filling
• B Inflammatory infiltration of choroidal stroma reduces fluorescein leakage
• C Bisretinoid lipofuscin deposits in RPE block choroidal fluorescence ✓
• D Drusen deposits at Bruch's membrane impede fluorescein diffusion

Explanation

In Stargardt disease, ABCA4 mutations impair the flipping of N-retinylidene-PE from inner to outer leaflet in photoreceptor discs, leading to accumulation of bisretinoid lipofuscin (A2E) in RPE cells. This excess lipofuscin creates an orange-yellow fundus appearance (pisciform flecks) and critically absorbs fluorescein excitation wavelengths, masking choroidal fluorescence and producing the pathognomonic 'dark/silent choroid' on FA. Choroidal vascularity is normal.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.