Fluorescein angiography of a patient with branch retinal vein occlusion shows a 'blocked' or hypofluorescent area corresponding to the distribution of flame haemorrhages. The mechanism of this hypofluorescence is:
- A Choroidal non-perfusion
- B RPE window defect
- C Masking of background fluorescence by preretinal blood ✓
- D Late staining from fibrous tissue
Correct answer: C. Masking of background fluorescence by preretinal blood
Explanation
In branch retinal vein occlusion, superficial flame haemorrhages overlie the retina and physically block (mask) transmission of background choroidal fluorescence, producing hypofluorescent areas that correspond exactly to the haemorrhages. This is called a 'masking' or 'blocking' defect. Window defects are caused by RPE atrophy and appear hyperfluorescent. Choroidal non-perfusion and fibrous staining are distinct FFA patterns.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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