Choroideremia

An 18-year-old male presents with night blindness since childhood and progressive peripheral visual field loss. Visual acuity is 6/9 OU with constricted fields. Fundus examination reveals extensive peripheral chorioretinal atrophy with a characteristic scalloped edge and bare white sclera visible through atrophic patches, sparing only a small central macular island. The optic disc appears normal. Full-field electroretinography shows severely reduced rod and cone responses. Genetic testing confirms a hemizygous loss-of-function mutation in the CHM gene encoding REP-1 (RAB Escort Protein-1). The structure marked **A** in the diagram shows scalloped choriocapillaris atrophy. Which of the following best explains the pathophysiology underlying this finding in choroideremia?