Pachychoroid Spectrum Disease: Underlying Pathology, Classification, and Phenotypes

Pachychoroid spectrum disease encompasses a set of macular disorders secondary to an abnormally thick choroid. However, the pathological process underlying pachychoroid spectrum disease and its overlap with age-related macular degeneration (AMD) remain unclear. This review aimed to understand the underlying pathology, classification, and phenotypes of pachychoroid spectrum disease.

This comprehensive literature review was performed based on a search of peer-reviewed published papers relevant to the current knowledge of pachychoroid disease spectrum.

Pachychoroid is primarily a bilateral phenomenon; the main pathological lesions include choriocapillaris attenuation and abnormally dilated pachyvessels. Chronic central serous chorioretinopathy (CSC) and pachychoroid neovasculopathy (PNV) show similar morphological changes and angiogenic cytokine levels. The subretinal fluid in PNV may not accurately indicate PNV activity. Besides, types 1 and 2 of choroidal neovascularization (CNV) may be involved in primary pachychoroidal disease. Both choroidal arteriosclerosis and higher hydrostatic pressure contribute to hyalinized choroidal arteries and aneurysmal dilatations, resulting in PNV progression to polypoidal choroidal vasculopathy (PCV). Thus, pachychoroid-related type 2 CNV and chronic CSC could be considered as PNV (IIIc) and as a precursor of PNV (IIIa), respectively. Tangled PCV on optical coherence tomography angiography that fails to develop aneurysms should be classified as a subtype of PNV or a forme fruste of PCV.

Multiple disorders of the pachychoroid spectrum are considered as a continuous disease process, ultimately stimulated by choroidal malfunction. PCV overlaps both AMD and pachychoroid disease, especially for thin-choroid and bilateral types. The terminology and classification of pachychoroid spectrum disease should be used cautiously.