Geometric Decomposition of OCT Angiography in RVO: Unmasking Congestive Versus Compensatory Phenotypes and Deep Retina-Choroid Coupling.

Fellow eyes of RVO patients exhibit 'inefficient compensation' in the deep capillary plexus characterized by increased vessel length density and decreased vessel diameter index compared to controls.

• Fellow eyes showed significantly increased VLD (25.17 ± 4.98 vs. 20.83 ± 4.02 mm/mm²) compared to healthy controls (P < 0.001)
• Fellow eyes showed decreased VDI (1.42 ± 0.07 vs. 1.47 ± 0.04) compared to controls (P < 0.001)
• This pattern was termed 'inefficient compensation' — more vessel length but narrower caliber
• Linear mixed-effects models were used to account for intereye correlation in a cohort of 226 eyes (88 RVO-affected, 88 fellow, 50 healthy controls)

RVO-affected eyes demonstrate 'congestive failure' in the deep capillary plexus with decreased vessel length density and increased vessel diameter index.

• Affected eyes had decreased VLD (16.06 ± 4.84 mm/mm²) compared to controls (P < 0.05)
• Affected eyes had increased VDI (1.51 ± 0.09) compared to controls (P < 0.05)
• This pattern of decreased vessel abundance but increased caliber was termed 'congestive failure'
• The pattern is the inverse of the compensatory phenotype seen in fellow eyes

Deep capillary plexus ischemia is strongly correlated with total retinal thickness as a measure of macular edema severity.

• DCP ischemia correlated with total retinal thickness (TRT) with ρ = -0.43, P < 0.001
• The negative correlation indicates that greater ischemia is associated with greater macular edema
• TRT was used as a surrogate marker for macular edema severity

A progressive 'disease gradient' in retina-choroid coupling (DCP to choroidal vascularity index correlation) was identified across healthy, fellow, and affected eyes.

• Correlation between DCP and choroidal vascularity index was ρ = 0.37 in healthy controls
• Correlation increased to ρ = 0.42 in fellow eyes
• Correlation further increased to ρ = 0.54 in RVO-affected eyes
• The progressive increase in coupling strength across the disease gradient suggests increasing pathologic synchronization of deep retinal and choroidal degeneration

Sensitivity analysis revealed a biphasic synchronization sequence in retina-choroid coupling dependent on edema severity.

• In mild macular edema, there was temporary functional decoupling with ρ = 0.30
• In severe congestive disease (TRT ≥ 400 µm), there was profound pathologic synchronization with ρ = 0.63
• This biphasic pattern suggests an initial decoupling followed by pathologic resynchronization as disease progresses
• The authors interpret this as evidence for a 'pathologic collapse of neurovascular autoregulation'

Swept-source OCTA was used to perform geometric decomposition of vessel density into vessel length density and vessel diameter index across three study groups.

• Study included 226 eyes total: 88 RVO-affected, 88 fellow, and 50 healthy control eyes
• Vessel density (VD) was decomposed into vessel length density (VLD; measuring vessel abundance) and vessel diameter index (VDI; measuring vessel caliber)
• Linear mixed-effects models were used to account for intereye correlation
• Swept-source optical coherence tomography angiography was used for all imaging

RVO is characterized as a bilateral and hierarchical disorder in which conventional vessel density analysis obscures subclinical compensatory remodeling in fellow eyes.

• Conventional VD analysis does not distinguish between changes in vessel length and vessel caliber
• Decomposing density into length (VLD) and diameter (VDI) provided superior biomarkers for detecting early subclinical changes
• Fellow eyes showed compensatory remodeling that was not detectable by conventional VD analysis alone
• The authors conclude that 'decomposing density into length and diameter provides superior biomarkers for detecting early subclinical changes and monitoring the congestive status of RVO eyes'