Background: Vascular phenomena are considered important to optic nerve and visual field progression in open-angle glaucoma (OAG). A recently described formulation, the Pressure Attenuation Index (PAI), links arteriolar caliber variations to pressure loss along the retinal arteriolar system.
Objective: To examine whether the PAI could predict ocular hypertension (OHT) progression to OAG.
Methods: The PAI was calculated for 27 eyes of 14 patients with OHT using initial and final digitized optic disc photographs taken during a follow-up interval of 5 to 18 years. Serial stereo color disc photographs and visual fields were analyzed to determine progression.
Results: At baseline, the arteriolar tree of 8 subjects with OHT that progressed to OAG (n = 8 eyes) demonstrated a 45.8% greater mean PAI value than that of 7 subjects who did not progress (n = 7 eyes) (mean +/- SEM, 5.31 +/- 0.93 vs 3.64 +/- 0.34; r = 0.83). Progression was independent of baseline cup-disc ratio. The PAI values of subjects with stable OHT remained stable after a median follow-up interval of 12.0 years. The PAI values of subjects with OHT that progressed demonstrated a further increase of 19.97% +/- 11.24% during a median follow-up period of 6.0 years.
Conclusions: The results support the hypothesis that low end-arteriolar pressure predicts the progression from OHT to OAG. The PAI provides a new, early, reproducible, and physiological method to study vascular phenomena in glaucoma.