Optical Coherence Tomography-Derived Excavation Index and Structure-Function Damage in Glaucoma

The Excavation Index is a novel OCT-based parameter that quantifies optic nerve head excavation, shows independent associations with RNFL thickness and the lamina cribrosa curvature index, and demonstrates sensitivity to early structural changes in glaucoma.

Glaucomatous optic neuropathy is characterized by progressive deformation of the lamina cribrosa (LC) and the scleral canal, leading to optic disc (OD) excavation and visual field (VF) loss. This study proposes the Excavation Index (EI), a novel optical coherence tomography-based parameter designed to quantify the OD excavation.

A total of 107 eyes (23 controls, 84 with primary open angle glaucoma of varying severity) underwent OCT and VF testing. The EI was defined as the ratio of excavation width (Ew) to peripheral LC depth (PLCD), multiplied by 100 (EI=Ew/PLCD×100). Correlations with LC curvature index (LCCI), retinal nerve fiber layer (RNFL) thickness, and visual field indices were analyzed using univariate and multivariate models.

EI values increased progressively from control to advanced glaucoma (14.72±2.79-31.00±10.21; P <0.001) and showed strong correlations with RNFL thickness ( r =-0.749), MD ( r =-0.696), PSD ( r =0.570), VFI ( r =-0.701), and LCCI ( r =0.710) (all P <0.001). In multivariate analysis, intraocular pressure, RNFL thickness, and LCCI were independently associated with EI ( P <0.05). ROC analysis showed that the AUC of EI was 0.860, comparable to LCCI (AUC=0.864, P =0.923). EI significantly differentiated control from all disease stages (all P <0.01).

The EI provides a reliable measurement of glaucomatous OD excavation. Its structural-functional correlations suggest potential utility as a complementary biomarker for disease staging and monitoring of OD excavation in glaucoma. EI may represent a promising parameter for detecting early-stage glaucoma, suggesting sensitivity to glaucomatous changes; however, further studies are needed to confirm its diagnostic role.