Measurements of OCT Angiography Complement OCT for Diagnosing Early Primary Open-Angle Glaucoma

Abstract

Purpose: To compare measurements of global and regional circumpapillary capillary density (cpCD) with retinal nerve fiber layer (RNFL) thickness and characterize their relationship with visual function in early primary open-angle glaucoma (POAG).

Design: Cross-sectional study.

Participants: Eighty healthy eyes, 64 preperimetric eyes, and 184 mild POAG eyes from the Diagnostic Innovations in Glaucoma Study.

Methods: Global and regional RNFL thickness and cpCD measurements were obtained using OCT and OCT angiography (OCTA). For direct comparison at the individual and diagnostic group level, RNFL thickness and capillary density values were converted to a normalized relative loss scale.

Main outcome measures: Retinal nerve fiber layer thickness and cpCD normalized loss at the individual level and diagnostic group. Global and regional areas under the receiver operating characteristic curve (AUROC) for RNFL thickness and cpCD to detect preperimetric glaucoma and glaucoma, R² for the strength of associations between RNFL thickness function and capillary density function in diagnostic groups.

Results: Both global and regional RNFL thickness and cpCD decreased progressively with increasing glaucoma severity (P < 0.05, except for temporal RNFL thickness). Global and regional cpCD relative loss values were higher than those of RNFL thickness (P < 0.05) in preperimetric glaucoma (except for the superonasal region) and glaucoma (except for the inferonasal and superonasal regions) eyes. Race, intraocular pressure (IOP), and cpCD were associated with greater cpCD than RNFL thickness loss in early glaucoma at the individual level (P < 0.05). Global measurements of capillary density (whole image capillary density and cpCD) had higher diagnostic accuracies than RNFL thickness in detecting preperimetric glaucoma and glaucoma (P < 0.05; except for cpCD/RNFL thickness comparison in glaucoma [P = 0.059]). Visual function was significantly associated with RNFL thickness and cpCD globally and in all regions (P < 0.05, except for temporal RNFL thickness-function association [P = 0.070]).

Conclusions: Associations between capillary density and visual function were found in the regions known to be at highest risk for damage in preperimetric glaucoma eyes and all regions of mild glaucoma eyes. In early glaucoma, capillary density loss was more pronounced than RNFL thickness loss. Individual characteristics influence the relative magnitudes of capillary density loss compared with RNFL thickness loss. Retinal nerve fiber layer thickness and microvascular assessments are complementary and yield valuable information for the detection of early damages seen in POAG.

Keywords: Early glaucoma; OCT angiography; Retinal nerve fiber layer; Visual field.

Figure 1.

Global and Regional Retinal Nerve Fiber Layer Thickness and Capillary Density Associations in Each Diagnostic Group. The values of R-squared are shown in color coded format.

Figure 2.

Global and Regional Retinal Nerve Fiber Layer and Capillary Density Relative Loss in Pre-perimetric and Mild Perimetric Primary Open Angle Glaucoma

Figure 3.

Two-dimensional representation of relative global RNFL thickness (RNFLT) loss and relative circumpapillary capillary density (cpCD) loss for pre-perimetric glaucoma (blue) and mild perimetric glaucoma (orange) eyes. Points above the dashed line have higher relative loss values for circumpapillary capillary density compared to global RNFL thickness while those below the line show greater relative RNFL thickness loss.

Figure 4.

Global and Regional Retinal Nerve Fiber Layer Thickness-Total Deviation and circumpapillary Capillary Density-Total Deviation Associations in Each Diagnostic Group. The values of R-squared are shown in color coded format.