Enhanced Structure-Function Relationship in Glaucoma with an Anatomically and Geometrically Accurate Neuroretinal Rim Measurement

Abstract

 

Purpose

 

To determine whether the relationship between the visual field (VF) and the standard optic disc margin based rim area (DM-RA) could be improved by using the Bruch's membrane opening based minimum rim width (BMO-MRW), an anatomically and geometrically accurate optic nerve head (ONH) parameter.

 

Methods

 

Structure-function relationships were determined in one eye of 151 glaucoma patients tested with automated perimetry, confocal scanning laser tomography (CSLT) and spectral domain optical coherence tomography (SD-OCT, Spectralis) on the same day. SD-OCT images of the ONH with 24 radial B-scans were acquired conventionally, relative to a fixed coordinate system (acquired image frame, AIF), and also relative to the eye-specific fovea-BMO centre (FoBMO) axis. Variables examined were visual field (VF) sensitivity, DM-RA (obtained with CSLT), BMO-MRW_AIF and BMO-MRW_FoBMO. VF locations were mapped to ONH sectors with fixed Garway-Heath maps, VF_GH (Garway-Heath et al., 2000), a method commonly used for assessing structure-function relationships, and with patient-specific maps customized for a series of biometric parameters, VF_PS (Denniss et al., 2012).

 

Results

 

Globally and regionally, the relationship between BMO-MRW_FoBMO and VF_PS was significantly stronger than that between DM-RA and VF_GH (Fig. 1). The R² for the relationship between BMO-MRW_FoBMO and VF_PS (in linear scale, 1/L) ranged from 5% (nasal) to 31% (inferotemporal) while that between DM-RA and VF_GH ranged from 0.3% (inferonasal) to 11% (superotemporal). The R² between BMO-MRW_AIF and VF_GH ranged from 5% (nasal) to 30% (inferotemporal), indicating that the structure-function relationship did not improve significantly with data acquisition and analysis in FoBMO coordinates (Fig. 2). Further, the impact of customized VF mapping was modest as the R² corresponding to the relationship between BMO-MRW_FoBMO and VF_GH [ranging 5% (nasal) to 30% (inferotemporal)] was not significantly different from that between BMO-MRW_FoBMO and VF_PS.

 

Conclusions

 

The structure-function relationship enhanced significantly with BMO-MRW, likely because of its anatomical and geometric accuracy. While the clinical utility of customized VF mapping and FoBMO image acquisition in individual subjects is likely high, due to the relatively large sectors used conventionally, their impact on improving the structure-function relationship was marginal.

 

 

 

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 758 visual fields • 627 optic disc