Correlation of retinal nerve fiber layer thickness and visual fields in glaucoma: a broken stick model

Abstract

Purpose: To determine the retinal nerve fiber layer (RNFL) thickness at which visual field (VF) damage becomes detectable and associated with structural loss.

Design: Retrospective cross-sectional study.

Methods: Eighty-seven healthy and 108 glaucoma subjects (1 eye per subject) were recruited from an academic institution. All patients had VF examinations (Swedish Interactive Threshold Algorithm 24-2 test of the Humphrey Visual Field Analyzer 750i) and spectral-domain optical coherence tomography RNFL scans. Comparison of RNFL thickness values with VF threshold values showed a plateau of VF threshold values at high RNFL thickness values and then a sharp decrease at lower RNFL thickness values. A broken stick statistical analysis was used to estimate the tipping point at which RNFL thickness values are associated with VF defects. The slope for the association between structure and function was computed for data above and below the tipping point.

Results: The mean RNFL thickness value that was associated with initial VF loss was 89 μm. The superior RNFL thickness value that was associated with initial corresponding inferior VF loss was 100 μm. The inferior RNFL thickness value that was associated with initial corresponding superior VF loss was 73 μm. The differences between all the slopes above and below the aforementioned tipping points were statistically significant (P < .001).

Conclusions: In open-angle glaucoma, substantial RNFL thinning or structural loss appears to be necessary before functional visual field defects become detectable.

Copyright © 2014 Elsevier Inc. All rights reserved.

Figures

Figure 1. Using the Broken Stick Model to Determine the Tipping Point, the Point at Which Retinal Nerve Fiber Layer Thinning is First Associated with Visual Field Loss

Graphs correlate retinal nerve fiber layer (RNFL) thickness values with corresponding VF values, where each of the 52 testing points were unlogged, averaged, then log transformed back to decibel scale. Graphs are presented for the global RNFL values versus average VF total deviation values (upper), the superior RNFL region versus inferior VF (middle left), the inferior RNFL region versus superior VF (middle right), the temporal RNFL region versus central subfield (lower left), and the nasal RNFL region versus corresponding visual subfield (lower right). Broken stick model is represented by the black lines. Empty squares represent healthy eyes. Filled circles represent glaucoma eyes. Filled triangles represent the tipping points.

Figure 1. Using the Broken Stick Model to Determine the Tipping Point, the Point at Which Retinal Nerve Fiber Layer Thinning is First Associated with Visual Field Loss

Graphs correlate retinal nerve fiber layer (RNFL) thickness values with corresponding VF values, where each of the 52 testing points were unlogged, averaged, then log transformed back to decibel scale. Graphs are presented for the global RNFL values versus average VF total deviation values (upper), the superior RNFL region versus inferior VF (middle left), the inferior RNFL region versus superior VF (middle right), the temporal RNFL region versus central subfield (lower left), and the nasal RNFL region versus corresponding visual subfield (lower right). Broken stick model is represented by the black lines. Empty squares represent healthy eyes. Filled circles represent glaucoma eyes. Filled triangles represent the tipping points.

Figure 1. Using the Broken Stick Model to Determine the Tipping Point, the Point at Which Retinal Nerve Fiber Layer Thinning is First Associated with Visual Field Loss

Graphs correlate retinal nerve fiber layer (RNFL) thickness values with corresponding VF values, where each of the 52 testing points were unlogged, averaged, then log transformed back to decibel scale. Graphs are presented for the global RNFL values versus average VF total deviation values (upper), the superior RNFL region versus inferior VF (middle left), the inferior RNFL region versus superior VF (middle right), the temporal RNFL region versus central subfield (lower left), and the nasal RNFL region versus corresponding visual subfield (lower right). Broken stick model is represented by the black lines. Empty squares represent healthy eyes. Filled circles represent glaucoma eyes. Filled triangles represent the tipping points.

Figure 2. Using the Broken Stick Model to Determine the Tipping Point, the Point at Which Retinal Nerve Fiber Layer Thinning is First Associated with Visual Field Loss

Graph correlates global retinal nerve fiber layer (RNFL) with mean deviation visual field (VF) values for healthy and glaucoma eyes. The broken stick model is represented by the black lines. Empty squares represent healthy eyes. Filled circles represent glaucoma eyes. The filled triangle represents the tipping point.

Figure 2. Using the Broken Stick Model to Determine the Tipping Point, the Point at Which Retinal Nerve Fiber Layer Thinning is First Associated with Visual Field Loss

Graph correlates global retinal nerve fiber layer (RNFL) with mean deviation visual field (VF) values for healthy and glaucoma eyes. The broken stick model is represented by the black lines. Empty squares represent healthy eyes. Filled circles represent glaucoma eyes. The filled triangle represents the tipping point.

Figure 2. Using the Broken Stick Model to Determine the Tipping Point, the Point at Which Retinal Nerve Fiber Layer Thinning is First Associated with Visual Field Loss

Graph correlates global retinal nerve fiber layer (RNFL) with mean deviation visual field (VF) values for healthy and glaucoma eyes. The broken stick model is represented by the black lines. Empty squares represent healthy eyes. Filled circles represent glaucoma eyes. The filled triangle represents the tipping point.