Structure versus Function in Glaucoma: An Application of a Linear Model

Abstract

A linear model that relates RNFL thickness to losses in SAP sensitivity describes the results for arcuate regions of glaucomatous visual fields. The linear model provides a framework for assessing the relative efficacy of structural and functional tests throughout the course of the disease.

Correlation of localized glaucomatous visual field defects and spectral domain optical coherence tomography retinal nerve fiber layer thinning using a modified structure–function map for OCT

“…3 In this model, the measured RNFL thickness is T M (T M ¼ T A0 Â 10 À D/10 þ T R ). [3][4][5] In this formula, T A0 is the RNFL thickness attributable to the RGC axons in the healthy normal state, D is the VF defect value (dB), and T R is the residual or base thickness, including glial cells and blood vessels. In normal eyes (assuming D ¼ 0), T M consists of two components: T A0 (normal RGC axon thickness) and T R (base thickness).…”

“…T R was determined for each sector as the median of the RNFL thickness when localized VF losses were 4 À 10 dB; because when field losses are worse than À 10 dB, the RNFL thickness reaches an asymptotic value according to the function formula (T M ¼ T A0 Â 10 À D/10 þ T R) . 3,5 T A0 is the RNFL thickness attributable to the RGC axons in the healthy normal state and was calculated by assuming D ¼ 0. T M in normal subjects was the average RNFL thickness of age-matched control subjects for each sector.…”

“…[2][3][4][5][6]12,14,[16][17][18] However, most of these studies used the Stratus time Correlation of localized glaucomatous VF defects and SD-OCT RNFL thinning H Wu et al domain OCT to measure RNFL thickness. [2][3][4]6,13,14,16,17 Although in two of these studies, SD-OCT was used to evaluated RNFL thickness, 5,18 the structure-function correspondence maps made in those studies correlated VF test points to regions of the ONH. In the present study, we created a modified OCT-based structurefunction map that shows significant correlation between localized areas of VF loss and SD-OCT measurements of RNFL thinning.…”

“…Significant correlations have been described between glaucomatous structural changes of the optic disc and/or retinal nerve fiber layer (RNFL) and functional changes on VF testing. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Determining whether there is good correlation between localized VF defects and localized RNFL defects may be important in deciding whether glaucomatous progression has occurred and in understanding the pathogenesis of the disease.…”

“…This paper, in particular, focuses on the topographic association between specific areas of glaucomatous VF loss and specific locations in the course of the RNFL bundles, and this topographic association can be delineated by structure-function correspondence maps. Many studies 3,4,9,10,13,15,18 have used the Garway-Heath map, 19 which maps VF test point locations to specific regions of the ONH. Weber et al 20 described another structure-function map that correlated VF test points to optic disc margin locations, which were then extrapolated to OCT RNFL defects.…”