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T. Redmond, R. S. Anderson, M. B. Zlatkova, D. P. Crabb, D. F. Garway-Heath; Relating Retinal Nerve Fibre Layer Thickness and Functional Measures of Localised Ganglion Cell Density in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3516.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the relationship between retinal nerve fibre layer thickness (RNFLT) and estimates of localized ganglion cell (GC) density using peripheral grating resolution acuity (PGRA) and standard automated perimetry (SAP) in eyes of healthy volunteers and those with primary open angle glaucoma (POAG).
22 patients with early POAG (MD <-8dB) and 26 age-similar normal subjects underwent SAP (HFAII: SITA-Standard 24-2) and measurement of PGRA using achromatic Gabor stimuli at 4 locations at 10 degrees eccentricity. GC density at the 4 corresponding PGRA and SAP locations was estimated: PGRA using the method of Thibos et al JOSA 1987;4:1524-1529 and SAP from data reported in Garway-Heath et al IOVS 2000;41:1774-82. RNFLT was measured with a Zeiss Stratus OCT. Structure/function relationships for all subjects were assessed using the Garway-Heath et al map (Garway-Heath et al Ophthalmology 2002;107:1809-15).
RNLFT/GC associations appeared stronger (although not statistically significantly; p > 0.7) in the upper than lower field (PGRA r2 = 0.23 versus r2 = 0.13; SAP r2 = 0.25 versus r2 = 0.13; all p < 0.05). The RNFLT/GC association appears curvilinear with SAP but linear with PGRA. SAP and PGRA method agreement for GC density was moderate (figure), with marked heteroskedasticity (larger disagreements at higher values). Relative (to PGRA) over-estimates of GC numbers arise from small increases in SAP threshold sensitivity at the upper end of the dB scale.
The association of RNFLT with functional GC numbers estimated from PGRA appears linear, whilst the association from SAP estimates appears curvilinear. SAP threshold measurements result in large errors in GC density estimates at locations of high sensitivity, owing in part to the large linear differences between incremental and decremental step size that result from the logarithmic SAP staircase.
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