Determinants of peripapillary retinal nerve fiber layer’s grayscale value in normal eyes by spectral domain optical coherence tomography

Abstract

To determine and evaluate the distribution, variation, and determinants of peripapillary retinal nerve fiber layer (pRNFL) grayscale value with spectral-domain optical coherence tomography (SD-OCT) in normal eyes. In this cross-sectional study, three hundred ninety-seven normal eyes from 397 healthy Chinese adults aged 18–80 were consecutively recruited from a tertiary eye care center. An SD-OCT instrument took pRNFL imaging. We used a customized software to measure pRNFL parameters, including thickness and grayscale value. Univariable and multiple linear regression analyses were performed to examine the relationship between pRNFL grayscale value with ocular (e.g., axial length [A.L.], spherical equivalent [S.E.], intraocular pressure [IOP]), and systemic (e.g., age, sex) factors. A total of 397 eyes from 397 healthy subjects were included in the final analysis with mean (±\u2009SD) age 44.63\u2009±\u200916.43 years (range 18–80 years) and 196 (49.4%) males. The mean average of pRNFL grayscale value and thickness 164.82\u2009±\u20095.69 and 106.68\u2009±\u20098.89 μm, respectively. pRNFL grayscale value in nasal sectors (163.26\u2009±\u20099.31) was significantly lower comparing those in all other five sectors (all with p\u2009<\u20090.001)]. In multivariable analysis, average pRNFL grayscale value was independently correlated to older age (β\u2009=\u2009−\u20090.053, p\u2009=\u20090.002), longer axial length (β\u2009=\u2009−\u20090.664, p\u2009=\u20090.003), lower RPE grayscale value (β\u2009=\u20090.372, p\u2009<\u20090.001) and lower ImageQ (β\u2009=\u20090.658, p\u2009<\u20090.001). In this study, we provided normative SD-OCT data on the pRNFL grayscale value profile in nonglaucomatous eyes. Lower average pRNFL grayscale value was independently correlated to older age, longer axial length, lower RPE grayscale value, and lower ImageQ. These determinants should be considered when interpreting pRNFL grayscale value in glaucoma assessment.