The Effect of Glaucoma on the Optical Attenuation Coefficient of the Retinal Nerve Fiber Layer in Spectral Domain Optical Coherence Tomography Images

Abstract

The measurements clearly demonstrated that the μ(att) of the RNFL decreased with increasing disease severity. The RNFL attenuation coefficient may serve as a new method to quantify glaucoma in SD-OCT images.

Retinal nerve fiber layer reflectometry must consider directional reflectance

“…Recent studies have shown that a decrease in RNFL reflectance occurs prior to thinning of the RNFL [5][6][7][8][9][10][11], and suggest that direct OCT measurement of RNFL reflectance may provide a powerful new method for the early detection of glaucoma. Although directional reflectance is a major source of variability for RNFL reflectance measurements [24][25][26], none of the in vivo studies took this into account.…”

“…For instance, Optical Coherence Tomography (OCT), which is widely used in clinical diagnosis of glaucoma, measures RNFL thickness by identifying the RNFL as a highly reflective layer under the retinal surface, with change of thickness used as a biomarker for axonal damage [1][2][3][4]. Recent studies of glaucomatous retinas reveal that a decrease of RNFL reflectance occurs prior to thinning of the RNFL [5][6][7][8][9][10][11]. Glaucoma damages retinal ganglion cells (RGC) and their axons [12][13][14][15][16][17][18][19][20].…”

“…Many of these RNFL reflectance studies were performed in vivo in humans and other primates and RNFL reflectance was derived from OCT images [5,6,[8][9][10]. The reflected signal in an OCT image is related to the scattering properties of the RNFL and, in addition, depends on other factors, such as ocular media opacities and the intensity of the light beam that reaches the retina.…”

“…The reflected signal in an OCT image is related to the scattering properties of the RNFL and, in addition, depends on other factors, such as ocular media opacities and the intensity of the light beam that reaches the retina. To compensate the effects of these factors, the ratio of the OCT reflected signal within the RNFL to a reference layer was often calculated to normalize the reflectance of the RNFL alone [5,6,[8][9][10]. Although this normalization may eliminate the effect of other factors on estimations of RNFL reflectance, directional reflectance of the RNFL could be a major source of variability for measured RNFL reflectance [24][25][26], and none of the in vivo studies took this variable into account.…”

Individual A-Scan Signal Normalization Between Two Spectral Domain Optical Coherence Tomography Devices

“…22,23 Many studies solved the A-scan profile intensity variation by normalizing the RNFL signal intensity to the brightest layer in the OCT image, usually the RPE, as a preprocessing step before thickness measurement to reduce the variation. Those methods are simple and easy to implement, and can be applied to the entire OCT image.…”