Quantitative Measurements of Retinal Nerve Fiber Layer (RNFL) Thickness Decay Along the Retinal Nerve Fiber Bundle Path (RNFBP) With Three-Dimensional (3D) Spectral Domain Optical Coherence Tomography (SD-OCT)

Abstract

 

Purpose:

 

Previously we reported the RNFL thickness decay along straight radial lines without taking the natural curvature of the RNFBP. The purpose of this study was to revisit the RNFL thickness decay measurements along the individual RNFBP pattern on 3D SD-OCT images.

 

Methods:

 

Forty-six eyes of 46 healthy subjects were scanned with 3D SD-OCT (Cirrus HD-OCT; Carl Zeiss Meditec, Inc., Dublin, CA; ONH Cube 200x200 scan protocol). Two major RNFBPs (superior and inferior) were manually traced as two parabolic curves passing the disc center on two-dimensional RNFL thickness maps generated from 3D SD-OCT images. RNFBPs in the remaining area were automatically generated by interpolating the major RNFBP curve in either superior or inferior hemi-field assuming the horizontal meridian was a straight line. RNFL thickness was then re-sampled along RNFBPs at 1 degree interval (total 360 RNFBPs).

 

Results:

 

NFL thickness data showed consistent characteristics across all subjects: a plateau of high NFL thickness was seen near the disc margin in inferior quadrant, while NFL thickness decayed without a plateau in the superior, temporal and nasal quadrants, just like the previously reported results sampled along the straight radial lines (Figure). Linear model was used to fit the decay. In the pair-wise comparison, RNFL decay slopes were statistically significantly different to each others in 4 quadrants except for nasal comparing with superior quadrants.

 

Conclusions:

 

RNFL decay characteristics were confirmed with the new model along the individual RNFBP. This method may permit advanced research about spatial progression of glaucomatous damage.  

 

Keywords: imaging/image analysis: non-clinical • image processing • nerve fiber layer