Optical Coherence Tomography Scan Circle Location Affects Mean Retinal Nerve Fiber Layer Thickness Measurements

Abstract

 

Purpose:

 

To investigate the effect of the standard 3.4mm diameter circle location on mean retinal nerve fiber layer (RNFL) thickness measurements using high-speed ultrahigh resolution optical coherence tomography (hsUHR-OCT).

 

Methods:

 

Fifteen healthy subjects had hsUHR-OCT raster scanning of the optic nerve head (ONH) region (501x180 samplings in a 6x6 mm region around the ONH; scan time 3.84 seconds). RNFL thickness was measured on this three-dimensional dataset using a software program of our own design. RNFL thickness was resampled along 3.4mm diameter circles starting at the ONH center, then along 3.4mm diameter circles shifted horizontally (x-shift) and vertically (y-shift) up to ±500µm with a 100µm interval. All measurements were normalized to mean thickness at the starting position for all subjects to permit an intersubject comparison. A range of circle placement shifts that corresponded to the variability inherent to the commercial device (2.68µm) was determined.

 

Results:

 

Mean RNFL thickness tended to decrease with both positive and negative x- and y- shifts (quadratic fit, R²=0.40 and R²=0.43, respectively, both p<0.0001) (Figure). The ranges of shifts that caused a decrease of 2.68µm from the maximum value on the fitted quadratic were ±320µm for the horizontal shift and ±280µm for the vertical shift.  

 

Conclusions:

 

Scan circle location affected mean RNFL thickness measurements. However, within a shift range of ~±300µm, the change in mean RNFL thickness was within the measurement error reported for the commercial unit.

 

Clinical Trial:

 

www.clinicaltrials.gov NCT00343746

 

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • nerve fiber layer • imaging/image analysis: clinical