Circle versus Raster Scans Using Cirrus HD-OCT - Reproducibility of Retinal Nerve Fiber Layer Thickness Measurements

Abstract

 

Purpose:

 

Spectral domain optical coherence tomography (SDOCT) provides high-speed, high-resolution images and permits the acquisition of three-dimensional (3D) raster scans. The purpose of this study was to compare the reproducibility of circumpapillary retinal nerve fiber layer (RNFL) thickness measurements obtained from circle scans with circular measurements extracted from raster scans.

 

Methods:

 

Fifty healthy subjects (100 eyes) were scanned with SDOCT Cirrus HD-OCT: Carl Zeiss Meditec, Dublin, CA. All subjects had ≥ 3 circumpapillary scans centered at the optic nerve head (ONH) and ≥ 3 raster scans of the ONH region. RNFL thickness was automatically extracted from the 3D data along a circle with a diameter identical to that of the circle scan.Linear mixed effects models were used to determine reproducibility (presented as standard deviation (SD)) for average, quadrant and clock-hour RNFL thickness.

 

Results:

 

RNFL measurements from the raster scan were statistically significantly thinner than those obtained from the circle scan for all tested parameters. The table summarizes the mean and SD with their 95% confidence intervals for average and quadrant parameters. Raster derived clock-hour measurements had a smaller SD in the range of 45.0%-67.8% (clock-hours 8 and 10, respectively) as compared to circle scan SD. The differences in SD for average and all sectoral measurements were statistically significant.

 

Conclusions:

 

Circumpapillary RNFL measurements extracted from raster scans of the ONH region had significantly better reproducibility than actual physical circumpapillary scans. While the physical circumpapillary scan is prone to inadvertent eye motion, extracting measurements from the raster scan permits a more consistent sampling of the tissue at an identical location from scan to scan.  

 

Clinical Trial:

 

www.clinicaltrials.gov NCT 00343746

 

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