Optical coherence tomography scan circle location and mean retinal nerve fiber layer measurement variability.
OBJECTIVE
To investigate the effect on optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) thickness measurements of varying the standard 3.4-mm-diameter circle location.


METHODS
The optic nerve head (ONH) region of 17 eyes of 17 healthy subjects was imaged with high-speed, ultrahigh-resolution OCT (hsUHR-OCT; 501 x 180 axial scans covering a 6 x 6-mm area; scan time, 3.84 seconds) for a comprehensive sampling. This method allows for systematic simulation of the variable circle placement effect. RNFL thickness was measured on this three-dimensional dataset by using a custom-designed software program. RNFL thickness was resampled along a 3.4-mm-diameter circle centered on the ONH, then along 3.4-mm circles shifted horizontally (x-shift), vertically (y-shift) and diagonally up to +/-500 microm (at 100-microm intervals). Linear mixed-effects models were used to determine RNFL thickness as a function of the scan circle shift. A model for the distance between the two thickest measurements along the RNFL thickness circular profile (peak distance) was also calculated.


RESULTS
RNFL thickness tended to decrease with both positive and negative x- and y-shifts. The range of shifts that caused a decrease greater than the variability inherent to the commercial device was greater in both nasal and temporal quadrants than in the superior and inferior ones. The model for peak distance demonstrated that as the scan moves nasally, the RNFL peak distance increases, and as the circle moves temporally, the distance decreases. Vertical shifts had a minimal effect on peak distance.


CONCLUSIONS
The location of the OCT scan circle affects RNFL thickness measurements. Accurate registration of OCT scans is essential for measurement reproducibility and longitudinal examination (ClinicalTrials.gov number, NCT00286637).
Gabriele
Michelle L
ML
UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
Ishikawa
Hiroshi
H
Wollstein
Gadi
G
Bilonick
Richard A
RA
Townsend
Kelly A
KA
Kagemann
Larry
L
Wojtkowski
Maciej
M
Srinivasan
Vivek J
VJ
Fujimoto
James G
JG
Duker
Jay S
JS
Schuman
Joel S
JS
D000328:Adult; D000465:Algorithms; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D009412:Nerve Fibers; D009898:Optic Disk / Q000033:anatomy & histology*; D011446:Prospective Studies; D012165:Retinal Ganglion Cells / Q000166:cytology*; D041623:Tomography, Optical Coherence