Abstract
PurposeOptical coherence tomography (OCT) allows quantification of the thickness of the retinal nerve fibre layer (RNFL) thickness, a potential biomarker for neurodegeneration. The estimated annual RNFL loss in multiple sclerosis amounts to 2 μm using time domain OCT. The recognition of measurement artifacts exceeding this limit is relevant for the successful use of OCT as a secondary outcome measure in clinical trials.MethodsProspective study design. An exploratory pilot study (ring and volume scans) followed by a cohort study (1,980 OCT ring scans). The OCT measurement beam was placed off–axis to the left, right, top and bottom of the subjects pupil and RNFL thickness of these scans were compared to the centrally placed reference scans.ResultsOff–axis placement of the OCT measurement beam resulted in significant artifacts in RNFL thickness measurements (95%CI 9μm, maximal size of error 42μm). Off–axis placement gave characteristic patterns of the OCT live images which are not necessarily saved for review. Off–axis placement also causes regional inhomogeneity of reflectivity in the outer nuclear (ONL) and outer plexiform layers (OPL) which remains visible on scans saved for review.ConclusionOff–axis beam placement introduces measurement artifacts at a magnitude which may mask recognition of RNFL loss due to neurodegeneration in multiple sclerosis. The resulting pattern in the OCT live image can only be recognised by the technician capturing the scans. Once the averaged scans have been aligned this pattern is lost. Retrospective identification of this artifact is however possible by presence of regional inhomogeneity of ONL/OPL reflectivity. This simple and robust sign may be considered for quality control criteria in the setting of multicentre OCT studies. The practical advice of this study is to keep the OCT image in the acquisition window horizontally aligned whenever possible.
Highlights
Accurate assessment of neurodegeneration is important for prognosis and evaluation of neuroprotective treatment strategies
With temporal/nasal off-axis placement the path-length for light reflected from the nasal and temporal proportion of the optic nerve head (ONH) differ such that the optical coherence tomography (OCT) live B–scan appears to be tilted in opposite directions (Figure 1 B&C)
The resulting measurement artifacts in per sector ranged from 25 mm for the PMB in the temporal sector to +7 mm (Figure 1 D&E)
Summary
Accurate assessment of neurodegeneration is important for prognosis and evaluation of neuroprotective treatment strategies. Spectral–domain (SD) optical coherence tomography (OCT) allows to quantify RNFL thickness changes with a precision in the range of 1.14–2.39 mm [1]. It has been proposed that OCT measurements of the retina may provide promising primary outcome measures for neuroprotective treatment trials in multiple sclerosis (MS) [2,3]. The estimated annual loss of RNFL thickness in MS is about 1– 2 mm [4] Longitudinal, observational studies are underway to validate these findings with the newer, high resolution SD–OCT technology. As with other imaging studies of neurodegeneration, [2] qualified assessment of the OCT will become a requirement for high quality multicentre studies. At present there are no validated reading centre criteria available for the assessment of OCT scans in MS. A review of the literature shows that the most frequently reported errors are related to boundary line errors, poor signal strength or bad placement of the ring scan at the optic nerve head (ONH) [5] To the best of our knowledge, the potential artifact introduced by off–axis placement of the measurement beam is not known and is investigated in this study
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
