Many ocular factors contribute to the incidence of artifacts. Myopic patients are not represented in the normative database even though it is an important cause of errors or misinterpretation.
Reviewed by David S. Greenfield, MD
An assessment of the quality of optical coherence tomography (OCT) scans can impact clinical decisions related to the diagnosis of glaucoma and its progression, according to David S. Greenfield, MD. Because imaging artifacts are common, found in as many as 20% of nerve fiber layer scans and almost 30% of scans involving the macular region, particularly in those patients that have coexisting macular pucker, clinicians should pay careful attention to all aspects of their scans, said Dr. Greenfield, Douglas R. Anderson distinguished professor of Ophthalmology and vice chair for academic affairs at the Bascom Palmer Eye Institute, University of Miami Miller School of Medicine.
A number of ocular factors contribute to the incidence of artifacts, a frequent one being that highly myopic patients are not represented in the normative database despite the fact that high myopia is known to be an important cause of errors or misinterpretation, Dr. Greenfield said. Other factors to watch for include significant ocular surface disease, opacification in the lens or vitreous, and peripapillary atrophy.
Four parts of the scan to study closely are signal strength (refer to the manufacturer’s specifications); the thickness map (look for the presence or absence of shadowing artifacts); the deviation map (has the optic disk been automatically and accurately delineated, and can any subtle features related to motion artifacts be detected); and individual tomograms (search for signs of segmentation failure).
Monitoring the recommended individual signal-to-noise ratios is clinically relevant because a reduction in the signal strength will not only affect the estimation of retinal fiber layer (RNFL) thickness, but is also highly associated with an increase in the measurement’s variability and failure of the measurement algorithm (as demonstrated in the figure).
Details in the imaging
RNFL imaging artifacts can be very subtle, arising from causes such as a horizontal translation of the blood vessels due to eye movement during imaging acquisition. Other common problems are blink artifacts and shadowing artifacts from vitreous opacities.
Eyes with severe pathologic myopia often have what Dr. Greenfield refers to as the “trifecta,” an incorrect axial alignment with shadowing artifacts, poor delineation of the optic disc border, and clear evidence of segmentation failure, all contributing to RNFL measurements that are “off the chart.”
Macular artifacts are even more common than RNFL artifacts and can be found in eyes with pathology on the surface of the macula, intraretinal edema, and even associated with subretinal pathology such as choroidal neovascularization, confounding the GCIPL measurement algorithm. Extremely large regions of macular pathology can also adversely affect the RNFL thickness algorithm and resemble glaucomatous RNFL atrophy.
David S. Greenfield, MD
P: 516/515-1500 E: [email protected]
This article was adapted from Dr. Greenfield’s presentation at the 2019 meeting of the American Glaucoma Society. He did not report any relevant financial disclosures.