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G. Somfai, C.E. Denis, H.M. Salinas, Z.Z. Nagy, J. Németh, C.A. Puliafito, D. Cabrera; Evaluation of Potential Pitfalls Related to Operator Errors During OCT Image Acquisition . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2631.
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© ARVO (1962-2015); The Authors (2016-present)
To discuss and illustrate how retinal structure information on OCT images is affected by potential artifacts related to the OCT operator errors.
All OCT data (8 normal eyes) was collected by a single operator on a StratusOCTTM device. Standard 7 mm long horizontal OCT scans were acquired under specific error’s operator related artifacts. These artifacts included: defocusing, depolarization and a combination of defocusing and depolarization. Artifacts associated to the patient’s eye orientation relative to the imaging system were modeled by decentration of the fixation point (downward gaze). The OCT raw data were exported and analyzed using an automated computer algorithm of our own design capable of segmenting the various cellular layers of the retina. Then, mean reflectance and average thickness of the automatically extracted retinal sublayers (NFL, GCL+IPL, INL, OPL and ONL) was measured on the corresponding OCT images. The misleading information on false color images was also explored taking into account the information present in the grayscale format of the same images.
A marked decrease in reflectance was observed due to defocus artifact in all retinal sublayers, while depolarization resulted in a less marked decrease. In the case of average thickness, a greater effect of depolarization was observed on measurements compared to defocus. The two artifacts together had the greatest altering effect on all measurements in both cases. Decentration had only slight influence on reflectance and thickness data. As expected, a loss of retinal structure information on OCT images was observed as a result of the error’s operator related artifacts. Grayscale OCT images showed more clearly these losses than false color images, demonstrating a more accurate visual representation of the scanned retinal structure.
Our results show that both defocusing and depolarization have a substantial effect on the quality and precision of information extracted from OCT images. As visual analysis of the scan results in clinical practice is very similar to the automated algorithm, optimal settings are necessary. To avoid pitfalls the operator should always check correct focusing and optimal polarization setting for the scanning. An awareness of these pitfalls and possible solutions is crucial for avoiding misinterpretation of OCT images.
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