Importance: All automated image quality indicators for en face optical coherence tomography angiography (OCTA) images require gold standard validation for determining optimum thresholds.
Background: A manual grading system (gold standard) for OCTA images was validated and compared to two automated image quality indicators: signal strength index (SSI) and scan quality index (SQI) generated by different software versions of the Optovue OCTA device.
Design: Retrospective cross-sectional study.
Participants: A total of 52 eyes of 52 healthy individual and 77 eyes of 51 patients with retinal vascular diseases.
Methods: A total of 129 OCTA images of the superficial vascular plexus were graded manually by three independent examiners. Each image was assigned grades 1 to 4 (1-2, unacceptable; 3-4, acceptable) masked to the software-generated quality indicators.
Main outcome measures: Inter-grader agreement and comparison of the utility of SSI and SQI in discriminating between acceptable and unacceptable OCTA images.
Results: There was a substantial agreement between the three graders (κ = 0.63). Mean SSI and SQI was significantly different between acceptable and unacceptable images (P < .001). SQI outperformed SSI in separating acceptable from unacceptable images (areas under the receiver operating characteristic curve: 0.87 vs 0.80) and the optimum cut-off was ≥7 for SQI and ≥70 for SSI for acceptable images. Up to 30% of images with quality indicators reaching the optimum SQI and SSI cut-off thresholds still had unacceptable quality on manual grading. Unacceptable images were found in 33% and 66% of healthy and diseased eyes, respectively.
Conclusions and relevance: SQI is closely related to manual grading but we caution reliance on the optimized threshold to determine image quality. SQI is superior to SSI in discriminating between acceptable and unacceptable images.
Keywords: grading system; image quality; optical coherence tomography angiography; retinal angiography; retinal vascular disease.
© 2019 Royal Australian and New Zealand College of Ophthalmologists.