First Author: R.Schwartz UK
Co Author(s): A. Bagchi A. Dubis P. Hykin P. Vasilopolus S. Sivaprasad
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To demonstrate the size of the foveal avascular zone (FAZ) in the four retinal vascular layers delineated by the Heidelberg optical coherence tomography angiography (OCT-A) machine and measure the interobserver variability in measurement of FAZ dimension.
Healthy volunteers with no ocular pathology were examined using the Heidelberg OCT-A machine at the clinical research facility at Moorfields Eye Hospital.
Both eyes of each subject were examined using the OCT-A machine. The generated images were analyzed using ImageJ software. Two graders measured the FAZ area in each layer (superficial vascular plexus (SVP) – From the internal limiting membrane (ILM) to the inner plexiform layer (IPL), deep vascular plexus (DVP) - from the IPL to the outer plexiform layer (OPL), nerve fibre layer (NFL) – From the ILM to the NFL, ganglion cell layer (GCL) – From the NFL to the GCL, IPL-INL – from the IPL to the inner nuclear layer (INL), and INL-OPL – from the INL to the OPL. Each measurement was completed three times by each grader.
Forty-seven eyes of 25 subjects (9 male, 16 female) were included in the study. The FAZ area was not clearly delineated in the NFL and GCL layers, and therefore was not measured. The mean FAZ area in each layer (mm2) was 0.323 ± 0.1, 0.323 ± 0.1, 0.316 ± 0.1, 0.326 ± 0.1 for the SCP, DCP, IPL-INL, and INL-OPL layers, respectively. There was a high level of agreement between measurements of FAZ size of the different layers (intraclass correlation coefficient (ICC) 0.996-0.999) There was no statistically significant difference between fellow eyes in the FAZ size of each layer. The interobserver agreement between graders and the intraobserver agreement between measurements for each grader were high (ICC > 0.98, ICC ≥ 0.998, respectively).
Manual measurement of FAZ dimensions using OCT-A is a noninvasive and reliable method for quantifying FAZ. The new Heidelberg OCT-A machine allows more segmentation options for retinal vascular layers than was previously available with other devices. In healthy patients, there was a very high correlation between FAZ sizes among the different layers. Further studies on pathologic conditions are required to assess the significance of the additional segmentation options. The interobserver and intraobserver agreement for FAZ measurements were excellent, suggesting that such measurements done on this machine may be a useful and reliable tool in the assessment of FAZ area.