Automated Method Outperforms Manual in Measuring Foveal Avascular Zone Area

The modified Kanno-Saitama macro (mKSM) method demonstrated superiority over using manual measurements for measuring foveal avascular zone (FAZ) area, according to research published in Archivos de la Sociedad Española de Oftalmología.

Researchers developed and examined an automated method to measure the FAZ area in healthy eyes on Heidelberg Spectralis Optical Coherence Tomography Angiography (HS-OCTA). This method, termed mKSM, is an upgrade of the original Kanno-Saitama macro (KSM) approach. 

The team enrolled 29 eyes of 25 participants (mean age 36.6 years, 16 women) who underwent HS-OCTA at a single center between November 2019 and January 2020. They included all images regardless of the quality. The mKSM processed macular data on the superficial vascular plexus, intermediate capillary plexus (ICP) and deep capillary plexus. The investigators measured the FAZ area twice automatically using the mKSM and KSM and twice manually via 2 independent examiners. 

After analyzing 174 images, researchers noted that KSM failed to measure 31% of images correctly (14% misidentified, 17% over measured), while mKSM successfully measured all of them. The intrascan intraclass coefficient for manual coefficient ranged from 0.948 to 0.993, while the intrascan intraclass coefficient for the mKSM method was 1. 

Although the difference between human examiners is smaller than between human examiners and mKSM based on Bland-Altman plots, the scatterplots revealed a strong correlation between human and automatic measurements. The most optimal results are obtained in the ICP, according to the study.  

“The use of the mKSM method for the measurement of the FAZ area implies more reliability, reproducibility and speed in measurements compared to human manual measurements,” according to the researchers. “While a human examiner takes about 1 minute to measure the FAZ area manually and its value changes with each measurement, the mKSM takes less than 3 seconds and its value is always the same for the same OCTA image.”

Study limitations include the relatively small sample size, the inclusion of only young and healthy patients, possibility of volunteer bias, and single center design.

Disclosure: One study author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures. 

Reference

Gutierrez-Benitez L, Palomino Y, Casas N, Asaad M. Automated measurement of the foveal avascular zone in healthy eyes on Heidelberg spectralis optical coherence tomography angiography. Arch Soc Esp Oftalmol. Published online May 3, 2022. doi:10.1016/j.oftale.2022.01.004