A novel and faster method of manual grading to measure choroidal thickness using optical coherence tomography

PurposeChoroidal thickness (CT) measurements are typically obtained from manual segmentation of optical coherence tomography (OCT) B-scans. This method is time-consuming. We aimed to describe a novel and faster technique to obtain CT measurements.Patients and methodsIn a prospective cohort study of 200 healthy eyes, Spectral-Domain OCT with enhanced depth imaging were performed with the Spectralis OCT using standardised imaging protocols. The OCT scans were independently graded by reading centre-certified graders. The standard method of manual adjustment of segmentation boundaries was performed. The new method consisted of adjusting the lower segmentation line to the choroid-scleral boundary to generate the combined choroid-retina thickness, and subtracting the original retinal thickness (RT) from it to measure CT. Mean CT in the respective Early Treatment Diabetic Retinopathy Study (ETDRS) subfields was measured via the two methods, and were compared with intraclass correlation coefficients (ICC) and Bland-Altman plots.ResultsThe mean central subfield CT was 324.4 μm using the original method, compared with 328.8 μm using the new method, with a mean difference of 4.5 μm (range: -14.0 to +4.0 μm; P<0.001), and ICC for agreement of 0.9996 (P<0.001). Similar comparability was achieved for mean CT across other ETDRS subfields, with mean differences ranging from 2.4 to 3.7 μm, and ICCs ranging from 0.9993 to 0.9995 (all P<0.001).ConclusionsMean CT can be measured by subtracting the original RT from the combined choroid-retina thickness. Only one segmentation line needs to be adjusted, instead of two, reducing time required for segmentation. This method is faster and reliable.