OCT imaging and analysis<\/p>\n
The OCT imaging protocol for macula (Fig.\u00a02<\/a>) was composed of 25 raster scans (20\u00b0\u00d7 20\u00b0) and a linear 30\u00b0 B-scan centered at the fovea. Choroidal thickness and volume were determined in the same manner as described in detail in our previous studies34<\/a>,37<\/a>. Briefly, the internal limiting membrane (ILM) and Bruch\u2019s membrane (BM) were detected automatically, while the choroidal\u2013scleral junction (CSJ) was manually marked on each scan. Retinal parameters were calculated from the ILM to the BM, and choroidal parameters – from the BM to the CSJ. Average thickness and volume maps were created automatically according to the conventional ETDRS grid with nine subfields including the central macular subfield (central field within a 500 \u00b5m radius)38<\/a>. Values of the choroidal parameters were calculated by subtracting retinal parameters from the summed retinal and choroidal parameters. The subfoveal choroidal thickness (SFCT) was defined as the distance between the BM and the CSJ at the fovea and was measured automatically. In our study, we used the term \u2018subfoveal\u2019 to specifically refer to the central point directly beneath the fovea (i.e., a single-point measurement), whereas \u2018central macular\u2019 referred to the 500\u00a0\u03bcm radius region centered on the fovea.<\/p>\n Fig. 2<\/b> Analyzed choroidal and retinal regions superimposed on the fundus image.<\/p>\n CVI assessment was performed according to the protocols of Sonoda et al.39<\/a> and Agrawal et al.13<\/a>, with minor modifications as detailed in a step-by-step description with screenshots in our previous publication34<\/a>. Binarization of the macular choroidal area was performed by two researchers (AZ and BP) (Fig.\u00a03<\/a>). The macular region was scanned using a single horizontal line scan (30\u00b0) centered on the fovea, with 100 frames averaged in a B-scan. The measurement area was defined as 1000\u00a0\u03bcm in width and centered on the fovea. The total choroidal area (TCA) was selected from the outer boundary of the RPE\u2013BM layer to the CSJ using the polygon selection tool. The images were converted into 8-bit images to allow for the application of the Niblack auto local threshold tool. The binarized images were reconverted into RGB images to allow for the color threshold tool to be used for selecting dark pixels that represented vascularized areas. The luminal area (LA) and TCA were measured, while the stromal area (SA) was calculated by subtracting the LA from the TCA. The CVI was determined as the ratio of the LA to the TCA (%). The parameters were assessed by two experienced researchers (AZ and BP) at the same time of the day (8\u201310 am) in both groups, with the averages from 2 measurements included in the analysis. Any doubts were resolved through discussion. The repeatability of measurements between observers was determined using the intraclass correlation coefficient (ICC) and overall agreement. The ICC was high, as shown in Table\u00a07<\/a>.<\/p>\n Fig. 3<\/b> Image binarization of the choroid. a<\/b> Total choroidal area marked on the analyzed enhanced depth imaging optical coherence tomography (EDI-OCT) scan. The horizontal white line length equals 1000\u00a0\u03bcm. b<\/b> The Niblack auto local threshold tool applied. c<\/b> The color threshold tool applied highlighting the luminal area. d<\/b> Overlay of luminal area on the original OCT scan.<\/p>\n Table 7 Intraclass correlation coefficient of choroidal parameters measurements between two raters in two groups.<\/b><\/p>\n According to the related literature40<\/a>, the ICC values below 0.5 are indicative of poor reliability, the values between 0.5 and 0.75 indicate moderate reliability, the values between 0.75 and 0.9 indicate good reliability, and the values greater than 0.90 indicate excellent reliability.<\/p>\n With respect to ocular magnification correction, axial and transverse measurements must be handled separately. Axial depth on the Heidelberg Spectralis is optically calibrated for tissue refractive indices (e.g., choroidal thickness), so axial scaling is independent of ocular magnification and requires no further correction41<\/a>. In contrast, the Spectralis does not auto-correct lateral scaling for individual axial lengths42<\/a>. However, because our PPH and control groups did not differ in axial length, corneal curvature, or spherical equivalent (Table\u00a01<\/a>; all p\u2009>\u20090.05), any residual magnification error is likely to be minimal and unlikely to bias between-group comparisons. Moreover, our primary lateral metric,\u00a0the CVI,\u00a0is the ratio of LA to TCA\u00a013<\/a>, so a uniform scaling factor applies equally to numerator and denominator and thus has no effect on the CVI. Together, these factors render magnification error minimal and non-differential; therefore, we omitted individual ocular magnification corrections.<\/p>\n Post-hoc power calculation<\/p>\n The relatively small number of patients is due to the rarity of PPH and the sample size was partly determined by the number of participants who had met our inclusion criteria.<\/p>\n The post-hoc power calculation, assuming \u03b1\u2009=\u20090.05 and using the means and SDs obtained in the study for the comparison of PPH and controls patients, resulted in a power (1-\u03b2) of 0.96 for central macular choroidal thickness, volume, and SFCT, and 0.90 for total choroidal volume. The power calculation for the CVI equaled 0.16.<\/p>\n Statistical analysis<\/p>\n![\"figure](\"https:\/\/www.europesays.com\/ie\/wp-content\/uploads\/2025\/08\/41598_2025_17425_Fig2_HTML.png\")
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