Regarding the diagnosis of SGF, according to a previous study, the mean SGI was 0.649 in SGF+ and 0.578 in SGF−.
6 Here, the mean SGI was 0.636 in the SGF+ group and 0.589 in the SGF−. Furthermore, the CVAI differed earlier between the SGF− and SGF+ groups than did the SGI. ROC curve analyses and AUCs indicated that the CVAI was a good biomarker at 1 month and an excellent biomarker at 3 and 6 months, whereas SGI was poor at 1 and 3 months, and only a good biomarker at 6 months. Therefore, as a predictive biomarker, CVAI is more sensitive than SGI in the early stage of VKH disease. In the evaluation of CVAI, each color fundus photograph was separated into 8-bit RBG (red, green, blue) components, and the R-component image was used in the detection of choroidal vessels. The R component was also used for SGI calculation, however, not to evaluate the choroidal vessels but rather the redness of the color fundus photographs, as determined by both the choroidal and retinal vessels. Therefore, we propose that during the development of the SGF, choroidal vascular-related changes occur before the fundus becomes reddish. The orange-red discoloration of SGF is due to depigmentation of the inflamed choroid,
18 and the choroidal stroma contains a large number of melanocytes with melanin.
21 Miura et al. provided objective evaluation of melanin loss in chronic VKH disease by using PS-OCT, and eyes with SGF showed a lack of choroidal melanin and the preservation of melanin in the retinal pigment epithelium.
6 Thus, the decrease in melanin content may increase the transparency of choroidal vessels. We suggest that in the process of decreasing choroidal melanin, the medium and large choroidal vessels are the first to become more visible, and second that redness develops because of further thinning of the choroidal stroma and severe decrease in melanin, causing the CVAI to differ between the SGF− and SGF+ groups before SGI differences occur. Furthermore, of 8 patients with SGF, only 1 developed the SGF at 3 months after treatment, but the other 7 patients progressed to the SGF by 6 months. As described above, CVAI in SGF+ patients already tended to be greater than in SGF− patients by 1 or 3 months. Therefore, CVAI may indicate the possibility of developing into SGF, although the color fundus pictures do not yet show any SGF at that time. Moreover, CVAI changed more over time than did SGI. CVAI was approximately 2.6 times greater at 3 months (0.12 ± 0.026) and 2.5 times greater at 6 months (0.11 ± 0.029) than it was at baseline (0.046 ± 0.019), whereas SGI was only approximately 10% greater at 6 months (0.64 ± 0.055) than at baseline (0.59 ± 0.040).