OCTA is a non-invasive diagnostic method of assessing the retinal and choroidal vascular layers. It is currently suggested that the corollary atrophy of the choriocapillaris resulting from its hypoperfusion, as first reported as a loss of choriocapillary homogeneity on OCTA by Khan et al., causes the consecutive destruction of RPE and photoreceptors which leads to vision loss [20, 22].
In our study, OCTA images showed a clear atrophy of the choriocapillaris in 100% of our patients as it was corroborated by EDI-OCT.
The atrophic areas in the RPE represented by OCTA, greatly and reliably corresponded to the same areas seen in FA, ICGA and FAF. However, the extent of choriocapillaris atrophy was greater than the atrophic areas of the RPE, which can be explained by the choroidal origin of the disease. These atrophic areas are also referred to as choriocapillaris hypoperfusion in some case reports, where the same phenomenon could be observed. These same areas were hypoautofluorescent in all eyes, since the disease was inactive. According to the literature, hypoautofluorescent lesions with hyperautofluorescent borders were to be expected in active disease [20, 21, 22]. The study of Montorio et al found a complete loss of detectable flow in 2 active eyes with SC, whereas choroidal vessel rarefaction and loss of choriocapillaris could be seen in inactive eyes (20 eyes) .
The pathophysiology of the 3 different forms of SC remains unclear. No differences could be seen between these forms in all imaging modalities and none have been described to date.
Although OCTA proved to be useful for imaging of the choriocapillaris, the representation of the deeper choroidal layers contained challenges. The Sattler’s layer examination did not reveal much information. Whereas a conversion from a “black-on-white” effect to a “white-on-black” effect could be seen in the Haller’s layer below the atrophic regions as demonstrated in the literature. This effect remains to be explained . Current theories explain it as a consequence of the physics of wave propagation through the different retinal and choroidal layers, in that the propagation through the atrophic lesions is not hampered by so many layers/cells as it is in the neighbor regions, causing this “white-on-black” effect much later if at all. Another hypothesis is that this effect can be a consequence of the absence of or different flow (e.g. too slow or too fast) or characteristics of the vessels and surrounding tissues within these regions due to inflammation as first proposed by Montorio et al. .
The standard adjustments of the retinal and choroidal layers did not correspond very well with the structures of deeper layers.
SE’s were the main problem in patients with macular edema or scarring so that the interpretation of these images was difficult and led to the exclusion of one eye. Statistically significant differences of mean BCVA could be seen between patients with and without SE’s which may be due to a missing fixation of the patients and a longer examination time of OCTA. The newer software with faster examination time and auto-fixation program will overcome some of these problems.
One last disadvantage concerned the lack of detection of fluid dynamics (pooling, staining, leakage) even though one could argue that this provided in-depth-selective images, free of masking affects.
Although this study’s conclusions are limited by the numbers of eyes evaluated and there is missing knowledge of the pathophysiology of SC, lesions presenting in the disease can be visualized using OCTA as reliably as the current gold-standard techniques (ICGA, FA and FAF). The use of OCTA offers a non-invasive and high-resolution means to assess the disease in three dimensions, allowing for the ability to precisely locate the atrophic area. Furthermore, OCTA may help determine if the disease is in an active phase via, for example, identification of CNV (a known complication of this and other entities) even when ICGA is not able to do so, as reported by Mandadi et al. and as observed in tuberculous serpiginous-like Choroiditis. In this study, it was not possible to prove this hypothesis as all enrolled patients were in inactive disease stages .
Additionally, analogies could be seen between the changes of the choriocapillaris and choroid caused by SC and geographic atrophy. These included a focal flow impairment and rarefaction in the choriocapillaris beneath the area of the atrophic lesions, which is argued to represent non-perfused or hypo-perfused choroidal vessels with non-detectable flow in the literature [27, 28, 29].
OCTA is clinically valuable in the management of patients with SC. Even though the representation of the lesions with OCTA corresponded to the ones seen in the FA/ICGA/FAF/EDI-OCT, the inclusion of this tool in a multimodal approach for the diagnosis and management of SC should be considered.