To the Editor:

We have read with great interest the article entitled “Assessments of Vessel Density and Foveal Avascular Zone Metrics in Multiple Sclerosis: An Optical Coherence Tomography Angiography Study” by Yilmaz et al. [1]. They reported that vessel densities (VD) of both macular and peripapillary areas were reduced in multiple sclerosis (MS) patients, but the foveal avascular zone (FAZ) metrics (area, perimeter and circularity index-CI-) did not significantly differ between the MS and healthy groups.

We have just analyzed the OCT results yielded by Cirrus AngioPlex (Carl Zeiss Mediatec, Dublin, CA, USA) in 12 MS patients with monocular optic neuritis recruited before COVID pandemic. Similar to Yilmaz et al. [1]. the VDs were significantly reduced in comparison with 12 healthy controls matched by age and gender, and the mean area and perimeter of FAZ did not differ between MS and controls. By contrast, the mean CI of FAZ was significantly reduced in the MS (0.68 ± 0.06) compared to controls (0.73 ± 0.06; p = 0.012) despite the small size sample.

Although Yilmaz et al. did not investigate differences between MS + ON and healthy eyes, (0.47 vs 0.49, respectively), this difference was small (0.02). We like to emphasize that the mean CI for healthy eyes obtained by Yilmaz et al. was 0.24 smaller than ours (0.49 vs 0.73). This discrepancy could be attribute to differences between OCT-A devices (Cirrus AngioPlex vs RS-3000 Advance Nidek). Although both OCT-A devices have shown good reproducibility in the FAZ assessment, their measurements are not interchangeable [2]. Differences in values and diagnostic accuracy in MS between several OCT devices are well known [3, 4].

A decrease in circularity index represents a disruption of the parafoveal capillary network with focal losses and could be a marker of early vascular damage. Despite the small sample size evaluated, as the other structural and vascular parameters are consistent with previously reported findings [1, 5], we consider that a significant reduction of CI in the FAZ deserves more research. Larger longitudinal studies are required to improve our knowledge about the role of CI as a potentially useful tool in MS patients.