The mirror artifact effect on OCTA reconstructions of patients with high myopia

Abstract

Optical coherence tomography angiography (OCTA) is a useful technique for the noninvasive study of retinal vascularization; nevertheless artifacts may occur, especially in myopic patients, and this may lead to diagnostic issues. Four myopic patients (2 males, mean age 45 years, axial length 27–30 mm) were analyzed using swept source OCT Triton Topcon (DRI Triton; Topcon, Tokyo, Japan) and 3 × 3, 4.5 × 4.5, and 9 × 9 mm scans were obtained. Topcon Image6 software was used to segment retinal layers and to extract both OCTA reconstructions of superficial, deep and choriocapillary plexa, and en face images. OCT analysis clearly revealed retinochoroidal structures, including both inner and outer choroidal segments, the external limiting membrane, and the retinal pigment epithelium in all patients. OCTA analysis was able to reconstruct superficial, deep and choriocapillary plexa in all patients. On 9 × 9 OCTA and en face reconstructions of every patient, a circular, linear, hyporeflective area was found circumscribing the retinal vascular arcades, as a frame; no vessels were detected in this area. In accordance with previous studies, vessel rarefaction was reported. The dark circular area found in 9 × 9 scans had characteristic aspects, as the presence in both eyes, specularity, absence of vascularization, and lack of ophthalmoscopic evidence. In the B‑scan images, a mirror reflection of retinal profile, appearing upside down, was observed. This aspect can be due to the reflection of retinal reconstruction caused by the high curvature of the eye and to the staphyloma. Differential diagnosis might be choroidal rupture, even though the specularity and the presence of the dark area in all the layers clear the picture. This study confirmed that OCTA in high myopia can be affected by a number of pitfalls and this should be taken into account for the right interpretation of OCTA reconstructions.