Multiple sclerosis (MS) is a chronic, autoimmune, and neurogenerative disease involving demyelinating plaques in the central nervous system [1]. This disease is characterized by periventricular inflammatory lesions and, eventually, the development of irreversible axonal damage [2]. While MS is most often observed in young adults between the ages of 20 and 40 years, women are more commonly affected than men. Ocular involvement is common in this disease, which has seen a global increase in prevalence [3]. In the clinical course of MS, the most common ocular finding is optic neuritis (ON), which appears as the initial symptom in approximately 20 % of patients [4].

Optical coherence tomography angiography (OCT-A) is a high-resolution, non-invasive imaging method that shows blood flow in retinal, choroidal, and optic disk vascular structures. In addition, it is possible to simultaneously evaluate the retinal nerve fiber layer (RNFL) and optic disk perfusion [5]. Deep ocular structures, such as the choroid and the choroid–sclera junction, can be better visualized on OCT images taken in the enhanced depth imaging (EDI-OCT) mode [6]. Recently, the choroidal vascularity index (CVI)—defined as the ratio of the choroidal vascular area to the total choroidal area (TCA) derived from EDI-OCT images—has been used as a biomarker to evaluate the vascular status of the choroid [7].

Dysfunctions in the cerebral endothelial cells of MS patients lead to vascular abnormalities. This may be related to the pathogenesis of MS lesions and the progression of the disease [8]. Previous studies have reported that vascular comorbidities, such as ischemic stroke and cerebral hypoperfusion, are often observed in MS patients [9,10]. Examining retinal vascular changes may contribute to a better understanding of cerebral circulation disorder, which plays a role in the pathogenesis of MS. In this regard, reduced retinal vascular density (VD) and optic nerve head blood flow indices have been observed in MS patients [11,12].

Fluorescein angiography and indocyanine green angiography, which are methods applied in current clinical practice, allow for the qualitative evaluation of retinal and choroidal circulation. However, objective data cannot be obtained. Meanwhile, OCT-A and EDI-OCT images allow for quantitative vascular evaluation. The aims of this study were to evaluate OCT—A data in order to examine retinal microcirculation and to evaluate CVI calculations obtained from EDI-OCT images in order to examine choroidal vascular changes in MS patients with and without histories of ON attacks. To our knowledge, this was the first study in which OCT-A and CVI measurements were evaluated concurrently in the same group of MS patients.