This observational cross-sectional study was conducted in Bakırköy Dr. Sadi Konuk Education and Research Hospital (İstanbul, Turkey). Patients with NAION were recruited from neurophthalmology clinic.
The research protocols were approved by the institutional review board and adhered to the tenets of the Declaration of Helsinki.
Written informed consent was obtained from all volunteers prior to their participation in this study.
Diagnostic criteria for NAION were a sudden onset of painless vision loss; sectorial or generalized optic disc edema, peripapillary hemorrhage and normal erythrocyte sedimentation rate or C-reactive protein. All of the patients underwent ophthalmic evaluation, including best-corrected visual acuity (BCVA) and refraction assessments, slit-lamp biomicroscopy, intraocular pressure measurement, ONH evaluation, fundus examination and digital color fundus photography (Digital Non-Mydriatic Retinal Camera; Topcon), carotid colour doppler sonography. Representative cases of NAION are shown in Fig. 1.Twentytwo patients were retrospectively identified from an internally maintained OCT-A imaging database (at least 3 months of the initial evaulaton). OCT-A images of fellow, unaffected eyes were also evaluated in the study. NAİON patients were categorized as either NAION with CS "CS-NAION" or NAION without CS "NCS-NAION" based on the presence or absence of CS, at the carotid colour doppler sonography.
The control group comprised age-matched subjects with a BCVA ≥ 0,8, IOP ≤ 21 mm Hg, an open angle, normal optic disc appearance on fundus examination, and no RNFL defects.
Exclusion criteria were as follows: 1) refractive error greater than + 3.0 diopters (D) or less than − 4.0 D; 2 ) previous intraocular surgery other than cataract; 3) any other ophthalmic disorder, including corneal opacity, vitreous opacity, diabetic retinopathy, and diseases affecting the optic disc (glaucoma, optic neuritis, uveitis, retinal or choroidal diseases, and trauma); and 4) neurologic diseases that may affect the optic nerve such as multiple sclerosis, Alzheimer disease, and Parkinson disease 5) poor cooperation in OCT imaging studies.
OCT-A was performed with the spectral domain system RTVue-XR Avanti (Optovue Inc. Fremont, California, USA). The peripapillary RNFL was determined using the ONH protocol. A standard 360°, 3.4-mm-diameter circular scan was utilized to measure the RNFL thickness, and superior, nasal, temporal and inferior RNFL values were recorded. The macula cube scanning protocol measured the ganglion cell complex (GCC) thickness over a 7mm diameter centered on the fovea, inferior, superior and total GCC values were recorded.
The flow density map software AngioAnalytics (RTVue XR version 2018.0.0.18) was automatically employ to quantify vessel density in this study. The OCT-A images were acquired within the peripapillary area (Fig. 2). The retinal peripapillary capillaries (RPC) mode, which included the signals from internal limiting membrane to the nerve fiber layer was employed in this study. In the optic disc scan, the software automatically fits an ellipse to the optic disc margin and calculates the average vessel density within the ONH and peripapillary area. The peripapillary area is defined as a 0.75 mm-wide elliptical annulus that extends from the optic disc boundary. The peripapillary region is divided into sectors, and the vessel densities in each sector are calculated (nasalinferior, nasalsuperior, inferonasal, inferotemporal, superotemporal, superonasal, temporalinferior and temporalsuperior sectors). For each scanned region, the software automatically calculates the vessel densities. The vessel density (VD) was defined as the percentage of the area occupied by vessels within the segmented area. The signal strength index was employed to control for image quality. Images with a signal strength index less than 7 were excluded, and scans with movement or decentration artifacts were repeated.