30 patients clinically diagnosed with NAION (unilateral affected) who presented to Beijing Friendship Hospital from July 2017 to January 2019 were selected. The mean age at diagnosis of the 30 patients was 62.1±7.3 years (range, 47 to 72 years), and there were 18 male and 12 female. The mean interval between onset of NAION and measurement was 5.2±2.7days. All participants provided written informed consent.This study was approved by the local ethics committee of Beijing Friendship Hospital and was conducted in conformance with the Declaration of Helsinki (the 2013 revision), the guideline of the International Conference on Harmonisation of Good Clinical Practice.
Inclusion criteria for patients with NAION were as follows: 1) conformed to the diagnostic criteria of NAION, 2) unilateral optic disc swelling on ophthalmoscopy during the acute stage, 3)first time outbreak of NAION without previous treatment, and 4) completed all the examinations and follow- up visits.
Exclusion criteria were as follows: 1)any other ophthalmic diseases affecting the optic disc, including glaucoma, optic neuritis, uveitis, retinal or choroidal diseases, and trauma; and 4) any neurologic disease that may affect the optic nerve,such as multiple sclerosis, Alzheimer disease, and Parkinson disease.
The control group consisted of 30 age- matched subjects. The mean age of the 30 controls was 62.7±6.4 years (range, 49 to 72 years), and there were 18 male and 12 female. No participant had ever had any eye disease or impaired vision function at the same period of patient recruiting. No participant had ever had cardiovascular or cerebrovascular diseases before.
All the participants were performed fundus imaging, fundus fluorescein angiography (FFA, Heidelberg, Germany) and spectral-domain optical coherence tomography scans (SD-OCT, Heidelberg, Germany) (Figure 1).
Head-and-neck computed tomographic angiography (CTA) (GE revolution CT, U.S.A) examination was performed to measure the diameter of ICAS and OA. Measurement process of the diameter of ICAS: firstly, choose the starting and the end point of ICAS segment; secondly, straighten the chosen vessel using software (GE post processing workstation AW4.6); finally, measure the narrowest part of the vessel defined as the diameter of ICAS. Measurement process of the diameter of OA: choose the vessel 5mm above the level of optic canal outlet and measure the diameter of OA (Figure 2).
Color Doppler Flow Imaging (CDI) (HITCHI ALOKA, Japan) examination was employed to evaluate the hemodynamic parameters (Vm) of ICA, with the use of linear 5–10MHz transducer (Figure 3). Blood ﬂow velocities of OA were performed with a Esaote Mylab ClassC LA332 instrument (Esaote, Italy), with the use of linear 3–11MHz transducer (Figure 4). All measurements were performed in the supine position.
The blood flow volume (A) of ICAS and OA was calculated using the following formula:
A = πr2×Vm （r = 1/2 diameter）
All the measurements were performed by experienced operators unaware of the subject’s condition. The left side measurements were defined as the results of each control.
Heart rate and blood pressure (BP) were determined by sphygmomanometry in a sitting position after a rest of 5 min. Intraocular pressure (IOP) was measured before CDI examination using Goldmann applanation tonometry. Ocular perfusion pressure (OPP) was calculated using the following formula:
OPP = 2/3(diastolic BP+1/3 (systolic BP–diastolic BP))–IOP
Data were expressed as mean ± SEM. The Kolmogorov-Smirnov test was used to identify the normality of distribution. Differences in the parameters between the affected sides and the controls, and between the unaffected healthy sides and the affected sides were compared using the Mann–Whitney test, Wilcoxon test or t test. p value <0.05 was considered statistically signiﬁcant. Statistical analysis was performed using the IBM SPSS software version 21.