Demographic and clinical data
The mean age of MS patients was 33.75 ± 9.43 years while the mean age of controls was 33.25 ± 6.12 years; out of 40 patients with MS, 17 patients (42.5%) were males and 23 patients (57.5%) were females, while in the control group, 11 subjects (39.3%) were males and 17 subjects (60.7%) were females.
The age of onset of the disease ranged from 12 to 43 years with a mean age of onset 25.53 ± 8.67 years. The duration of the disease ranged from 1 to 27 years with a mean 8.25 ± 6.59 years. The duration since optic neuritis attack in patients with previous ON ranged from 1 to 15 years with mean 4.3 ± 3.36 years.
EDSS of patients ranged from 1.5 to 7 with a mean EDSS of 4.11 ± 1.89.
Among the 40 MS patients, 12 patients (30.0%) were diagnosed to have secondary progressive MS (SPMS) while 28 patients (70.0%) were diagnosed to have relapsing-remitting MS (RRMS).
Frequency of ON
Twenty-one MS patients had previous ON at least 3 months before the examination. Of these patients, 3 patients had ON in the right eye, 6 patients had ON in the left eye, and 12 patients had ON in both eyes, with a total number of 33 affected eyes. Nineteen MS patients had no previous ON with a total number of 47 unaffected eyes included in the study.
Comparative results
Eyes of MS patients had significant lower OND and ONSD than control eyes (p value = 0.032, 0.023) respectively. Moreover, there was a statistically significant difference in OND and ONSD between the MS eyes with previous ON, MS eyes without previous ON, and healthy control eyes (p value = 0.029, 0.019) respectively. By post hoc analysis, there was a statistically significant decrease in OND and ONSD in the group of MS eyes with previous ON than the control group (p value 0.024, 0.015) respectively. However, no statistically significant difference in OND and ONSD between MS eyes with previous ON and MS eyes without previous ON (p value = 0.33, 0.64) respectively. Also, no statistically significant difference was found between MS eyes without previous optic neuritis and control eyes in both OND and ONSD (p value = 0.74, 0.648) respectively.
Regarding assessment of orbital hemodynamics in the studied groups using color Doppler imaging, there was a statistically significant difference in peak systolic velocity (PSV), mean velocity (MV), and end-diastolic velocity (EDV) of the posterior ciliary artery (PCA) between MS eyes with, without previous ON, and healthy controls (p value = 0.002, 0.002, and 0.022) respectively. By post hoc analysis, MS eyes with and without previous ON had statistically significant higher PSV and MV of PCA than healthy controls (p value < 0.05) (Fig. 1). Moreover, MS eyes without previous ON had a statistically significant higher EDV than the control group (p value = 0.018). However, there was no statistically significant difference between MS eyes with and without previous ON and the control group in PSV, MV, EDV, RI (resistivity index), and PI (pulsatility index) of the central retinal artery( CRA) and ophthalmic artery (OA). There was a statistically significant decrease in PSV, EDV, and MV of CRA in SPMS patients compared to RRMS patients. However, there was no statistically significant difference between RRMS eyes and SPMS eyes in PSV, MV, EDV, RI, and PI of the ophthalmic and posterior ciliary arteries.
Correlations between ultrasound findings and clinical data in MS eyes with previous optic neuritis
Central retinal artery PSV was negatively correlated with both EDSS and duration of disease (p = 0.01, r = 0.044; p = 0.009, r = 0.44) respectively (Fig. 2). Ophthalmic artery PSV and MV were also negatively correlated with the duration of the disease (p = 0.01, r = − 0.044; p = 0.014, r = 0.42) respectively (Fig. 3). However, no correlation was found between OND and ONSD with the age of onset of the disease, duration of the disease, or EDSS of the patients.
The multivariate linear regression analysis was used to detect the predictors for PSV of CRA in MS eyes with previous optic neuritis. The duration of the disease and disease severity assessed by EDSS were used as independent predictors in the model. We found that the only predictor for PSV of CRA was EDSS (beta = − 0.41, p value = 0.018).