In the current study, we evaluate the serum ACE level in ON patients based on the following hypothesis: on the one hand, ON is an immunologically mediated central nervous system disease and on the other hand, ACE activity may be involved in its pathogenesis of the inflammatory process; therefore, measurement of serum ACE levels can be included as a screening test in the initial evaluation of patients suspected of having ON [17]. Here, ACE is linked to central nervous system disorder.