Abstract:
Background As a new noninvasive and simple subjective examination method, critical flicker fusion frequency (CFF) can dynamically reflect the changes of visual function of human eyes.
Objective To explore the application of critical flicker fusion frequency (CFF) in differentiating optic neuritis (ON) from non-arteritic anterior ischemic optic neuropathy (NAION).
Methods A cross-sectional study was performed in the Department of Ophthalmology, Chinese PLA General Hospital from January to September in 2021. Subjects underwent best-corrected visual acuity (BCVA), visual field, optical coherence tomography, flash visual evoked potential (F-VEP) and CFF examinations, including CFF for red (rCFF), green (gCFF), yellow (yCFF). The ophthalmic results of the healthy and affected eyes were compared. The affected eyes were divided into different subgroups: < 1, 1-< 3, 3-< 6, and ≥ 6 months according to disease course; mild, moderate, and severe visual impairment according to BCVA≥0.5, 0.1-0.5, <0.1. And the CFF value of affected eyes were compared according to different subgroups in sequence. For patients with monocular involvement within 1 month onset, the difference value and difference ratio of CFF between the two groups were further analyzed. Moreover, for patients with severe visual impairment, the CFF threshold for differentiating the two groups was analyzed by receiver operating characteristic (ROC) curve.
Results A total of 69 ON patients (102 affected eyes and 29 healthy eyes, 50 females) with median age of 31 years and 58 NAION patients (71 affected eyes and 33 healthy eyes, 25 females) with median age of 50 years were included. The CFF value either in healthy eyes or in affected eyes showed no statistical difference between the two groups (P > 0.05). And when compared the CFF trichromatic value in affected eyes, the CFF value in the ON patients was lower than that in the NAION patients within 1-month onset (P<0.05), and higher than that in the NAION group within 3-6 months onset (P<0.05), whereas, no statistical differences were found at any other time points (P > 0.05). When compared the affected eyes with monocular involvement within 1-month onset, both difference value and difference ratio of CFF in the ON group were greater than that of the NAION eyes (P<0.05). In eyes with severe visual impairment, the rCFF and gCFF of the NAION groups were lower than those of the ON eyes (P=0.037, 0.049), and ROC analysis showed that the AUC of rCFF, gCFF and yCFF was 0.75, 0.76, 0.74, respectively, in discriminating ON and NAION eyes.
Conclusion For patients with newly-onset or severe symptoms, CFF examination may be useful to distinguish ON from NAION.