Application of the digital flicker test in optic neuritis and optic neuropathies of different aetiologies

Background Eyes with acute optic neuritis (ON) perceive a flickering field at medium frequencies as darker than a steady one (darkness enhancement (DE)), which may be examined by the digital flicker test (DFT). This study analysed, for the first time, the specificity of the DFT in optic neuropathies of different aetiologies. Methods We used the DFT on 238 eyes, including 40 eyes with ON, 95 eyes with other diagnoses (anterior ischaemic optic neuropathy (AION; n=36), compressive optic neuropathy (CON; n=11), hereditary optic neuropathy (n=34), neuroretinitis and retinal pathologies (n=8), non-organic visual loss (NOVL; n=6) and 103 healthy eyes. To assess the diagnostic accuracy of the test, receiver operating characteristic (ROC) analyses were conducted. Results Median DE for ON was 1.61, for all differential diagnoses 0.88 and for healthy eyes 0.57, with significant differences between all groups (p<0.001). Based on measurements in healthy eyes, an abnormal DE value was set to >1.10. Subanalyses revealed a median DE of 1.25 for CON, 0.80 for AION and 0.63 if only acute AION were included. Optimised cut-off values for ON versus healthy eyes led to a sensitivity of 95%, for ON versus all differential diagnoses to a specificity of 92% and for only acute AION 96%. Conclusions The DFT can be a valuable complementary tool in the diagnosis of optic neuropathies of different aetiologies, particularly in clinically and/or MRI-inconclusive cases. Furthermore, the DFT can be helpful in the differentiation between ON, NOVL and healthy eyes. However, the specificity is not high enough for differentiation of, for example, atypical ON and AION in individual cases. Trial registration number DRKS DRKS00031081.