Optic nerve lesion length is a biomarker of visual disability in the pre-chronic phase of Leber's hereditary optic neuropathy.

Objective: The current research aims to investigate relationships between the optic nerve (ON) lesion length with visual function in the pre-chronic phase ( illness duration < 12 months) of LHON.

Methods: Orbital MRI was retrospectively analyzed for 45 patients with LHON in the pre-chronic phase. ON lesion length was measured by 2 trained independent readers and it was recorded as multiplication of the number of abnormal MRI slices and slice thickness on T2-STIR sequence in the coronal plane. Decimal visual acuity was converted to the logarithm of minimum angle of resolution. Intra-class correlation coefficients (ICCs) were used to assess intra- and inter-observer agreements. Pearson's correlation analysis and multivariate linear regression models were performed to analyze the correlations of the lesion length with best corrected visual acuity (BCVA) and visual field parameters.

Results: 81 afflicted eyes were selected. The ICCs for intra-observer and inter-observer analyses were 0.989 and 0.980 respectively. Both Pearson's correlation analysis and multivariate linear regression models indicated a significant positive correlation between the BCVA or mean deviation (MD) and ON lesion length (r=0.368, P=0.001; r=-0.269, P=0.045) with a coefficient of determination (R) of 0.152 and 0.114 respectively adjusted for patients' sex, age of onset, onset of vision loss to performance of MRI, mitochondrial DNA mutations.

Conclusion: ON length with T2-STIR hyperintensities was positively associated with both BCVA and MD, and it was suspected to be a biomarker of visual disability in the pre-chronic phase of LHON.