Fractional anisotropy of the optic radiations correlates with the visual field after epilepsy surgery

This study assessed whether optic radiations (OR) microstructure after temporal lobe epilepsy (TLE) surgery correlated with visual field defects (VFD).

Patients were subjected to diffusion tensor imaging (DTI) tractography of the OR and Humphrey perimetry after TLE surgery. We used Spearman's test to verify correlations between tractographic parameters and perimetry mean deviation. Tractographic variables were compared between patients with VFD or intact perimetry. Multiple logistic regression was applied between DTI and perimetry values. DTI sensitivity and specificity were assessed with a receiver operating characteristic (ROC) curve to evaluate VFD.

Thirty-nine patients had reliable perimetry and OR tractography. There was a significant correlation between (1) fractional anisotropy (FA) and both total (rho = 0.569, p = 0.0002) and quadrant (rho = 0.453, p = 0.0037) mean deviation and (2) radial diffusivity and total mean deviation (rho = - 0.350, p = 0.0286). There was no other significant correlation. Patients with VFD showed a significantly lower FA compared with patients with normal perimetry (p = 0.0055), and a 0.01 reduction in FA was associated with a 44% increase in presenting VFD after surgery (confidence interval, CI = 1.10-1.88; p = 0.0082). Using a FA of 0.457, DTI tractography showed a specificity of 95.2% and a sensitivity of 50% to detect VFD after surgery (area under the curve = 0.7619, CI = 0.6020-0.9218).

The postoperative OR microstructure correlated with visual loss after epilepsy surgery. DTI postoperative OR tractography may be helpful in evaluating VFD.