Changes in the Parameters of Visual Evoked Potentials in Media Opacities

This study compared flash visual evoked potentials (VEPs) parameter differences between eyes with unilateral opaque media and their normal contralateral counterparts.

We included 178 patients with unilateral media opacity and normal contralateral eye in each patient. The diseased eyes had normal ultrasonographic findings and were candidates for keratoplasty or anterior segment reconstruction. The patients underwent electrophysiological testing by the flash VEPs recording with the use of 1.4Hz (transient) and 8Hz (flicker) frequencies.

The medians of P2 implicit times were significantly higher in eyes with media opacity than in normal eyes, with median differences between both eyes of -6.7 ms. Furthermore, the median N2P2 amplitude was 9.70 µv with media opacity compared with 11.00 µv in the normal eyes, with a significant difference of 1.3 (p = 0.002). The flash VEPs median parameters recorded at a frequency of 8-Hz showed significant differences in medians of spectral plots of 0.6 µv between normal and abnormal eyes. The same for the signal-to-noise ratio, where the difference in medians was 3 dB. Analysis of the difference between both eyes (normal-abnormal) in each patient showed in P2 implicit time a difference range of -49 to 54.7 ms with a median difference of -3 ms. The difference in amplitudes of recorded N2P2 showed a median of 2.13 µv. There was a statistically significant but weak negative correlation between N2P2 amplitude (r _spearman = -0.173, p = 0.021) and the grades of corneal opacity.

Preoperative flash VEPs recording is useful for evaluating visual function in patients with unilateral media opacity to determine the future benefits of keratoplasty or anterior segment reconstruction. There are no correlations between the flash VEP parameters or the difference between the 2 eyes and the grades of corneal opacity.