Retinal nerve fibre layer characteristics with vigabatrin-associated visual field loss--could scanning laser polarimetry aid diagnosis?

PURPOSE

To describe the retinal nerve fibre layer (RNFL) characteristics in patients suffering vigabatrin-associated visual field loss or behaviour consistent with field loss.

METHODS

Eight patients with visual field loss attributed to vigabatrin use had their RNFL evaluated by scanning laser polarimetry.

RESULTS

All eight patients managed to perform the test reliably. The mean length of vigabatrin treatment was 81 months with a mean cumulative dose of vigabatrin being 5.4 kg. All patients had significantly reduced RNFL parameters; mean TSNIT=36.5 microm, mean nerve fibre indicator=63.1, mean superior average=42.7 microm, and mean inferior average=39.2 microm. There was no correlation between cumulative dose or time on treatment and RNFL thickness.

CONCLUSION

Scanning laser polarimetry can be performed safely and reliably on patients with vigabatrin-associated field loss. RNFL thickness is reduced in these patients with vigabatrin-associated field loss. RNFL loss concentrates on the long nerve fibres, which explains the nasal pattern of field loss seen in these patients. This investigation shows promise in the screening of vigabatrin patients, especially in those patients that may not tolerate formal field testing well.