Some ophthalmologists (eye specialists) in the Netherlands studied 92 patients with epilepsy who had been taking Sabril (vigabatrin). Their objective was to find out whether the amount of Sabril taken was related to the percentage of the visual field area lost. (In other words, did the medicine affect the size of the area in which these patients could see objects without moving their eyes?)

They found that the total amount of Sabril taken was the most important factor in predicting the visual loss. Other seizure medicines taken did not make a difference. Men were more affected than women. These doctors recommended that Sabril should be taken only when there are no alternatives and that regular examinations of the visual field should be performed before the medication is started and then every 6 months.

Here's a link to a summary of this study:

Hardus P, Verduin WM, Engelsman M, et al. Visual field loss associated with vigabatrin: quantification and relation to dosage. Epilepsia. 2001;42(2):262-267. PMID: 11240600

Reviewed February 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.