Patterns of peripapillary retinal nerve fiber layer thinning in vigabatrin-exposed individuals.

PURPOSE: To explore the relationship of peripapillary retinal nerve fiber layer (ppRNFL) thinning in individuals exposed to the antiepileptic drug vigabatrin with respect to 2 separate variables: cumulative vigabatrin exposure and severity of vigabatrin-associated visual field loss (VAVFL). DESIGN: Cross-sectional observational study. PARTICIPANTS: Subjects were older than 18 years, 129 with vigabatrin-treated epilepsy (vigabatrin-exposed group) and 87 individuals with epilepsy never treated with vigabatrin (nonexposed group). METHODS: All subjects underwent ppRNFL imaging using spectral-domain optical coherence tomography. Eighty-four vigabatrin-exposed individuals underwent Goldmann kinetic perimetry. The visual field examined from the right eye was categorized as normal (n = 47), mildly abnormal (n = 18), or moderately to severely abnormal (n = 19). In 91 vigabatrin-exposed individuals, the cumulative vigabatrin exposure could be ascertained: 41 subjects received 1000 g or less, 23 subjects received more than 1000 g but equal to or less than 2500 g, 16 subjects received more than 2500 g but equal to or less than 5000 g or less, and 11 subjects received more than 5000 g. MAIN OUTCOME MEASURES: Differences in ppRNFL thickness across the twelve 30° sectors: (1) among all nonexposed individuals and all vigabatrin-exposed individuals, (2) between each vigabatrin-exposed group, according to cumulative vigabatrin exposure, and the nonexposed group, (3) among different vigabatrin-exposed subjects grouped according to cumulative vigabatrin exposure, and (4) among vigabatrin-exposed subjects grouped according to severity of VAVFL. RESULTS: The ppRNFL was significantly thinner in vigabatrin-exposed compared with nonexposed individuals in most 30° sectors (P<0.004). The temporal, temporal superior, and temporal inferior 30° sectors, as well as the nasal 30° sector, were not affected. There was a trend for increasing ppRNFL thinning with increasing cumulative vigabatrin exposure. The nasal-superior 30° sector was significantly thinner in group 1 (≤1000 g) compared with nonexposed individuals (P<0.05) and in vigabatrin-exposed individuals with normal visual fields compared with nonexposed individuals (P<0.05). CONCLUSIONS: After vigabatrin exposure in individuals receiving cumulative doses of 1000 g or less or in the presence of normal visual fields, ppRNFL thinning in the nasal superior 30° sector may occur. With higher cumulative doses of vigabatrin exposure, additional ppRNFL thinning was observed. The temporal aspects of the ppRNFL are spared, even in individuals with large cumulative vigabatrin exposures and moderate or severe VAVFL.

Retinal nerve fiber layer thickness in vigabatrin-exposed patients.

OBJECTIVE: Vigabatrin-associated visual field loss (VAVFL) occurs in 25 to 50% of exposed patients and is routinely monitored using perimetry, which has inherent limitations. Using optical coherence tomography (OCT), retinal nerve fiber layer (RNFL) thinning has been described in a small number of vigabatrin-exposed patients. We explored the relationship between RNFL thickness and visual field size, to determine whether OCT is a suitable tool to use in patients exposed to vigabatrin. METHODS: Two hundred one vigabatrin-exposed subjects with epilepsy, divided into 2 groups, and 90 healthy controls participated. Visual fields were obtained using Goldmann kinetic perimetry and quantified using mean radial degrees (MRD). RNFL imaging was performed using either spectral-domain (Group 1) or time-domain (Group 2) OCT. RESULTS: Thirty-nine of 201 (19.4%) patients were unable to perform perimetry. Thirteen (6.5%) patients were unable to perform OCT. A total of 51.6% of patients showed VAVFL. Average RNFL thickness was significantly thinner in patients (77.9 µm) compared to healthy controls (93.6 µm) (p < 0.001). There was a strong correlation between MRD and average RNFL thickness for Group 1 (r = 0.768, p < 0.001) and Group 2 (r = 0.814, p < 0.001). OCT RNFL imaging showed high repeatability. INTERPRETATION: OCT provides a useful tool to assess people exposed to vigabatrin, and can provide an accurate estimate of the extent of visual field loss in the absence of a reliable direct measure of the visual field. The strong linear relationship found between RNFL thickness and visual field size provides some evidence that irreversible VAVFL may be related to loss of retinal ganglion cell axons.