The antiepileptic drug vigabatrin (VGB) has been shown to be one of the best treatments against a special form of epilepsy in infants, called infantile spasm. However, its use has been limited in many countries because it has been shown to cause a permanent narrowing of visual fields in approximately 40 percent of adults who have been exposed at school age or later.
A new study published in Epilepsia examined school-aged children who had been treated with VGB in infancy. The findings showed normal visual fields in 15 of the 16 children studied children.
While VGB is an effective drug for infantile spasms, there have been no previous reports on later visual field testing after treatment in infancy. This study used a form of peripheral vision testing, called kinetic perimetry, which is effective in detecting peripheral field defects typical of VGB toxicity, and produces more reliable results in children.
Vigabatrin treatment began at a mean age of 7.6 months, and the mean duration of therapy was 21 months, with a mean cumulative dose of 655 grams. Three of the children had been previously treated with another anti-epileptic drug (AED), five had received only hormonal treatment, and eight children had never been treated with any form of AED.
The findings show that the risk of permanent visual field defects caused by VGB may be lower for treatments in infants than in adults. Results showed that 15 children had normal visual fields and mild visual field loss was observed in one child who had been treated with VGB for 19 months and received a cumulative dose of 572 grams. This frequency is lower than previous observations using kinetic perimetry in older children or adults.
The cumulative VGB doses and treatment durations in the study were, on average, lower than in previous studies, which correspond to the much younger age and weight of the tested patients.
“Our results may encourage doctors to use vigabatrin to treat infantile spasms as the risk for visual field damage may be relatively low in many children compared to the risks caused by continuous seizures,” says Dr. Eija Gaily, co-author of the study.
Visual field testing can be carried out in normally developed children from the age of six years. It is important to note that not all children with normal fields manifest normal results at the first visual field testing because good cooperation and attention are required in order to get reliable results. All abnormal findings in children should always be confirmed by repeating the test.
- Eija Gaily, Henna Jonsson, Marjatta Lappi. Visual fields at school-age in children treated with vigabatrin in infancy. Epilepsia, 2009; 50 (2): 206 DOI: 10.1111/j.1528-1167.2008.01961.x
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