Vigabatrin vision loss

Short answer: vigabatrin can permanently narrow side vision in both eyes and can also reduce sharpness of vision. The risk rises with dose and with total time on the medicine, and no dose is known to be free of risk.¹ Based on adult studies, the label says 30% or more of patients can be affected, which is why everyone on vigabatrin has regular vision checks.²

This is the boxed warning on every vigabatrin label, and it is the main reason the medicine is used only when its benefits are judged to outweigh this risk.¹ No form changes the risk: the ready-to-use liquid, the powder and the tablets all contain the same medicine.¹

What the vision loss is

The medical term is bilateral concentric visual field constriction. "Visual field" means everything you can see while looking straight ahead, including what is off to the sides. "Bilateral concentric constriction" means that field shrinks from the outside edges inward, in both eyes. Central vision may also become less sharp.¹ In severe cases the remaining field can be within 10 degrees of the center, which is tunnel vision.²

In a study of 138 children, mostly babies, checked with regular eye tests, three had a characteristic pattern: thinning of the nerve fibers at the outer edges of the retina, with matching changes in the optic nerve.³ The retina is the light-sensing layer at the back of the eye.

Not every narrowed field is caused by vigabatrin. Similar field loss is also seen, less often, in people with epilepsy who have never taken it.⁴

How common it is

The numbers vary a great deal by age, dose and how long people took vigabatrin.

• Took vigabatrin
• Never took vigabatrin

Adults who took vigabatrin

52%

Children who took vigabatrin

34%

Controls who never took it

7%

Show as a table

Group	Measure	Value
Visual field loss across 32 studies	Adults who took vigabatrin	52%
Visual field loss across 32 studies	Children who took vigabatrin	34%
Visual field loss across 32 studies	Controls who never took it	7%

In the review of 32 studies, the risk rose with total dose and with age.⁵ In the long-term adult study, the estimated risk leveled off at about 76% after roughly 6 years.⁶

What is known about babies

Under 1 year

9%

12 to 24 months

30%

More than 2 years

63%

32 children followed up; small numbers in each group.

Show as a table

Group	Measure	Value
Field loss at school age after vigabatrin in infancy, by length of treatment	Under 1 year	9%
Field loss at school age after vigabatrin in infancy, by length of treatment	12 to 24 months	30%
Field loss at school age after vigabatrin in infancy, by length of treatment	More than 2 years	63%

The evidence in babies is mixed, and much of it is hard to read because babies cannot do the standard field test.

• A school-age follow-up of children treated for infantile spasms found field loss in 11 of 32 (34%). The rate climbed with length of treatment: 9% under 1 year, 30% at 12 to 24 months and 63% beyond 2 years.⁷
• A smaller study of 16 children treated in infancy found mild loss in only one, and suggested the risk may be lower when the medicine is taken in infancy.⁸
• At UCLA, 143 babies treated for a median of 8.6 months had no clinically apparent vision loss that could be blamed on vigabatrin. Vision problems from any cause were about as common with vigabatrin (31%) as without it (32%).⁹

"No clinically apparent loss" is not the same as no loss. Babies cannot do the standard field test, so mild loss is hard to detect at this age, and the school-age study above found more loss after longer treatment. The warning applies to babies as much as to adults.¹ Keeping treatment as short as the condition allows matters: the label advises stopping vigabatrin for infantile spasms if it has not clearly helped within 2 to 4 weeks.²

Dose and how long treatment lasts

The label says the risk increases with higher doses and longer exposure.¹ Large reviews link field loss to total (cumulative) dose.^5,6 One small study of 31 adults found that the highest daily dose, rather than total dose or time on treatment, best predicted how severe the defect was.¹⁰ That is a single small study, so it should not be over-read, but it is one more reason to give the prescribed dose and no more. See dosage.

How vision is monitored

The labels set out this schedule:¹

• Before or soon after starting: a vision assessment no later than 4 weeks after the first dose.
• During treatment: at least every 3 months.
• After stopping: about 3 to 6 months after the last dose.

The REMS program was designed around this baseline exam and ongoing checks.¹¹

Adults and older children usually have a visual field test (perimetry), in which they look at a central point and press a button when a light appears to the side. Babies and young children cannot do this. For them, eye specialists may use an electroretinogram (ERG), which records the retina's electrical response to flashes of light, and visual evoked potentials (VEP), which record the brain's response to patterns.¹¹ In one center, ERG every 6 months identified children with retinal damage.³ In another study, children with ERG signs of damage also had lower sharpness of vision on VEP testing.¹²

Ask the eye team which tests your child will have, how often, and what the results mean for continuing treatment.

Signs to tell the doctor about

Babies cannot tell you what they see. These are general signs that something may be wrong with vision. They are not specific to vigabatrin, but tell the prescriber or eye doctor if your child:

• does not follow faces or toys with their eyes as before
• seems to miss things held off to the side
• bumps into objects or seems newly clumsy
• has unusual eye movements, or squints or blinks a lot
• seems frustrated or unsettled in a way that may be linked to seeing

Older children and adults may notice tripping, bumping into door frames, or trouble seeing cars or people coming from the side. Do not stop vigabatrin on your own because of these signs: stopping suddenly can bring on seizures.¹ Call the prescriber.

Taurine

One review discusses the idea that a shortage of taurine, an amino acid, plays a part in how vigabatrin damages the retina.⁴ This is a hypothesis. There is no evidence in the sources here that taurine supplements prevent vigabatrin vision loss, so do not give one without talking to the prescriber.

For other side effects, see side effects.