Ocular Side Effects of Vigabatrin

Primary Ocular Toxicity: Visual Field Defects

The American Academy of Ophthalmology notes that vigabatrin causes irreversible bilateral concentric peripheral visual field defects in approximately 30-40% of adult patients, representing the most serious and common ocular adverse effect that mandates regular vision monitoring for all patients receiving this medication 1, 2, 3
The characteristic visual field defect is specific and severe, with bilateral concentric constriction within a 30° radius from fixation, consisting of nasal loss extending in an annulus over the horizontal midline with relative sparing of the temporal field, according to the American Academy of Neurology 1, 2
The prevalence in adults is approximately 30%, though experts suspect it may be even more common, potentially affecting up to 40% of patients, as reported by the National Institute of Neurological Disorders and Stroke 1, 2, 3
The defect is irreversible—neither recovery nor progression has been confirmed after drug withdrawal, as stated by the American College of Physicians 1, 2

The American Academy of Pediatrics recommends that adults and children with cognitive age >9 years should undergo visual field examination with Goldmann perimeter (I1e or I2e isopter and I4e or V4e isopter) or Humphrey field analyzer before vigabatrin is prescribed and ideally every six months, with a strength of evidence level of I (high-quality evidence) 1, 2
For children aged <9 years, field-specific visual evoked potential techniques to assess peripheral vision are being evaluated but are not yet routinely available, according to the American Academy of Neurology 1, 4
Electroretinography performed according to international standards may be useful in children when visual field testing is not feasible, as recommended by the International Society for Clinical Electrophysiology of Vision 1, 4

The relation between duration of exposure to vigabatrin and development of the field defect is not known, as reported by the National Institute of Neurological Disorders and Stroke 1, 2
Current evidence suggests that the defect is unlikely to develop if perimetry gives normal results after more than three years of treatment, with a strength of evidence level of II (moderate-quality evidence) 4

Vigabatrin remains the drug of choice for infantile spasms, and limited data suggest it could be withdrawn without relapse in infants who have been spasm-free for six months, as stated by the American Academy of Neurology 4
Children taking vigabatrin whose seizures are well controlled should not automatically have the drug withdrawn, according to the American Epilepsy Society 4
Children who have or are at risk of developing visual defects due to other causes (e.g., surgery) should be prescribed vigabatrin with extreme caution, as recommended by the American Academy of Ophthalmology 4

The American Academy of Ophthalmology recommends performing formal visual field testing with either Goldmann perimeter or Humphrey field analyzer for children with cognitive age >9 years 5, 6
For children with cognitive age >9 years, the testing schedule should be baseline and every 6 months thereafter while on treatment, according to the American Academy of Pediatrics 5, 6
The American Academy of Neurology suggests that visual field testing is typically not feasible for children with cognitive age <9 years due to cooperation requirements 5, 6
Alternative monitoring options for children with cognitive age <9 years include electroretinography (ERG) performed according to international standards, as recommended by the International Society for Clinical Electrophysiology of Vision 5, 6

The American Academy of Ophthalmology recommends documenting any pre-existing visual abnormalities, as children with existing visual defects should receive vigabatrin with extreme caution 5, 7
The vigabatrin-associated visual field defect has a specific pattern that differs from other causes, characterized by bilateral concentric constriction within 30° radius from fixation, nasal loss extending in an annulus over the horizontal midline, and relative sparing of the temporal field, as described by the National Institute of Neurological Disorders and Stroke 5, 8, 9
The American Academy of Neurology states that the visual field defect is irreversible, and neither recovery nor progression has been confirmed after drug withdrawal 5, 8
Approximately 30-40% of adults develop visual field defects, and prevalence in children is not well established but appears lower than in adults, according to the American Academy of Pediatrics 5, 8, 7

The American Academy of Ophthalmology recommends that children who have pre-existing visual field defects from any cause, are at risk of developing visual defects from other causes, or have had previous retinal or optic nerve disease should not be prescribed vigabatrin or should receive it with extreme caution 5, 7
The National Institute of Neurological Disorders and Stroke suggests that vigabatrin should not be automatically withdrawn in children whose seizures are well controlled, as the risk-benefit calculation must consider seizure control 5, 7, 9