We read with interest, and with overall agreement, Dr. Steve Newman’s editorial about our recent article: “Evidence-Based Review Of Recommendations For
Visual Function Testing In Patients Treated With Vigabatrin”.
He has captured the major goal of our combined effort by neuro-ophthalmologists and epilepsy specialists that “consensus studies ….remain important in advising best clinic practice in the absences of multi-centered trials.” We hope that our article serves as a point of reference not only for clinical practice but also for developing future clinical investigations including Phase IV investigations.
Only after reaching a like-minded consensus concerning the data in the current peer-reviewed publications will we be able to define the following crucial issues: [1] when is the earliest onset of visual field constriction; [2] what are the demographics of the patients affected by the retinal toxicity; [3] what is the incidence, prevalence, progression, and severity of visual problems; [4] does visual field loss progress after discontinuation of the medication; and [5] what is the role of spectral domain optical coherence tomography [OCT] and do changes with OCT precede visual field loss?
We could not agree more with Dr. Newman’s opinion that the potential beneficial effects of vigabatrin for controlling some of the severest forms of epilepsy must be weighed against possible visual disability. The key to this risk/benefit algorithm will be continued discussions with the patients, their care-givers, epilepsy specialists, and neuro-ophthalmologists.
We differ with Dr. Newman in his view that baseline evaluations are “probably unnecessary”. Epilepsy patients present critical challenges for all visual assessments, especially perimetry. These patients frequently have unique issues with cognition, attention, fatigue, and understanding [some of these problems may be related to their epilepsy medication]. Among epilepsy patients, there is a wide range of the degrees of visual field extent with perimetric testing. This is why comparison to a patient’s own baseline visual field is likely to be more sensitive for picking up a significant vigabatrin-associated change. For younger patients with infantile spasms, the ERG response is frequently abnormal before vigabatrin therapy. The baseline measurement is required so that sustained reduction from baseline can be detected. We propose that any patient will benefit from one, and probably multiple baseline measurements, so that their test/retest variability can be characterized, which will allow a better discovery of any significant reduction in their visual field compared to their baseline state. Also, we believe that “one size will not fit all” for these patients and baseline testing will establish which patients will perform better with various automated static programs or automated or manual kinetic perimetry.
We agree that ERG testing is difficult to standardize across centers but represents another potential source of critical information for some, but not, all patients. If the ERG is compared with baseline data useful information will ensue, and if the ERG is conducted under sedation the result is easier and not harder to interpret
In closing, our expert panel has forged an on-going relationship with Lundbeck, the sponsoring organization, so that the fundamental questions raised by our article and by Dr. Newman can be addressed with industry and physicians working together, united by the common goal of establishing the safest possible use of vigabatrin.
Sincerely yours,
Robert C. Sergott, MD
Randy H. Kardon MD, PhD
James W. Wheless, MD
Michael C. Smith, MD
Carol A. Westall, PhD
Anthony Arnold, MD
Rod Foroozan, MD
Stephen M. Sagar, MD