A 16 year old female referred to the ophthalmology clinic for visual difficulties, "like a part of the waxed area that I can't see, especially for the last 3 weeks". Her mother reports that "she has gone from being an active child to being slowed down, with difficulty in thinking, speaking and now she can't see properly". Since the age of 7 she has had epileptic seizures that are difficult to control. Her treatment was carbamazepine, hydantoin and for 3 months Topamax 125 mg a day. The last ophthalmological examination performed a year earlier was normal. On examination, spontaneous visual acuity (VA) was 1 in both eyes, with normal anterior biomicroscopy. Pupils were isochoric and normoreactive. Funduscopic examination showed no abnormalities. Computerised campimetry showed a non-congruent left homonymous hemianopsia. The colour test showed no alterations in either eye. Brain magnetic resonance imaging (MRI) with gadolinium was normal as well as diffusion MRI. The rest of the neurological examination was normal. In view of the suspicion of a Topamax toxic phenomenon, Topamax was progressively discontinued, with subjective improvement of the patient and partial recovery of the visual field.