The effect of antiepileptic drugs on visual performance

Abstract

Visual disturbances are a common side-effect of many antiepileptic drugs. Non-specific retino- and neurotoxic visual abnormalities, that are often reported with over-dosage and prolonged AED use, include diplopia, blurred vision and nystagmus. Some anticonvulsants are associated with specific visual problems that may be related to the mechanistic properties of the drug, and occur even when the drugs are administered within the recommended daily dose. Vigabatrin, a GABA-transaminase inhibitor, has been associated with bilateral concentric visual field loss, electrophysiological changes, central visual function deficits including reduced contrast sensitivity and abnormal colour perception, and morphological alterations of the fundus and retina. Topiramate, a drug that enhances GABAergic transmission, has been associated with cases of acute closed angle glaucoma, while tiagabine, a GABA uptake inhibitor, has been investigated for a potential GABAergic effect on the visual field. Only mild neurotoxic effects have been identified for patients treated with gabapentin, a drug designed as a cyclic analogue of GABA but exhibiting an unknown mechanism while carbamazepine, an inhibitor of voltage-dependent sodium channels, has been linked with abnormal colour perception and reduced contrast sensitivity. The following review outlines the visual disturbances associated with some of the most commonly prescribed anticonvulsants. For each drug, the ocular site of potential damage and the likely mechanism responsible for the adverse visual effects is described.

Retinal function and histopathology in rabbits treated with Topiramate

“…1,2 Another antiepileptic drug that increases cerebral GABA-levels is vigabatrin (inhibits GABA-transaminase), which has been shown to cause severe, persistent visual field constriction. [3][4][5][6] Several electrophysiological studies of patients treated with vigabatrin, have demonstrated reduced photopic amplitudes indicating actual dysfunction of an unspecified cell level in the retina.…”

Psychotropic Drugs and Ocular Side Effects

“…In patients of one year carbamazepine treatment, central and paracentral colour vision function decrease transparently.87 However, as this case was not identified in some human studies, this effect is not accepted by everyone. 72 In a cross-sectional study done on 18 patients being treated by valproate monotherapy for two-twenty years, colour vision defect was only seen on 2 patients at minor level. 88 Cones sensitive to short wavelength are thought to be effected by antiepileptic drugs.…”

“…[72][73][74] In the year of 2001, Young et. al 75 have shown that clonazepam is 100% effective in treatment of 5 patients with idiopathic downbeat nystagmus.…”

“…Disorders in diplopia and eye movements are especially stated in low-high dose lamotrigine monotherapy. 72,91 When lamotrigine is used in high dose or combined with carbamazepine, eye movement anomalies should be expected. 92,93 …”

Antiepileptic drugs: properties and recommended use

“…Topiramate has also been associated with an increased risk of renal calculus formation and with cases of closed-angle glaucoma. 23 Topiramate has up to 95 per cent bioavailability and is, in the absence of an enzyme inducer, largely renally excreted in an unchanged form. It is potentially susceptible to large reductions in plasma concentration (up to 50 per cent) when co-administered with an enzyme-inducing drug.…”