Assessment of colour vision in epileptic patients exposed to single-drug therapy

Retinal ganglion cell complex and visual evoked potentials in levetiracetam treatment

PURPOSE

To examine central macular, RNFL (retinal nerve fibre layer), GCC (ganglion cell complex) thicknesses; and VEPs (visual evoked potential) in epileptic patients using levetiracetam for at least one year.

MATERIALS AND METHODS

Sixteen focal epileptic patients receiving levetiracetam monotherapy and 16 healthy subjects were included in the study. Central macular, RNFL and GCC thicknesses according to spectral domain OCT (optical coherence tomography); and VEPs parameters were compared between patients and healthy subjects.

RESULTS

The mean age of patient and control groups were 40 ± 16 and 38 ± 12 years respectively (p > 0.05). The patient group was on levetiracetam therapy for 64 ± 45 (12-168) months. Central macular thickness was thinner in the patient group (p = 0.008). There was no difference among groups regarding RNFL thicknesses. GCC thicknesses in all quadrants were similar among groups, except the superior quadrant; which was thinner in the patient group (p = 0.03). P100 amplitude in 30 min pattern was lower in the patient group (p = 0.04). N135 latency in 15 min (p = 0.03) and 7 min patterns (p = 0.01) was longer in the patient group.

CONCLUSION

Central macular and GCC thicknesses; and VEP parameters in patients receiving levetiracetam treatment may differ from healthy subjects.

Phenytoin - An anti-seizure drug: Overview of its chemistry, pharmacology and toxicology

Phenytoin is a long-standing, anti-seizure drug widely used in clinical practice. It has also been evaluated in the context of many other illnesses in addition to its original epilepsy indication. The narrow therapeutic index of phenytoin and its ubiquitous daily use pose a high risk of poisoning. This review article focuses on the chemistry, pharmacokinetics, and toxicology of phenytoin, with a special focus on its mutagenicity, carcinogenicity, and teratogenicity. The side effects on human health associated with phenytoin use are thoroughly described. In particular, DRESS syndrome and cerebellar atrophy are addressed. This review will help in further understanding the benefits phenytoin use in the treatment of epilepsy.

An investigation of the ocular toxic effects of levetiracetam therapy in children with epilepsy

OBJECTIVE

To investigate the potential toxic effects of levetiracetam monotherapy on ocular tissues in cases of pediatric epilepsy using optical coherence tomography (OCT).

METHODS

Thirty epileptic children (group 1) receiving levetiracetam monotherapy at a dosage of 20-40 mg/kg/day for at least 1 year with a first diagnosis of epilepsy and 30 age- and gender-matched healthy children (group 2) were included in the study. In addition to a detailed eye examination, peripapillary retinal nerve fiber layer (RNFL) thickness, ganglion cell complex (GCC) thickness, foveal thickness (FT), and central corneal thickness (CCT) were measured in all children by means of spectral domain OCT. The data obtained from the two groups were then subjected to statistical analysis.

RESULTS

The mean age of both groups was 12 ± 3.64 years [1-12]. The mean duration of levetiracetam in group 1 was 24.07 ± 12.82 months. Mean RNFL values in groups 1 and 2 were 106.1 ± 10.42 and 104.98 ± 10.04 μm, mean GCC values were 94.72 ± 6.26 and 94.4 ± 6 μm, mean FT values were 240.73 ± 17.94 and 240.77 ± 15.97 μm, and mean CCT values were 555.1 ± 44.88 and 540.97 ± 32.65 μm, respectively. No significant difference was determined between the two groups in terms of any parameter. Best corrected visual acuity values of the subjects in both groups were 10/10, and no color vision or visual field deficit was determined.

CONCLUSION

Levetiracetam monotherapy causes no significant function or morphological change in ocular tissues in pediatric epilepsies.

Ocular dysfunctions and toxicities induced by antiepileptic medications: Types, pathogenic mechanisms, and treatment strategies

INTRODUCTION

Ocular dysfunctions and toxicities induced by antiepileptic drugs (AEDs) are rarely reviewed and not frequently received attention by treating physicians compared to other adverse effects (e.g. endocrinologic, cognitive and metabolic). However, some are frequent and progressive even in therapeutic concentrations or result in permanent blindness. Although some adverse effects are non-specific, others are related to the specific pharmacodynamics of the drug. Areas covered: This review was written after detailed search in PubMed, EMBASE, ISI web, SciELO, Scopus, and Cochrane Central Register databases (from 1970 to 2019). It summarized the reported ophthalmologic adverse effects of the currently available AEDs; their risks and possible pathogenic mechanisms. They include ocular motility dysfunctions, retinopathy, maculopathy, glaucoma, myopia, optic neuropathy, and impaired retinal vascular autoregulation. In general, ophthalmo-neuro- or retino-toxic adverse effects of AEDs are classified as type A (dose-dependent), type B (host-dependent or idiosyncratic) or type C which is due to the cumulative effect from long-term use. Expert opinion: Ocular adverse effects of AEDs are rarely reviewed although some are frequent or may result in permanent blindness. Increasing knowledge of their incidence and improving understanding of their risks and pathogenic mechanisms are crucial for monitoring, prevention, and management of patients' at risk.

The effects of vitamin B6 on lens antioxidant system in valproic acid-administered rats

Valproic acid (VPA, 2-propyl pentanoic acid) is a broad-spectrum antiepileptic drug (AED) and is commonly used in the treatment of bipolar disorders and epilepsy. AEDs are known to result in vascular disturbances. Vitamin B6 (Vit B6) is water soluble vitamin essential for normal growth, development, and metabolism. In this study, we aimed to investigate the protective effects of Vit B6 against VPA-induced lens damage in experimental animals. In this study, male 4-month-old, Sprague-Dawley rats were used. The animals were divided into four groups. Group I was intact control animals. Group II rats were administered with Vit B6 (50 mg/kg/day) for 7 days. Group III rats were administered with only VPA (500 mg/kg/day) for 7 days. Group IV was given VPA + Vit B6 (in a same dose and time). Vit B6 was given to rats by gavage and VPA was given by intraperitoneally. On the 8th day of experiment, all of the animals were fasted overnight and then killed under ether anesthesia. Lens tissues were taken from animals, homogenized in 0.9% saline to make up a 10% homogenate. The homogenates was used for glutathione (GSH), lipid peroxidation (LPO), protein levels, and enzyme analysis. In VPA groups, levels of lens GSH and LPO and activities of glutathione- S-transferase, glutathione peroxidase, glutathione reductase, and aldose reductase were increased, while superoxide dismutase activity was decreased. Treatment with Vit B6 reversed these effects. These results demonstrated that administration of Vit B6 is potentially beneficial agent to reduce the lens damage in VPA toxicity, probably by decreasing oxidative stress.

The long-term safety of antiepileptic drugs

Antiepileptic drugs (AEDs) are used by millions of people worldwide for the treatment of epilepsy, as well as in many other neurological and psychiatric conditions. They are frequently associated with adverse effects (AEs), which have an impact on the tolerability and success of treatment. Half the people who develop intolerable AEs discontinue treatment early on after initiation, while the majority of people will continue to be exposed to their effects for long periods of time. The long-term safety of AEDs reflects their potential for chronic, cumulative dose effects; rare, but potentially serious late idiosyncratic effects; late, dose-related effects; and delayed, teratogenic or neurodevelopmental effects. These AEs can affect every body system and are usually insidious. With the exception of delayed effects, most other late or chronic AEs are reversible. To date, there is no clear evidence of a carcinogenic effect of AEDs in humans. While physicians are aware of the long-term AEs of old AEDs (the traditional liver enzyme-inducing AEDs and valproate), information about AEs of new AEDs (such as lamotrigine, levetiracetam, oxcarbazepine, topiramate or zonisamide), particularly of their teratogenic effects, has emerged over the years. Sporadic publications have raised issues about AEs of the newer AEDs eslicarbazepine, retigabine, rufinamide, lacosamide and perampanel but their long-term safety profiles may take years to be fully appreciated. Physicians should not only be aware of the late and chronic AEs of AEDs but should systematically enquire and screen for these according to the individual AED AE profile. Care should be taken for individuals with comorbid conditions that may render them more susceptible to specific AEs. Prevention and appropriate management of long-term AED AEs is expected to improve adherence to treatment, quality of life and control of epilepsy.

Antiepileptic drugs and visual function

Antiepileptic drugs are known to result in visual disturbances. A number of antiepileptic drugs have recently been reported to result in various abnormalities of vision, particularly deficiencies in visual fields and color vision. Moreover, there has been a marked improvement in the diagnosis and understanding of the pathophysiology of visual disturbance. This review collects evidence for visual adverse effects induced by the older antiepileptic drugs (barbiturates, benzodiazepine, carbamazepine, valproic acid, ethosuximide, and phenytoin) and the newer ones (vigabatrin, topiramate, tiagabine, levetiracetam, lamotrigine, gabapentin, felbamate, and oxcarbazepine).

Color vision and macular recovery time in epileptic adolescents treated with valproate and carbamazepine

Visual dysfunction has been reported in patients diagnosed with epilepsy. Some of these visual disturbances may be attributable to either the disease process, or the anticonvulsant therapy prescribed to control the seizures. The aims of our study were to evaluate whether color vision and macular function are impaired in epileptic adolescents, to study if the monotherapy with valproic acid (VPA) and carbamazepine (CBZ) can affect color vision and macular function and to determine the possible relationship between color vision, retinal function and antiepileptic drugs (AEDs) dosage and their serum concentrations. We examined 45 (16 male and 29 female, mean age +/- SD, 15.71 +/- 2.01 years) Caucasian epileptic patients suffering from various types of cryptogenic epilepsy before the beginning of therapy and after 1 year of VPA or CBZ monotherapy and 40 sex- and age-matched healthy controls. Color vision was assessed by Farnsworth Munsell (FM) 100-hue test and total error score (TES) was evaluated. This test consists of colored caps: the testee has to arrange the caps according to their colors macular function was assessed by nyctometry evaluating initial recovery time (IRT) and summation method (SM). This test evaluates visual acuity after a period of intense illumination of macula. Analysis of variance was used to evaluate the difference between controls and patients; moreover, Pearson's correlation test have been performed. Before the beginning of therapy, there were no differences in color vision and macular function between controls and epileptic patients. After 1 year, the patients, treated with VPA or CBZ, showed a deficit in FM 100-hue test. At nyctometry, all patients showed no significant variation of macular function between baseline evaluation and second evaluation at end of the follow-up. Our study demonstrates that, in our group of epileptic patients, epilepsy per se does not affect color vision and retinal function. In contrast, after 1 years of therapy with VPA and CBZ these patients showed a deficit in FM 100-hue test although nyctometry evaluation continued to be normal allowing to exclude an impairment in macular function. Further investigations are required to determine the pathophysiological alteration(s) that are at the basis of color perception defects.

Color vision and contrast sensitivity in epilepsy patients treated with initial tiagabine monotherapy

The purpose of the study was to determine whether the use of a GABAergic antiepileptic drug (AED), tiagabine, affects color vision and contrast sensitivity. Twenty newly diagnosed patients with partial epilepsy (aged 19-72 years), receiving tiagabine as their initial monotherapy for 5-41 months were examined. Color vision was examined with the Standard Pseudoisochromatic Plates 2 (SPP2), with the Farnsworth-Munsell 100 Hue Test (FM100) and with the Color Vision Meter 712 (CVM) anomaloscope. Contrast sensitivity was measured with the Pelli-Robson letter chart. Three patients excluded from the color vision evaluation for congenital red-green color vision defects. Seven out of 17 patients (41%) had acquired color vision deficit examined with the FM100. The CVM anomaloscope revealed minor defects in two patients. Contrast sensitivity function was within normal ranges. The present study suggests that AED therapy with tiagabine, like with other established and newer AEDs may interfere with color perception.

Epilepsy and Medication Effects on the Pattern Visual Evoked Potential*

Visual disruption in patients diagnosed with epilepsy may be attributable to either the disease itself or to the anti-epileptic drugs prescribed to control the seizures. Effects on visual function may be due to perturbations of the GABAergic neurotransmitter system, since deficits in GABAergic cortical interneurons have been hypothesized to underlie some forms of epilepsy, some anti-epileptic medications increase cortical GABA levels, and GABAergic neural circuitry plays an important role in mediating the responses of cells in the visual cortex and retina. This paper characterizes the effects of epilepsy and epilepsy medications on the visual evoked response to patterned stimuli. Steady-state visual evoked potentials (VEP) evoked by onset-offset modulation of high-contrast sine-wave stimuli were measured in 24 control and 54 epileptic patients. Comparisons of VEP spectral amplitude as a function of spatial frequency were made between controls, complex partial, and generalized epilepsy groups. The effects of the GABA-active medication valproate were compared to those of carbamezepine. The amplitude of the fundamental (F1) component of the VEP was found to be sensitive to epilepsy type. Test subjects with generalized epilepsy had F1 spatial frequency-amplitude functions with peaks shifted to lower spatial frequencies relative to controls and test subjects with complex partial epilepsy. This shift may be due to reduced intracortical inhibition in the subjects with generalized epilepsy. The second harmonic component (F2) response was sensitive to medication effects. Complex partial epilepsy patients on VPA therapies showed reduced F2 response amplitude across spatial frequencies, consistent with previous findings that showed the F2 response is sensitive to GABA-ergic effects on transient components of the VEP.

Color vision in epileptic adolescents treated with valproate and carbamazepine

OBJECTIVE

The aims of our study were to evaluate whether deficits in color vision exist in epileptic adolescents, to study if monotherapy with valproic acid (VPA) and carbamazepine (CBZ) can affect color vision, and to determine the possible relationship between abnormal color vision tests and AEDs dosage and their serum concentrations.

PATIENTS

We examined 45 epileptic patients before the beginning of therapy and after 1 year of VPA or CBZ monotherapy and 40 sex- and age-matched healthy controls.

METHODS

Color vision was evaluated with Farnsworth Munsell 100 (FM100) hue test and achromatic and short-wavelength automated perimetry (SWAP).

STATISTICAL ANALYSIS

To evaluate intergroup differences we used ANOVA with Scheffe's post hoc test, when appropriate. Repeated measures ANOVA was used to evaluate the intragroup modifications of total error score (TES) and perimetric threshold during the follow-up. Pearson's correlation test was performed to correlate chromatic sense and perimetric data and AEDs dosage and serum concentrations.

RESULTS

Before the beginning of therapy, there were no differences in central color vision and SWAP between controls and epileptic patients. After 1 year, patients treated with VPA or CBZ showed a deficit in FM100 hue test and SWAP parameters while no significant deficit was found in achromatic perimetry. In particular, with the FM100 hue test a higher number of errors was found in both groups of patients (CBZ patients: 166.00 +/- 27.72 TES; VPA patients: 151.19 +/- 44.09, P < 0.001) in comparison with controls (controls: 109.29 +/- 24.73) and baseline values (CBZ patients: 110.65 +/- 22.9; VPA patients 107.43 +/- 21.70). With SWAP patients of both groups showed significant variation of foveal threshold (controls: 21.07 +/- 2.01 dB; CBZ patients: 19.35 +/- 1.32, P < 0.001; VPA patients: 18.88 +/- 1.89, P < 0.001), full-field mean threshold perimetric sensitivity (controls: 18.50 +/- 1.24 dB; CBZ patients: 16.60 +/- 1.47, P < 0.001; VPA patients: 16.23 +/- 1.55, P < 0.001) and mean threshold perimetric sensitivity of the three evaluated subareas of the visual field (area 1 controls: 21.01 +/- 1.15; CBZ patients: 19.45 +/- 1.74, P = 0.001; VPA patients: 18.25 +/- 1.61, P < 0.001; area 2 controls: 18.40 +/- 1.43; CBZ patients: 16.07 +/- 1.58, P +/- 0.001; VPA patients: 16.13 +/- 1.46, P = 0.001; area 3 controls: 17.20 +/- 1.49; CBZ patients: 14.28 +/- 1.51, P < 0.001; VPA patients: 14.31 +/- 2.90, P = 0.001).

CONCLUSIONS

Our study demonstrates that treatment with VPA or CBZ can affect significantly both central and paracentral color vision after a short treatment period.

The effect of antiepileptic drugs on visual performance

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.

Color vision and occupational chemical exposures: I. An overview of tests and effects

The paper presents a summary of the literature published until December 2000 on effects from some industrial chemical exposures on color perception, as well as short descriptions of the tests applied. Several different tests have been used to study acquired alterations of color vision. These changes are frequently found in the blue-yellow axis. Many of the tests were originally designed to detect congenital alterations in the red-green axis, and thus have relatively low sensitivity when studying chemically induced deficits in color perception. At present, the Lanthony D15-desaturated panel seems most suitable for application in industrial settings, since it is clearly the most sensitive and easily administered test. Color vision seems to be a physiological function very sensitive to several chemicals. The potency of industrial chemicals to induce color vision deficiencies has often been investigated during the last two decades. The chemicals most frequently studied are different solvents and mercury. Pronounced effects on color perception have been reported following chronic exposure to organic solvents such as styrene, carbon disulphide, perchloroethylene, n-hexane and solvent mixtures, and to organic as well as inorganic mercury. The effect of occupational toluene exposure seems not as well established, since only slight effects and several negative studies have been reported. For some of these compounds the effect on color vision has been further established through the finding of clear dose-effect relationships. In a few cases, even acute exposure situations, e.g. exposure to toluene for a few hours or acute alcohol intake, seem to affect color perception. Follow-up studies are needed to investigate the possible reversibility of effects in relation to discontinued or reduced exposures.

Visual fields and tiagabine: a quandary

This case report describes the development of asymptomatic visual field defects (VFDs) in a psychiatric patient with bipolar disorder receiving adjunctive tiagabine treatment. These defects were apparently reversible upon the discontinuation of tiagabine. Controlled clinical trials are indicated to determine if this finding is indicative of a class effect for all GABAergic antiepileptic drugs (AEDs), as already noted with vigabatrin, or if this case represents an incidental finding with tiagabine (41 references).