Retinal function and histopathology in rabbits treated with Topiramate

Presumed topiramate-induced retinopathy in a 58-year-old woman

We present a case of presumed topiramate-induced retinopathy in a 58-year-old woman who presented with progressive, bilateral visual loss following a 3- to 4-year history of oral topiramate intake for migraine. She reported difficulty with light adaptation, hemeralopia, and color desaturation. Her best-corrected visual acuity was 1/60 (20/1200) in the right eye and 6/18 (20/60) in the left eye, and she performed poorly on Ishihara color plate testing. Anterior segment examination was normal; dilated funduscopy showed mild macular pigmentary changes. Optical coherence tomography revealed subtle thinning and reduced reflectivity of the subfoveal ellipsoid zone and interdigitation zone bilaterally, associated with increased foveal autofluorescence. Humphrey visual field 24-2 revealed central defects. Electrodiagnostic testing showed a reduced and delayed b-wave and a normal a-wave on photopic full-field electroretinogram (ERG), with normal scotopic responses; multifocal ERG revealed reduced responses in the inner 10° in both eyes. She underwent extensive investigations including whole-body computed tomography and positron emission tomography scan, magnetic resonance imaging of the brain, uveitis screening, retinal autoantibody testing, and genetic testing on the retinal dystrophy panel to rule-out other causes for her presentation, all of which were normal or negative.

Use of Visual Electrophysiology to Monitor Retinal and Optic Nerve Toxicity of Medications

It is important for clinicians to consider exposure to toxic substances and nutritional deficiencies when diagnosing and managing cases of vision loss. In these cases, physiologic damage can alter the function of key components of the visual pathway before morphologic changes can be detected by traditional imaging methods. Electrophysiologic tests can aid in the early detection of such functional changes to visual pathway components, including the retina or optic nerve. This review provides an overview of various electrophysiologic techniques, including multifocal electroretinogram (mfERG), full-field ERG (ffERG), electrooculogram (EOG), pattern electroretinogram (PERG), and visual evoked potential (VEP) in monitoring the retinal and optic nerve toxicities of alcohol, amiodarone, cefuroxime, cisplatin, deferoxamine, digoxin, ethambutol, hydroxychloroquine, isotretinoin, ocular siderosis, pentosane, PDE5 inhibitors, phenothiazines (chlorpromazine and thioridazine), quinine, tamoxifen, topiramate, vigabatrin, and vitamin A deficiency.

Paeonol attenuates retinopathy in streptozotocin-induced diabetes in rats by regulating the oxidative stress and polyol pathway

The current research work was planned to study the effects of paeonol in the management of diabetic retinopathy. Diabetes was induced in male Sprague Dawley rats using Streptozotocin (55 mg/kg, i.p.). After 4 weeks, the diabetic animals were treated with paeonol at a dose of 50, 100, and 200 mg/kg body weight daily for the next 4 weeks. At the end of treatment, retinal physiology was studied by recording an electroretinogram (ERG); biochemical parameters and oxidative stress were estimated. The histopathology of the retina was also carried out at the end of the study. The ERG of paeonol-treated animals showed a significant improvement in a-wave amplitude, b-wave amplitude, a-wave latency, and b-wave latency (p < 0.001) at 15 cd s/m² when compared with the diabetic control animals. The paeonol treatment (200 mg/kg) in diabetic animals showed a significant decrease in the plasma glucose level (p < 0.001) when compared to the animals in diabetic control group. Paeonol also significantly decreased the lactate dehydrogenase, aldose reductase, and sorbitol dehydrogenase levels when compared with the diabetic control animals. The oxidative stress in the eye was significantly reduced after the paeonol treatment in the diabetic rats. The histopathology showed a significant reduction (p < 0.05) in the retinal thickness after the paeonol treatment. The results of the study indicate that paeonol can be considered an effective management option for diabetic retinopathy.

The Ophthalmic Side Effects of Topiramate: A Review

Topiramate (TPM) is a sulfonamide drug with multiple modes of action. It inhibits carbonic anhydrase, blocks sodium channels, enhances potassium channels, and stimulates postsynaptic gamma-aminobutyric acid (GABA) receptors. Pharmacists Joe Gardocki and Bruce Maryanoff synthesized TPM for the first time in 1979. The FDA did not approve it for medical use in the US until 1996. Around 2004, it was authorized for the prevention of migraine headaches. TPM, like any medication, has several side effects. Common aftermaths include weight loss, diarrhea, dizziness, sleepiness, fatigue, and coordination issues. Some people may experience mental health issues like memory problems, confusion, and speech or language difficulties. The most well-known ocular side effects of TPM are choroidal effusion syndrome, angle-closure glaucoma, and myopic shift. Aside from these, other ophthalmic adverse effects may arise in some people, including retinal problems, uveitis, visual field defects, myokymia, and neuro-ophthalmology complications. If such complications are not identified and treated promptly, they can be severe and vision-threatening, potentially leading to permanent blindness. TPM's application as a standalone and adjunctive therapy has increased over time. In 2019, more than 10 million prescriptions of TPM were issued. Due to its extensive use, medical professionals and patients must be aware of its potential repercussions, especially ophthalmic issues. The current review paper likewise makes a step in this direction. This article's primary purpose is to educate readers by providing a comprehensive assessment of the research on TPM's ocular side effects. All the information has been collected via a thorough search of the Google Search Engine and PubMed.

Supersaturation of VEP in Migraine without Aura Patients Treated with Topiramate: An Anatomo-Functional Biomarker of the Disease

Migraine is a primary headache with high prevalence among the general population, characterized by functional hypersensitivity to both exogenous and endogenous stimuli particularly affecting the nociceptive system. The hyperresponsivity of cortical neurons could be due to a disequilibrium in the excitatory/inhibitory signaling. This study aimed to investigate the anatomo-functional pathway from the retina to the primary visual cortex using visual evoked potentials (VEP). Contrast gain protocol was used in 15 patients diagnosed with migraine without aura (at baseline and after 3 months of topiramate therapy) and 13 controls. A saturation (S) index was assessed to monitor the response of VEP’s amplitude to contrast gain. Non-linear nor monotone growth of VEP (S < 0.95) was defined as supersaturation. A greater percentage of migraine patients (53%) relative to controls (7%) showed this characteristic. A strong inverse correlation was found between the S index and the number of days separating the registration of VEP from the next migraine attack. Moreover, allodynia measured through the Allodynia Symptoms Check-list (ASC-12) correlates with the S index both at baseline and after 3 months of topiramate treatment. Other clinical characteristics were not related to supersaturation. Topiramate therapy, although effective, did not influence electrophysiological parameters suggesting a non-intracortical nor retinal origin of the supersaturation (with possible involvement of relay cells from the lateral geniculate nucleus). In conclusion, the elaboration of visual stimuli and visual cortex activity is different in migraine patients compared to controls. More data are necessary to confirm the potential use of the S index as a biomarker for the migraine cycle (association with the pain-phase) and cortical sensitization (allodynia).

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.

Comprehensive review of visual defects reported with topiramate

Objective

The objective of this study was to analyze clinical patterns of visual field defects (VFDs) reported with topiramate treatment and assess possible mechanism of action (MOA) for antiepileptic drug (AED) associated VFDs.

Methods

A comprehensive topiramate database review included preclinical data, sponsor’s clinical trials database, postmarketing spontaneous reports, and medical literature. All treatment-emergent adverse events (TEAEs) suggestive of retinal dysfunction/damage were summarized. Relative risk (RR) was computed from topiramate double-blind, placebo-controlled trials (DBPCTs) data.

Results

Preclinical studies and medical literature review suggested that despite sharing gamma-aminobutyric acid (GABA)-ergic MOA with other AEDs, topiramate treatment was not associated with VFDs. TEAEs suggestive of retinal dysfunction/damage were observed in 0.3%–0.7% of adults and pediatric patients with topiramate (N=4,679) versus ≤0.1% with placebo (N=1,834) in DBPCTs for approved indications (epilepsy and migraine prophylaxis); open-label trials (OLTs) and DBPCTs for investigational indications had similar incidence. Overall, 88% TEAEs were mild or moderate in severity. Serious TEAEs were very rare (DBPCTs: 0%; OLTs: ≤0.1%), and most were not treatment limiting, and resolved. The most common visual TEAEs (approved indications) were VFD, scotoma, and optic atrophy. The incidence of TEAEs in DBPCTs (approved and investigational indications) was higher in topiramate-treated (N=9,169) versus placebo-treated patients (N=5,023; 0.36% vs 0.24%), but the RR versus placebo-treated patients was not significant (RR: 1.51 [95% confidence interval: 0.78, 2.91]).

Conclusion

VFDs do not appear to be a class effect for AEDs with GABA-ergic MOA. The RR for VFDs is not significantly different between topiramate and placebo treatment.

Effect of topiramate on choroidal thickness and anterior chamber parameters in the treatment of patients with migraine

OBJECTIVE

To investigate the effects of topiramate on choroidal thickness and anterior chamber parameters using optical coherence tomography in the treatment of patients with migraine.

METHODS

A total of 22 eyes of 22 adults (12 females, 10 males) diagnosed with migraine and scheduled to topiramate treatment for pain control were recruited in this prospective study. Choroidal thickness (CT), anterior chamber depth (ACD), anterior chamber angle (ACA), spherical refractive equivalent (SphEq) and intraocular pressure (IOP) measurements were recorded at baseline (prior the topiramate therapy), first and second month visits for the statistical analysis. One-way ANOVA with repeated measures test was used for the statistical evaluation.

RESULTS

Mean age of the patients was 40.2 ± 6.5 years. Mean CT at central fovea was 324 ± 47 μm initially, 341 ± 45 μm in the first month and 344 ± 46 μm in the second month, thus first and second month measures were significantly higher than base values (p < 0.001). There was also a slight increase in IOP values among baseline (15.5 ± 2.4 mmHg) and follow-up visits (17.5 ± 2.6 mmHg, 19.0 ± 3.3 mmHg, respectively, ` p = 0.001). Baseline ACD (3.66 ± 0.22 mm) measures significantly decreased at the first month (3.63 ± 0.22 mm) and second month (3.62 ± 0.22 mm, p = 0.009). Also, a significant reduction was detected in the first (36.2 ± 4.9°) and second month (35.9 ± 5.1°) ACA measures comparing with baseline (39.1 ± 5.1°, p = 0.05). A significant myopic shift was determined in the first and second month SphEq values (-0.08 ± 0.6, -0.10 ± 0.6, respectively, p = 0.05).

CONCLUSIONS

The study revealed increased CT and altered anterior chamber parameters and IOP due to topiramate therapy. Therefore, the patients using topiramate should be carefully monitored by an ophthalmologist considering the possible side effects.

Presumed topiramate retinopathy: a case report

Background

We report a case of peripheral pigmentary retinopathy and visual field loss following topiramate use for uncontrolled seizures. Such side effects have not been well documented despite the increasing use of topiramate in the past 10 years. A thorough search of available English literature revealed only a small number of reports of topiramate-induced retinopathy or visual field defects in humans. One similar case has been described. We are concerned about the possible rare instances of this occurrence in future patients and hence would like to propose a presumed correlation.

Case presentation

A 48-year-old Chinese woman developed blurred vision after 9 months of topiramate use. Her visual acuity dropped from 1.2 to 0.7 in both eyes, with bilateral diffuse pigmentary retinopathy and a constricted visual field. Despite an improvement in visual acuity after cessation of the drug, the other clinical findings remained. The temporal relationship between the initiation of topiramate and the visual disturbance suggests that topiramate could be the cause of such signs and symptoms.

Conclusion

Topiramate potentially causes pigmentary retinopathy and constricted visual field.

Topiramate associated non-glaucomatous visual field defects

We report a 34-years-old woman who presented with bilateral incongruous inferior visual field defects after the commencement of topiramate for management of migraine. Investigations did not reveal any underlying angle closure glaucoma, reported in current literature to be associated commonly with topiramate associated visual field defects. The changes in the peripheral visual fields gradually improved over several months after the medication was withdrawn. There were only minor changes persistent on the left side on a background of pre-existing myopia and keratoconus. Visual field deficits secondary to topiramate are more commonly attributed to angle closure glaucoma due to ciliochoroidal effusion syndrome. In such instance, the visual field defects are associated with considerable pain due to raised intra-ocular pressure. There have also been reports of visual scotomas due to retinal damage and maculopathy in patients taking topiramate. It is worthwhile to obtain a baseline perimetry in patients being considered for topiramate therapy in order to gauge any changes in their peripheral field of vision during the treatment. Changes in visual fields during the course of medication use and after cessation can be easily compared especially if there are other possible confounders such as refractive errors or a history of migraine.

Evaluation of Ocular Side Effects in the Patients on Topiramate Therapy for Control of Migrainous Headache

INTRODUCTION

Topiramate, a sulfa-derivative monosaccharide, is an antiepileptic drug which is administered in the control of migraine. It is reported to cause various ocular side effects such as visual field defect and myopic shift. To investigate the alterations in refractive error, properties of the cornea and changes in the anterior chamber in patients that receive Topiramate for migraine control.

MATERIALS AND METHODS

This is a hospital-based, non-interventional, observational study that is conducted at Imam Hossein Hospital, affiliated to Shahid Beheshti University of Medical Sciences, Department of Neurology, in collaboration with the department of Ophthalmology. Thirty three consecutive patients with the diagnosis of migraine that were candidate for Topiramate therapy were recruited. Patients with history of ocular trauma or surgery, keratoconus, glaucoma, congenital ocular malformations and any history of unexplained visual loss were excluded. After thorough ophthalmic examination, all the patients underwent central corneal thickness (CCT) measurement, and Pentacam imaging (Scheimpflug camera) at the baseline. Various parameters were extracted and used for analysis. Anterior chamber volume (ACV), anterior chamber depth (ACD), and anterior chamber angle (ACA) measurement was performed. These measurements were repeated on day 30(th) and 90(th) after the initiation of Topiramate therapy. According to the normality tests, parameters with normal distribution were analysed using the repeated measures test and the remaining parameters (with non-normal distribution) were analysed using the non-parametric k-sample test. A p-value< 0.05 was considered statistically significant, according to Bonferroni post hoc correction.

RESULTS

There were 66 eyes of 33 patients under the diagnosis of migrainous headache, that Topiramate was initiated for headache control, included in the study. The mean value of refractive error had a statistically significant myopic change, from -0.23 diopters (D) at the baseline to -0.61 D at the 90(th) day of follow-up period (p-value < 0.001). Mean CCT was 531.43 μm at the baseline and increased to 534.72 μm at the 30(th) day, and 537.51 μm at the 90(th) day after the administration of Topiramate (p-value=0.001). Mean value of other parameters, ACV, ACD, and ACA, did not reveal statistically significant change.

CONCLUSION

Myopic shift and gradually increasing CCT in the patients after Topiramate administration should be considered before any refractive surgery. We found no gradual change in the anterior chamber and angle parameters in our patients in the 90 days of follow up. More studies with a longer duration of follow-up are needed to elucidate dose-dependent ocular manifestations.

Sweep visually evoked potentials and visual findings in children with West syndrome

BACKGROUND

West syndrome (WS) is a type of early childhood epilepsy characterized by progressive neurological development deterioration that includes vision.

AIM

To demonstrate the clinical importance of grating visual acuity thresholds (GVA) measurement by sweep visually evoked potentials technique (sweep-VEP) as a reliable tool for evaluation of the visual cortex status in WS children.

METHODS

This is a retrospective study of the best-corrected binocular GVA and ophthalmological features of WS children referred for the Laboratory of Clinical Electrophysiology of Vision of UNIFESP from 1998 to 2012 (Committee on Ethics in Research of UNIFESP n° 0349/08). The GVA deficit was calculated by subtracting binocular GVA score (logMAR units) of each patient from the median values of age norms from our own lab and classified as mild (0.1-0.39 logMAR), moderate (0.40-0.80 logMAR) or severe (>0.81 logMAR). Associated ophthalmological features were also described.

RESULTS

Data from 30 WS children (age from 6 to 108 months, median = 14.5 months, mean ± SD = 22.0 ± 22.1 months; 19 male) were analyzed. The majority presented severe GVA deficit (0.15-1.44 logMAR; mean ± SD = 0.82 ± 0.32 logMAR; median = 0.82 logMAR), poor visual behavior, high prevalence of strabismus and great variability in ocular positioning. The GVA deficit did not vary according to gender (P = .8022), WS type (P = .908), birth age (P = .2881), perinatal oxygenation (P = .7692), visual behavior (P = .8789), ocular motility (P = .1821), nystagmus (P = .2868), risk of drug-induced retinopathy (P = .4632) and participation in early visual stimulation therapy (P = .9010).

CONCLUSIONS

The sweep-VEP technique is a reliable tool to classify visual system impairment in WS children, in agreement with the poor visual behavior exhibited by them.

Ocular toxicity from systemically administered xenobiotics

INTRODUCTION

The eye is considered as the most privileged organ because of the blood-ocular barrier that acts as a barrier to systemically administered xenobiotics. However, there has been a significant increase in the number of reports on systemic drug-induced ocular complications. If such complications are left untreated, then it may cause permanent damage to vision. Hence, knowledge of most recent updates on ever-increasing reports of such toxicities has become imperative to develop better therapy while minimizing toxicities.

AREAS COVERED

The article is mainly divided into anterior and posterior segment manifestations caused by systemically administered drugs. The anterior segment is further elaborated on corneal complications where as the posterior segment is focused on optic nerve, retinal and vitreous complications. Furthermore, this article includes recent updates on acute and chronic ocular predicaments, in addition to discussing various associated symptoms caused by drugs.

EXPERT OPINION

Direct correlation of ocular toxicities due to systemic drug therapy is evident from current literature. Therefore, it is necessary to have detailed documentation of these complications to improve understanding and predict toxicities. We made an attempt to ensure that the reader is aware of the characteristic ocular complications, the potential for irreversible drug toxicity and indications for cessation.

Topiramate and the vision: a systematic review

BACKGROUND AND PURPOSE

Topiramate (TPM) is a sulfa-derivative monosaccharide that is used mainly for treating epilepsy and preventing migraine. Within the gamut of side effects attributable to this drug, ophthalmologic manifestations are of crucial importance. In this study, for the first time, the aim was to provide a systematic literature review regarding this issue.

METHODS

For the time period 1996-2011, a PubMed search was made for the studies concerning the adverse/beneficial effects of TPM on vision. Overall, 404 citations out of a total of 2756 TPM-related studies were examined for relevance.

RESULTS

A total of 74 relevant studies were reviewed, 65 of which comprise small observational studies describing the ophthalmic side effects of TPM in 84 patients. Of these patients, 66 were affected by ciliochoroidal effusion syndrome as the cardinal ocular side effect of TPM (17 cases of myopic shift and 49 cases of angle closure glaucoma). A comprehensive statistical analysis is provided on these 66 subjects. Other rare side effects of TPM on the vision were also reviewed, including massive choroidal effusion, ocular inflammatory reactions, visual field defects, probable effects on retina, cornea, and sclera, and neuroophthalmologic complications. In addition, a framework is provided to classify these results.

DISCUSSION

Due to the expanding spectrum of indications for the administration of TPM, neurologists and psychiatrists should be aware of its diverse ocular side effects. In conclusion, ocular complications following this drug should be taken seriously and be subjected to ophthalmic counseling.

Topiramate and visual loss in a patient carrying a Leber hereditary optic neuropathy mutation

We describe a 43-year-old patient who experienced visual loss 4 years after beginning antiepileptic therapy with topiramate. Ophthalmological and neurological examinations led to a preliminary diagnosis of bilateral toxic optic neuritis. Mitochondrial genome sequence analysis detected a Leber hereditary optic neuropathy 11778G>A mutation. The possibility that topiramate might favor a conversion disease, alerts physicians to seek a history of blindness in patients undergoing chronic antiepileptic therapy.

Massive bilateral choroidal detachment induced by administration of topiramate

Topiramate is a sulfa-derivative antiepileptic drug which is also used for other indications such as essential tremor. A 79-year-old male was admitted to our center due to acute bilateral painless decline of vision. One month before admission, he had experienced essential tremor and treatment with topiramate 50 mg/day and propranolol 40 mg/day. Best-corrected visual acuity was 20/800 OD and 20/600 OS. Both eyes had normal anterior chamber depths and irides. Intraocular pressure was 10 mm Hg in the right eye and 11 mm Hg in the left eye. Retinal examination showed notable choroidal detachments in all quadrants of the periphery, which were confirmed by ultrasonography. Refraction showed no myopic shift. The administration of topiramate was discontinued as a potential causative agent for this condition. During follow-up, choroidal detachment and visual acuity gradually resolved. In this study, we described the first case of isolated massive choroidal detachment induced by topiramate.

Effect of pregnancy on topiramate pharmacokinetics in rabbits

Pregnancy is associated with various physiological changes that may lead to significant alterations in the pharmacokinetic profiles of many drugs. The present study was designed to investigate the potential effects of pregnancy on the pharmacokinetics of topiramate (TPM) in the rabbit model. Nineteen female New Zealand white rabbits (nine pregnant and 10 non-pregnant) were used in this study. Blood samples were collected from the animals just before receiving TPM orally at a dose of 20 mg/kg and then serially for up to 24 h. TPM plasma samples were analysed using a validated tandem mass spectrometric (LC-MS/MS) method. The mean values of TPM pharmacokinetic parameters (t(1/2), T(max), AUC(0-∞), and CL/F) were significantly modified in pregnant rabbits as compared with non-pregnant group. Pregnancy significantly (P < 0.05) increased TPM half-life (t(1/2)), time to attain the maximum plasma concentration (T(max)), and the area under TPM plasma concentration-time curve (AUC(0-∞)) and decreased the drug's oral clearance (CL/F) compared with non-pregnancy state in rabbits. The present study demonstrates that pregnancy alters the pharmacokinetics of TPM in rabbits in late gestational period and considerable inter-animal variability was observed. The findings of the present study indicate that TPM CL/F is decreased during late pregnancy in the rabbit model.

Antagonists of ionotropic gamma-aminobutyric acid receptors impair the NiCl2-mediated stimulation of the electroretinogram b-wave amplitude from the isolated superfused vertebrate retina

PURPOSE

NiCl(2) (15 microM) stimulates the electroretinogram (ERG) b-wave amplitude of vertebrate retina up to 1.5-fold through its blocking of E/R-type voltage-gated Ca(2+) channels. Assuming that such an increase is mediated by blocking the release of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) via ionotropic GABA receptors, we tested the effect of both GABA itself and GABA-receptor antagonists such as (-)bicuculline (1.51-fold increase) and (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA; 1.46-fold increase) on the b-wave amplitude.

METHODS

Recording of the transretinal potentials from the isolated bovine retina.

RESULTS

GABA (100 microM) reduced the b-wave amplitude only when NiCl(2) (15 microM) was applied first. Each antagonist applied on its own stimulated the b-wave amplitude only partially: subsequent NiCl(2) superfusion caused a small but additional increase, leading to a 1.69- and a 1.88-fold total increase of the amplitude by Ni(2+) plus (-)bicuculline or Ni(2+) plus TPMPA, respectively. Only the application of both antagonists in combination, before superfusing low NiCl(2) (15 microM), completely prevented subsequent stimulation by NiCl(2) with a similar 1.90-fold total increase of b-wave amplitude. Those retina segments that did not respond to NiCl(2) could not be stimulated by (-)bicuculline and vice versa.

CONCLUSION

The stimulatory effect of NiCl(2) on the ERG b-wave amplitude is mainly, but not only, mediated by a NiCl(2)-sensitive, Ca(v)2.3-triggered GABA release acting through ionotropic GABA-A and GABA-C receptors.

Presumed topiramate-induced maculopathy

The case of a patient who developed decreased vision while taking topiramate (TPM) for symptomatic epilepsy is described. Ophthalmological examination revealed findings suggestive of maculopathy. TPM was discontinued; however, vision failed to improve significantly over 6 months of follow-up. We hypothesize that the patient's maculopathy was induced by TPM. TPM, like vigabatrin, may exert retinal toxicity causing persistent visual impairment.

Ocular adverse effects of Topiramate: Two case reports

Topiramate, an antiepileptic drug is reported to cause various ocular adverse effects like acute onset myopia, glaucoma. Visual field defect is an uncommon, serious treatment emergent adverse effect. We are reporting two cases of suspected topiramate induced visual field defects.Both the cases were on topiramate for more than 6 months as add-on therapy at daily doses ranging from 100-150mg. The presenting complaints were insidious onset visual disturbances. Diagnosis was based of temporal association with drug intake, clinical examination and investigations. Automated perimetry revealed bilateral superior quadrantic and arcuate field defects in the two cases respectively. Marked improvement with drug dechallenge was noted which was also corroborated by perimetry. Using Naranjo's ADR Probability Scale, both cases revealed a "probable" association with topiramate. This report intends to improve awareness amongst clinicians to facilitate early diagnosis and intervention.

Electronegative electroretinogram associated with topiramate toxicity and vitelliform maculopathy

Topiramate is known to cause ocular side effects such as refractive changes and angle closure. We describe a patient with an electronegative electroretinogram (ERG) which may have been related to topiramate use. Electronegative ERG's have been associated with other drugs in humans as well as topiramate use in rabbits. However, this would be the first suggestion of causality in humans.