Retinal nerve fibre layer thinning is associated with drug resistance in epilepsy

The thickness of the retinal nerve fiber layer, macula, and ganglion cell-inner plexiform layer in people with drug-resistant epilepsy

OBJECTIVE

Using Optical coherence tomography (OCT), we evaluated the association between peripapillary retinal nerve fiber, macular thickness, macular ganglion cell-inner plexiform layer, and drug resistance.

METHODS

In this cross-sectional study, we recruited people diagnosed with epilepsy and healthy controls. People with epilepsy were further stratified as drug-resistant or non-drug-resistant based on their response to anti-seizure medications. OCT measurements were conducted, and findings in right eye were analyzed.

RESULTS

Fifty-one drug-resistant participants, 37 non-drug-resistant, and 45 controls were enrolled. The average peripapillary retinal nerve fiber layer, ganglion cell-inner plexiform layer, and macular thickness were thinner in the epilepsy groups than in controls. The drug-resistant group had significantly lower average ganglion cell-inner plexiform layer thickness (p = 0.004) and a higher proportion of abnormal/borderline GC/IPL thickness (p = 5.40E-04) than the non-drug-resistant group. Nevertheless, no significant differences were seen between the average thickness of peripapillary retinal nerve fiber and macular thickness. The temporal sectors of these three parameters were also significantly thinner in the drug-resistant group than in the non-drug-resistant. In a multivariate regression model, drug resistance was an independent predictor of reduced ganglion cell-inner plexiform thickness (Odds ratios OR = 10.25, 95% CI 2.82 to 37.28). Increased seizure frequency (r = -0.23, p = 0.039) and a higher number of anti-seizure medications ever used (r = -0.27, p = 0.013) were negatively associated with ganglion cell-inner plexiform layer thickness.

SIGNIFICANCE

Individuals with drug-resistant epilepsy had a consistent reduction in average ganglion cell-inner plexiform layer thickness and the temporal sector of peripapillary retinal nerve fiber layer and macular thickness. This suggests that ganglion cell-inner plexiform layer thickness could potentially serve as an indicator of the burden of drug resistance, as it correlated with reduced thickness in individuals having more frequent seizures and greater exposure to ASMs.

PLAIN LANGUAGE SUMMARY

In our study, we used a special tool called OCT to measure how thick the retina is in people with epilepsy and in healthy control. We found that the retina was consistently thinner in all areas for those with epilepsy compared to healthy control. Particularly, a specific layer called the ganglion cell-inner plexiform layer was a lot thinner in the group that didn't respond to medications, and this thinning was related to how often seizures occurred and how much medications were taken. Also, certain parts of the retina were thinner in the drug-resistant group.

Microstructural Changes in Intraretinal Layers and Macular Structures of People with Epilepsy Measured Using Optical Coherence Tomography

Introduction

Epilepsy is a network disorder that can cause alterations in retinal morphology due to microstructural changes in the brain. The aim of our study was to use spectral optical coherence tomography (OCT) to assess the possible effects of neuronal degeneration on the intraretinal layers and macular structures of people with epilepsy and epilepsy subgroups.

Methods

We enrolled 52 consecutive people with epilepsy (37 females, 15 males; mean age 29.8±9.9 years; range, 17-48 years) and 40 healthy volunteers (27 females, 13 males; mean age 33.3±10.2 years; range, 19-49 years) in this study. Both eyes of all participants were assessed by using spectral-domain OCT. Optical coherence tomography was used to assess the thickness of the peripapillary retinal nerve fiber layer (RNFL), ganglion cell layer-inner plexiform layer (GCC-IPL), central macula, and central macular volume.

Results

In comparison to healthy controls, people with epilepsy showed a thinner GCC-IPL in the superior and superior-nasal quadrants, as well as reduced macular thickness and macular volume (p<0.05). The thickness of the GCC-IPL layer in the superior and inferior subquadrants was negatively affected by frequent seizures (>5 seizures/year), polytherapy, and long-duration of epilepsy (≥10 years) (p<0.05). However, we did not find any other statistically significant associations between OCT measurements, age, sex, and epilepsy type (focal and generalized onset epilepsy).

Conclusion

Individuals with epilepsy exhibited microstructural alterations in the retinal layers, primarily in the superior and inferior quadrants. Frequent seizures, polytherapy, and long-duration of epilepsy may result in neuronal damage in the afferent visual system.

The effect of epilepsy and anti-epileptic drugs on the anterior and posterior segment of the eye

CLINICAL RELEVANCE

Understanding the causes of visual symptoms in epilepsy patients is important for early diagnosis and taking precautions.

BACKGROUND

The aim of this study is to evaluate the anterior and posterior segment parameters in patients with generalized tonic-clonic epilepsy (GTCE).

METHODS

This retrospective study included 50 eyes of 50 patients with GTCE and 55 eyes of 55 healthy controls. For all participants, detailed ophthalmic examinations were obtained from the files of patients. Anterior segment parameters were measured using corneal topography and non-contact specular microscopy, and posterior segment parameters were measured using swept-source optical coherence tomography.

RESULTS

The mean age of the patients with GTCE was 43.3 ± 13.2 years, and in the healthy controls it was 47.6 ± 10.7 years (p = 0.405). In GTCE patients, 34 patients were treated with monotherapy (MT) and 16 patients with polytherapy (PT). Central macular thickness (CMT) was statistically significantly thin in GTCE patients (p = 0.001). The average and four quadrants (superior, inferior, nasal, temporal) retinal nerve fibre layer (RNFL) were thinner in GTCE patients than in the healthy controls, but there was no statistically significant difference (p > 0.05, all). The central corneal thickness was statistically significantly thin in GTCE patients (p = 0.04). Endothelial cell density (ECD), endothelial cell number (ECN), and average cell area (ACA) were statistically significantly lower in GTCE patients than in the healthy controls (p < 0.05, all). Although the CMT, average, and four-quadrants RNFL were thinner in the PT group compared to the MT group, no statistically significant difference was observed (p > 0.05, all). Total high-order aberrations (HOAs) were 0.6 ± 0.4 in the MT group and 0.4 ± 0.1 in the PT group (p = 0.01). ECD, ECN, and ACA measurements were observed to be lower in the PT group compared to the MT group, but no statistically significant difference was detected (p > 0.05, all).

CONCLUSION

There could be statistically significant differences between GTCE patients and healthy controls in anterior and posterior segment parameters. This situation may be due to the epilepsy itself or to the antiepileptic drugs.

Alzheimer's disease pathophysiology in the Retina

The retina is an emerging CNS target for potential noninvasive diagnosis and tracking of Alzheimer's disease (AD). Studies have identified the pathological hallmarks of AD, including amyloid β-protein (Aβ) deposits and abnormal tau protein isoforms, in the retinas of AD patients and animal models. Moreover, structural and functional vascular abnormalities such as reduced blood flow, vascular Aβ deposition, and blood-retinal barrier damage, along with inflammation and neurodegeneration, have been described in retinas of patients with mild cognitive impairment and AD dementia. Histological, biochemical, and clinical studies have demonstrated that the nature and severity of AD pathologies in the retina and brain correspond. Proteomics analysis revealed a similar pattern of dysregulated proteins and biological pathways in the retina and brain of AD patients, with enhanced inflammatory and neurodegenerative processes, impaired oxidative-phosphorylation, and mitochondrial dysfunction. Notably, investigational imaging technologies can now detect AD-specific amyloid deposits, as well as vasculopathy and neurodegeneration in the retina of living AD patients, suggesting alterations at different disease stages and links to brain pathology. Current and exploratory ophthalmic imaging modalities, such as optical coherence tomography (OCT), OCT-angiography, confocal scanning laser ophthalmoscopy, and hyperspectral imaging, may offer promise in the clinical assessment of AD. However, further research is needed to deepen our understanding of AD's impact on the retina and its progression. To advance this field, future studies require replication in larger and diverse cohorts with confirmed AD biomarkers and standardized retinal imaging techniques. This will validate potential retinal biomarkers for AD, aiding in early screening and monitoring.

Ocular hemodynamics in epileptic children treated with antiepileptic drugs

PURPOSE

To evaluate the quantitative measurements obtained for vessel density (VD) of the optic nerve head, macula, peripapillary retinal nerve fibre layer (p-RNFL) and total retinal thicknesses (Trt) by optical coherence tomography angiography (OCT-A) and the choroidal vascular structure using an image binarization method in children with epilepsy using three different antiepileptic drugs (AEDs) and to compare these measurements with healthy participants.

METHODS

This observational, cross-sectional study included 124 patients divided into 4 groups: Group-1: patients receiving carbamazepine(n = 30), group-2: patients receiving levetiracetam (n = 31), group-3: patients receiving valproic acid (n = 32), and group 4: healthy controls (n = 31).A fully automated microstructural analysis of the VD of the retinal superficial capillary plexus (SCP), deep capillary plexus (DCP), and the choriocapillaris (CC) layers and radial peripapillary capillary, and Trt, p-RNFL thickness were analyzed by using OCT-A. Enhanced depth imaging (EDI)-OCT scans of the macula were obtained and the images were binarized using the ImageJ software.

RESULTS

The mean age, gender distribution and the duration of epilepsy were similar in all groups. Evaluation of the p-RNFL thickness and perifoveal Trt between the groups showed a statistically significant difference in all quadrants.The p-RNFL thickness was lower in patients receiving carbamazepine and valproic acid. The lowest values of the luminal area and choroidal vascular index (CVI) were found in patients receiving valproic acid; comparison with matched healthy controls showed statistically significant differences.

CONCLUSION

Valproic acid and carbamazepine are associated with thinning of the p-RNFL in epilepsy patients, but the macular and radial peripapillary VD were not affected.However, a reduction of choroidal vascular blood flow was found in epilepsy patients taking valproic acid.

Choroid and Retinal Effects of Epilepsy and Epilepsy Subgroups

Objectives

The objective were to evaluate structural alterations in the retina and choroid tissue of epilepsy patients and subtypes using enhanced depth imaging optic coherence tomography (EDI-OCT).

Methods

46 epilepsy patients and 50 sex- and age-matched control patients were analyzed in the study. Patients' epilepsy types were recorded. The central macular thickness (CMT), retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), and choroidal thickness (CT) were investigated through the Spectralis-OCT device (SD-OCT). Image-J program was used to calculate the total choroidal area (TCA), the luminal area (LA), stromal area (SA), and the choroidal vascularity index (CVI).

Results

CMT, TCA, LA, and SA outcomes were substantially reduced in epilepsy patients than in healthy controls. There was no significant difference between CT, RNFL, GCL, CVI results. There were no statistically significant differences between patients with partial and generalized epilepsy (p>0.05 for each).

Conclusion

According to the results of our study, epilepsy disease has effects on the posterior segment of the eye. To the best of our knowledge, our study is the first to evaluate CVI in patients with epilepsy and the epilepsy subgroups.

Effects of sodium valproate and levetiracetam on posterior segment parameters in children with epilepsy

PURPOSE

To evaluate changes in posterior segment parameters in pediatric patients with epilepsy using sodium valproate or levetiracetam monotherapy for at least 12 months.

METHODS

This study included 45 children with generalized epilepsy aged 6-17 years and 32 age- and gender-matched healthy subjects. The patients were assigned to three groups: Group 1 included patients using valproate monotherapy at a dose of 20-40 mg/kg/day, group 2 included patients using levetiracetam monotherapy at a dose of 20-40 mg/kg/day, and group 3 consisted of healthy controls. Peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell layer-inner plexiform layer (mGCIPL) thicknesses were measured using spectral-domain optical coherence tomography (OCT).

RESULTS

No significant differences were noted between the groups regarding age, gender distribution, visual acuity, spherical equivalent, and intraocular pressure (p > 0.05). The average and temporal, nasal, and superior quadrants RNFL values were significantly thinner in group 1 than in group 2 (p = 0.001, p = 0.023, p = 0.011, and p = 0.001, respectively) and group 3 (p < 0.001, p = 0.032, p < 0.001, and p = 0.001, respectively). The OCT parameters were similar in groups 2 and 3 (p > 0.05). A negative correlation was observed in group 1 between only the average mGCIPL and the treatment dose (r =  - 0.501). In group 2, no significant correlation was found between OCT parameters and the duration of epilepsy treatment, dose of treatment, and age at treatment onset values (p > 0.05).

CONCLUSION

These findings support that there is an association between sodium valproate treatment and the reduction of RNFL thickness in epilepsy. Levetiracetam treatment appears to be a safe option, but care should be taken regarding ocular side effects that may occur with long-term and high-dose use of sodium valproate.

Association between retinal thickness and disease characteristics in adult epilepsy: A cross-sectional OCT evaluation

OBJECTIVE

Thinning of the peripapillary retinal nerve fiber layer (p-RNFL), as measured by optical coherence tomography (OCT), was recently introduced as a promising marker for cerebral neuronal loss in people with epilepsy (PwE). However, its clinical implication remains to be elucidated. We thus aimed to (1) systematically characterize the extent of the retinal neuroaxonal loss in a broad spectrum of unselected PwE and (2) to evaluate the main clinical determinants.

METHODS

In this prospective study, a spectral-domain OCT evaluation was performed on 98 well-characterized PwE and 85 healthy controls (HCs) (18-55 years of age). All inner retinal layers and the total macula volume were assessed. Group comparisons and linear regression analyses with stepwise backward selection were performed to identify relevant clinical and demographic modulators of the retinal neuroaxonal integrity.

RESULTS

PwE (age: 33.7 ± 10.6 years; 58.2% female) revealed a significant neuroaxonal loss across all assessed retinal layers (global pRNFL, P = 0.001, Δ = 4.24 μm; macular RNFL, P < 0.001, Δ = 0.05 mm3 ; ganglion cell inner plexiform layer, P < 0.001, Δ = 0.11 mm3 ; inner nuclear layer, INL, P = 0.03, Δ = 0.02 mm3 ) as well as significantly reduced total macula volumes (TMV, P < 0.001, Δ = 0.18 mm3 ) compared to HCs (age: 31.2 ± 9.0 years; 57.6% female). The extent of retinal neuroaxonal loss was associated with the occurrence and frequency of tonic-clonic seizures and the number of antiseizure medications, and was most pronounced in male patients.

SIGNIFICANCE

PwE presented an extensive retinal neuroaxonal loss, affecting not only the peripapillary but also macular structures. The noninvasive and economic measurement via OCT bears the potential to establish as a practical tool to inform patient management, as the extent of the retinal neuroaxonal loss reflects aspects of disease severity and sex-specific vulnerability.

PLAIN LANGUAGE SUMMARY

The retina is an extension of the brain and closely connected to it. Thus, cerebral alterations like atrophy reflect also on the retinal level. This is advantageous, as the retina is easily accessible and measureable with help of the optical coherence tomography. Here we report that adults with epilepsy have a significantly thinner retina than healthy persons. Especially people with many big seizures and a lot of medications have a thinner retina. We propose that measurement of the retina can be useful as a marker of disease severity and to inform patient management.

Evaluation of ganglion cell complex and retinal nerve fiber layer thinning in epilepsy patients

Purpose

This study aimed to compare the perimacular ganglion cell complex (GCC) and peripapillary retinal nerve fiber layer (RNFL) thickness measurements of epileptic and healthy individuals.

Methods

The right eyes of 38 epileptic and 38 healthy individuals who had been using antiepileptic drugs (AEDs) for at least 1 year were included in the study. Central macular thickness, perimacular GCC thickness and volume, and peripapillary retinal nerve fiber layers were measured by optical coherence tomography (OCT) device. Perimacular 1, 3, and 6 mm circle diameters of Early Treatment of Diabetic Retinopathy Study (ETDRS.

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were selected for GCC measurements.

Results

In epilepsy patients, GCC was significantly lower in the 3 mm superior quadrant and 6 mm in all quadrants compared to the control group (P < 0.05). RNFL was significantly thinner in epilepsy patients only in the temporal-inferior quadrant (P < 0.05). There was no significant difference between the patients who received AEDs as monotherapy and polytherapy (P > 0.05).

Conclusion

We found that epilepsy patients had significant thinning in the GCC layers and temporal-inferior quadrant of RNFL compared to the control group. Our findings from the study show that early retinal changes in epilepsy patients, especially perimacular GCC layers, can be followed up with OCT.

Evaluation of optical coherence tomography findings in adolescents with genetic generalized epilepsy

OBJECTIVE

To evaluate retinal nerve fiber layer (RNFL) thickness, central macular thickness (CMT), and subfoveal choroid thickness (CT) by using optical coherence tomography (OCT) in adolescents with newly diagnosed epilepsy and patients who had been using Na valproate (VPA) for at least 1 year.

METHODS

We examined 60 patients with genetic generalized epilepsy (GGE) aged 8-17 years. Thirty patients with newly diagnosed GGE who were evaluated before the beginning of the therapy and another 30 patients who were chosen from among adolescents with epilepsy using VPA for at least 1 year were included in the study.

RESULTS

Nasal quadrant RNFL thickness and CMT measurements were significantly lower in the monotherapy group compared with the newly diagnosed group (p = 0.044 and p = 0.032, respectively). CT measurements were not significantly different between the groups (p = 0.413). There was a negative correlation in regression analysis between the duration of drug use and RNFL thickness in all quadrants.

CONCLUSION

According to our study, we observed thinning of the nasal RNFL and macular thickness in adolescents with epilepsy who were using Na valproate for at least 1 year and that as the duration of use increased, the thinning occurred in all RNFL quadrants. Further studies with larger series are needed to better understand the effects of both epilepsy and VPA on the eye.

Reduction of Retinal Thickness Ipsilateral to Hippocampal Sclerosis in Epilepsy

Objectives: Reductions in the peripapillary retinal nerve fiber layer (pRNFL) have been reported in epilepsy, namely in drug-resistant people. Hippocampal sclerosis (HS) is the most frequent cause of drug-resistant epilepsy in tertiary care centers. We aimed to evaluate the likelihood and characteristic of RNFL loss in individuals with epilepsy having HS.

Methods: Fifty-five adults diagnosed with unilateral HS (mean age of 25 years; 42 female) by magnetic resonance imaging were included in this observational cross-sectional study, 58 age-matched individuals with epilepsy with no detectable structural brain abnormality were included as non-HS, and 55 people without neurological diseases were included as healthy controls. pRNFL of both eyes was measured by optical coherence tomography (OCT). In each individual disease related information was recorded.

Results: Among the 55 individuals with unilateral HS, one (1.82%) and ten (18.18%) had significant or borderline abnormal thinning of the pRNFL of the ipsilateral eye to the HS. The average pRNFL ipsilateral to the side of HS was significantly thinner than people with epilepsy non-HS (p = 0.013) and healthy controls (p = 0.000), especially in the inferior quadrants. Only age was significantly correlated with the average and inferior quadrant pRNFL thickness of the ipsilateral eye to the HS (R = −0.286, p = 0.035; R = −0.353, p = 0.008 respectively).

Conclusion: These preliminary findings suggest that retinal abnormalities associated with HS may have a specific pattern. Further studies need to confirm this finding and to unravel the underlying mechanism.

LMR-101, a novel derivative of propofol, exhibits potent anticonvulsant effects and possibly interacts with a novel target on γ-aminobutyric acid type A receptors

OBJECTIVE

LMR-101 is a bisphenol derivative of propofol, a short-acting general anesthetic, which is also used to manage status epilepticus (SE). We evaluated the sedative and anticonvulsant effects of LMR-101 to discover its potential to manage epilepsy and SE in the clinic.

METHODS

Comparative studies between LMR-101 and propofol were performed in mice to elucidate an appropriate dose range for LMR-101 that produced anticonvulsant effects without significant sedation. Then, the anticonvulsive efficacy for LMR-101 was evaluated using seizure models induced by pentylenetetrazol and (+)-bicuculline. The ability of LMR-101 to inhibit SE was assessed using a rat model of SE induced by pilocarpine. Radioligand binding assay profiles for LMR-101 were performed to evaluate the potential mechanisms of action underlying its anticonvulsant properties.

RESULTS

In the mouse study, LMR-101 exhibited greater anticonvulsant and lesser sedative effect compared with propofol. LMR-101 completely inhibited pentylenetetrazol-induced seizures at a dose of 50 mg/kg and exhibited heavy sedation at 300 mg/kg. Propofol anesthetized all mice and only decreased the seizure rate at 25 mg/kg. LMR-101 also suppressed seizure behaviors evoked by (+)-bicuculline in mice in a dose-dependent manner. In the pilocarpine-induced SE model, LMR-101 significantly decreased the maximum seizure score and seizure duration in a dose-dependent manner. The median effective dose for LMR-101 was 14.30 mg/kg and 121.87 mg/kg to prevent and inhibit sustained SE, respectively. In binding assays, LMR-101 primarily inhibited tert-[³⁵ S] butylbicyclophosphorothionate binding to γ-aminobutyric acid type A (GABA_A ) receptors (half-maximal inhibitory concentration = 2.06 μmol·L^-1 ), but it did not affect [³ H] flunitrazepam or [³ H] muscimol binding.

SIGNIFICANCE

It is anticipated that LMR-101 might play an essential role in the clinical management of epilepsy and SE. LMR-101 also might bind to a novel target site on the GABA_A receptor that is different from existing antiepileptic drugs. Further study of the mechanisms of action of LMR-101 would be of considerable value in the search for new active drug sites on GABA_A receptors.

Detection of Neurological and Ophthalmological Pathologies with Optical Coherence Tomography Using Retinal Thickness Measurements: A Bibliometric Study

We carry out a bibliometric analysis on neurological and ophthalmological pathologies based on retinal nerve fiber layer (RNFL) thickness measured with optical coherence tomography (OCT). Documents were selected from Scopus database. We have applied the most commonly used bibliometric indicators, both for production and dispersion, as Price’s law of scientific literature growth, Lotka’s law, the transient index, and the Bradford model. Finally, the participation index of the different countries and affiliations was calculated. Two-hundred-and-forty-one documents from the period 2000–2019 were retrieved. Scientific production was better adjusted to linear growth (r = 0.88) than exponential (r = 0.87). The duplication time of the documents obtained was 5.6 years. The transience index was 89.62%, which indicates that most of the scientific production is due to very few authors. The signature rate per document was 5.2. Nine journals made up the Bradford core. USA and University of California present the highest production. The most frequently discussed topics on RNFL thinning are glaucoma and neurodegenerative diseases (NDD). The growth of the scientific literature on RNFL thickness was linear, with a very high rate of transience, which indicates low productivity and the presence of numerous authors who sporadically publish on this topic. No evidence of a saturation point was observed. In the last 10 years, there has been an increase in documents relating the decline of RNFL to NDD.

Optical coherence tomography and neurodegeneration in epilepsy

PURPOSE

To compare optical coherence tomography measurements; central macular thickness, ganglion cell complex, and retinal nerve fiber layer thickness in patients with epilepsy versus healthy controls.

METHODS

We evaluated 28 eyes of 28 patients with epilepsy and 34 eyes of 34 healthy subjects. Central macular thickness, ganglion cell complex, and retinal nerve fiber layer thickness measurements were performed by spectral-domain optical coherence tomography.

RESULTS

Superior and superotemporal quadrant ganglion cell complex, average, and superior quadrant retinal nerve fiber layer thickness measurements were significantly lower in epilepsy group compared to healthy control subjects. Central macular thickness was significantly lower in polytherapy group compared to monotherapy group. Ganglion cell complex and retinal nerve fiber layer thickness measurements were not significantly different between polytherapy and monotherapy groups.

CONCLUSION

The present study shows that epileptic patients taking antiepileptic drugs have reduced ganglion cell complex and retinal nerve fiber layer thickness compared to healthy controls. This can be related to the epileptic process in the brain. Optical coherence tomography may be a useful tool for showing the neurodegeneration in patients with epilepsy.

Peripapillary retinal nerve fibre layer thinning in genetic generalized epilepsy

PURPOSE

The purpose of this study was to compare the peripapillary retinal nerve fibre layer (RNFL) between patients with genetic generalized epilepsy (GGE) and healthy controls.

METHODS

This prospective observational study was conducted on adults aged 18-60 years. The study group comprised 26 consecutive patients who met the inclusion criteria and 26 healthy age- and sex-matched healthy adults. Peripapillary RNFL thickness was measured by spectral domain optical coherence tomography.

RESULTS

The average peripapillary RNFL thickness was significantly thinner for GGE patients (98.61 μm) than for healthy controls (104.77 μm) (p = 0.016). Similar results were obtained for the left eye. The peripapillary RFNL thickness of all quadrants was lower for GGE patients than for healthy controls, but it was significant only in the superior (p = 0.009) and inferior (p = 0.024) quadrants for both eyes.

CONCLUSIONS

Our results suggest that the peripapillary RNFL is significantly thinner in GGE patients than in healthy participants. We concluded that this microstructural feature might be an intrinsic feature of GGE.

Attenuation of retinal nerve fibre layer in people with epilepsy receiving valproate

OBJECTIVES

Valproate (VPA) is one of the most frequently used anti-epileptic drugs (AEDs) worldwide. Its effects in decreasing the retinal nerve fibre layer (RNFL) thickness remain debatable. We aimed to evaluate the effect of VPA usage on the RNFL in comparison with other AEDs and no AED usage in people with epilepsy (PWE).

METHODS

In this observational case-control study, PWE were enrolled and divided into three groups: PWE 1) receiving VPA monotherapy throughout their clinical course; 2) receiving an AED other than VPA as monotherapy; and 3) who never took any AED. RNFL thickness of the right eye was measured by optical coherence tomography (OCT). In each individual, disease-related information was recorded.

RESULTS

A total of 86 individuals (51 males; median age, 25 years) with an average epilepsy duration of 6.88 years were enrolled. No difference in the demographics except for sex was noted between the groups. The average RNFL thickness in 26 individuals who had received VPA (group I) was 93.73 ± 9.24 μm, which was significantly lower than the corresponding values for the 31 individuals who received other single AED regimens (group II; 99.71 ± 8.50 μm; p = 0.031) or the 29 individuals who never used any AED (group III; 102.79 ± 8.05 μm; p = 5.67 × 10^-4), especially in the superior and inferior quadrants. The RNFL attenuation was significantly correlated with the epilepsy duration in groups II and III (r = 0.351, p = 0.006). However, no correlation between epilepsy duration, cumulative dosage of VPA, duration of treatment with VPA and RNFL thickness was found in group Ⅰ.

CONCLUSION

These preliminary findings suggest an association between VPA usage and reduction of retinal thickness in PWE, especially in the superior and inferior quadrants. Epilepsy itself might also be another risk factor for RNFL attenuation. Further studies need to confirm this finding and to unravel the underlying mechanism.

The Topographical Relationship between Visual Field Loss and Peripapillary Retinal Nerve Fibre Layer Thinning Arising from Long-Term Exposure to Vigabatrin

BACKGROUND

The antiepileptic drug vigabatrin is associated with characteristic visual field loss (VAVFL) and thinning of the peripapillary retinal nerve fibre layer (PPRNFL); however, the relationship is equivocal.

OBJECTIVE

The aim of this study was to determine the function-structure relationship associated with long-term exposure to vigabatrin, thereby improving the risk/benefit analysis of the drug.

METHODS

A cross-sectional observational design identified 40 adults who had received long-term vigabatrin for refractory seizures, who had no evidence of co-existing retino-geniculo-cortical visual pathway abnormality, and who had undergone a standardized protocol of perimetry and of optical coherence tomography (OCT) of the PPRNFL. Vigabatrin toxicity was defined as the presence of VAVFL. The function-structure relationship for the superior and inferior retinal quadrants was evaluated by two established models applicable to other optic neuropathies.

RESULTS

The function-structure relationship for each model was consistent with an optic neuropathy. PPRNFL thinning, expressed in micrometres, asymptoted at an equivalent visual field loss of worse than approximately - 10.0 dB, thereby preventing assessment of more substantial thinning. Transformation of the outcomes to retinal ganglion cell soma and axon estimates, respectively, resulted in a linear relationship.

CONCLUSIONS

Functional and structural abnormality is strongly related in individuals with vigabatrin toxicity and no evidence of visual pathway comorbidity, thereby implicating retinal ganglion cell dysfunction. OCT affords a limited measurement range compared with perimetry: severity cannot be directly assessed when the PPRNFL quadrant thickness is less than approximately 65 µm, depending on the tomographer. This limitation can be overcome by transformation of thickness to remaining axons, an outcome requiring input from perimetry.

Optical Coherence Tomography: Basic Concepts and Applications in Neuroscience Research

Optical coherence tomography is a micrometer-scale imaging modality that permits label-free, cross-sectional imaging of biological tissue microstructure using tissue backscattering properties. After its invention in the 1990s, OCT is now being widely used in several branches of neuroscience as well as other fields of biomedical science. This review study reports an overview of OCT's applications in several branches or subbranches of neuroscience such as neuroimaging, neurology, neurosurgery, neuropathology, and neuroembryology. This study has briefly summarized the recent applications of OCT in neuroscience research, including a comparison, and provides a discussion of the remaining challenges and opportunities in addition to future directions. The chief aim of the review study is to draw the attention of a broad neuroscience community in order to maximize the applications of OCT in other branches of neuroscience too, and the study may also serve as a benchmark for future OCT-based neuroscience research. Despite some limitations, OCT proves to be a useful imaging tool in both basic and clinical neuroscience research.