This prospective, longitudinal observational study investigates whether epilepsy involves a progressive neurodegenerative process. Retinal structural and microvascular changes assessed by optical coherence tomography (OCT) and optical coherence (OCTA) will be analyzed alongside inflammatory biomarkers (sCD14, sCD163, CCL2, IL-1β). The study aims to explore their association with epilepsy pathophysiology, clinical phenotype, prognosis, and drug-resistant epilepsy (DRE). Among participants with epilepsy, seizure severity and antiseizure medication-related adverse-effect burden will also be assessed longitudinally using the National Hospital Seizure Severity Scale (NHS3) and the Turkish version of Liverpool Adverse Events Profile (LAEP-TR).
Epilepsy may be associated with neuroinflammatory and neurodegenerative mechanisms. The retina provides a non-invasive window for evaluating neuroaxonal and microvascular changes through OCT and OCTA. This study will investigate whether retinal structural, microvascular, and serum inflammatory biomarker measures are associated with epilepsy phenotype, disease severity, prognosis, and drug-resistant epilepsy. Participants will be enrolled into three cohorts: adults with epilepsy, adults using antiseizure medications for non-epileptic indications, and healthy controls. Clinical data will include demographic characteristics, epilepsy history, mean monthly seizure frequency derived from seizure diaries and clinical records, antiseizure medication use, neurological examination findings, electroencephalography (EEG) findings, and magnetic resonance imaging (MRI) findings. Among participants with epilepsy, clinical epilepsy activity will be characterized using two prespecified components: mean monthly seizure frequency and seizure severity assessed with the National Hospital Seizure Severity Scale (NHS3). These components will be analyzed separately and jointly in multivariable models rather than combined into a study-specific unvalidated total score. The NHS3 will be administered at baseline and at 18 months based on the participant's most severe habitual seizure during the preceding 6 months. Patient-reported adverse effects associated with antiseizure medication treatment will be assessed separately at the same visits using the Turkish version of Liverpool Adverse Events Profile (LAEP-TR). All participants will undergo ophthalmological assessment, including visual acuity, intraocular pressure measurement, and refraction assessment. OCT and OCTA imaging will be used to measure peripapillary retinal nerve fiber layer thickness, ganglion cell-inner plexiform layer thickness, inner nuclear layer thickness, macular volume, hyperreflective retinal foci, capillary density, and foveal avascular zone area. Peripheral venous blood samples will be collected only from participants in the epilepsy group at baseline and at 18 months for serum biomarker analysis. Serum samples will be stored at -80°C. Serum soluble CD14, soluble CD163, C-C motif chemokine ligand 2, and interleukin-1 beta concentrations will be measured using commercial enzyme-linked immunosorbent assay kits according to the manufacturers' protocols. Serum biomarker outcomes and serum biomarker-based prediction analyses will therefore be restricted to participants with epilepsy.
Study Type
OBSERVATIONAL
Enrollment
250
Saglik Bilimleri University Haydarpasa Numune Education and Research Hospital Neurology Clinic
Istanbul, Turkey (Türkiye)
Annualized percentage change in peripapillary retinal nerve fiber layer thickness measured by OCT
Peripapillary RNFL thickness will be assessed with Heidelberg OCT at baseline and 18 months using the optic nerve head-centered circular scan protocol. Eye-tracking and follow-up registration will ensure reproducibility. Automated segmentation will be reviewed for centration and accuracy; global and quadrant values (superior, inferior, nasal, temporal) will be recorded. Images will be checked for quality and artifacts; scans failing criteria or with uncorrectable errors will be repeated or excluded. For participants with two eligible eyes, mean thickness will be analyzed; if one eye is eligible, that measurement will be used. Annualized percentage change will be calculated as: \[((18-month pRNFL thickness - baseline pRNFL thickness) / baseline pRNFL thickness) × 100\] / 1.5 years. Unit of measure: Percent change per year
Time frame: Baseline to 18 months after enrollment.
Annualized percentage change in ganglion cell-inner plexiform layer thickness measured by OCT
Ganglion cell-inner plexiform layer (GC-IPL) thickness will be measured with Heidelberg OCT at baseline and 18 months using a fovea-centered 6 × 6 mm macular scan. Identical parameters and eye-tracking functions will ensure reproducibility. Automated segmentation will be reviewed for centration, accuracy, and artifacts; errors will be corrected when possible. GC-IPL thickness will be calculated as the sum of ganglion cell and inner plexiform layers. Scans failing quality criteria or with uncorrectable artifacts will be repeated or excluded. For two eligible eyes, mean thickness will be analyzed; if one eye is eligible, that measurement will be used. Annualized percentage change will be calculated as: {\[(18-month GC-IPL thickness - baseline GC-IPL thickness) / baseline GC-IPL thickness\] × 100} / 1.5 years. Unit of measure: Percent change per year
Time frame: Baseline to 18 months after enrollment
Difference in annualized percentage change in peripapillary retinal nerve fiber layer thickness between drug-resistant and non-drug-resistant epilepsy groups
Annualized percentage change in peripapillary retinal nerve fiber layer thickness measured by optical coherence tomography will be compared between participants with drug-resistant epilepsy and participants without drug-resistant epilepsy. This analysis will be performed only among participants with epilepsy. Drug-resistant epilepsy will be defined as failure of adequate trials of two tolerated, appropriately chosen and used antiseizure medication schedules to achieve sustained seizure freedom. Unit of measure: Percent change per year
Time frame: Baseline to 18 months after enrollment.
Difference in annualized percentage change in ganglion cell-inner plexiform layer thickness between drug-resistant and non-drug-resistant epilepsy groups
Annualized percentage change in ganglion cell-inner plexiform layer thickness measured by macular optical coherence tomography will be compared between participants with drug-resistant epilepsy and participants without drug-resistant epilepsy. This analysis will be performed only among participants with epilepsy. Drug-resistant epilepsy will be defined as failure of adequate trials of two tolerated, appropriately chosen and used antiseizure medication schedules to achieve sustained seizure freedom. Unit of measure: Percent change per year
Time frame: Baseline to 18 months after enrollment.
Change in hyperreflective foci count measured on optical coherence tomography
Hyperreflective retinal foci (HRF) will be assessed with Heidelberg OCT at baseline and 18 months using fovea-centered 6 × 6 mm macular scans. Identical parameters will be applied at both visits. HRF will be counted twice per scan volume, and the mean of the two counts will be analyzed. For participants with two eligible eyes, the mean of both eyes will be used; if only one eye is eligible, that measurement will be included. Change will be calculated as the 18-month count minus the baseline count. Unit of measure: Number of hyperreflective foci
Time frame: Baseline to 18 months after enrollment.
Difference in hyperreflective retinal foci count between drug-resistant and non-drug-resistant epilepsy groups
Hyperreflective retinal foci count measured on optical coherence tomography will be compared between participants with drug-resistant epilepsy and participants without drug-resistant epilepsy. This analysis will be performed only among participants with epilepsy. Hyperreflective retinal foci will be counted twice on the same scan volume, and the average count will be used for analysis. Unit of measure: Number of hyperreflective retinal foci
Time frame: Baseline to 18 months after enrollment.
Change in superficial macular vessel density measured by optical coherence tomography angiography
Superficial macular vessel density will be measured using optical coherence tomography angiography at baseline and at 18 months. The OCTA device-derived superficial capillary plexus vessel density value will be recorded. The mean value of both eyes will be used for analysis. Unit of measure: Percentage points
Time frame: Baseline to 18 months after enrollment.
Change in deep macular vessel density measured by optical coherence tomography angiography
Deep macular vessel density will be measured using optical coherence tomography angiography at baseline and at 18 months. The OCTA device-derived deep capillary plexus vessel density value will be recorded. The mean value of both eyes will be used for analysis. Unit of measure: Percentage points
Time frame: Baseline to 18 months after enrollment.
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Change in peripapillary capillary vessel density measured by optical coherence tomography angiography
Peripapillary capillary vessel density will be measured using optical coherence tomography angiography at baseline and at 18 months. The OCTA device-derived peripapillary capillary density value will be recorded. The mean value of both eyes will be used for analysis. Unit of measure: Percentage points
Time frame: Baseline to 18 months after enrollment.
Change in foveal avascular zone area measured by optical coherence tomography angiography
Foveal avascular zone area will be measured using optical coherence tomography angiography at baseline and at 18 months. The OCTA device-derived foveal avascular zone area will be recorded. The mean value of both eyes will be used for analysis. Unit of measure: Square millimeters
Time frame: Baseline to 18 months after enrollment.
Change from baseline in serum interleukin-1 beta concentration measured by enzyme-linked immunosorbent assay in participants with epilepsy
Serum interleukin-1 beta concentration will be measured only in participants with epilepsy from peripheral venous blood samples collected at baseline and at 18 months. Measurements will be performed using a commercial enzyme-linked immunosorbent assay kit according to the manufacturer's protocol. Change from baseline will be calculated as the 18-month value minus the baseline value. Unit of measure: Picograms per milliliter(pg/mL)
Time frame: Baseline to 18 months after enrollment.
Change from baseline in serum C-C motif chemokine ligand 2 concentration measured by enzyme-linked immunosorbent assay in participants with epilepsy
Serum C-C motif chemokine ligand 2 concentration will be measured only in participants with epilepsy from peripheral venous blood samples collected at baseline and at 18 months. Measurements will be performed using a commercial enzyme-linked immunosorbent assay kit according to the manufacturer's protocol. Change from baseline will be calculated as the 18-month value minus the baseline value. Unit of Measure: Picograms per milliliter(pg/mL)
Time frame: Baseline to 18 months after enrollment.
Change from baseline in serum soluble CD14 concentration measured by enzyme-linked immunosorbent assay in participants with epilepsy
Serum soluble CD14 concentration will be measured only in participants with epilepsy from peripheral venous blood samples collected at baseline and at 18 months. Measurements will be performed using a commercial enzyme-linked immunosorbent assay kit according to the manufacturer's protocol. Change from baseline will be calculated as the 18-month value minus the baseline value. Unit of measure: Nanograms per milliliter(ng/mL)
Time frame: Baseline to 18 months after enrollment.
Change from baseline in serum soluble CD163 concentration measured by enzyme-linked immunosorbent assay in participants with epilepsy
Serum soluble CD163 concentration will be measured only in participants with epilepsy from peripheral venous blood samples collected at baseline and at 18 months. Measurements will be performed using a commercial enzyme-linked immunosorbent assay kit according to the manufacturer's protocol. Change from baseline will be calculated as the 18-month value minus the baseline value. Unit of measure: Nanograms per milliliter(ng/mL)
Time frame: Baseline to 18 months after enrollment.
Association of mean monthly seizure frequency and baseline National Hospital Seizure Severity Scale score with annualized percentage change in peripapillary retinal nerve fiber layer thickness
Among participants with epilepsy, mean monthly seizure frequency during follow-up will be calculated from seizure diaries and clinical records. Baseline seizure severity will be assessed with the National Hospital Seizure Severity Scale (NHS3), based on all seizure types experienced in the past 6 months and their severity. Annualized percentage change in peripapillary RNFL thickness will be derived from baseline and 18-month OCT measurements. Independent associations of seizure frequency and NHS3 total score with RNFL change will be evaluated using multivariable linear regression. Unit of Measure: Regression coefficient
Time frame: Baseline to 18 months after enrollment.
Association of mean monthly seizure frequency and baseline National Hospital Seizure Severity Scale score with annualized percentage change in ganglion cell-inner plexiform layer thickness
Among participants with epilepsy, mean monthly seizure frequency during follow-up will be calculated from seizure diaries and clinical records. Baseline seizure severity will be assessed with the National Hospital Seizure Severity Scale (NHS3), based on all seizure types experienced in the past 6 months and their severity. Annualized percentage change in ganglion cell-inner plexiform layer (GC-IPL) thickness will be derived from baseline and 18-month OCT measurements. Independent associations of seizure frequency and NHS3 total score with GC-IPL change will be evaluated using multivariable linear regression. Unit of Measure: Regression coefficient
Time frame: Baseline to 18 months after enrollment.
Correlation between number of antiseizure medications and ganglion cell-inner plexiform layer thickness measured by optical coherence tomography
The number of antiseizure medications will be recorded from clinical records. Ganglion cell-inner plexiform layer thickness will be measured using macular optical coherence tomography. The correlation between the number of antiseizure medications and ganglion cell-inner plexiform layer thickness will be assessed using Pearson or Spearman correlation according to data distribution. Unit of Measure: Correlation coefficient
Time frame: Baseline to 18 months after enrollment.
Difference in peripapillary retinal nerve fiber layer thickness across epilepsy syndrome groups
Peripapillary retinal nerve fiber layer thickness measured by optical coherence tomography will be compared across epilepsy syndrome groups classified according to the International League Against Epilepsy classification. The mean value of both eyes will be used for analysis. Unit of Measure: Micrometers(µm)
Time frame: Baseline to 18 months after enrollment.
Difference in ganglion cell-inner plexiform layer thickness across epilepsy syndrome groups
Ganglion cell-inner plexiform layer thickness measured by macular optical coherence tomography will be compared across epilepsy syndrome groups classified according to the International League Against Epilepsy classification. The mean value of both eyes will be used for analysis. Unit of Measure: Micrometers(µm)
Time frame: Baseline to 18 months after enrollment.
Predictive performance of a predefined retinal-inflammatory biomarker model for drug-resistant epilepsy status
A predefined multivariable prediction model will include retinal structural measures, optical coherence tomography angiography-derived vascular measures, hyperreflective retinal foci count, and serum inflammatory biomarker concentrations. The model's ability to predict drug-resistant epilepsy status will be evaluated using the area under the receiver operating characteristic curve. Unit of Measure: Area under the receiver operating characteristic curve
Time frame: Baseline to 18 months after enrollment.
Change from baseline in National Hospital Seizure Severity Scale score among participants with epilepsy
The National Hospital Seizure Severity Scale (NHS3) will be administered to participants with epilepsy at baseline and 18 months. All seizure types experienced in the past 6 months and their severity will be evaluated, applying the same predefined seizure-selection rule at both visits. Change from baseline will be calculated as the 18-month NHS3 total score minus the baseline score. Unit of Measure: Points.
Time frame: Baseline to 18 months after enrollment
Change from baseline in Turkish version of Liverpool Adverse Events Profile total score among participants with epilepsy
The Turkish version of Liverpool Adverse Events Profile (LAEP-TR) will be administered to participants with epilepsy at baseline and 18 months to assess patient-reported adverse effects of antiseizure medications. Change from baseline will be calculated as the 18-month LAEP-TR total score minus the baseline score. Unit of Measure: Points.
Time frame: Baseline to 18 months after enrollment