Comparison of Visual Evoked Potentials in Patients Affected by Optic Neuritis From Multiple Sclerosis or Neuromyelitis Optica Spectrum Disorder

To compare the visual evoked potentials (VEPs) of optic neuritis (ON) patients with multiple sclerosis (MS), neuro-myelitis optica spectrum disorder (NMOSD), and controls. To evaluate correlations between VEP and optical coherence tomography (OCT), contrast sensitivity (CS), and automated perimetry.

Original Contribution Section Editors: Clare Fraser, MD Susan Mollan, MD Comparison of Visual Evoked Potentials in Patients Affected by Optic Neuritis From Multiple Sclerosis or Neuromyelitis Optica Spectrum Disorder Thiago G. Filgueiras, MD, PhD, Maria K. Oyamada, MD, PhD, Kenzo Hokazono, MD, PhD, Leonardo P. Cunha, MD, PhD, Samira L. ApóstolosPereira, MD, PhD, Dagoberto Callegaro, MD, PhD, Mário L. R. Monteiro, MD, PhD Purpose: To compare the visual evoked potentials (VEPs) of optic neuritis (ON) patients with multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), and controls. To evaluate correlations between VEP and optical coherence tomography (OCT), contrast sensitivity (CS), and automated perimetry. Methods: Fifty-five eyes with ON from 29 patients (MS = 14 and NMOSD = 15) and 57 eyes from 29 controls were evaluated using VEP, automated perimetry, CS, and optical coherence tomography. Three groups were analyzed: 1) MS eyes with history of ON (ON-MS), 2) NMOSD eyes with ON (ONNMOSD), and 3) healthy controls. Groups were compared and associations between the parameters were tested. Results: Compared to controls, ON-MS eyes showed significantly delayed N75 and P100 latencies when using a medium-sized stimulus (309 ), and delayed P100 latency when using a large stimulus (1.5°), but similar amplitudes. Compared to controls, ON-NMOSD eyes showed significantly lower N75/P100 amplitudes (both Laboratory of Investigation in Ophthalmology (LIM 33) (TGF, MKO, KH, LPC, MLRM), Division of Ophthalmology, University of São Paulo Medical School, São Paulo, Brazil; Department of Ophthalmology (KH), Federal University of Paraná, Curitiba, Paraná, Brazil; Department of Ophthalmology (LPC), Federal University of Juiz de Fora Medical School, Juiz de Fora, Minas Gerais, Brazil; and Department of Neurology (SLA-P, DC), University of São Paulo Medical School, São Paulo, Brazil. Supported by grants from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Grant No 2013/26585-5), CAPES—Coordenação de Aperfeiçoamento de Nível Superior, Brasília, Brazil, and CNPq— Conselho Nacional de Desenvolvimento Científico e Tecnológico, (No 308172/2018-3), Brasília, Brazil. The funding organizations had no role in the design or conduct of this research. The authors report no conflicts of interest. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www. jneuro-ophthalmology.com). Address correspondence to Mario L. R. Monteiro, MD, PhD, Laboratory of Investigation in Ophthalmology (LIM 33), Division of Ophthalmology, University of São Paulo Medical School, Av. Angélica 1757 conj. 61, 01227-200, São Paulo, Brazil; E-mail: [e-mail]. e32 stimulus sizes) and P100/N135 amplitudes (with the 309 stimulus), but latencies did not differ, except for a delayed P100 latency with the 309 stimulus. When comparing the 2 ON groups using the 1.5° stimulus, there was significant delay in P100 latency in ON-MS eyes and a reduction in N75/P100 amplitude in ONNMOSD eyes. Peripapillary retinal nerve fiber layer, macular inner retinal layers, and CS measurements were significantly smaller in ON patients than in controls. A strong correlation was found between VEP parameters and inner retinal layer thickness in ON-NMOSD eyes. Conclusions: ON-MS eyes had normal amplitude and delayed VEP latency, whereas ON-NMOSD eyes displayed reduced amplitude and preserved latency when elicited by checkerboard stimulus with large 1.5° checks. Under such conditions, VEP may help distinguish resolved MS-related ON from resolved NMOSD-related ON. Journal of Neuro-Ophthalmology 2022;42:e32–e39 doi: 10.1097/WNO.0000000000001285 © 2021 by North American Neuro-Ophthalmology Society O ptic neuritis (ON) is a common optic nerve disease and an important clinical finding in patients with multiple sclerosis (MS) and neuromyelitis optica (NMO) due to the risk of significant visual loss (1). Although ON may appear similar at presentation in both conditions, NMO is a much more disabling condition requiring early diagnosis, and current treatment is often significantly different in the 2 diseases. Until some years ago, the diagnosis of NMO required a history of both ON and transverse myelitis (2,3). The discovery of the NMO-immunoglobulin G autoantibody (4), targeting aquaporin4 (AQ4) (5), led to significant changes in the diagnosis of NMO, expanding it to include clinical and laboratory criteria for NMO spectrum disorder (NMOSD) (6). Thus, patients with isolated ON may now be diagnosed with NMOSD, provided they test positive for anti-AQ4 antibody or have a specific combination of clinical and radiological findings (6,7). Testing for anti-AQ4 Filgueiras et al: J Neuro-Ophthalmol 2022; 42: e32-e39 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution antibody is a useful aid in distinguishing whether ON is caused by MS or NMOSD (8), but the sensitivity of the assay remains relatively low, and 20%–50% of patients with NMOSD are seronegative for this antibody (7,9). Other antibodies targeting myelin oligodendrocyte glycoprotein and aquaporin 1 have been reported, which may play a role in NMOSD (10,11), highlighting the difficulty of establishing a diagnosis based on laboratory testing alone. Careful analysis of clinical data is still of the essence when an ON patient is suspected of NMOSD rather than MS. Clinically, ON from NMOSD often differs from MSrelated ON with regard to the severity of visual loss at presentation, the amount of visual recovery after resolution, and optical coherence tomography (OCT) and electrophysiological findings (1,12–15). Previous studies have shown that both visual acuity (VA) and visual field (VF) are significantly worse after NMOSD-related ON than after MS-related ON (1,16). Contrast sensitivity (CS) is also affected in ON patients, but while this parameter has been extensively evaluated in patients after idiopathic or MS-related ON (17), to the best of our knowledge, no similar investigations have been conducted for NMOSD-related ON. Likewise, loss of peripapillary retinal nerve fiber layer (pRNFL) and macular ganglion cell layer (GCL) thickness on OCT is usually more severe in NMO-related ON than in MS-related ON (12–14). Another important tool in the evaluation of optic nerve diseases is the visual evoked potential (VEP), a test for assessing the integrity of the visual pathway (18). VEP signals are extracted from the electroencephalographic activity of the visual cortex, recorded through electrodes positioned on the scalp in the overlying occipital area. Because the visual cortex is activated primarily by the central VF, VEPs depend on the functional integrity of central vision at all levels of the visual pathway, including the eye, retina, optic nerve, optic radiations, and occipital cortex (19). Classically, patients with MS display an abnormally prolonged VEP latency with preserved amplitude (20), but no consensus exists regarding the standard VEP abnormalities in patients with NMOSD (21). For example, one study found that patients with NMOSD had prolonged latency and normal amplitudes, similar to what is observed in patients with MS (22), whereas another found reduced P100 without latency abnormalities (21). Thus, additional information regarding the differentiation of ON outcome based on VEP findings would be important to help differentiating the 2 conditions. The purpose of this study was therefore to compare pattern-reversal VEP data in eyes of patients with MS or NMOSD recovering from ON and in normal controls. We also evaluated possible correlations between VEP findings and OCT, CS, and VF on standard automated perimetry (SAP) in both groups of patients. METHODS Participants were recruited from the Department of Neurology of the University of São Paulo Medical School Filgueiras et al: J Neuro-Ophthalmol 2022; 42: e32-e39 in this prospective, cross-sectional study. The study was approved by the Institutional Review Board Ethics Committee, and followed the Declaration of Helsinki norms. Informed consent was obtained from all patients to the study. A total of 55 eyes with ON from 29 patients (14 with MS and 15 with NMOSD) and 57 eyes from 29 healthy controls were evaluated. The eyes were distributed into 3 groups: 1) Eyes with history of ON from MS (ON-MS), 2) eyes with history of ON from NMOSD (ON-NMOSD), and 3) controls. The diagnosis of MS or NMOSD was based on previously described diagnostic criteria (2,6,23). Information was collected on the time of diagnosis, symptoms that helped establish the diagnosis of ON, and the number of ON crises. The latter was based on selfreporting and physicians’ reports and confirmed by medical record review. Patients whose most recent attack of ON had occurred less than 6 months earlier were not included in the study because ON-related axonal loss is known to occur up to 6 months after disease onset (24). The neurological and systemic exclusion criteria for all patients were central nervous system manifestations of infectious disease, brain MRI abnormalities other than those of MS or NMOSD, and diabetes mellitus. The controls were normal healthy volunteers recruited from among companions of patients participating in the study and hospital staff. Ophthalmic Examination and Visual Function Testing All subjects were submitted to a complete ophthalmic examination, including best-corrected monocular VA evaluation and CS. VA was assessed with Early Treatment Diabetes Retinopathy Study (ETDRS) charts at 3.2 m (Lighthouse Low-Vision Products, Long Island City, NY). Snellen equivalents were also recorded for ETDRS VA measurements. The CS evaluation was performed using the “Vision Contrast Test System” (VCTS 6500, Vistech Consultants Inc, Dayton, OH). In this test, spatial frequencies (represented in cycles by degrees) are used to measure the patient’s sensitivity to an object of specific size. Five frequencies are tested: A = 1.5, B = 3.0, C = 6.0, D = 12.0, and E = 18.0. Low frequencies test sensitivity to large objects, and vice-versa. Each frequency tested starts with a high level of contrast, which is then progressively decreased. The patient simply reports the lowest perceptible contrast “patch.” (25). Table distance and ambient illumination (in cd/m2) were standardized for each spatial frequency, as instructed by the manufacturer. VF was assessed with SAP performed with a Humphrey Field Analyzer (Carl Zeiss Meditec, Dublin, CA) using the 24-2 SITA-standard strategy, with a Goldmann size III stimulus. Each point tested on SAP estimates the difference in luminance threshold (2) between the study subject and the age-matched normal value. The extent of VF defect was averaged and expressed as mean deviation (MD), that is, the e33 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution mean value of the data on the total deviation plot after excluding the 2 outer nasal points (totaling 50 points), and as central MD (CMD), corresponding to the mean value of the 12 central points on the 24-2 strategy VF test. The ophthalmological inclusion criteria for patients were: i) a best-corrected VA of 20/200 or better in at least one eye, ii) spherical refraction within ±5 D and cylinder refraction within ±3 D, iii) intraocular pressure ,21 mm Hg, iv) no concomitant ocular or other systemic diseases, and v) reliable VF. A reliable VF was defined as one with fewer than 20% fixation losses, false-positive responses, or false-negative responses. The inclusion criteria for controls were similar, with the exception of best-corrected VA, which had to be normal. Pattern Reversal Visual Evoked Potential VEP recordings were made using the RETiscan System (Roland Consult, Wiesbaden, Germany) equipped with the software RETIport32, following the guidelines of the International Society for Clinical Electrophysiology of Vision (19). This involved full-field monocular stimulation with a checkerboard-structured stimulus consisting of alternating black and white squares reversing at a predefined regular frequency. Two stimulus sizes were used: a medium-sized stimulus, subtending 309 visual angle, and a large stimulus, subtending 1.5° visual angle, both with a static frequency of 1.5 Hz, totaling 80 reversions per cycle, to elicit a foveal and parafoveal retinal response. The stimulus sizes were chosen taking into account the inclusion criterion of VA = 20/200 or better. The electrodes were placed in the positions (Oz, Cz, FPz) specified by the International Electroencephalogram 10/20 system. The subjects were asked to sit at 1 m from a 97% contrast screen in a semidark environment, with the best optical correction for the eye-to-screen distance. Two cycles of 80 reversals were presented for each stimulus. A 1–50 Hz filter was applied to reduce noise and standardize responses. We then measured the N75 and P100 peak latencies and the N75-P100 and P100-N135 peak-to-peak amplitudes. Optical Coherence Tomography On the same day as the ophthalmic examination, the subjects were submitted to OCT scanning (Spectralis OCT, Heidelberg Engineering, Heidelberg, Germany) of the macular and peripapillary area, after pupil dilation with 1% tropicamide. pRNFL thickness measurements were based on the average of 100 high-resolution scans aligned to the center of the optic nerve head. The scanning protocol for the macular area consisted of 61 horizontal B-scans (16 frames each), covering an area of 30° · 25° (9.2 · 7.6 mm) centered on the fovea, with 40,000 scans per second and an axial resolution of approximately 5 mm. Optic nerve and macular e34 images were acquired using the automated eye alignment eyetracking software (TruTrack, Heidelberg Engineering, Heidelberg, Germany). Images were reviewed with respect to their subjective and objective quality (26,27). The criteria for acceptable Spectralis fundus images included absence of large eye movements (abrupt shifts completely disconnecting a large retinal vessel), consistent signal intensity level across the scan, and absence of black bands (caused by blinking) throughout the examination. To be included in the study, images also had to have centered scans, display a signal strength above 20 dB, and comply with the previously described OSCAR-IB quality criteria (28). Macular thickness measurements were determined according to the ETDRS grid, using the anatomic quadrants (superior, inferior, nasal, and temporal) of the inner (3 mm) and outer (6 mm) circles centered on the fovea (29). pRNFL measurements were acquired in a circle of 1536 A-scan points subtending 12° centered on the optic disc, corresponding to the area inside a circle with a diameter of 3.5 mm. The temporal margin of the optic disc was chosen as a landmark and labeled 0°. From this point, the software divided the pRNFL into 6 sectors: temporal (310–41°), superotemporal (41–80°), superonasal (80–120°), nasal (121–230°), inferonasal (231–270°), and inferotemporal (271–310°), clockwise in the right eye and counterclockwise in the left eye. To better evaluate the pRNFL corresponding to the central VF, we averaged the temporal, superotemporal, and inferotemporal thickness measurements, corresponding to the 170° temporal area of the disc. Macular scans qualified for analysis were processed using the segmentation software supplied by the manufacturer. Seven retinal layers were identified with the automatic segmentation of the equipment’s software. A reviewer assessed each of the 61 B-scan frames of the volume to check for segmentation errors, which were manually corrected when necessary. After segmentation, the thickness of the following layers was measured: the RNFL, the GCL, the inner plexiform layer (IPL), the inner nuclear layer (INL), the outer plexiform layer (OPL), the outer nuclear layer (ONL), and the photoreceptor layer (PRL). The average thickness of each layer was also calculated according to the ETDRS grid and evaluated as the weighted average of the sectoral measurements, excluding the fovea. Data Analysis and Statistics The results of the descriptive statistics were expressed as mean values ± SD. The normality assumption was verified with the Shapiro–Wilk test. The groups were compared using generalized estimating equation (GEE) models that accounted for age and within-patient intereye correlations. Potential associations between variables were evaluated with Pearson correlation coefficients. The software IBM SPSS Statistics v. 21.0 was used for all analyses, with the level of significance set at 5% (P , 0.05). Filgueiras et al: J Neuro-Ophthalmol 2022; 42: e32-e39 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution TABLE 1. Demographic characteristics, visual acuity, and visual field data of patients with neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS) with history of optic neuritis and normal controls Subjects Eyes studied Age, years, mean (SD) Gender, M/F Positive anti-NMO titer (eyes) Visual acuity (median [range]) Visual field (VF) MD, median (SD) CMD, mean (SD) ON-MS ON-NMOSD Controls 14 22 36.5 (12.5) 1/13 — 20/20 (20/20 - 20/30) 15 23 35.0 (11.1) 2/13 9 (14) 20/40 (20/20 - 20/200) 29 57 45.4 (10.6) 9/20 — 20/20 (20/20 - 20/20) 26.27 (1.28)* 24.65 (0.88)* 29.03 (2.23)* 27.55 (2.20)* 21.23 (0.26) 21.22 (0.22) Covariable: age = 39.6 years and sex. *P , 0.05 compared with controls, generalized estimated equations models. MD, mean deviation; CMD, central mean deviation. RESULTS A total of 22 eyes of patients with MS and 23 eyes of patients with NMOSD randomly selected from the outpatient clinic of the Neurology Department of the University of São Paulo Medical School were included in the study. The control group consisted of 29 healthy individuals recruited from among companions of patients participating in the study and hospital staff. The ON-MS group eatured 14 MS patients (13 females) with history of relapsing or nonrelapsing episodes of ON (both eyes, affected on different occasions, in 8 patients and one eye affected in 6 patients). Because no eyes were excluded from the study, 22 eyes with history of ON were included in the group. Three eyes of 3 patients presented relapsing episodes of ON and 19 eyes of 11 patients presented nonrelapsing ON. The average time from diagnosis to evaluation was 9.60 ± 6.68 years. The mean age at diagnosis was 27.65 ± 10.01 years (range: 15–56). The ON-NMOSD group included 23 eyes from 15 patients (13 females) with history of ON (bilateral in 12 patients and unilateral in 3 patients). Four eyes with history of ON were excluded because VA was worse than 20/200. The clinical course was relapsing in 4 subjects (5 eyes) and nonrelapsing in 11 (18 eyes). The mean time from diagnosis to evaluation was 6.35 ± 5.63 years, and the mean age at diagnosis was 28.60 ± 9.74 years (range: 12–43). Nine of the 15 ON-NMOSD patients were positive for anti-AQP4 antibody, corresponding to 14 of the 23 eyes analyzed. The control group included 57 eyes of 29 subjects. One eye was excluded due to reduced VA from an epiretinal macular membrane. The demographic data of all the individuals included in the study are shown in Table 1. VF, MD, and CMD were significantly lower in ON-MS and ON-NMOSD than in controls (P , 0.001 for both), but did not differ significantly between the 2 groups of patients (Table 1). In the group of MS-ON, 2 eyes had VA of 20/30, 2 eyes had VA of 20/25, and 18 eyes had VA of 20/20. In the group of NMOSD-ON, 16 eyes had TABLE 2. Mean values (±SD) of visual evoked potentials (VEP) of patients with multiple sclerosis (ON-MS) and neuromyelitis optica spectrum disorder (ON-NMOSD) with history of optic neuritis and controls VEP 309 Stimulus N75 latency (ms) P100 latency (ms) N75-P100 amplitude (mV) (*1026) P100-N135 amplitude (mV) (*1026) 1.5° Stimulus N75 latency (ms) P100 latency (ms) N75-P100 amplitude (mV) (*1026) P100-N135 amplitude (mV) (*1026) ON-MS ON-NMOSD 88.4 ± 18.1* 129.1 ± 19.4* 11.0 ± 5.6 11.8 ± 5.9 85.1 ± 22.0 114.8 ± 18.8* 9.22 ± 7.0* 8.8 ± 8.5* 80.2 ± 16.7 127.8 ± 19.29* 11.4 ± 5.4 13.0 ± 2.62 83.1 ± 19.0 114.7 ± 17.8 9.06 ± 6.16* 13.4 ± 2.7 Controls 77.8 108.3 11.2 13.7 ± ± ± ± ON-MS versus ON-NMOSD 8.8 8.3 9.2 9.3 P P P P = = = = 0.59 0.40 0.05 0.16 76.2 ± 13.1 110.0 ± 6.72 12.1 ± 6.5 13.5 ± 3.1 P P P P = = = = 0.58 0.02† 0.01† 0.67 Covariable: age = 39.6 years and sex. *P ,0.05 compared with controls. † P ,0.05 when 2 groups were compared. Filgueiras et al: J Neuro-Ophthalmol 2022; 42: e32-e39 e35 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution TABLE 3. Mean values (±SD) of optical coherence tomography (OCT, in micrometers) of patients with multiple sclerosis and neuromyelitis optica spectrum disorder with history of optic neuritis (ON-MS and ON-NMOSD) and controls OCT Macula FT RNFL GCL IPL INL OPL ONL PRL Optic nerve RNFL (170°) ON-MS ON-NMOSD Controls ON-MS versus ON-NMOSD 297.6 ± 20.9* 25.2 ± 7.6* 34.4 ± 8.2* 29.2 ± 6.1* 35.4 ± 2.8 29.9 ± 2.4 65.2 ± 7.0 79.7 ± 2.0 289.4 ± 30.6* 25.1 ± 7.8* 33.1 ± 11.4* 29.1 ± 6.6* 36.8 ± 3.5 29.5 ± 2.8 62.1 ± 6.7 79.1 ± 1.5 314.6 ± 19.8 31.1 ± 4.3 42.5 ± 4.1 35.0 ± 2.9 35.4 ± 3.0 29.6 ± 3.4 62.5 ± 9.4 79.3 ± 3.6 P P P P P P P P 86.3 ± 22.7* 75.8 ± 36.2* 107.3 ± 19.2 P = 0.24 = = = = = = = = 0.30 0.97 0.66 0.96 0.14 0.64 0.13 0.25 Covariable: age = 39.6 years and sex. *P ,0.05 compared with controls. FT, full thickness; RNFL, macular retinal nerve fiber layer; GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; PRL, photoreceptor layer; pRNFL, peripapillary retinal nerve fiber layer. VA of 20/20, 2 eyes had VA of 20/50, and the remaining eyes had VA of 20/200, 20/150, 20/100, 20/60, and 20/25 (one eye each). Table 2 shows the results of the VEP study. Compared to controls, patients in the ON-MS group presented delayed N75 (P = 0.008) and P100 (P , 0.001) latencies with the medium-sized stimulus, and delayed P100 latency with the large stimulus (P = 0.001). ON-NMOSD patients presented lower N75-P100 amplitude with the mediumsized stimulus (P = 0.017) and large stimulus (P = 0.004), and lower P100-N135 amplitude (P = 0.02) and delayed P100 latency (P = 0.045) with the medium-sized stimulus. When the large stimulus was used, the N75-P100 amplitude was significantly smaller in ON-NMOSD than in ON-MS (P = 0.01). Table 3 shows OCT-measured macular parameters for each retinal layer and the mean pRNFL thickness of the temporal 170° disc segment in all groups. The mean macular RNFL thickness was significantly lower in eyes with history of ON than in controls (ON-MS P = 0.001; ONNMOSD P , 0.001). The mean pRNFL thickness and mean macular GCL and IPL thickness were also lower in patients than in controls. No significant difference was observed between patients and controls with regard to INL, OPL, ONL, and PRL. As expected, mean CS values were lower in patients than in controls, regardless of the spatial frequency tested. In the paired analysis, no significant difference was found between the 2 groups of patients (See Supplemental Digital Content, Table E1, http://links.lww.com/WNO/A468). Table 4 shows correlation coefficients between VEP and OCT, CS, and SAP findings. In the ON-NMOSD group, a strong positive correlation was found between the VEP amplitude and pRNFL and segmented inner retinal layers in the macula (range: 0.70–0.90). However, a strong nege36 ative correlation (range: 20.41 to 20.64) was found in the same group regarding VEP latency and macular inner retinal layer thickness. In the MS-ON group, the correlation coefficients between VEP and OCT measurements were almost all nonsignificant, with the following exceptions: OPL thickness was significantly correlated with most VEP variables, and significantly positive correlations were identified between pRNFL thickness and N75/P100 amplitude parameters. In both groups, the correlations between CS and VEP were most evident for amplitudes, especially when using the medium-sized stimulus. Only one negative correlation was identified for P100 latency in the ON-NMOSD group, using the large stimulus. Changes in VF correlated strongly and positively with VEP amplitudes (MD and CMD) in both MS and NMOSD. No significant correlation was found between VF and VEP latencies (Table 4). DISCUSSION Considering that ON leads to more severe axonal and visual damage in NMOSD than in MS (30), the detection of anatomical and functional patterns specific to each disease is of great importance for diagnosis and treatment. VEP is the main electrophysiological test capable of directly determining functional changes in the optic pathways, especially in the optic nerve, and therefore is very useful in the evaluation of clinical and subclinical optic nerve damage (31). The VEP pattern most widely associated with MS is the combination of preserved amplitude and reduced latency (especially P100), suggesting a process of optic nerve demyelination (32–35). However, the patterns reported for NMOSD have been highly inconsistent. For example, one study found waves of reduced amplitude and preserved latency (suggestive of axonal injury) (21), whereas another found a pattern of latency delay similar to that of MS (22). Filgueiras et al: J Neuro-Ophthalmol 2022; 42: e32-e39 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Filgueiras et al: J Neuro-Ophthalmol 2022; 42: e32-e39 VEP—309 Stimulus N75 LAT OCT FT RNFL GCL IPL INL OPL ONL PRL pRNFL Contrast sensitivity A B C D E Visual field MD CMD P100 LAT VEP—1.5° Stimulus N75/P100 AMP P100/N135 AMP N75 LAT P100 LAT N75/P100 AMP P100/N135 AMP MS NMOSD MS NMOSD MS NMOSD MS NMOSD MS NMOSD MS NMOSD MS NMOSD MS NMOSD 20.11 20.10 20.20 20.25 20.20 0.32 20.02 0.52 20.25 20.38 20.38 20.33 20.32 0.13 20.36 20.11 20.02 20.28 20.26 20.29 20.39 20.42 0.20 0.49 20.07 0.50 20.38 20.55 20.52 20.46 20.46 20.04 20.41 20.05 20.12 20.41 0.27 0.26 0.36 0.38 0.12 20.48 0.09 0.27 0.49 0.76 0.80 0.85 0.81 20.15 20.08 0.08 0.13 0.84 0.34 0.34 0.36 0.33 20.0.8 20.63 0.38 20.25 0.28 0.77 0.78 0.72 0.70 20.19 0.05 0.22 0.23 0.74 20.17 20.13 20.25 20.28 20.24 0.24 20.06 0.53 20.25 20.47 20.54 20.47 20.45 0.12 20.48 0.03 20.17 20.39 20.15 20.12 20.24 20.30 20.18 0.34 20.04 0.34 20.31 20.64 20.55 20.56 20.56 0.10 20.53 20.16 20.27 20.52 0.34 0.30 0.41 0.47 0.24 20.40 0.02 20.20 0.57 0.80 0.79 0.86 0.84 20.12 0.20 0.07 0.19 0.83 0.20 0.27 0.28 0.30 20.10 20.60 0.06 20.02 0.29 0.90 0.85 0.84 0.81 20.17 20.03 0.21 0.22 0.84 20.11 20.40 20.17 20.23 20.28 20.12 20.13 20.16 20.16 20.03 20.19 20.43 20.28 20.31 20.28 20.10 20.21 20.16 20.17 20.01 0.66 0.27 0.71 0.65 0.68 0.24 0.42 0.37 0.32 0.31 0.46 0.38 0.58 0.46 0.47 0.37 0.48 0.39 0.43 0.45 20.13 20.36 20.17 20.22 20.27 20.21 20.28 20.25 20.28 20.08 20.27 20.29 20.19 20.27 20.23 20.19 20.43 20.39 20.32 20.19 0.73 0.20 0.74 0.74 0.74 0.18 0.40 0.34 0.29 0.21 0.35 0.34 0.42 0.45 0.37 0.40 0.55 0.45 0.48 0.44 0.10 20.07 20.02 20.10 0.05 20.11 20.10 20.15 0.66 0.59 0.43 0.54 0.59 0.51 0.43 0.42 0.17 20.19 20.01 20.24 0.11 20.20 20.02 20.30 0.74 0.70 0.36 0.49 0.69 0.68 0.48 0.57 Data are Pearson correlation coefficients: bold = P , 0.05; bold and italic = P , 0.01. Spatial frequency in evaluation of contrast sensitivity in cycles/degree: A = 1,5; B = 3.0; C = 6.0; D = 12.0; E = 18.0. AMP, amplitude; CMD, central mean deviation; LAT, latency; MD, mean deviation. Original Contribution e37 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. TABLE 4. Relationship between VEP, OCT-measured macular layers, peripapillary RNFL, contrast sensitivity, and visual field of patients with multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) with history of optic neuritis Original Contribution More recently, when submitting NMOSD patients with history of ON to VEP and time-domain OCT, Kim et al (36) found mean pRNFL thickness to be strongly correlated with VEP latency and amplitude and concluded that the 2 methods were equally sensitive at detecting ON in NMOSD. However, the authors evaluated only pRNFL thickness and not the macular layers, and the OCT image resolution was low. Our study confirmed the hallmark VEP findings for patients with MS: delayed latency and preserved amplitude. In comparison, ON-NMOSD patients displayed a different pattern, with significantly reduced amplitude (regardless of stimulus size) and normal latency measurements, except for a slightly delayed P100 latency when the medium-sized stimulus was used. However, it should be stressed that, based on the tests conducted with both medium and large stimuli, comparisons between the 2 sets of patients were more meaningful when the large stimulus was used. This is because many ON-NMOSD eyes had reduced VA, potentially rendering testing with the 309 stimulus suboptimal. The results obtained with the 1.5° stimulus are likely to have been less biased by reduced VA and therefore more reliable. Also, we consider the N75-P100 wave to be the most suitable for analysis because it is a prominent peak with little variation between subjects, minimal withinsubject interocular variation, and minimal variation in repeated measurements. In other words, and based on our results, using a stimulus of appropriate size to obtain the N75/P100 wave, one might expect to see a VEP pattern in ON-NMOSD eyes consisting of reduced amplitude and preserved latency, in marked contrast with the delayed latency and preserved amplitude of ON-MS eyes. These findings are compatible with the notion of a predominant demyelinating process in MS and axonal damage in NMOSD, and suggest that VEP can help differentiate ON-MS from OD-NMOSD. VEP findings (especially amplitude) were much more strongly associated with OCT, CS, and SAP parameters (specifically OCT-measured pRNFL, and inner and even some outer segmented retinal layers) in the ON-NMOS group than in the ON-MS group (Table 4). This may be due to the more severe structural damage observed in ONNMOSD and therefore generally greater extent of testing data, rendering potential correlations more apparent. However, CS abnormalities were more strongly correlated with VEP parameters, especially (although not exclusively) latency, in the ON-MS group than in the ON-NMOS group. One possible explanation is that CS loss is more directly related to demyelination―which is more frequent in MS―than to axonal cell damage. Finally, the relationship between VEP and VF findings in the 2 groups of patients revealed no obvious differences, but it should be noted that VF abnormalities were clearly correlated with VEP amplitude and not with latency (Table 4). e38 One important limitation of our study is the relatively small number of subjects enrolled. In addition, because MS and NMOSD affect slightly different age ranges, we used a somewhat heterogeneous control group. However, we attempted to compensate for this limitation by using GEE (37), which made it possible to analyze both eyes of many patients and controls (compensating for the intrasubject correlation) and to adjust for age and sex differences in each group. Our study is also limited because of the exclusion, to avoid recording problems, of eyes with VA worse than 20/200, therefore removing possible important clinical data from eyes with severe VA loss, presumably more frequent in NMOSD. However, the range of VA included is the most common outcome of a first episode of ON, therefore the type of patients where differentiating MS-ON from NMOSD-ON is more difficult to make. In conclusion, the current study confirmed the standard VEP findings described in the literature for patients with MS. However, a different pattern of changes, involving both amplitude and latency, was observed for patients with NMOSD and history of ON, suggesting VEP testing can help distinguish patients with MS from patients with NMOSD, especially those with ON. In any case, further investigations are necessary to confirm our findings. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: T. G. Filgueiras and M. K. Oyamada; b. Acquisition of data: T. G. Filgueiras and M. K. Oyamada; c. Analysis and interpretation of data: T. G. Filgueiras, M. K. Oyamada, K. Hokazono, L. P. Cunha, and M. L. R. Monteiro. Category 2: a. Drafting the manuscript: T. G. Filgueiras and M. L. R. Monteiro; b. Revising it for intellectual content: T. G. Filgueiras, M. K. Oyamada, K. Hokazono, L. P. Cunha, S. L. Apóstolos-Pereira, D. Callegaro, and M. L. R. Monteiro. Category 3: a. Final approval of the completed manuscript: T. G. Filgueiras, M. K. Oyamada, K. Hokazono, L. P. Cunha, S. L. Apóstolos-Pereira, D. 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