Current Eye Research
ISSN: 0271-3683 (Print) 1460-2202 (Online) Journal homepage: http://www.tandfonline.com/loi/icey20
Evaluation of the Innermost Retinal Layers and Visual Evoked Potentials in Patients with Multiple Sclerosis Ebru Esen, Selcuk Sizmaz, Mehmet Balal, Kemal Yar, Meltem Demirkiran, Ilker Unal & Nihal Demircan To cite this article: Ebru Esen, Selcuk Sizmaz, Mehmet Balal, Kemal Yar, Meltem Demirkiran, Ilker Unal & Nihal Demircan (2016): Evaluation of the Innermost Retinal Layers and Visual Evoked Potentials in Patients with Multiple Sclerosis, Current Eye Research, DOI: 10.3109/02713683.2015.1119283 To link to this article: http://dx.doi.org/10.3109/02713683.2015.1119283
Published online: 16 Feb 2016.
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Date: 28 February 2016, At: 13:48
CURRENT EYE RESEARCH http://dx.doi.org/10.3109/02713683.2015.1119283
ORIGINAL ARTICLE
Evaluation of the Innermost Retinal Layers and Visual Evoked Potentials in Patients with Multiple Sclerosis Ebru Esena, Selcuk Sizmaza, Mehmet Balalb, Kemal Yara, Meltem Demirkiranb, Ilker Unalc, and Nihal Demircana
Downloaded by [New York University] at 13:48 28 February 2016
a Department of Ophthalmology, School of Medicine, Cukurova University, Adana, Turkey; bDepartment of Neurology, School of Medicine, Cukurova University, Adana, Turkey; cDepartment of Biostatistics, School of Medicine, Cukurova University, Adana, Turkey
ABSTRACT
ARTICLE HISTORY
Purpose: The present study was conducted to investigate alterations in the innermost layers of the retina using optical coherence tomography (OCT) and to assess potential associations of structural measures with functional markers in patients with Multiple Sclerosis (MS). Materials and Methods: Ninety-four eyes of 47 MS patients and 60 eyes of 30 healthy individuals were included in the study. All patients underwent complete ophthalmological examination and OCT imaging to analyze peripapillary retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL) thickness. Visual evoked potentials (VEPs) and expanded disability status scale (EDSS) score were assessed for MS patients. Results: The average RNFL and GCIPL thicknesses were thinner in MS patients (86.2 ± 11.9 µm and 73.6 ± 9.7 µm, respectively) when compared with those of healthy controls (96.7 ± 8.2 µm and 85.9 ± 4.6 µm, respectively, p < 0.001 for both). Within MS patients, the average RNFL and GCIPL thicknesses were lower in eyes with a prior history of optic neuritis (MS ON) than in eyes with no optic neuritis history (MS non-ON) (p = 0.012 and p < 0.001, respectively). RNFL and GCIPL thicknesses were inversely correlated with VEP latency (r = −0.40, p < 0.001 and r = −0.36, p < 0.001, respectively) in MS patient eyes. There was a correlation between GCIPL thickness and VEP amplitude in eyes with previous ON history (r = 0.34, p = 0.035). No significant correlations were found between OCT measurements and EDSS score. Conclusions: Innermost layers of the retina are highly affected by the pathophysiologic process in MS disease, manifesting as a reduction in RNFL and GCIPL thickness. The structural retinal changes show correlation with alterations in potentials showing the optic pathway function.
Received 14 July 2015 Revised 27 October 2015 Accepted 8 November 2015
Introduction Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination and axonal degeneration. Acute optic neuritis (ON), due to inflammatory demyelinating lesions of the optic nerve, is the most common ocular manifestation and the leading cause of visual impairment in MS. Apart from acute inflammation of the optic nerve, demyelinating lesions in other parts of the visual pathway, from the optic nerve to the visual cortex, are proposed to result in retrograde degeneration and axonal loss.1–3 Retinal ganglion cell axons, lacking myelin sheath, constitute the retinal nerve fiber layer (RNFL) which gives rise to the optic nerve that becomes myelinated after passing through the lamina cribrosa. This anatomical privilege of the RNFL might allow the assessment of the retrograde effects of the demyelination process on the anterior optic pathway, providing a diagnostic window for monitoring neurodegeneration. Optical coherence tomography (OCT), so-called optical biopsy, has gained an increasing popularity to visualize the retinal structures in detail. Over the last few years, majority of the studies about MS has mainly focused on the evaluation of the peripapillary RNFL by OCT. In these reports, axonal loss
KEYWORDS
Ganglion cell-inner plexiform layer thickness; multiple sclerosis; optical coherence tomography; retinal nerve fiber layer thickness; visual evoked potentials
affecting the anterior optic pathway in MS has been reflected with the thinning of RNFL, even in patients without a history of ON.1,4–7 On the other hand, there is histological evidence that not only RNFL, but also cellular retinal layers are also affected in MS.8 Advances in OCT technology have enabled high-resolution cross-sectional retinal images that allow in vivo differentiation and quantification of the retinal layers separately. The ability of OCT to obtain thickness measurements of discrete retinal layers highlighted its role in clinical MS trials conducted for the assessment of structural changes in retinal layers.9–11 The relationship between RNFL and visual evoked potentials (VEPs) in MS patients was studied by several investigators and a correlation was identified between these parameters.1 Ganglion cell-inner plexiform layer (GCIPL) thickness was previously reported to represent a better structure–function correlation than RNFL, and its relation with functional measures has been of particular interest.11 In the current study, we evaluated the innermost retinal-layer thicknesses, and their correlation with VEP measurements in MS patients. Our aim was to investigate the potential associations of structural measures with functional markers, to provide insights to the pathophysiology of the disease. We also sought
CONTACT Ebru Esen [email protected] Department of Ophthalmology, School of Medicine, Cukurova University, Adana, Turkey (Cukurova Universitesi Tip Fakultesi, Goz Hastaliklari Anabilim Dali, 01330 Adana, Turkıye). © 2016 Taylor & Francis
2
E. ESEN ET AL.
to compare the relation of OCT measurements with disease disability, to find out whether RNFL and GCIPL are eligible to be used as potential indicators of disease burden.
Materials and methods
Downloaded by [New York University] at 13:48 28 February 2016
Subjects This observational cross-sectional study involved adult MS patients recruited between March and December 2014. The patients were diagnosed with MS according to the revised McDonald criteria, based on clinical and radiologic findings.12 A complete neurological examination was performed and disability score was assessed using expanded disability status scale (EDSS) for each patient. Subjects with any coexisting systemic disease or an acute episode of ON less than 6 months prior to the analysis were excluded. Each eye of the MS patients was designated as MS ON (with a previous history of acute ON) or MS non-ON (without an ON history) according to the presence of a prior episode of ON ascertained by the patient’s description or clinician’s reports. Age- and gender-matched control group consisted of healthy individuals with no history of ocular or systemic disease. All participants underwent comprehensive ophthalmologic examinations including the best-corrected visual acuity, intraocular pressure measurement, slit-lamp examination of the anterior segment and fundoscopic examination. Subjects with any ocular disorder (for MS patients, other than previous ON findings) and a spherical equivalent refractive error of more than 3.0 diopters were excluded from the study. This study protocol was approved by the Cukurova University ethics committee (KN: 8/26-2013) and conducted in accordance with the tenets of the Declaration of Helsinki. A written informed consent was taken before each individual’s participation in the study. OCT examination Retinal imaging was performed using spectral-domain OCT (Cirrus HD-OCT, Carl Zeiss Meditec Inc, Dublin, California, USA) scanning for measurement of RNFL and GCIPL. All OCT scans were performed by the same experienced technician. OCT scans with signal strength above 7 were acceptable for analysis, otherwise they were repeated. RNFL thickness measurements were made using the optic disc cube 200 × 200 protocol by collecting data through a 6 mm square-shaped grid and an automatically placed calculation circle of 3.46 mm diameter around the optic disc. Average RNFL thickness for peripapillary retina 360° around the optic disc was calculated automatically by the equipment software. Macular data were obtained using the macular cube 512 × 128 protocol, which forms a 6 × 6 × 2 mm volume cube. GCIPL thickness was measured automatically with the ganglion cell analysis algorithm. The outer boundaries of RNFL and inner plexiform layer were identified, the distance between the two boundaries provided a measurement of the combined GCIPL layer thickness. Average GCIPL thickness was calculated automatically by the equipment software.
Visual evoked potentials VEPs were elicited by 48 checkerboard pattern of black and white squares, reversing at 1 Hz on a television monitor, with the patient sitting 1 meter away from the screen in a dark room. The mean luminance of the checkerboard was 50 cd m−2 and the contrast between black and white squares was 99%. VEP recordings were performed according to the International Society for Clinical Electrophysiology of Vision (ISCEV) guidelines.13 The reference electrode was placed on the midline frontal point (Fz), an active electrode on the midline at the occipital region (Oz according to the 10–20 system), and the ground electrode on the forearm. Ag/AgCl disposable needle electrodes were used and their impedance was maintained below 5 k Ohm. The responses were analyzed with a Nicolet 1000 Viking Quest, with a 1–100 Hz bandpass filter and a sweep time of 500 ms. The stimuli were presented uni-ocularly. A hundred responses were averaged in each run and two runs were performed for each eye. The latency and amplitude (“peak to peak”) of the P100 component were determined for each eye. Normative value was 100 ± 10 ms for VEP latency and ≥ 5 μV for VEP amplitude. Statistical analysis All analyses were performed using SPSS 20.0 statistical software package (SPSS, Inc., Chicago, IL). Categorical variables were expressed as numbers and percentages, whereas continuous variables were summarized as mean and standard deviation. Chi-square test was used to compare the categorical variables between the groups. The normality of distribution for continuous variables was confirmed with the Kolmogorov–Smirnov test. For comparison of continuous variables between two groups, the Student t-test was used. Generalized estimating equation models accounting for within-subject inter-eye correlations were applied to compare the parameters between the study groups. To evaluate the correlations between measurements, Pearson Correlation Coefficient was used. Partial correlation analysis was used for adjusting the inter-eye effect in correlation analysis. The statistical level of significance for all tests was considered to be 0.05.
Results Ninety-four eyes of 47 MS patients (43 relapsing-remitting MS, two secondary progressive MS, two primary progressive MS) were included. There were 31 (66%) female and 16 (34%) male patients, with a mean age of 39.8 ± 8.9 (range 24–59) years. The mean disease duration was 92.1 ± 63.5 (range 6–300) months. Of the 47 MS patients, 13 had bilateral and 14 had unilateral ON history, 20 patients did not experience an acute ON episode in either eye. Thus, there were 40 (42.6%) MS ON eyes, and 54 (57.4%) MS non-ON eyes. The mean EDSS score of MS patients was 2.1 ± 1.6 (range 0–5.5). Sixty eyes of 30 healthy individuals, 20 (66.7%) female and 10 (33.3%) male subjects, constituted the control group with a mean age of 38.9 ± 7.7 (range 26–55) years. The study and
Downloaded by [New York University] at 13:48 28 February 2016
CURRENT EYE RESEARCH
control groups showed no significant difference by means of age (p = 0.66) and gender (p = 0.95). The average RNFL thickness was significantly thinner in MS patients (86.2 ± 11.9 μm) when compared with healthy controls (96.7 ± 8.2 μm) (p < 0.001). The average RNFL thickness in MS ON eyes was significantly thinner than those in MS non-ON eyes (p = 0.012). Both MS ON and MS non-ON eyes had significantly reduced RNFL thickness measurements when compared with healthy controls (p < 0.001 and p = 0.001, respectively) (Figure 1). The average GCIPL thickness was significantly thinner in MS patients (73.6 ± 9.7 μm) when compared with healthy controls (85.9 ± 4.6 μm) (p < 0.001). In MS ON eyes the average GCILP thickness was significantly thinner than those in MS non-ON eyes (p < 0.001). Both MS ON and MS non-ON eyes had significantly reduced GCIPL thickness measurements when compared with healthy controls (p < 0.001 for both) (Figure 1). The mean RNFL and GCIPL thicknesses of the groups are detailed in Table 1. The average VEP latency was 120.7 ± 21.1 (range 82–198) ms in MS patient eyes; it was 125.3 ± 20.2 (range 91.3−176) ms for MS ON eyes and 117.3 ± 21.2 (range 82−198) ms for MS non-ON eyes. The average VEP amplitude was 7.9 ± 4.6 (range 1.5−20) μV in MS patient eyes; it was 7.2 ± 4.2 (range 1.5−18.6) μV for MS ON eyes and 8.9 ± 4.9 (range 1.6−20) μV for MS non-ON eyes. As shown in Table 2, correlation analysis demonstrated that RNFL thickness significantly correlated with GCIPL thickness in MS eyes (Figure 2), but not in healthy controls (r = 0.23, p = 0.225). The correlation was also significant for MS ON eyes and MS non-ON eyes separately. In all MS eyes, regardless of ON, RNFL thickness reduction was significantly correlated with the delay in VEP latency (Figure 3a). This correlation was also significant for MS ON and MS non-ON eyes separately. GCIPL thickness showed significant negative correlation with VEP latency in MS eyes (Figure 3b). This correlation was also significant for MS ON eyes and MS non-
Figure 1. There were significant differences in retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL) thicknesses between controls, MS non-ON and MS ON eyes (p < 0.05 for each comparison).
3
ON eyes, respectively. There was no correlation between RNFL and VEP amplitude in MS eyes. Considering all MS eyes and MS non-ON eyes, GCIPL thickness did not show correlation with VEP amplitude either. However, in MS ON eyes GCIPL thickness significantly correlated with VEP amplitude. The correlations of RNFL and GCIPL thicknesses with EDSS score were not significant. The correlation coefficients between OCT measurements and VEP recordings and EDSS scores in study groups are shown in Table 2.
Discussion Recently, numerous reports have suggested that OCT parameters might detect and monitor axonal loss in MS patients. Some authors advocated OCT as a useful biomarker of disease activity and recommended that OCT should be part of the routine monitoring of patients with MS.14 Peri-papillary RNFL has been forefront among these parameters and thinning of the RNFL, demonstrated by OCT, became a strong evidence of axonal injury related to the inflammatory demyelination process in MS.1 The advancements in OCT technology enabled measurement of discrete retinal layer thicknesses. Following this improvement, the assessment of GCIPL has been advocated to be taken into consideration for patients with various ophthalmic diseases including glaucoma or neuro-ophthalmologic disorders.15 Previously the histopathological evidence of qualitative atrophy of nerve fiber and ganglion cell layers was demonstrated in over 70% of the cases with MS in postmortem analysis.16 Saidha et al.11 detected RNFL and GCIPL thinning in vivo by OCT, highlighting that inner retinallayer changes are prominent in MS patients. Garcia-Martin et al.10 detected greater atrophy in the inner retinal layers of MS patients with previous ON, using automated segmentation technology of the OCT. These findings were consistent with the results of the histopathologic study by Green et al.8 who observed retinal nerve and ganglion cell-layer atrophy in patients with MS. Our study showed that both RNFL and GCIPL thicknesses measured by OCT were all reduced in MS eyes with and without ON episode, when compared with controls. These results were in accordance with previous reports, which demonstrated thinning of RNFL and GCIPL in MS eyes, irrespective of a history of ON.10,11,17,18 In MS ON eyes, optic nerve demyelination is thought to result in degeneration of the constituent axons of the optic nerve, leading to RNFL thinning and ganglion cell atrophy.19,20 Reduced RNFL and GCIPL thickness in the absence of acute attacks of ON supports the possibility of subclinical episodes of ON. Besides, apart from optic nerve and optic tract involvement, MS lesions in the posterior visual pathways might cause ganglion cell damage and axonal loss as a result of retrograde transsynaptic degeneration.3,21–23 It is noteworthy that MS ON eyes had significantly thinner RNFL and GCIPL when compared with MS non-ON eyes and this is in accordance with other published reports.11,17,24,25 It might be suggested that more pronounced thinning follows acute neuritis, causing immediate changes on neuronal and axonal structures in MS ON eyes. While in subclinical inflammation of optic nerve and posterior visual pathway lesions, rather than acute
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Table 1. Retinal never fiber layer and ganglion cell-inner plexiform layer thickness measurements in healthy controls, all MS eyes, MS non-ON eyes, and MS ON eyes. p value
RNFL (μm) Mean ± SD Range GCIPL (μm) Mean ± SD Range
Control Eyes (n = 60)
All MS Eyes (n = 94)
MS non-ON Eyes (n = 54)
MS ON Eyes (n = 40)
All MS eyes vs. Control
MS non-ON vs. Control
MS ON vs. Control
MS ON vs. MS non-ON
96.7 ± 8.2
86.2 ± 11.9
89.2 ± 11.2
82.2 ± 11.8
ISSN: 0271-3683 (Print) 1460-2202 (Online) Journal homepage: http://www.tandfonline.com/loi/icey20
Evaluation of the Innermost Retinal Layers and Visual Evoked Potentials in Patients with Multiple Sclerosis Ebru Esen, Selcuk Sizmaz, Mehmet Balal, Kemal Yar, Meltem Demirkiran, Ilker Unal & Nihal Demircan To cite this article: Ebru Esen, Selcuk Sizmaz, Mehmet Balal, Kemal Yar, Meltem Demirkiran, Ilker Unal & Nihal Demircan (2016): Evaluation of the Innermost Retinal Layers and Visual Evoked Potentials in Patients with Multiple Sclerosis, Current Eye Research, DOI: 10.3109/02713683.2015.1119283 To link to this article: http://dx.doi.org/10.3109/02713683.2015.1119283
Published online: 16 Feb 2016.
Submit your article to this journal
Article views: 17
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=icey20 Download by: [New York University]
Date: 28 February 2016, At: 13:48
CURRENT EYE RESEARCH http://dx.doi.org/10.3109/02713683.2015.1119283
ORIGINAL ARTICLE
Evaluation of the Innermost Retinal Layers and Visual Evoked Potentials in Patients with Multiple Sclerosis Ebru Esena, Selcuk Sizmaza, Mehmet Balalb, Kemal Yara, Meltem Demirkiranb, Ilker Unalc, and Nihal Demircana
Downloaded by [New York University] at 13:48 28 February 2016
a Department of Ophthalmology, School of Medicine, Cukurova University, Adana, Turkey; bDepartment of Neurology, School of Medicine, Cukurova University, Adana, Turkey; cDepartment of Biostatistics, School of Medicine, Cukurova University, Adana, Turkey
ABSTRACT
ARTICLE HISTORY
Purpose: The present study was conducted to investigate alterations in the innermost layers of the retina using optical coherence tomography (OCT) and to assess potential associations of structural measures with functional markers in patients with Multiple Sclerosis (MS). Materials and Methods: Ninety-four eyes of 47 MS patients and 60 eyes of 30 healthy individuals were included in the study. All patients underwent complete ophthalmological examination and OCT imaging to analyze peripapillary retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL) thickness. Visual evoked potentials (VEPs) and expanded disability status scale (EDSS) score were assessed for MS patients. Results: The average RNFL and GCIPL thicknesses were thinner in MS patients (86.2 ± 11.9 µm and 73.6 ± 9.7 µm, respectively) when compared with those of healthy controls (96.7 ± 8.2 µm and 85.9 ± 4.6 µm, respectively, p < 0.001 for both). Within MS patients, the average RNFL and GCIPL thicknesses were lower in eyes with a prior history of optic neuritis (MS ON) than in eyes with no optic neuritis history (MS non-ON) (p = 0.012 and p < 0.001, respectively). RNFL and GCIPL thicknesses were inversely correlated with VEP latency (r = −0.40, p < 0.001 and r = −0.36, p < 0.001, respectively) in MS patient eyes. There was a correlation between GCIPL thickness and VEP amplitude in eyes with previous ON history (r = 0.34, p = 0.035). No significant correlations were found between OCT measurements and EDSS score. Conclusions: Innermost layers of the retina are highly affected by the pathophysiologic process in MS disease, manifesting as a reduction in RNFL and GCIPL thickness. The structural retinal changes show correlation with alterations in potentials showing the optic pathway function.
Received 14 July 2015 Revised 27 October 2015 Accepted 8 November 2015
Introduction Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination and axonal degeneration. Acute optic neuritis (ON), due to inflammatory demyelinating lesions of the optic nerve, is the most common ocular manifestation and the leading cause of visual impairment in MS. Apart from acute inflammation of the optic nerve, demyelinating lesions in other parts of the visual pathway, from the optic nerve to the visual cortex, are proposed to result in retrograde degeneration and axonal loss.1–3 Retinal ganglion cell axons, lacking myelin sheath, constitute the retinal nerve fiber layer (RNFL) which gives rise to the optic nerve that becomes myelinated after passing through the lamina cribrosa. This anatomical privilege of the RNFL might allow the assessment of the retrograde effects of the demyelination process on the anterior optic pathway, providing a diagnostic window for monitoring neurodegeneration. Optical coherence tomography (OCT), so-called optical biopsy, has gained an increasing popularity to visualize the retinal structures in detail. Over the last few years, majority of the studies about MS has mainly focused on the evaluation of the peripapillary RNFL by OCT. In these reports, axonal loss
KEYWORDS
Ganglion cell-inner plexiform layer thickness; multiple sclerosis; optical coherence tomography; retinal nerve fiber layer thickness; visual evoked potentials
affecting the anterior optic pathway in MS has been reflected with the thinning of RNFL, even in patients without a history of ON.1,4–7 On the other hand, there is histological evidence that not only RNFL, but also cellular retinal layers are also affected in MS.8 Advances in OCT technology have enabled high-resolution cross-sectional retinal images that allow in vivo differentiation and quantification of the retinal layers separately. The ability of OCT to obtain thickness measurements of discrete retinal layers highlighted its role in clinical MS trials conducted for the assessment of structural changes in retinal layers.9–11 The relationship between RNFL and visual evoked potentials (VEPs) in MS patients was studied by several investigators and a correlation was identified between these parameters.1 Ganglion cell-inner plexiform layer (GCIPL) thickness was previously reported to represent a better structure–function correlation than RNFL, and its relation with functional measures has been of particular interest.11 In the current study, we evaluated the innermost retinal-layer thicknesses, and their correlation with VEP measurements in MS patients. Our aim was to investigate the potential associations of structural measures with functional markers, to provide insights to the pathophysiology of the disease. We also sought
CONTACT Ebru Esen [email protected] Department of Ophthalmology, School of Medicine, Cukurova University, Adana, Turkey (Cukurova Universitesi Tip Fakultesi, Goz Hastaliklari Anabilim Dali, 01330 Adana, Turkıye). © 2016 Taylor & Francis
2
E. ESEN ET AL.
to compare the relation of OCT measurements with disease disability, to find out whether RNFL and GCIPL are eligible to be used as potential indicators of disease burden.
Materials and methods
Downloaded by [New York University] at 13:48 28 February 2016
Subjects This observational cross-sectional study involved adult MS patients recruited between March and December 2014. The patients were diagnosed with MS according to the revised McDonald criteria, based on clinical and radiologic findings.12 A complete neurological examination was performed and disability score was assessed using expanded disability status scale (EDSS) for each patient. Subjects with any coexisting systemic disease or an acute episode of ON less than 6 months prior to the analysis were excluded. Each eye of the MS patients was designated as MS ON (with a previous history of acute ON) or MS non-ON (without an ON history) according to the presence of a prior episode of ON ascertained by the patient’s description or clinician’s reports. Age- and gender-matched control group consisted of healthy individuals with no history of ocular or systemic disease. All participants underwent comprehensive ophthalmologic examinations including the best-corrected visual acuity, intraocular pressure measurement, slit-lamp examination of the anterior segment and fundoscopic examination. Subjects with any ocular disorder (for MS patients, other than previous ON findings) and a spherical equivalent refractive error of more than 3.0 diopters were excluded from the study. This study protocol was approved by the Cukurova University ethics committee (KN: 8/26-2013) and conducted in accordance with the tenets of the Declaration of Helsinki. A written informed consent was taken before each individual’s participation in the study. OCT examination Retinal imaging was performed using spectral-domain OCT (Cirrus HD-OCT, Carl Zeiss Meditec Inc, Dublin, California, USA) scanning for measurement of RNFL and GCIPL. All OCT scans were performed by the same experienced technician. OCT scans with signal strength above 7 were acceptable for analysis, otherwise they were repeated. RNFL thickness measurements were made using the optic disc cube 200 × 200 protocol by collecting data through a 6 mm square-shaped grid and an automatically placed calculation circle of 3.46 mm diameter around the optic disc. Average RNFL thickness for peripapillary retina 360° around the optic disc was calculated automatically by the equipment software. Macular data were obtained using the macular cube 512 × 128 protocol, which forms a 6 × 6 × 2 mm volume cube. GCIPL thickness was measured automatically with the ganglion cell analysis algorithm. The outer boundaries of RNFL and inner plexiform layer were identified, the distance between the two boundaries provided a measurement of the combined GCIPL layer thickness. Average GCIPL thickness was calculated automatically by the equipment software.
Visual evoked potentials VEPs were elicited by 48 checkerboard pattern of black and white squares, reversing at 1 Hz on a television monitor, with the patient sitting 1 meter away from the screen in a dark room. The mean luminance of the checkerboard was 50 cd m−2 and the contrast between black and white squares was 99%. VEP recordings were performed according to the International Society for Clinical Electrophysiology of Vision (ISCEV) guidelines.13 The reference electrode was placed on the midline frontal point (Fz), an active electrode on the midline at the occipital region (Oz according to the 10–20 system), and the ground electrode on the forearm. Ag/AgCl disposable needle electrodes were used and their impedance was maintained below 5 k Ohm. The responses were analyzed with a Nicolet 1000 Viking Quest, with a 1–100 Hz bandpass filter and a sweep time of 500 ms. The stimuli were presented uni-ocularly. A hundred responses were averaged in each run and two runs were performed for each eye. The latency and amplitude (“peak to peak”) of the P100 component were determined for each eye. Normative value was 100 ± 10 ms for VEP latency and ≥ 5 μV for VEP amplitude. Statistical analysis All analyses were performed using SPSS 20.0 statistical software package (SPSS, Inc., Chicago, IL). Categorical variables were expressed as numbers and percentages, whereas continuous variables were summarized as mean and standard deviation. Chi-square test was used to compare the categorical variables between the groups. The normality of distribution for continuous variables was confirmed with the Kolmogorov–Smirnov test. For comparison of continuous variables between two groups, the Student t-test was used. Generalized estimating equation models accounting for within-subject inter-eye correlations were applied to compare the parameters between the study groups. To evaluate the correlations between measurements, Pearson Correlation Coefficient was used. Partial correlation analysis was used for adjusting the inter-eye effect in correlation analysis. The statistical level of significance for all tests was considered to be 0.05.
Results Ninety-four eyes of 47 MS patients (43 relapsing-remitting MS, two secondary progressive MS, two primary progressive MS) were included. There were 31 (66%) female and 16 (34%) male patients, with a mean age of 39.8 ± 8.9 (range 24–59) years. The mean disease duration was 92.1 ± 63.5 (range 6–300) months. Of the 47 MS patients, 13 had bilateral and 14 had unilateral ON history, 20 patients did not experience an acute ON episode in either eye. Thus, there were 40 (42.6%) MS ON eyes, and 54 (57.4%) MS non-ON eyes. The mean EDSS score of MS patients was 2.1 ± 1.6 (range 0–5.5). Sixty eyes of 30 healthy individuals, 20 (66.7%) female and 10 (33.3%) male subjects, constituted the control group with a mean age of 38.9 ± 7.7 (range 26–55) years. The study and
Downloaded by [New York University] at 13:48 28 February 2016
CURRENT EYE RESEARCH
control groups showed no significant difference by means of age (p = 0.66) and gender (p = 0.95). The average RNFL thickness was significantly thinner in MS patients (86.2 ± 11.9 μm) when compared with healthy controls (96.7 ± 8.2 μm) (p < 0.001). The average RNFL thickness in MS ON eyes was significantly thinner than those in MS non-ON eyes (p = 0.012). Both MS ON and MS non-ON eyes had significantly reduced RNFL thickness measurements when compared with healthy controls (p < 0.001 and p = 0.001, respectively) (Figure 1). The average GCIPL thickness was significantly thinner in MS patients (73.6 ± 9.7 μm) when compared with healthy controls (85.9 ± 4.6 μm) (p < 0.001). In MS ON eyes the average GCILP thickness was significantly thinner than those in MS non-ON eyes (p < 0.001). Both MS ON and MS non-ON eyes had significantly reduced GCIPL thickness measurements when compared with healthy controls (p < 0.001 for both) (Figure 1). The mean RNFL and GCIPL thicknesses of the groups are detailed in Table 1. The average VEP latency was 120.7 ± 21.1 (range 82–198) ms in MS patient eyes; it was 125.3 ± 20.2 (range 91.3−176) ms for MS ON eyes and 117.3 ± 21.2 (range 82−198) ms for MS non-ON eyes. The average VEP amplitude was 7.9 ± 4.6 (range 1.5−20) μV in MS patient eyes; it was 7.2 ± 4.2 (range 1.5−18.6) μV for MS ON eyes and 8.9 ± 4.9 (range 1.6−20) μV for MS non-ON eyes. As shown in Table 2, correlation analysis demonstrated that RNFL thickness significantly correlated with GCIPL thickness in MS eyes (Figure 2), but not in healthy controls (r = 0.23, p = 0.225). The correlation was also significant for MS ON eyes and MS non-ON eyes separately. In all MS eyes, regardless of ON, RNFL thickness reduction was significantly correlated with the delay in VEP latency (Figure 3a). This correlation was also significant for MS ON and MS non-ON eyes separately. GCIPL thickness showed significant negative correlation with VEP latency in MS eyes (Figure 3b). This correlation was also significant for MS ON eyes and MS non-
Figure 1. There were significant differences in retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL) thicknesses between controls, MS non-ON and MS ON eyes (p < 0.05 for each comparison).
3
ON eyes, respectively. There was no correlation between RNFL and VEP amplitude in MS eyes. Considering all MS eyes and MS non-ON eyes, GCIPL thickness did not show correlation with VEP amplitude either. However, in MS ON eyes GCIPL thickness significantly correlated with VEP amplitude. The correlations of RNFL and GCIPL thicknesses with EDSS score were not significant. The correlation coefficients between OCT measurements and VEP recordings and EDSS scores in study groups are shown in Table 2.
Discussion Recently, numerous reports have suggested that OCT parameters might detect and monitor axonal loss in MS patients. Some authors advocated OCT as a useful biomarker of disease activity and recommended that OCT should be part of the routine monitoring of patients with MS.14 Peri-papillary RNFL has been forefront among these parameters and thinning of the RNFL, demonstrated by OCT, became a strong evidence of axonal injury related to the inflammatory demyelination process in MS.1 The advancements in OCT technology enabled measurement of discrete retinal layer thicknesses. Following this improvement, the assessment of GCIPL has been advocated to be taken into consideration for patients with various ophthalmic diseases including glaucoma or neuro-ophthalmologic disorders.15 Previously the histopathological evidence of qualitative atrophy of nerve fiber and ganglion cell layers was demonstrated in over 70% of the cases with MS in postmortem analysis.16 Saidha et al.11 detected RNFL and GCIPL thinning in vivo by OCT, highlighting that inner retinallayer changes are prominent in MS patients. Garcia-Martin et al.10 detected greater atrophy in the inner retinal layers of MS patients with previous ON, using automated segmentation technology of the OCT. These findings were consistent with the results of the histopathologic study by Green et al.8 who observed retinal nerve and ganglion cell-layer atrophy in patients with MS. Our study showed that both RNFL and GCIPL thicknesses measured by OCT were all reduced in MS eyes with and without ON episode, when compared with controls. These results were in accordance with previous reports, which demonstrated thinning of RNFL and GCIPL in MS eyes, irrespective of a history of ON.10,11,17,18 In MS ON eyes, optic nerve demyelination is thought to result in degeneration of the constituent axons of the optic nerve, leading to RNFL thinning and ganglion cell atrophy.19,20 Reduced RNFL and GCIPL thickness in the absence of acute attacks of ON supports the possibility of subclinical episodes of ON. Besides, apart from optic nerve and optic tract involvement, MS lesions in the posterior visual pathways might cause ganglion cell damage and axonal loss as a result of retrograde transsynaptic degeneration.3,21–23 It is noteworthy that MS ON eyes had significantly thinner RNFL and GCIPL when compared with MS non-ON eyes and this is in accordance with other published reports.11,17,24,25 It might be suggested that more pronounced thinning follows acute neuritis, causing immediate changes on neuronal and axonal structures in MS ON eyes. While in subclinical inflammation of optic nerve and posterior visual pathway lesions, rather than acute
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Table 1. Retinal never fiber layer and ganglion cell-inner plexiform layer thickness measurements in healthy controls, all MS eyes, MS non-ON eyes, and MS ON eyes. p value
RNFL (μm) Mean ± SD Range GCIPL (μm) Mean ± SD Range
Control Eyes (n = 60)
All MS Eyes (n = 94)
MS non-ON Eyes (n = 54)
MS ON Eyes (n = 40)
All MS eyes vs. Control
MS non-ON vs. Control
MS ON vs. Control
MS ON vs. MS non-ON
96.7 ± 8.2
86.2 ± 11.9
89.2 ± 11.2
82.2 ± 11.8
