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ORIGINAL ARTICLE
Year : 2020  |  Volume : 113  |  Issue : 1  |  Page : 26-32

Early detection of neurodegeneration in type 2 diabetic patients without diabetic retinopathy using electroretinogram and spectral-domain optical coherence tomography


Ophthalmology Department, Benha Faculty of Medicine, Benha University, Benha, Egypt

Date of Submission21-Dec-2019
Date of Acceptance17-Feb-2020
Date of Web Publication15-May-2020

Correspondence Address:
MD Marwa A Tabl
Faculty of Medicine, Ophthalmology Department, Benha University, 1 El Amira Fawzya Street, Benha, El Qalubiya Governorate, Benha 13512
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ejos.ejos_72_19

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  Abstract 

Purpose The aim was to assess early functional and structural changes in the neural retina in type 2 diabetic patients with no clinical signs of diabetic retinopathy (DR).
Patients and methods A total of 92 eyes of 48 patients were included, which were divided into the following groups: 30 eyes of 16 participants with type 2 diabetes mellitus without clinical DR, with a mean age of 48.75±3.09 years, as group 1; 30 eyes of 16 participants with type 2 diabetes mellitus with DR, with a mean age of 51.75±2.86 years, as group 2; and a control group of 32 eyes of 16 healthy age-matched and sex-matched participants, with a mean age of 49.88±4.26 years. After full ophthalmologic examination, spectral-domain optical coherence tomography scans, multifocal electroretinogram (Mf-ERG), pattern electroretinogram (PERG), and photonegative response (PhNR) were tested for all participants. Statistical analysis was performed to compare ganglion cell complex (GCC) thicknesses, multifocal electroretinogram, PERG, and phNR values between the groups.
Results There were no statistically significant differences between the studied groups regarding age, sex, refraction, or intraocular pressure (P=0.056,0.72, 0.16, and 0.35, respectively). There were significant differences of total GCC thickness values among group 1 (107.13±7.04 μm), group 2 (97.27±10.97 μm), and control group (113.81±5.26 μm) (P<0.001). The superior and inferior quadrants of GCC were significantly thinner in the groups 1 and 2 in comparison with the control group. Mf-ERG foveal P1 wave amplitude was significantly reduced in groups 1 and 2 in comparison with control group (P<0.001). There were significant differences of PERG/N95, phNR amplitude, and implicit time between the studied groups.
Conclusion The preclinical DR presents with neural loss in the macular area, evident by the reduction GCC thickness and impairments of mf-ERG, PERG, and phNR parameters. Neurodegenerative changes precede the microvascular damage in these patients.

Keywords: ganglion cell complex, multifocal electroretinogram, optical coherence tomography, photopic negative response, type 2 diabetes


How to cite this article:
Tabl MA. Early detection of neurodegeneration in type 2 diabetic patients without diabetic retinopathy using electroretinogram and spectral-domain optical coherence tomography. J Egypt Ophthalmol Soc 2020;113:26-32

How to cite this URL:
Tabl MA. Early detection of neurodegeneration in type 2 diabetic patients without diabetic retinopathy using electroretinogram and spectral-domain optical coherence tomography. J Egypt Ophthalmol Soc [serial online] 2020 [cited 2020 Jun 5];113:26-32. Available from: http://www.jeos.eg.net/text.asp?2020/113/1/26/284341


  Introduction Top


Diabetic retinopathy (DR) is one of the serious consequences of diabetes mellitus (DM) and considered as the most common cause of vision loss among the developed countries [1].

The current treatments of DR are targeting late stages of this disease, whereas the early detection of diabetic changes and management of early stages of DR are more critical to be evaluated [2],[3].

Controversy regarding the pathogenesis of DR as a primary microvasculopathy, neurodegenerative disease, or combination of both had been evolved. The common understanding of DR as a microvascular disorder has changed; now retinal neurodegeneration is considered to play a significant role in its pathogenesis. It is now believed that microvascular abnormalities and angiogenesis are not the primarily factor of retinal damage in DR, but in fact, they are late presentations [4],[5],[6].

Recent studies stated that diabetic retinal neurodegenerations may precede the microvascular abnormalities. Many researches have recently focused on the retinal neurodegeneration and neuroprotective mechanisms for preventing vision loss in diabetic patients [1],[4].

The early functional and structural assessment of retinal neurodegenerations could be a valuable tool to identify participants at high risk for developing DR, even before appearance of a clinically visible micro-vascular changes [7],[8].

The aim of the current study was to assess early functional and structural changes in the neural retina in type 2 diabetic patients, with no clinical signs of DR.


  Patients and methods Top


Patients

A total of 92 eyes of 48 patients were included in this prospective study. It was conducted between April 2018 and October 2019, with the participants recruited from the outpatients’ clinics of Benha…… university hospital. Approval for the research was obtained from the University Ethics Local Committee, and an informed consent was signed by all participants in compliance with the requirements of the Declaration of Helsinki. The participants were divided into three groups. Group 1 included 30 eyes of 16 participants with type 2 DM with no clinical signs of DR [based on fundus examination and optical coherence tomography (OCT) scans]. Group 2 included 30 eyes of 16 participants with type 2 DM with DR, and a control group comprised 32 eyes of 16 healthy age-matched and sex-matched participants. The diagnosis of type 2 DM was done according to the criteria of the American Diabetes Association [9]. The classification of the ocular diabetic changes was done in compliance to the International Clinical Disease Severity Scale for DR [10]. Inclusion criteria were diabetic patients with type 2 DM (diagnosis of at least 12 months), intraocular pressure (IOP) less than 20 mmHg, and best-corrected visual acuity (BCVA) not less than 6/60 (using a Snellen chart). Healthy participants had BCVA better than 6/9, with no evidence of any ocular or neurologic disorders.

Exclusion criteria were the presence of diabetic macular edema, history of any treatment of DR, IOP greater than or equal to 20 mmHg, media opacity, and history of other retinal diseases or systemic neurodegenerative diseases that affect the visual system, such as multiple sclerosis, dementia, or Parkinson’s disease.

Ophthalmological examination

Full ophthalmologic examination was performed for all cases including slit-lamp examination, IOP measurement, refraction, BCVA, fundus examination, and fundus fluorescein angiography. Glycosylated hemoglobin (HbA1C) was measured for all diabetic patients.

The average and sectoral ganglion cell complex (GCC) thickness including the retinal nerve fiber layer+the ganglion cell layer+inner plexiform layer thickness (RNFL+GCL+IPL) was measured for all participants by spectral-domain (SD)-OCT scans (Topcon 3D OCT model 2000 FA version 8.30, Topcon Corporation Campany, Tokyo, Japan), using the 3 D macular map scan 7 mm2 area, which is centered on the fovea, with a scan density of 512 (vertical)×128 (horizontal).

The functional status of the neural retina and retinal ganglion cell was assessed for all participants by performing multifocal electroretinogram (mfERG), pattern electroretinogram (PERG), and photopic negative response (phNR), which is the negative potential wave that follows the b-wave of the full field electroretinogram by using RETI-port/scan 21 (Roland Consult, Brandenburg, Germany). The patients’ preparation and recording parameters of the all tests were done according to the International Society for Clinical Electrophysiology of Vision standards [11],[12],[13]. The implicit time and amplitude of mfERG foveal P1wave (ring 1), PERG-N95 wave, and phNR were measured for all participants.

Statistical analysis

The univariate, bivariate, and stratified analyses of the data were performed by using the Statistical Package for the Social Sciences software (version 20.0 for Windows; SPSS Inc., Chicago, Illinois, USA). Kruskal–Wallis test was used for multiple comparisons of quantitative variables, and Mann–Whitney test was used for the comparison of quantitative variables after establishing their non-normality by K-S test of normality. It compares median and interquartile range. Analysis of variance test was used for comparing the means of parametric variable with using post-hoc test (LSD) for multiple comparisons. Student’s t-test was used for comparing the means of both groups. χ2-test was used to compare frequencies. Receiver operating characteristics (ROC) curve was used to detect validity of variables in prediction of early diabetic changes. Pearson’s and Spearman’s correlation coefficients were used to detect relationships between variables.

Differences were considered significant at P less than or equal to 0.05.


  Results Top


A total of 30 eyes of 16 patients (eight females and eight males), as group 1, with a mean age of 48.75±3.09 years (group 1); 30 eyes of 16 patients (eight females and eight males), as group 2, with a mean age of 51.75±2.86 years (group 2); and a control group of 32 eyes of 16 healthy participants (six females and 10 males), with a mean age of 49.88±4.26 years, were included in this study. There were no significant differences in the age, sex, refraction, or IOP among the studied groups (P=0.056, 0.72, 0.16, and 0.35, respectively). DM disease duration was 6.5±1.63 years in group 1 and 13.63±4.76 years in group 2. Mean BCVA was significantly more high in control group in comparison with the other groups (P<0.001) ([Table 1] and [Table 2]).
Table 1 Demographical comparison between the studied groups

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Table 2 Clinical characteristics of the studied groups

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There were significant differences of total GCC (RNFL+GCL+IPL) thickness values between group 1 (107.13±7.04 μm), group 2 (97.27±10.97 μm), and control group (113.81±5.26 μm) (P<0.001).

Superior and inferior quadrants of GCC were significantly more thinner in the groups 1 and 2 in comparison with control group ([Table 3]).
Table 3 Comparison of total, superior, and inferior ganglion cell complex thickness between the studied groups

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Mf-ERG foveal P1 wave amplitude was significantly reduced in group 1 and group 2 in comparison with control group (P<0.001).

PERG-N95 amplitude showed a significant reduction in group 1 and group 2 in comparison with control group (P<0.001). PERG-N95 implicit time was significantly prolonged in latency in groups 1 and 2 in comparison with control group (P<0.001).

phNR amplitude and implicit time showed significant difference between the studied groups (P<0.001) ([Table 4]).
Table 4 Comparison of multifocal electroretinogram, pattern electroretinogram, and photonegative response values between the studied groups

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In the diabetic patients without retinopathy, there was a significant negative correlation between superior and inferior GCC thicknesses with HBA1c, duration of DM, PERG-N95, as well as phNR latency (P<0.001). On the contrary, there was a significant positive correlation between superior and inferior GCC thicknesses with PERG-N95, mfERG P1, and photonegative response (PhNR) amplitude (P<0.001), as shown in [Table 5].
Table 5 Correlations between superior and inferior ganglion cell complex thicknesses and different parameters in group I

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The sensitivity and specificity were examined with the area under the receiver operating characteristic curve (AUC). In diabetic patients without DR, the widest parts of the ROC curves of GCC thickness were found in the inferior quadrants (AUC=0.831, 95% confidence interval (CI.)=0.729–0.934, cutoff =100.5) followed by the superior quadrants (AUC=0.753) ([Figure 1] and [Table 6]).
Figure 1 Receiver operating characteristics curve to detect validity of total, superior, and inferior ganglion cell complex thickness in prediction of early neurodegenerations in diabetic patients without diabetic retinopathy.

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Table 6 Receiver operating characteristics curve to compare validity of tested parameters in detection of early neurodegenerations in diabetic patients without retinopathy

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Regarding electroretinogram, the PERG/N95 amplitude was with the widest AUC (95% CI) of 0.931 (0.842-1), with 100% sensitivity, 86.7% specificity, and 93.3 accuracy, followed by the phNR amplitude, with AUC (95% CI) of 0.90 (0.806–0.994), with 100% sensitivity, 66.7% specificity, and 83.3% accuracy ([Table 6]).


  Discussion Top


Retinal neurodegeneration represents an early stage in DR pathogenesis that may precede the microvascular abnormalities [5],[14]. Many studies have reported diabetes-induced neural changes such as reactive gliosis, apoptosis, thinning of the neural retina, and changes in the neurofilament and macroglia even before the appearance of microangiopathy [15],[16],[17]. Functional changes of the neural retina such as abnormalities of contrast sensitivity, electroretinogram, or microperimetry have been also reported in diabetic patients [18],[19],[20].

The point of the present study was to assess early morphologic and functional changes in the neural retina (GCL, IPL, and RNFL) in diabetic patients without DR and detect validity of the tested parameters in prediction of early diabetic changes.

Garcia-Martin et al. [21] reported thinning of the GCL in diabetic patients without retinopathy in comparison with controls (P<0.001) and reduced thickness of macular RNFL in the inferior quadrant (P=0.033). These findings concur with the present study in which there were significant differences of total GCC thickness values between the studied groups (P<0.001) with more thinning in the superior and inferior quadrants of GCC in groups 1 and 2 in comparison with the control group.

Chhablani et al. [7] in their study using SD-OCT stated significant thinning of the GCL, IPL, and RNFL in diabetic patients with no evidence of vascular changes in comparison with controls (P<0.05), suggesting that neurodegeneration of the inner retina can occur in early stages of diabetes.

Multiple previous studies also reported thinning of the inner retinal layers and GCC in diabetic patients without or with minimal vascular changes [22],[23],[24].

mfERG is an objective standard test for evaluating retinal functional abnormalities [25]. PERG is used to assess macular and GCL functions [12]; phNR is another method to assess GCL function [13].

In the present study, there was an impairment of the retinal function in the diabetic patients in absence of microvascular changes, and the mfERG foveal P1 wave amplitude was significantly reduced in group 1 and group 2 in comparison with control group (P<0.001). These results are in agreement with previous studies which used mfERG to assess the neural retinal dysfunction in diabetic patients and concluded that the increased P1 implicit time and reduced traces can foretell the development of microvascular abnormalities over the next 1–3 years [25],[26],[27].Santos et al. [28] also found mfERG impairment in 58% of their patients without visible retinopathy, with P1 amplitude being significantly reduced (P=0.005). They concluded that the amplitude of mfERG P1 wave was more sensitive than the implicit time and reported an association between SD-OCT thinning with mfERG, which increases in the presence of any microvascular abnormalities.

Yang et al. [29] reported significant impairments of PERG responses and accelerated GCL apoptosis in diabetic db/db mice with no evidence of retinal microvascular changes in comparison with the control group.

In the present study, the amplitude of PERG-N95 and phNR showed significant reduction in group 1 and group 2 in comparison with control group (P<0.001), and the implicit time was also significantly delayed in latency as compared with control group (P<0.001). These changes reflect impairments of the retinal neuronal function especially the GCL in which its integrity is crucial for good visual function.

A previous study reported impaired PERG responses in diabetic patients without DR, with more severe abnormalities in patients with DR [30]. Another study by Kim et al. [31] also stated significant reduction of phNR amplitude and increased implicit time in patients with DR compared with normal volunteers. These results are comparable to the present study.

In this study, a comparison has been done between GCC, mfERG, PhNR, and PERG parameters regarding their sensitivity and specificity to detect early changes in the neural retina. There was a significant positive correlation between GCC thicknesses with PERG-N95, mfERG P1, and PhNR amplitude (P<0.001) and a significant negative correlation between GCC thicknesses with HBA1c, duration of DM, PERG-N95, as well as phNR implicit time (P<0.001).

The inferior GCC thickness was more sensitive at early stages of the DM with widest parts of the ROC curves (AUC=0.831, cutoff 100.5, 93.3% sensitivity, and 66.7% specificity). These findings suggest that inferior GCC thickness is useful in detecting early structural changes of the neural retina.

The sensitivity of the amplitude of PERG/N95, phNR, and mf-ERG was 100, 100, and 93.3%, respectively. The PERG/N95 amplitude was with the widest AUC (0.931), followed by the phNR amplitude with AUC of 0.90. Thus, the diagnostic validity of PERG and phNR is comparable to that of the GCC parameters and may be very useful in early detection of functional changes in the neural retina.

One limitation of the current study was the small sample size. Further studies involving bigger numbers of samples and using other technologies like OCT-angiography are needed to assess the relative sensitivity between neural dysfunction and microvascular damage.


  Conclusion Top


In conclusion, the preclinical DR presents with neural loss in the macular area evident by the reduction of GCC thickness and impairments of mf-ERG, PERG, phNR parameters. Neurodegenerative changes may precede the microvascular damage in these patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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