Multifocal electroretinography in diabetic retinopathy and diabetic macular edema

Clinical electroretinography in diabetic retinopathy: a review

The electroretinogram (ERG) is a noninvasive, objective technique to evaluate retinal function that has become increasingly important in the study of diabetic retinopathy. We summarize the principles and rationale of the ERG, present findings from recent clinical studies that have used the full-field ERG, multifocal ERG, and pattern ERG to evaluate neural dysfunction in patients with diabetes, and weigh the strengths and limitations of the technique as it applies to clinical studies and management of patients with diabetic retinopathy. Taken together, ERG studies have provided convincing evidence for dysfunction of the neural retina in patients with diabetes, including those who have no clinically-apparent retinal vascular abnormalities. Recent full-field ERG findings have pointed to the intriguing possibility that photoreceptor function is abnormal in early-stage disease. Pattern ERG data, in conjunction with recently developed photopic negative response analyses, indicate inner retina dysfunction. In addition, multifocal ERG studies have shown spatially localized neural abnormalities that can predict the location of future microaneurysms. Given the insights provided by the ERG, it is likely to play a growing role in understanding the natural history of neural dysfunction in diabetes, as well as providing an attractive outcome measure for future clinical trials that target neural preservation in diabetic retinopathy.

Photoreceptor cells and RPE contribute to the development of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness. It has long been regarded as vascular disease, but work in the past years has shown abnormalities also in the neural retina. Unfortunately, research on the vascular and neural abnormalities have remained largely separate, instead of being integrated into a comprehensive view of DR that includes both the neural and vascular components. Recent evidence suggests that the most predominant neural cell in the retina (photoreceptors) and the adjacent retinal pigment epithelium (RPE) play an important role in the development of vascular lesions characteristic of DR. This review summarizes evidence that the outer retina is altered in diabetes, and that photoreceptors and RPE contribute to retinal vascular alterations in the early stages of the retinopathy. The possible molecular mechanisms by which cells of the outer retina might contribute to retinal vascular damage in diabetes also are discussed. Diabetes-induced alterations in the outer retina represent a novel therapeutic target to inhibit DR.

Reduction of Glut1 in the Neural Retina But Not the RPE Alleviates Polyol Accumulation and Normalizes Early Characteristics of Diabetic Retinopathy

Hyperglycemia is a key determinant for development of diabetic retinopathy (DR). Inadequate glycemic control exacerbates retinopathy, while normalization of glucose levels delays its progression. In hyperglycemia, hexokinase is saturated and excess glucose is metabolized to sorbitol by aldose reductase via the polyol pathway. Therapies to reduce retinal polyol accumulation for the prevention of DR have been elusive because of low sorbitol dehydrogenase levels in the retina and inadequate inhibition of aldose reductase. Using systemic and conditional genetic inactivation, we targeted the primary facilitative glucose transporter in the retina, Glut1, as a preventative therapeutic in diabetic male and female mice. Unlike WT diabetics, diabetic Glut1 ^+/- mice did not display elevated Glut1 levels in the retina. Furthermore, diabetic Glut1 ^+/- mice exhibited ameliorated ERG defects, inflammation, and oxidative stress, which was correlated with a significant reduction in retinal sorbitol accumulation. Retinal pigment epithelium-specific reduction of Glut1 did not prevent an increase in retinal sorbitol content or early hallmarks of DR. However, like diabetic Glut1 ^+/- mice, reduction of Glut1 specifically in the retina mitigated polyol accumulation and diminished retinal dysfunction and the elevation of markers for oxidative stress and inflammation associated with diabetes. These results suggest that modulation of retinal polyol accumulation via Glut1 in photoreceptors can circumvent the difficulties in regulating systemic glucose metabolism and be exploited to prevent DR.SIGNIFICANCE STATEMENT Diabetic retinopathy affects one-third of diabetic patients and is the primary cause of vision loss in adults 20-74 years of age. While anti-VEGF and photocoagulation treatments for the late-stage vision threatening complications can prevent vision loss, a significant proportion of patients do not respond to anti-VEGF therapies, and mechanisms to stop progression of early-stage symptoms remain elusive. Glut1 is the primary facilitative glucose transporter for the retina. We determined that a moderate reduction in Glut1 levels, specifically in the retina, but not the retinal pigment epithelium, was sufficient to prevent retinal polyol accumulation and the earliest functional defects to be identified in the diabetic retina. Our study defines modulation of Glut1 in retinal neurons as a targetable molecule for prevention of diabetic retinopathy.

Long-term full-field and multifocal electroretinographic changes after treatment with ranibizumab in patients with diabetic macular edema

PURPOSE

To investigate changes in macular and panretinal neuroretinal functions by electroretinographic examinations in eyes with diabetic macular edema (DME) treated with intravitreal ranibizumab.

MATERIAL AND METHODS

Sixty-four patients with DME were included in this prospective study. Patients were treated with ranibizumab injection according to the PRN regimen for over 12 months. Before treatment, all patients underwent fundus fluorescein angiography, optical coherence tomography (OCT), best-corrected visual acuity (BCVA) assessment, full-field (ff-ERG), and multifocal electroretinography (mf-ERG). In monthly visits, BCVA and OCT were performed. Besides, mf-ERG recordings were obtained at months 3, 6, 9, and 12, and ff-ERG was performed at month 12.

RESULTS

Fifty-eight patients completed the study. The mean age was 61.1 ± 8.5 (39-80) years. The mean number of injections was 6.19 ± 1.9. The decimal BCVA improved from 0.30 to 0.45 during the 12-month follow-up (p < 0.05). Macular thickness decreased from 413.5 μm to 329.5 μm (p < 0.05). The mf-ERG recordings in the central macular region showed improvements N1 and P1 amplitudes at months 9 and 12. There was a positive correlation between the baseline central (p < 001; r: - 0.378 and p < 0.05; r:-0.335, respectively), the second ring (p < 0.05; r: - 0.260 and p < 0.05; r: - 0.270, respectively) P1- and N1-wave amplitudes, and the BCVA at month 12. Full-field ERG recordings showed that peripheral neuroretinal responses were maintained or improved at month 12. Statistically significant improvements in BCVA and macular thickness were observed at all follow-up visits.

CONCLUSION

Multifocal electroretinographic recording started to improve 6 months after the beginning of intravitreal ranibizumab treatment in eyes with DME. This improvement was significant at months 9 and 12. A significant improvement in ff-ERG was observed at month 12.

Multifocal Electroretinogram Can Detect the Abnormal Retinal Change in Early Stage of type2 DM Patients without Apparent Diabetic Retinopathy

PURPOSE

To study retinal function defects in type 2 diabetic patients without clinically apparent retinopathy using a multifocal electroretinogram (mf-ERG).

METHODS

Seventy-six eyes of thirty-eight type 2 diabetes mellitus(DM) patients without clinically apparent retinopathy and sixty-four normal eyes of thirty-two healthy control (HC) participants were examined using mf-ERG.

RESULTS

Patients with type 2 DM without apparent diabetic retinopathy demonstrated an obvious implicit time delay of P1 in ring 1, ring 3, and ring 5 compared with healthy controls (t = 5.184, p ≤ 0.001; t = 8.077, p ≤ 0.001; t = 2.000, p = 0.047, respectively). The implicit time (IT) in ring 4 of N1wave was significantly delayed in the DM group (t = 2.327, p = 0.021). Compared with the HC group, the implicit time of the P1 and N1 waves in the temporal retina zone was significantly prolonged (t = 3.66, p ≤ 0.001; t = 2.187, p = 0.03, respectively). And the amplitude of P1 in the temporal retina decreased in the DM group, which had a significantly statistical difference with the healthy controls (t = -6.963, p ≤ 0.001). However, there were no differences in either the amplitude of the response or the implicit time of the nasal retina zone between DM and HC. The AUC of multiparameters of mf-ERG was higher in the diagnosis of DR patients.

CONCLUSIONS

Patients with type 2 DM without clinically apparent retinopathy had a delayed implicit time of P1 wave in temporal regions of the postpole of the retina compared with HC subjects. It demonstrates that mf-ERG can detect the abnormal retinal change in the early stage of type2 DM patients without apparent diabetic retinopathy. Multiparameters of mf-ERG can improve the diagnostic efficacy of DR, and it may be a potential clinical biomarker for early diagnosis of DR.

Correlation between optical coherence tomography, multifocal electroretinogram findings and visual acuity in diabetic macular edema

AIM

To analyze the correlation between macular morphology and function in eyes with diabetic macular edema (DME).

METHODS

Fifty-five eyes with different visual acuity (VA) of 32 patients who suffered from DME were analyzed using multifocal electroretinography (mfERG) and optical coherence tomography (OCT). The parameters of mfERG including implicit times and response amplitude were compared to those of 50 normal eyes of 36 age-matched subjects. Correlation analysis was performed between VA, the parameters of mfERG including implicit times and response amplitude, and the central macular thickness (CMT).

RESULTS

The amplitude of N1 and P1 were significantly decreased and their latency were significantly increased in five ring regions of the retina in patients with DME. There was statistically significant correlation between logMAR BCVA and P1 amplitude densities in rings 1-4 (r=-0.306, -0.536, -0.470, -0.362; P=0.023, <0.01, <0.01, 0.007 respectively), N1 amplitude in ring 2 and ring 3 (r=-0.035, -0.286; P=0.019, 0.034 respectively). There was poor correlation between the CMT and best-corrected visual acuity (BCVA; r=0.288, P=0.033), but there was no significant correlation between CMT and amplitude or implicit time of N1 and P1 (P>0.05) in the central macular ring. Multiple stepwise regression analysis showed that P1 amplitude density in ring 2 was the only contributor to the VA.

CONCLUSION

It seems to be more appropriate of combining use of mfERG with OCT for the evaluation of macular function in eyes with DME.

Microperimetry and mfERG as functional measurements in diabetic macular oedema undergoing intravitreal ranibizumab treatment

PURPOSE

To evaluate Microperimetry (MP) and multifocal electroretinogram (mfERG) as whole-macula functional markers of treatment response in naive diabetic macular oedema (DMO) patients undergoing ranibizumab treatment.

METHODS

An exploratory sub-analysis of a prospective study (NCT01947881-CHARTRES). Patients received three monthly ranibizumab injections (loading dose) followed by pro re nata (PRN) regimen during 1 year. At baseline, during and after treatment (Months 0, 3, 6 and 12), subjects were tested using BCVA, OCT, MP and mfERG. MP was performed in the central 12°, and retinal sensitivity was measured overall (mean sensitivity (MS)), and in three concentric rings (R1-R3). mfERG P1 amplitude and implicit time were measured over six concentric rings (R1-R6).

RESULTS

Thirty-two eyes were included. MP mean and rings sensitivity were significantly lower in DMO (p < 0.001). After loading dose, a significant improvement in retina sensitivity was observed, particularly in good BCVA responders (MS = +2.28 dB; R1 = +2.33 dB, R2 = +2.20 dB, R3 = +2.25 dB; p = 0.049). Overall retinal sensitivity was significantly correlated with BCVA improvement (r = 0.54; p = 0.026) and inversely correlated with OCT central subfield thickness improvement (r = -0.39; p = 0.026). mfERG amplitude and implicit time were also lower in DMO (p < 0.011). An improvement of mfERG P1 amplitude and implicit time in R1 was noted in good responders after ranibizumab loading dose (+16.49 nV/deg²; p = 0.013 and -0.005 ms; p = 0.048, respectively). When changing to PRN treatment regimen, BCVA was maintained during the 12 months of follow-up but worsening of the visual function was detected by MP and mfERG.

CONCLUSIONS

Microperimetry and mfERG were able to demonstrate DMO functional improvement after treatment loading dose, as well as early visual changes when treatment regimen was switched to PRN.

Role of multifocal electroretinogram in assessment of early retinal dysfunction in hypertensive patients

PURPOSE

To investigate localized retinal dysfunction in hypertensive patients using multifocal electroretinogram (mfERG) and to assess its sensitivity as an early predictor for the development of retinopathy in hypertensive patients.

METHODS

Ninety-eight eyes were included in this case-control study. Twenty-eight eyes of healthy subjects served as a control group (group I). Seventy eyes belonged to patients with systemic hypertension assigned into two groups; group II including 39 eyes of hypertensive patients with normal fundus and group III including 31 eyes of patients with signs of hypertensive retinopathy. All participants were subjected to complete ophthalmic and electrophysiological examination using mfERG. N1 and P1 wave amplitudes and implicit times from the central hexagon and four concentric rings across the visual field were analyzed.

RESULTS

mfERG amplitudes were significantly reduced in hypertensive group with retinopathy than in controls. N1 amplitude was significantly reduced in the most eccentric ring in eyes of hypertensive patients with normal fundus.

CONCLUSION

mfERG is a sensitive objective tool for assessment of retinal dysfunction in hypertensive patients. mfERG amplitude is a promising predictor for early development of retinopathy in systemic hypertension.

Subretinal surgery: functional and histological consequences of entry into the subretinal space

BACKGROUND AND OBJECTIVES

Gene-therapy, stem-cell transplantation and surgical robots hold the potential for treatment of currently untreatable retinal degenerative diseases. All of the techniques require entry into the subretinal space, which is a potential space located between the retina and the retinal pigment epithelium (RPE). Knowledge about obstacles and critical steps in relation to subretinal procedures is therefore needed. This thesis explores the functional and histological consequences of separation of the retina from the RPE, extensive RPE damage, a large cut in the retina (retinotomy) and RPE phagocytosis in a porcine model.

METHODS

Experiments were performed in 106 female domestic pigs of Danish landrace distributed over five studies. Under general anesthesia, different procedures for expansion of the subretinal space were conducted. Outcomes were visual function measured electrophysiologically with multifocal electroretinogram (mfERG) and retinal morphology examined histologically. Study I: The effect of anesthesia on mfERG was examined by repeated recordings for 3 hr in isoflurane or propofol anesthesia. Outcome was mfERG amplitude. Study II: Consequences of a large separation of the photoreceptors from the RPE were examined by injecting a perfluorocarbon-liquid (decalin) into the subretinal space. Two weeks after, in a second surgery, decalin was withdrawn. Outcomes were mfERG and histology 4 weeks after decalin injection. Study III: Extensive RPE damage was examined by expanding the subretinal space with saline and removing large sheets of RPE-cells through a retinotomy. Outcomes were mfERG and histology 2, 4 and 6 weeks after the procedure. Study IV: Consequences of a large retinotomy were examined by similar procedures as in Study III, but in study IV only a few RPE cells were removed. Outcomes were mfERG and histology 2 and 6 weeks after surgery. Study V: Clearance of the subretinal space was examined by injecting fluorescent latex beads of various sizes into the subretinal space. Outcome was histologic location of the beads at different time intervals after the procedure.

RESULTS

Study I: MfERG amplitudes decreased linearly as a function of time in propofol or isoflurane anesthesia. Duration of mfERG recording could be decreased without compromising quality, and thereby could time in anesthesia be reduced. Study II: MfERG and histology remained normal after reattachment of a large and 2-week long separation of the photoreceptors and RPE. Repeated entry into the subretinal space was well tolerated. Fluid injection into the subretinal space constitutes a risk of RPE-damage. Study III: Removal of large sheets of retinal pigment epithelial cells triggered a widespread rhegmatogenous-like retinal detachment resulting in visual loss. Study IV: A large retinotomy with limited damage of the RPE was well tolerated, and visual function was preserved. Study V: Subretinal latex beads up to 4 μm were phagocytosed by the RPE and passed into the sub-RPE space. Beads up to 2 μm travelled further through the Bruch's membrane and were found in the choroid, sclera and inside blood vessels.

CONCLUSION

A large expansion of the subretinal space, repeated entry, a large retinotomy and limited RPE damage is well tolerated and retinal function is preserved. Subretinal injection of fluid can damage the RPE and extensive RPE damage can induce a rhegmatogenous-like retinal detachment with loss of visual function. Foreign substances exit the subretinal space and can reach the systemic circulation.

Metalloproteinases mediate diabetes-induced retinal neuropathy and vasculopathy

Matrix metalloproteinases (MMPs) and related metalloproteinases with a disintegrin domain (ADAMs) have become interesting probes and targets in eye diseases, including diabetic retinopathy. We here summarize recent data about MMPs and ADAMs in retinopathies. Retinal diseases range from rare genetic afflictions to diabetic retinopathy, the latter of which is reaching epidemic proportions. MMPs and ADAMs play roles in normal eye development and in disease states, not only in local proteolysis but also signaling functions mediated by specific protein domains, interacting with cell surface receptors. In proliferative diabetic retinopathy, inflammation, hypoxia-induced vascular endothelial growth factor and oxidative stress collectively stimulate the production, activation and signaling functions of pro-MMP-9. This leads to angiogenesis, destruction of neuroprotective prominin-1, loss of photoreceptors and blood-retina barrier breakdown. Biological inhibition of proteolysis and control of signaling functions are executed by the tissue inhibitors of metalloproteases (TIMPs). Angiogenic, inflammatory and fibrotic reactions, in which MMPs, ADAMs and TIMPs are involved, co-determine common eye diseases. Therefore, visions about the use of these proteases as biomarkers and as targets for therapeutic inhibitors, including small molecule inhibitors and monoclonal antibodies, may lead to breakthroughs in tissue regeneration, maintenance of photoreceptors and neuroprotection.

Electrophysiological and pupillometric measures of inner retina function in nonproliferative diabetic retinopathy

PURPOSE

To evaluate three measures of inner retina function, the pattern electroretinogram (pERG), the photopic negative response (PhNR), and the post-illumination pupil response (PIPR) in diabetics with and without nonproliferative diabetic retinopathy (NPDR).

METHODS

Fifteen non-diabetic control subjects and 45 type 2 diabetic subjects participated (15 have no clinically apparent retinopathy [NDR], 15 have mild NPDR, and 15 have moderate/severe NPDR). The pERG was elicited by a contrast-reversing checkerboard pattern, and the PhNR was measured in response to a full-field, long-wavelength flash presented against a short-wavelength adapting field. The PIPR was elicited by a full-field, 450 cd/m², short-wavelength flash. All responses were recorded and analyzed using conventional techniques. One-way ANOVAs were performed to compare the pERG, PhNR, and PIPR among the control and diabetic groups.

RESULTS

ANOVA indicated statistically significant differences among the control and diabetic subjects for all three measures. Holm-Sidak post hoc comparisons indicated small, nonsignificant reductions in the pERG (8%), PhNR (8%), and PIPR (10%) for the NDR group compared to the controls (all p > 0.25). In contrast, there were significant reductions in the pERG (35), PhNR (34%), and PIPR (30%) for the mild NPDR group compared to the controls (all p < 0.01). Likewise, there were significant reductions in the pERG (40%), PhNR (32%), and PIPR (32%) for the moderate/severe NPDR group compared to the controls (all p < 0.01).

CONCLUSION

Abnormalities of the pERG, PhNR, and PIPR suggest inner retina neural dysfunction in diabetics who have clinically apparent vascular abnormalities. Taken together, these measures provide a noninvasive, objective approach to study neural dysfunction in these individuals.

Use of Direct Current Electroretinography for Analysis of Retinal Pigment Epithelium Function in Mouse Models

A monolayer of pigmented epithelial cells, the retinal pigment epithelium (RPE), supports photoreceptor function in many ways. Consistent with these roles, RPE dysfunction underlies a number of hereditary retinal disorders. To monitor RPE function in vivo models for these conditions, we adapted an electroretinographic (ERG) technique based on direct current amplification (DC-ERG). This chapter describes the main features of this approach and its application to mouse models involving the RPE.

Early and localized retinal dysfunction in patients with type 1 diabetes mellitus studied by multifocal electroretinogram

AIMS

To investigate the function of localized retinal areas in highly selected type 1 diabetes mellitus patients (DM1) with no or mild signs of diabetic retinopathy (NO DR and NPDR, respectively) and its correlation with age, diabetes duration and glycemic control.

METHODS

Multifocal electroretinograms (mfERG) were recorded in 35 eyes of 18 NO DR patients and 38 eyes of 19 NPDR patients. Thirty-one eyes of 17 normal subjects were enrolled as controls. N1-P1 response amplitude densities (RADs) and P1 implicit times (ITs) from isolated (R1: 0°-2.5°, R2: 2.5°-5°, R3: 5°-10°) and combined (R1 + R2, R2 + R3 and R1 + R2 + R3) annular rings and from four retinal sectors (nasal, N; temporal, T; superior, S and inferior, I) with increasing eccentricities up to 10° (S1, S2, S3, S1 + S2, S1 + S2 + S3) were measured. The statistical differences between DM1 groups and controls were tested by ANOVA. The electrophysiological data were correlated with age, duration of diabetes and glycated hemoglobin (HbA1c) level using the Pearson's test.

RESULTS

MfERG RADs, but not ITs, from all isolated and combined rings and sectors up to 10° of foveal eccentricity were statistically different between DM1 groups compared to controls. No significant differences were found between NO DR and NPDR patients. The mfERG abnormalities of the central retinal areas were correlated significantly with age in both DM1 groups and with diabetes duration mainly in NPDR group.

CONCLUSIONS

In DM1 patients, localized retinal dysfunction, described by reduced mfERG RAD, can be observed also in the absence of clinical signs of DR and it is related to aging.

Approach for a Clinically Useful Comprehensive Classification of Vascular and Neural Aspects of Diabetic Retinal Disease

The Early Treatment Diabetic Retinopathy Study (ETDRS) and other standardized classification schemes have laid a foundation for tremendous advances in the understanding and management of diabetic retinopathy (DR). However, technological advances in optics and image analysis, especially optical coherence tomography (OCT), OCT angiography (OCTa), and ultra-widefield imaging, as well as new discoveries in diabetic retinal neuropathy (DRN), are exposing the limitations of ETDRS and other classification systems to completely characterize retinal changes in diabetes, which we term diabetic retinal disease (DRD). While it may be most straightforward to add axes to existing classification schemes, as diabetic macular edema (DME) was added as an axis to earlier DR classifications, doing so may make these classifications increasingly complicated and thus clinically intractable. Therefore, we propose future research efforts to develop a new, comprehensive, and clinically useful classification system that will identify multimodal biomarkers to reflect the complex pathophysiology of DRD and accelerate the development of therapies to prevent vision-threatening DRD.

Decreased Retinal Thickness in Type 1 Diabetic Children with Signs of Nonproliferative Diabetic Retinopathy

The retina functions as a neurovascular unit. How early vascular alterations affect neuronal layers remains controversial; early vascular failure could lead to edema increasing retinal thicknesses, but alternatively neuronal loss could lead to reduced retinal thickness. Objective. To evaluate retinal thickness in a cohort of pediatric patients with type 1 diabetes mellitus (PwT1DM) and to analyze differences according to the presence or absence of nonproliferative diabetic retinopathy (NPDR), poor metabolic control, and diabetes duration. Patients and Methods. We performed retinographies and optical coherence tomography (OCT) (TOPCON 3D1000®) to PwT1DM followed at our center and healthy controls. Measurements of the control group served to calculate reference values. Results. 59 PwT1DM (age 12.51 ± 2.59) and 22 healthy controls (age 10.66 ± 2.51) volunteered. Only two PwT1DM, both adolescents with poor metabolic control, presented NPRD. Both showed decreased thicknesses and retinal volumes. The odds ratio of having decreased retinal thickness when signs of NPDR were present was 11.72 (95% IC 1.16-118.28; p = 0.036). Conclusions. PwT1DM with NPDR have increased odds of decreased retinal thicknesses and volumes. Whether these changes are reversible by improving metabolic control or not remains to be elucidated.

Time-Dependent Decline in Multifocal Electroretinogram Requires Faster Recording Procedures in Anesthetized Pigs

Purpose

The time-dependent effect of anesthetics on the retinal function is debated. We hypothesize that in anesthetized animals there is a time-dependent decline that requires optimized multifocal electroretinogram (mfERG) recording procedures.

Methods

Conventional and four-frame global-flash mfERG recordings were obtained approximately 15, 60, and 150 minutes after the induction of propofol anesthesia (20 pigs) and isoflurane anesthesia (nine pigs). In six of the propofol-anesthetized pigs, the mfERG recordings were split in 3-minute segments. Two to 4 weeks after initial recordings, an intraocular injection of tetrodotoxin (TTX) was given and the mfERG was rerecorded as described above. Data were analyzed using mixed models in SAS statistical software.

Results

Propofol significantly decreases the conventional and global-flash amplitudes over time. The only significant effect of isoflurane is a decrease in the global-flash amplitudes. At 15 minutes after TTX injection several of the mfERG amplitudes are significantly decreased. There is a linear correlation between the conventional P1 and the global-flash DR mfERG-amplitude (R² = 0.82, slope = 0.72, P < 0.0001). There is no significant difference between the 3-minute and the prolonged mfERG recordings for conventional amplitudes and the global-flash direct response. The global flash–induced component significantly decreases with prolonged mfERG recordings.

Conclusions

A 3-minute mfERG recording and a single stimulation protocol is sufficient in anesthetized pigs. Recordings should be obtained immediately after the induction of anesthesia. The effect of TTX is significant 15 minutes after injection, but is contaminated by the effect of anesthesia 90 minutes after injection. Therefore, the quality of mfERG recordings can be further improved by determining the necessary time-of-delay from intraocular injection of a drug to full effect.

Translational Relevance

General anesthesia is a possible source of error in mfERG recordings. Therefore, it is important to investigate the translational relevance of the results to mfERG recordings in children in general anesthesia.

Development of a Normative Database for Multifocal Electroretinography in the Context of a Multicenter Clinical Trial

PURPOSE

The aim of this study is to present the largest normative database using multifocal electroretinography (mfERG) in the context of a multicenter clinical trial.

METHODS

This investigational study included 156 eyes from 78 Caucasian subjects aged 45-70 years without known ophthalmic disease or diabetes mellitus; the subjects were recruited from 11 clinical sites in the setting of the EUROCONDOR project. Standardized mfERG acquisition (103 hexagons per eye) was established based on the International Society of Clinical Electrophysiology in Vision. At least one technician per site received both specialized training and certification. The main variables that could have influenced the results were considered in the analyses.

RESULTS

The normative database was based on 111 eyes. The overall mean P1-implicit time (IT) was 33.94 ± 1.70 ms, and the mean P1 amplitude was 30.58 ± 5.20 nV/deg2. Age and gender were independently related to predictors of P1-IT but not of P1 amplitude. The responses that were averaged for the 6 rings showed a longer P1-IT time in the fovea, decreasing progressively to the parafovea and perifovea. By contrast, P1 amplitude values sharply decreased with retinal eccentricity.

CONCLUSIONS

This normative database can be used as a comparative index of expected normal values in the clinical setting and for examining the effect of studies testing neuroprotective agents.

Therapeutic targeting of diabetic retinal neuropathy as a strategy in preventing diabetic retinopathy

Diabetes causes a panretinal neurodegeneration herein termed diabetic retinal neuropathy, which manifests in the retina early and progresses throughout the disease. Clinical manifestations include changes in the ERG, perimetry, dark adaptation, contrast sensitivity and colour vision which correlate with laboratory findings of thinning of the retinal neuronal layers, increased apoptosis in neurons and activation of glial cells. Possible mechanisms include oxidative stress, neuronal AGE accumulation, altered balance of neurotrophic factors and loss of mitohormesis. Retinal neural damage precedes and is a biologically plausible cause of retinal vasculopathy later in diabetes, and this review suggests that strategies to target it directly could prevent diabetes induced blindness. The efficacy of fenofibrate in reducing retinopathy progression provides a possible proof of concept for this approach. Strategies which may target diabetic retinal neuropathy include reducing retinal metabolic demand, improving mitochondrial function with AMPK and Sirt1 activators or providing neurotrophic support with neurotrophic supplementation.

Clinical biomarkers and molecular basis for optimized treatment of diabetic retinopathy: current status and future prospects

Diabetic retinopathy is a highly specific microvascular complication of diabetes and a leading cause of blindness worldwide. It is triggered by hyperglycemia which causes increased oxidative stress leading to an adaptive inflammatory assault to the neuroretinal tissue and microvasculature. Prolonged hyperglycemia causes increased polyol pathway flux, increased formation of advanced glycation end-products, abnormal activation of signaling cascades such as activation of protein kinase C (PKC) pathway, increased hexosamine pathway flux, and peripheral nerve damage. All these changes lead to increased oxidative stress and inflammatory assault to the retina resulting in structural and functional changes. In addition, neuroretinal alterations affect diabetes progression. The most effective way to manage diabetic retinopathy is by primary prevention such as hyperglycemia control. While the current mainstay for the management of severe and proliferative diabetic retinopathy is laser photocoagulation, its role is diminishing with the development of newer drugs including corticosteroids, antioxidants, and antiangiogenic and anti-VEGF agents which work as an adjunct to laser therapy or independently. The current pharmacotherapy of diabetic retinopathy is incomplete as a sole treatment option in view of limited efficacy and short-term effect. There is a definite clinical need to develop new pharmacological therapies for diabetic retinopathy, particularly ones which would be effective through the oral route and help recover lost vision. The increasing understanding of the mechanisms of diabetic retinopathy and its biomarkers is likely to help generate better and more effective medications.

Neuroretinal alterations in the early stages of diabetic retinopathy in patients with type 2 diabetes mellitus

PurposeTo study neuroretinal alterations in patients affected by type 2 diabetes with no diabetic retinopathy (DR) or mild nonproliferative diabetic retinopathy (NPDR) and without any sign of diabetic macular edema.Patients and methodsIn total, 150 type 2 diabetic patients with no (131 eyes) or mild NPDR (19 eyes) and 50 healthy controls were enrolled in our study. All underwent a complete ophthalmologic examination, including Spectral-Domain optical coherence tomography (SD-OCT). Ganglion cell-inner plexiform layer (GC-IPL) and retinal nerve fiber layer (RNFL) thickness values were calculated after automated segmentation of SD-OCT scans.ResultsMean best-corrected visual acuity was 0.0±0.0 LogMAR in all the groups. Mean GC-IPL thickness was 80.6±8.1 μm in diabetic patients and 85.3±9.9 μm in healthy controls, respectively (P=0.001). Moreover, evaluating the two different diabetic groups, GC-IPL thickness was 80.7±8.1 μm and 79.7±8.8 μm in no-DR and mild-NPDR group (P=0.001 and P=0.022 compared with healthy controls, respectively). Average RNFL thickness was 86.1±10.1 μm in diabetes patients and 91.2±7.3 μm in controls, respectively (P=0.003). RNFL thickness was 86.4±10.2 μm in no-DR group and 84.1±9.4 μm in mild-NPDR group (P=0.007 and P=0.017 compared with healthy controls, respectively).ConclusionWe demonstrated a significantly reduced GC-IPL and RNFL thickness values in both no-DR and mild-NPDR groups compared with healthy controls. These data confirmed neuroretinal alterations are early in diabetes, preceding microvascular damages.

Morphology and Function over a One-Year Follow Up Period after Intravitreal Dexamethasone Implant (Ozurdex) in Patients with Diabetic Macular Edema

Background

To investigate changes in macular morphology and function after an intravitreal dexamethasone implant for diabetic macular edema (DME).

Methods

Twenty-seven eyes in 27 treatment-naive patients affected by DME were treated with intravitreal Ozurdex® injections (IVOI) and followed up 12 months to evaluate morphological and functional changes by means of best-corrected visual acuity (BCVA), microperimetry (MP1), multifocal electroretinography (mfERG), pattern electroretinography (PERG) and spectral domain optical coherence tomography (SD-OCT).

Results

Both BCVA and retinal sensitivity improved significantly at one month after the IVOI (p = 0.031 and p<0.0001, respectively). After five months, the improvement of BCVA remained statistically significant compared with baseline values (p = 0.022); retinal sensitivity improvement was statistically significant for up to four months after the IVOI (p = 0.059). Moreover, central macular thickness significantly decreased for up to four months. Interestingly, PERG and mfERG values did not change significantly for up to four months post-IVOI, but then began to worsen.

Conclusions

In eyes with DME, intravitreal dexamethasone implant determined morphological and functional improvement as soon as one month and for up to four months after the treatment.

Neuroinflammatory responses in diabetic retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes and has been recognized as a vascular dysfunction leading to blindness in working-age adults. It becomes increasingly clear that neural cells in retina play an important role in the pathogenesis of DR. Neural retina located at the back of the eye is part of the brain and a representative of the central nervous system. The neurosensory deficits seen in DR are related to inflammation and occur prior to the clinically identifiable vascular complications. The neural deficits are associated with abnormal reactions of retina glial cells and neurons in response to hyperglycemia. Improper activation of the innate immune system may also be an important contributor to the pathophysiology of DR. Therefore, DR manifests characteristics of both vasculopathy and chronic neuroinflammatory diseases. In this article, we attempt to provide an overview of the current understanding of inflammation in neural retina abnormalities in diabetes. Inhibition of neuroinflammation may represent a novel therapeutic strategy to the prevention of the progression of DR.