Photopic full-field electroretinography and optical coherence tomography in type 1 diabetic retinopathy

Electrophysiological findings in long-term type 1 diabetes patients without diabetic retinopathy using different ERG recording systems

To assess full-field electroretinogram findings in long-term type 1 diabetes patients without diabetic retinopathy. Prospective study including 46 eyes of 23 patients with type 1 diabetes and 46 age-matched healthy eyes evaluated by the RETI-port/scan21 and the portable system RETeval following ISCEV guidelines. The average duration of diabetes was 28.88 ± 8.04 years. In scotopic conditions, using the RETI-port/scan21, diabetic patients showed an increase in b-wave implicit time (IT) (p = 0.017) with the lowest stimuli; a diminished b-wave amplitude (p = 0.005) in the mixed response, an increased IT (p = 0.004) with the high-intensity stimuli and an OP2 increased IT (p = 0.008) and decreased amplitude (p = 0.002). Under photopic conditions, b-wave amplitude was lower (p < 0.001) and 30-Hz flicker response was diminished (p = 0.021). Using the RETeval, in scotopic conditions, diabetic patients showed a reduction in the rod b-wave amplitude (p = 0.009), an increase in a-wave IT with the 280 Td.s stimulus (p = 0.005). OP2 had an increased IT and diminished amplitude (p = 0.003 and p = 0.002 respectively). 16 Td.s flicker showed an increased IT (p = 0.008) and diminished amplitude (p = 0.048). Despite variations in values between both systems, nearly all results displayed positive correlations. Long-term type 1 diabetes patients without diabetic retinopathy exhibit alterations in scotopic conditions, as evidenced by both conventional and portable electroretinogram devices. These findings suggest a modified retinal function, particularly in rod-driven pathways, even in the absence of vascular signs.

Retinal Functional Impairment in Diabetic Retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a neurodegenerative disease of the retina. The aim of our study was to analyze latency changes in a full-field electroretinogram (ERG) in patients with type 2 diabetes.

MATERIAL

This prospective study included 15 diabetic patients without DR, 16 diabetic patients with non-proliferative DR, 14 patients with pre-proliferative DR, 15 patients with proliferative DR, and 14 age-matched controls. All the participants underwent ophthalmologic examination and full-field ERGs. The ERGs were recorded with the Metrovision MonPackOne system. The latencies were analyzed for "a"- and "b"-waves in the dark-adapted (DA) 0.01 ERG, DA 3.0 ERG, DA oscillatory potentials, light-adapted (LA) 3.0 ERG, and 30 Hz flicker ERG.

RESULTS

The delayed responses of healthy subjects compared to diabetic patients without DR were the DA oscillatory potentials (25.45 ± 1.04 ms vs. 26.15 ± 0.96 ms, p = 0.027). When comparing diabetic patients without DR and with non-proliferative DR, we did not obtain statistically significant delays. Significant delays in the DA 0.01 "b"-wave (61.91 ± 5.52 ms vs. 66.36 ± 8.12 ms, p = 0.029), DA 3.0 "b"-wave (41.01 ± 2.50 ms vs. 44.16 ± 3.78 ms, p = 0.035), and LA 3.0 "a"-wave (16.21 ± 0.91 ms vs. 16.99 ± 1.16 ms, p = 0.045) were found between non-proliferative DR and pre-proliferative DR. When comparing the groups of patients with pre-proliferative DR and proliferative DR, the LA 3.0 ERG "b"-wave (32. 63 ± 2.53 ms vs. 36.19 ± 3.21 ms, p < 0.0001), LA 30 Hz flicker ERG "a"-wave (19.56 ± 3.59 vs. 21.75 ± 4.74 ms, p= 0.025), and "b"-wave (32.23 ± 4.02 vs. 36.68 ± 3.48 ms, p = 0.017) were delayed.

CONCLUSIONS

the electrophysiological findings from our study indicate that there is a substantial dysfunction of the neural retina in all stages of DR.

Full-field and multifocal electroretinogram in non-diabetic controls and diabetics with and without retinopathy

OBJECTIVE

To compare retinal function assessed by full-field electroretinography (ffERG) and multifocal electroretinography (mfERG) in diabetes without retinopathy, diabetes with moderate non-proliferative diabetic retinopathy (NPDR) and in the absence of diabetes.

METHODS

Scotopic and photopic ffERG and mfERG was made in non-fasting volunteers, including 26 diabetic participants without retinopathy, 22 diabetic participants with moderate NPDR and 22 participants without diabetes using full International Society for Clinical Electrophysiology of Vision protocols.

RESULTS

Of the ffERG responses, significant deviation (p ≤ 0.05, corrected for multiple sampling and other relevant confounders) from the non-diabetic participants was seen in the diabetic participants only for the OP1-OP3 oscillatory amplitudes and the OP2 implicit time. This finding was independent of whether retinopathy was present or not. For the mfERG, minor amplitude or implicit time deviations were found for a small number of rings (R2, R4 and R5). Receiver of operating characteristic analysis showed that the single most prominent abnormality of the ffERG in diabetes, regardless of whether retinopathy was present or not, was the OP2 implicit time (area under the curve ≥ 0.80).

CONCLUSION

This bi-modal study of electroretinographic characteristics found that the most prominent anomaly associated with diabetes was a prolongation of the implicit time of the OP2 of the scotopic ffERG, while the most prominent added effect of non-proliferative diabetic retinopathy was a further prolongation of the OP2 implicit time. Although the variation in ERG characteristics is far too large for diagnostic purposes, the close association of the oscillatory potentials with the amacrine cells of the retina indicate that their function is particularly sensitive to diabetes.

Correlation between optical coherence tomography angiography and multifocal electroretinogram findings in patients with diabetes mellitus

BACKGROUND

Diabetic retinopathy is characterized by microvascular, neural and glial cell damage. Optical coherence tomography angiography (OCTA) can detect subclinical microvasculopathy while multifocal electroretinography (mfERG) can detect subclinical local retinal dysfunction before onset of clinically observable retinopathy. Here, we investigated the relationship between retinal dysfunction in multifocal electroretinography and vascular changes in optical coherence tomography angiography.

METHODS

The study included 63 eyes of 63 diabetic patients without retinopathy (DM+DR-) and 68 eyes of 68 patients with non-proliferative diabetic retinopathy (NPDR). In addition, 64 eyes of 64 age and sex-matched subjects were included as the control group (CG). All subjects were evaluated using OCTA and mfERG.

RESULTS

The vascular density in the superficial and deep capillary plexus was significantly decreased in the DM+DR-group and the NPDR group compared with the CG group (except for the superficial foveal area, NPDR group vs. CG group) (p < 0.05). The vascular density of the superficial and deep parafoveal region was significantly decreased in the NPDR group compared to the DM+DR-group (p < 0.05). In circles of 2-, 5- and 10°, the amplitudes of the N1 and P1 waves were statistically significantly decreased in both the DM+DR- group and the NPDR group compared with the CG (p < 0.05). When the NPDR group was compared with the DM+DR- group, there was a statistically significant decrease in the amplitude of the N1 and P1 waves in the circles of 2- and 5° (p < 0.05). According to the correlation analysis, the amplitude and implicit times of the N1 and P1 waves showed weak-to-moderate correlation with vascular density (p < 0.05).

CONCLUSIONS

The decreased peaks of mfERG wave provides evidence regarding neurodegenerative effect of DM-associated hyperglycaemia. The decreased vascular density caused by hyperglycaemia was topographically associated with the retinal dysfunction and neurodegeneration.

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.

MD2 blockade prevents modified LDL-induced retinal injury in diabetes by suppressing NADPH oxidase-4 interaction with Toll-like receptor-4

Modified LDL-induced inflammation and oxidative stress are involved in the pathogenesis of diabetic retinopathy. Recent studies have also shown that modified LDL activates Toll-like receptor 4 (TLR4) to mediate retinal injury. However, the mechanism by which modified LDL activates TLR4 and the potential role of the TLR4 coreceptor myeloid differentiation protein 2 (MD2) are not known. In this study, we inhibited MD2 with the chalcone derivatives L2H17 and L6H21 and showed that MD2 blockade protected retinal Müller cells against highly oxidized glycated-LDL (HOG-LDL)-induced oxidative stress, inflammation, and apoptosis. MD2 inhibition reduced oxidative stress by suppressing NADPH oxidase-4 (NOX4). Importantly, HOG-LDL activated TLR4 and increased the interaction between NOX4 and TLR4. MD2 was required for the activation of these pathways, as inhibiting MD2 prevented the association of NOX4 with TLR4 and reduced NOX4-mediated reactive oxygen species production and TLR4-mediated inflammatory factor production. Furthermore, treatment of diabetic mice with L2H17 significantly reduced LDL extravasation in the retina and prevented retinal dysfunction and apoptosis by suppressing the TLR4/MD2 pathway. Our findings provide evidence that MD2 plays a critical role in mediating modified LDL-induced cell injury in the retina and suggest that targeting MD2 may be a potential therapeutic strategy.

Blocking the activity of a protein involved in triggering inflammation and oxidative stress in the retina may reduce diabetes-induced visual impairment and blindness. Besides hyperglycemia, plasma lipids and lipoproteins have also been proposed as potential risk factors for diabetic retinopathy. However, the precise mechanisms controlling low-density lipoprotein-induced retinal damage are unclear. In experiments on mice, Yi Wang at Wenzhou Medical University in Wenzhou, China, and co-workers found that retinal injury caused by highly oxidized glycated-LDL is mediated by the myeloid differentiation protein 2 (MD2). Blocking MD2 with an inhibitor suppressed two key signaling pathways, reducing the production of reactive oxygen species and inflammatory signaling proteins in the retina. Further investigations are needed, but the team believe MD2 could be a vital therapeutic target for diabetic retinopathy.

AMPLITUDE LOSS OF THE HIGH-FREQUENCY FLICKER ELECTRORETINOGRAM IN EARLY DIABETIC RETINOPATHY

PURPOSE

To evaluate retinal dysfunction in diabetic patients who have mild or no nonproliferative diabetic retinopathy (DR) using the high-frequency flicker electroretinogram.

METHODS

Light-adapted flicker electroretinograms were recorded from 15 diabetic patients who have no clinically apparent retinopathy, 15 diabetic patients who have mild nonproliferative DR, and 15 nondiabetic, age-equivalent controls. Electroretinograms were elicited by full-field flicker at 2 temporal frequencies, 31.25 and 62.5 Hz, and were recorded using conventional techniques. Amplitude and timing of the flicker responses were compared among the groups and correlated with clinical characteristics including age, acuity, disease duration, and HbA1c.

RESULTS

The 31.25-Hz flicker amplitude was slightly, but nonsignificantly, smaller for subjects with no DR and mild nonproliferative DR , compared with the control group (both t < 1.38, P > 0.31); small, nonsignificant response delays for both patient groups were also observed (both t < 1.57, P > 0.12). By contrast, there were significant amplitude reductions for the 62.5-Hz flicker stimulus: mean amplitude was reduced by 32% for subjects with no DR and by 41% for subjects with mild nonproliferative DR (both t > 2.92 and P < 0.01). Response timing at 62.5 Hz did not differ significantly from control for either group (both t < 1.2 and P > 0.39). Electroretinogram amplitude and timing were not correlated significantly with clinical characteristics.

CONCLUSION

The 62.5-Hz flicker electroretinogram is useful for evaluating retinal dysfunction in diabetic patients who have mild or no DR because this response can be significantly reduced. Attenuation of the high-frequency flicker electroretinogram, which is primarily generated by bipolar cells, suggests a relatively early retinal site of neural dysfunction.

Reproducibility of Fixed-luminance and Multi-luminance Flicker Electroretinography in Patients With Diabetic Retinopathy Using an Office-based Testing Paradigm

BACKGROUND

We evaluated the reproducibility of office-based flicker electroretinography (ERG) in patients with nonproliferative diabetic retinopathy (NPDR).

METHODS

An observational study was conducted in which ultra-widefield fluorescein angiography (UWF-FA) was performed on 20 patients with mild-to-moderate NPDR; images were graded by the Fundus Photography Reading Center (Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, WI, USA). Fixed- and multi-luminance flicker ERG was repeated four times (greater than or equal to seven days apart). Recording consistency was assessed using intra-class correlation coefficients (ICCs), coefficients of variation, and Pearson correlations.

RESULTS

82.5% and 17.5% of eyes had mild and moderate NPDR using UWF-FA; 90% of the angiograms were given a high confidence grade. Fixed-luminance phase values were highly reproducible (ICC: 0.949; P < .001). There was a significant negative correlation between fixed-luminance phase and log-corrected ischemic index values (-0.426; P = .015).

CONCLUSIONS

Office-based, fixed-luminance phase values are highly reproducible and negatively correlate with retinal ischemia in NPDR, suggesting that global retinal dysfunction may be reliably quantified early in patients with diabetes.

Electroretinography and retinal microvascular changes in type 2 diabetes

PURPOSE

To assess whether functional (electrophysiological) parameters are related to changes in the structural (microvascular) parameters in diabetic retina.

METHODS

This prospective cohort study included 380 eyes of patients with diabetes mellitus (DM) and 160 eyes of healthy controls. We analysed the electroretinogram (ERG) parameters and vascular parameters acquired from optical coherence tomography (OCT) angiography according to the diabetic retinopathy (DR) severity from early to late stages of DR.

RESULTS

After exclusion, 366 eyes of diabetes and 157 eyes of controls were included in the analysis. The mean age at enrolment was 65.4 ± 7.8 years, and 177 (33.84%) were male. The amplitude and implicit time of the rod and cone and combined response ERG b-wave were significantly reduced and prolonged in the eyes of patients with DM, compared to the controls. There was a positive correlation between the amplitude and vessel density (VD) of the superficial plexus and a negative correlation between the implicit time and superficial VD in the scotopic and combined response b-wave. Interestingly, there was no correlation between electrophysiological parameters and deep VD. These correlations between electrophysiological parameters and vascular parameters were not significant in the non-diabetic, healthy control group.

CONCLUSIONS

Functional and structural impairments precede the clinical manifestation of DR. We also found that these neural impairments, evaluated by ERG, were correlated with superficial VD. However, this correlation was absent in the healthy and early DR groups. These findings carefully suggest that neuronal dysfunction is linked to vascular dysfunction in type 2 diabetes.

Pupillary light responses in type 1 and type 2 diabetics with and without retinopathy

OBJECTIVE

We assessed the function of rod/cones and melanopsin in type 1 (T1DM) and type 2 diabetes mellitus (T2DM) with and without non-proliferative diabetic retinopathy (NPDR).

METHODS

We performed pupillometry on 22 healthy controls and four diabetic groups: 12 T1DM patients without NPDR and 12 with moderate NPDR, and 16 T2DM patients without NPDR and 12 with moderate NPDR. Monocular stimulations of 20 seconds with red (λ = 633 nm) and blue light (λ = 463 nm) at ~15 log quanta/cm² /second were performed. The primary outcome was the melanopsin-mediated late redilation phase of postillumination pupillary light response (PIPR_{L ate} ) to blue light. The secondary outcomes were the mixed rod/cone and melanopsin responses, that is maximal pupil constriction and the early redilation phase of PIPR (PIPR_{E arly} ).

RESULTS

Late redilation phase of PIPR (PIPR_{L ate} ) to blue and red light stimuli was not significantly different between healthy control and the four diabetic groups (n.s.). The maximal pupil contractions to blue light stimulus were significantly reduced in T1DM patients as well as in T2DM patients with NPDR (p ≤ 0.02), whereas for red light stimuli, the maximal pupil constriction was only reduced in T2DM with NPDR (p < 0.01). Early redilation phase of PIPR (PIPR_{E arly} ) to blue and red light stimuli was not significantly different between healthy controls and diabetic patients (n.s.).

CONCLUSION

Neither the PIPR_{E arly} nor the PIPR_{L ate} was significantly reduced in diabetics with or without NPDR compared to healthy controls. The reduced maximal pupil constrictions in diabetics with NPDR indicate decreased mixed rod/cone and melanopsin responses.

Retinal vasculature-function correlation in non-proliferative diabetic retinopathy

PURPOSE

To compare and correlate retinal microcirculation and function in patients with non-proliferative diabetic retinopathy (NPDR).

METHODS

Thirty-three healthy controls (33 eyes), 36 diabetic patients with no clinically detectable retinopathy (NDR, 36 eyes) and 101 patients (101 eyes) with NPDR (35 mild NPDR, 34 moderate NPDR, 32 severe NPDR) were involved in the study. We used optical coherence tomography angiography (OCTA) to quantify the macular vessel density (VD) of superficial capillary plexus (SCP), deep capillary plexus (DCP) and foveal density in a 300 μm region around foveal avascular zone. Retinal function was assessed by a mydriasis-free, full-field flicker electroretinogram (FERG) recording device, and the amplitudes and implicit time were recorded. The association between microvascular parameters and FERG results was analyzed with stepwise multiple linear regression model.

RESULTS

Decreased amplitudes and delayed implicit time, as well as lower parafoveal/perifoveal VD in both SCP and DCP, were found in NDR group and NPDR groups compared with the control group (all p < 0.05). Specifically, the FERG parameters and microvascular indices were comparable between NDR group and mild NPDR group (all p > 0.05). However, compared to mild NPDR, the reduction in FERG amplitude was more pronounced than the reduction in parafoveal VD (both SCP and DCP) in severe NPDR. Stepwise multiple linear regression analyses showed that delayed implicit time was significantly correlated with increased age and decreased VD of parafoveal region in both SCP and DCP in patients with NPDR. Meanwhile, decreased amplitude was significantly associated with decreased VD of parafoveal region in both SCP and DCP in patients with NPDR.

CONCLUSION

Macular VD in both superficial and deep capillary plexus correlated with ERG implicit time and amplitude in mild-to-severe NPDR. OCTA and FERG may both be useful in detection of preclinical DR and early DR, but once the disease deteriorates, FERG may be more sensitive to discern progression of DR.

Targeting long non-coding RNA MALAT1 alleviates retinal neurodegeneration in diabetic mice

AIM

To observe the effect of inhibiting long non-coding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) on diabetic neurodegeneration.

METHODS

Thirty-six 8-week-old C57BL/6 mice were randomly divided into normal control, diabetic control, diabetic scrambled small interfering RNAs (siRNAs) and diabetic MALAT1-siRNA groups. After diabetic induction with streptozocin intraperitoneally-injection, the diabetic MALAT1-siRNA group was intravitreally injected with 1 µL 20 µmol/L MALAT1 siRNA, and the diabetic scrambled siRNA group was injected with the same amount of scrambled siRNA. Electroretinography was performed to examine photoreceptor functions 16wk after diabetes induction. MALAT1 expression was detected via real time polymerase chain reaction. Cone morphological changes were examined using immunofluorescence. Rod morphological changes were examined by determining outer nuclear layer (ONL) thickness.

RESULTS

The upregulation of retinal MALAT1 expression was detected in the diabetic control mice, while MALAT1 expression in the diabetic MALAT1-siRNA mice was decreased by 91.48% compared to diabetic control mice. The diabetic MALAT1-siRNA and diabetic control mice showed lower a-wave and b-wave amplitudes than did the normal control mice in scotopic and photopic electroretinogram, while the diabetic MALAT1-siRNA mice showed higher amplitudes than diabetic control mice. Morphological examination revealed that ONL thickness in the diabetic MALAT1-siRNA and diabetic control mice was lower than normal control mice. However, ONL thickness was greater in the diabetic MALAT1-siRNA mice than diabetic control mice. Moreover, the diabetic control mice performed a sparser cone cell arrangement and shorter outer segment morphology than diabetic MALAT1-siRNA mice.

CONCLUSION

Inhibiting retinal MALAT1 results in mitigative effects on the retinal photoreceptors, thus alleviating diabetic neurodegeneration.

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.

Temporal Frequency Abnormalities in Early-Stage Diabetic Retinopathy Assessed by Electroretinography

Purpose

To define the nature and extent of temporal frequency abnormalities in diabetics who have mild or no nonproliferative diabetic retinopathy (NPDR) by using the flicker electroretinogram (ERG).

Methods

Light-adapted flicker ERGs were recorded from 20 diabetics who have no clinically apparent retinopathy, 20 diabetics who have mild NPDR, and 20 nondiabetic, age-equivalent controls. ERGs were elicited by full-field sinusoidal flicker across the temporal frequency range of 6 to 100 Hz and were recorded using conventional techniques. The amplitude and phase of the fundamental and harmonic response components were derived by Fourier analysis and compared among the groups.

Results

Analysis of variance indicated that compared with the controls, both patient groups had significant amplitude reductions of the fundamental ERG component for temporal frequencies greater than 56 Hz (all P ≤ 0.03). Modeling the amplitude measurements indicated that both patient groups had significant reductions in the high-frequency response cutoff. Response phase, however, did not differ significantly among the groups at any frequency. The amplitude and phase of the high-frequency harmonics (32–96 Hz) of the patients' responses to a low-frequency stimulus (16 Hz) were normal over the temporal frequency range that the fundamental response was abnormal.

Conclusions

Taken together, the diabetics' fundamental amplitude attenuation for rapid flicker combined with their normal high-frequency harmonic responses generated by slow flicker suggest that the likely site of the abnormal temporal filtering occurs prior to the nonlinearity that generates the harmonic components of the ERG, implicating a photoreceptor origin.

Retinal dysfunction parallels morphologic alterations and precede clinically detectable vascular alterations in Meriones shawi, a model of type 2 diabetes

Diabetic retinopathy is a major cause of reduced visual acuity and acquired blindness. The aim of this work was to analyze functional and vascular changes in diabetic Meriones shawi (M.sh) an animal model of metabolic syndrome and type 2 diabetes. The animals were divided into four groups. Two groups were fed a high fat diet (HFD) for 3 and 7 months, two other groups served as age-matched controls. Retinal function was assessed using full field electroretinogram (Ff-ERG). Retinal thickness and vasculature were examined by optical coherence tomography, eye fundus and fluorescein angiography. Immunohistochemistry was used to examine key proteins of glutamate metabolism and synaptic transmission. Diabetic animals exhibited significantly delayed scotopic and photopic ERG responses and decreases in scotopic and photopic a- and b-wave amplitudes at both time points. Furthermore, a decrease of the amplitude of the flicker response and variable changes in the scotopic and photopic oscillatory potentials was reported. A significant decrease in retinal thickness was observed. No evident change in the visual streak area and no sign of vascular abnormality was present; however, some exudates in the periphery were visible in 7 months diabetic animals. Imunohistochemistry detected a decrease in the expression of glutamate synthetase, vesicular glutamate transporter 1 and synaptophysin proteins. Results indicate that a significant retinal dysfunction was present in the HFD induced diabetes involving both rod and cone pathways and this dysfunction correlate well with the morphological abnormalities reported previously. Furthermore, neurodegeneration and abnormalities in retinal function occur before vascular alterations would be detectable in diabetic M.sh.

The Relationship between Peripheral Nerve Conduction Velocity and Ophthalmological Findings in Type 2 Diabetes Patients with Early Diabetic Retinopathy

PURPOSE

Nerve conduction velocity (NCV) is an indicator of neuronal damage in the distal segment of the peripheral nerves. Here, we determined the association between NCV and other systemic and ocular clinical findings, in type 2 diabetes patients with early diabetic retinopathy (DR).

METHODS

This study included 42 eyes of 42 type 2 diabetes patients (median age: 54 years) with no DR or with mild nonproliferative DR. Standard statistical techniques were used to determine associations between clinical findings.

RESULTS

Sural sensory conduction velocity (SCV) and tibial motor conduction velocity (MCV) were significantly lower in mild nonproliferative DR patients than patients with no DR (P = 0.008 and P = 0.01, resp.). Furthermore, logistic regression analyses revealed that sural SCV and tibial MCV were independent factors contributing to the presence of mild nonproliferative DR (OR 0.83, P = 0.012 and OR 0.69 P = 0.02, resp.). Tibial MCV was correlated with choroidal thickness (CT) (P = 0.01), and a multiple regression analysis revealed that age, tibial MCV, and carotid intima-media thickness were independent associating factors with CT (P = 0.035, P = 0.015, and P = 0.008, resp.).

CONCLUSIONS

Our findings suggest that reduced NCV may be closely associated with early DR in type 2 diabetes patients. Thus, reduced nerve conduction is a potential early biomarker of DR.

Foveal Microstructure Analysis in Eyes with Diabetic Macular Edema Treated with Vitrectomy

INTRODUCTION

The purpose of this study was to evaluate baseline and postoperative factors affecting outcomes after vitrectomy for diabetic macular edema (DME) using optical coherence tomography (OCT).

METHODS

Vitrectomy combined with inner limiting membrane (ILM) peeling and additional laser photocoagulation therapy was performed on 36 eyes of 30 DME patients. Evaluations included the logarithm of the minimal angle of resolution (logMAR), best-corrected visual acuity (BCVA) and OCT parameters at baseline and 1, 3, 6, and 12 months postoperatively. Correlations between OCT parameters and BCVA were assessed at each follow-up visit. Correlations among postoperative BCVA and preoperative BCVA, foveal macular thickness (FMT), outer foveal thickness (OFT), and photoreceptor outer segment (PROS) length were evaluated using multiple regression analysis.

RESULTS

BCVA significantly improved from 0.50 ± 0.25 to 0.34 ± 0.26 at 12 months postoperatively (P < 0.001). Mean FMT improved significantly from 526.4 ± 120.4 to 384.6 ± 120.5 at 1 month, 325.2 ± 100.3 at 3 months, 304.1 ± 102.5 at 6 months and 274.2 ± 86.6 μm at 12 months postoperatively (P < 0.001, respectively). OFT 1 month after surgery was significantly decreased 46.5 ± 14.7-40.2 ± 14.4 μm (P = 0.017), although at 3, 6, and 12 months it did not differ from the baseline value. PROS length 1 month after surgery significantly decreased from 31.7 ± 6.9-28.8 ± 6.8 μm (P = 0.015) and that at 3 months and 6 months recovered to the baseline value. PROS length 12 months after surgery was significantly increased to 34.3 ± 7.2 μm from baseline (P = 0.023). Mean FMT was not correlated with BCVA at any time point. Mean OFT and PROS length at 3, 6, and 12 months were correlated with BCVA. In multiple regression analysis, PROS length had the greatest effect on VA 12 months postoperatively (P = 0.0262, standard regression coefficient = -0.366).

CONCLUSION

Current surgery helps DME patients to maintain VA and foveal structures. The results suggest that PROS length predicts visual outcome in DME patients following vitrectomy with ILM peeling and additional laser photocoagulation.

Accelerated retinal aging in PACAP knock-out mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurotrophic and neuroprotective peptide. PACAP and its receptors are widely distributed in the retina. A number of reports provided evidence that PACAP is neuroprotective in retinal degenerations. The current study compared retina cell type-specific differences in young (3-4months) and aged adults (14-16months), of wild-type (WT) mice and knock-out (KO) mice lacking endogenous PACAP production during the course of aging. Histological, immunocytochemical and Western blot examinations were performed. The staining for standard neurochemical markers (tyrosine hydroxylase for dopaminergic cells, calbindin 28 kDa for horizontal cells, protein kinase Cα for rod bipolar cells) of young adult PACAP KO retinas showed no substantial alterations compared to young adult WT retinas, except for the specific PACAP receptor (PAC1-R) staining. We could not detect PAC1-R immunoreactivity in bipolar and horizontal cells in young adult PACAP KO animals. Some other age-related changes were observed only in the PACAP KO mice only. These alterations included horizontal and rod bipolar cell dendritic sprouting into the photoreceptor layer and decreased ganglion cell number. Also, Müller glial cells showed elevated GFAP expression compared to the aging WT retinas. Furthermore, Western blot analyses revealed significant differences between the phosphorylation state of ERK1/2 and JNK in KO mice, indicating alterations in the MAPK signaling pathway. These results support the conclusion that endogenous PACAP contributes to protection against aging of the nervous system.

Screening for diabetic retinopathy using new mydriasis-free, full-field flicker ERG recording device

Diabetic retinopathy (DR) is a leading cause of blindness among working-age adults. Therefore, it is important to detect DR accurately during mass screening. The purpose of this study was to determine whether a small, hand-held, mydriasis-free, full-field flicker electroretinographic (ERGs) device called RETeval can be used to screen for DR. To accomplish this, we recorded full-field flicker ERGs with this device from 48 normal eyes and 118 eyes with different severities of DR in patients with diabetes mellitus (DM). This system delivered a constant flash retinal luminance by adjusting the flash luminance that compensated for changes in the pupil size. Our results showed that there were significant correlations between the severity of DR and the implicit times (P < 0.001; r = 0.55) and the amplitudes (P = 0.001; r = −0.29). When the implicit time was used for the index, the area under the receiver operating characteristic curve was 0.84 for the detection of DR, and was 0.89 for the detection of DR requiring ophthalmic treatments. These results suggest that the implicit times of the flicker ERGs recorded by the small, mydryasis-free ERG system can be used as an adjunctive tool to screen for DR.

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.

Effects of intravitreal injection of netrin-1 in retinal neovascularization of streptozotocin-induced diabetic rats

Background

In a previous study, we confirmed that netrin-1 acts as an antiangiogenic factor by inhibiting alkali burn-induced corneal neovascularization in rats. Here, we continue working on the role of netrin-1 in retinal neovascularization.

Methods

Using an in vitro angiogenesis assay, we detected the effects of netrin-1 on human umbilical vein endothelial cell tube formation, viability and proliferation, migration, and invasion at concentrations of 0.1 μg/mL or 5 μg/mL. We intravitreally injected 0.1 μg/mL or 5 μg/mL netrin-1 into streptozotocin-induced rats to assess retinal neovascularization using retinal electrophysiology and electroretinography, enzyme-linked immunosorbent assay, fundus fluoresce in angiography, measurement of inner blood retinal barrier, retinal hematoxylin-eosin staining, and retinal flat-mount fluorescence assays.

Results

Human umbilical vein endothelial cell tube formation, viability and proliferation, migration, and invasion were upregulated by netrin-1 at a concentration of 0.1 μg/mL (P<0.05), while 5 μg/mL netrin-1 had an opposite effect (P<0.05) in our in vitro angiogenesis assay. Retinal electrophysiology testing revealed that intravitreal injection of netrin-1 affected the amplitude of a- and b-waves (a-wave: 0.1 μg/mL netrin-1 =17.67±3.39 μm, 5 μg/mL netrin-1 =28.50±1.31 μm, phosphate-buffered saline [PBS]-treated =17.67±3.39 μm; b-wave: 0.1 μg/mL netrin-1 =44.67±4.80 μm, 5 μg/mL netrin-1 =97.17±9.63 μm, PBS-treated =44.67±4.80 μm) and the expression of VEGF-A (no-treatment rats, 9.29±0.80 pg/mL; PBS-treated rats, 19.64±3.77 pg/mL; 0.1 μg/mL netrin-1 treated rats, 21.37±3.64 pg/mL; 5 μg/mL netrin-1 treated rats, 9.85±0.54 pg/mL, at 6 weeks after induction). By comparing fluoresce in angiography, level of inner blood retinal barrier breakdown (% of control), retinal hematoxylin-eosin staining, and collagen-IV fluorescence assays in the retinas of PBS-treated rats, netrin-1 was found to suppress and reverse retinal neovascularization at a concentration of 5 μg/mL (P<0.05), while 0.1 μg/mL netrin-1 (P<0.05) led to an increase in the number of new retinal blood vessels, after 6 weeks’ injection.

Conclusion

Netrin-1 could play a significant role in retinal neovascularization by dual-direction regulating angiogenesis dependent on dosage.

Retinal sensitivity in subjects with type 2 diabetes mellitus: Sankara Nethralaya Diabetic Retinopathy Epidemiology and Molecular Genetics Study (SN-DREAMS II, Report No. 4)

AIM

To evaluate retinal sensitivity (RS) in subjects with diabetes in a population-based study and to elucidate associated risk factors for abnormal RS.

METHODS

A subset of 357 subjects from Sankara Nethralaya Diabetic Retinopathy Epidemiology and Molecular Genetics Study-II was included in this study. All subjects underwent detailed ophthalmic evaluation including microperimetry and spectral domain optical coherence tomography.

RESULTS

The prevalence of abnormal mean retinal sensitivity (MRS) was 89.1%. MRS was significantly reduced in subjects with diabetes but no retinopathy when compared with non-diabetic subjects. MRS was reduced in moderate non-proliferative diabetic retinopathy (DR) and macular oedema (ME) at 8° (p=0.04, p=0.01, respectively) and in ME at 10° (p=0.009) and 12° (p=0.036) compared with no DR. Significant negative correlation was found between MRS and best corrected visual acuity, duration of diabetes, glycosylated haemoglobin and central foveal thickness. Increased retinal thickness remained a significant risk factor (OR, 1.02; p=0.044) for abnormal MRS. Altered inner retinal layers and foveal contour were associated with reduced MRS among subjects with DR and presence of epiretinal membrane, altered foveal contour and altered retinal pigment epithelium were associated with reduced MRS.

CONCLUSIONS

Reduced RS in those subjects with diabetes but no retinopathy suggests the early neuronal damage in type 2 diabetes mellitus.