ASSOCIATIONS BETWEEN INDIVIDUAL RETINAL LAYER THICKNESSES AND DIABETIC PERIPHERAL NEUROPATHY USING RETINAL LAYER SEGMENTATION ANALYSIS

Association of sudomotor dysfunction with risk of diabetic retinopathy in patients with type 2 diabetes

PURPOSE

Sudomotor dysfunction is considered as one of the earliest manifestations of diabetic peripheral neuropathy. We aimed to investigate the association between sudomotor dysfunction non-invasively detected by the SUDOSCAN device and diabetic retinopathy (DR) in patients with type 2 diabetes.

METHODS

A total of 2010 patients admitted to a tertiary hospital located in Shanghai were included from March 2020 to September 2023. Sudomotor function was assessed by the SUDOSCAN device, and sudomotor dysfunction was defined as feet electrochemical skin conductance (FESC) <60 μs. Fundus radiography was used for DR assessment, which was graded according to the severity, specifically: (1) non-DR; (2) mild nonproliferative DR (NPDR); (3) moderate NPDR/vision-threatening DR (VTDR).

RESULTS

Among the enrolled 2010 patients, 525 patients had sudomotor dysfunction; 648 were diagnosed with DR, which was equivalent to 32.2% of all patients. Patients with sudomotor dysfunction had a significantly higher prevalence of DR, compared to those with normal sudomotor function (40.8% vs. 29.2%, P < 0.05). After controlling for confounding factors including HbA1c, sudomotor dysfunction was significantly associated with any DR (odd ratio [OR] = 1.57, 95% CI 1.26-1.96). When FESC was considered as a continuous variable, the multivariable-adjusted OR of DR was 1.29 (95% CI 1.17-1.42) for per 1-SD decrease in FESC. Furthermore, multinomial logistic regression revealed significant associations between sudomotor dysfunction and all stages of DR (mild NPDR: OR = 1.40, 95% CI 1.11-1.78; moderate NPDR/VTDR: OR = 2.35, 95% CI 1.60-3.46).

CONCLUSIONS

Sudomotor dysfunction was significantly associated with DR in patients with type 2 diabetes.

Advanced Glycation End-Products and Diabetic Neuropathy of the Retina

Diabetic retinopathy is a tissue-specific neurovascular impairment of the retina in patients with both type 1 and type 2 diabetes. Several pathological factors are involved in the progressive impairment of the interdependence between cells that consist of the neurovascular units (NVUs). The advanced glycation end-products (AGEs) are one of the major pathological factors that cause the impairments of neurovascular coupling in diabetic retinopathy. Although the exact mechanisms for the toxicities of the AGEs in diabetic retinopathy have not been definitively determined, the AGE-receptor of the AGE (RAGE) axis, production of reactive oxygen species, inflammatory reactions, and the activation of the cell death pathways are associated with the impairment of the NVUs in diabetic retinopathy. More specifically, neuronal cell death is an irreversible change that is directly associated with vision reduction in diabetic patients. Thus, neuroprotective therapies must be established for diabetic retinopathy. The AGEs are one of the therapeutic targets to examine to ameliorate the pathological changes in the NVUs in diabetic retinopathy. This review focuses on the basic and pathological findings of AGE-induced neurovascular abnormalities and the potential therapeutic approaches, including the use of anti-glycated drugs to protect the AGE-induced impairments of the NVUs in diabetic retinopathy.

Reduced macula microvascular densities may be an early indicator for diabetic peripheral neuropathy

Purpose: To assess the alteration in the macular microvascular in type 2 diabetic patients with peripheral neuropathy (DPN) and without peripheral neuropathy (NDPN) by optical coherence tomography angiography (OCTA) and explore the correlation between retinal microvascular abnormalities and DPN disease. Methods: Twenty-seven healthy controls (42 eyes), 36 NDPN patients (62 eyes), and 27 DPN patients (40 eyes) were included. OCTA was used to image the macula in the superficial vascular complex (SVC) and deep vascular complex (DVC). In addition, a state-of-the-art deep learning method was employed to quantify the microvasculature of the two capillary plexuses in all participants using vascular length density (VLD). Results: Compared with the healthy control group, the average VLD values of patients with DPN in SVC (p = 0.010) and DVC (p = 0.011) were significantly lower. Compared with NDPN, DPN patients showed significantly reduced VLD values in the SVC (p = 0.006) and DVC (p = 0.001). Also, DPN patients showed lower VLD values (p < 0.05) in the nasal, superior, temporal and inferior sectors of the inner ring of the SVC when compared with controls; VLD values in NDPN patients were lower in the nasal section of the inner ring of SVC (p < 0.05) compared with healthy controls. VLD values in the DVC (AUC = 0.736, p < 0.001) of the DPN group showed a higher ability to discriminate microvascular damage when compared with NDPN. Conclusion: OCTA based on deep learning could be potentially used in clinical practice as a new indicator in the early diagnosis of DM with and without DPN.

Retinal Neurodegeneration in Diabetes: an Emerging Concept in Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR), the leading cause of blindness in working-aged adults, remains clinically defined and staged by its vascular manifestations. However, early retinal neurodegeneration may precede vascular pathology, suggesting that this neuronal damage may contribute to disease pathogenesis and represent an independent target for intervention. This review will discuss the evidence and implications for diabetic retinal neurodegeneration.

RECENT FINDINGS

A growing body of literature has identified progressive retinal thinning and visual dysfunction in patients with diabetes even prior to the onset of DR, though advances in retinal vascular imaging suggest that vascular remodeling and choroidal changes occur during these early stages as well. Animal models of diabetes and in vitro studies have also suggested that diabetes may directly affect the retinal neural and glial tissue, providing support to the concept that diabetic retinal neurodegeneration occurs early in the disease and suggesting potentially relevant molecular pathways. Diabetic retinal neurodegeneration may represent a "preclinical" manifestation of diabetic retinal disease and remains an active area of investigation. As the natural history and molecular mechanisms become increasingly understood, it may lead to upcoming developments in not only the treatment options but also the clinical definition of DR.

Diagnostic value of optic disc retinal nerve fiber layer thickness for diabetic peripheral neuropathy

OBJECTIVE

To investigate the value of optic disc retinal nerve fiber layer (RNFL) thickness in the diagnosis of diabetic peripheral neuropathy (DPN).

METHODS

Ninety patients with type 2 diabetes, including 60 patients without DPN (NDPN group) and 30 patients with DPN (DPN group), and 30 healthy participants (normal group) were enrolled. Optical coherence tomography (OCT) was used to measure the four quadrants and the overall average RNFL thickness of the optic disc. The receiver operator characteristic curve was drawn and the area under the curve (AUC) was calculated to evaluate the diagnostic value of RNFL thickness in the optic disc area for DPN.

RESULTS

The RNFL thickness of the DPN group was thinner than those of the normal and NDPN groups in the overall average ((101.07± 12.40) µm vs. (111.07±6.99) µm and (109.25±6.90) µm), superior quadrant ((123.00±19.04) µm vs. (138.93±14.16) µm and (134.47±14.34) µm), and inferior quadrant ((129.37±17.50) µm vs. (143.60±12.22) µm and (144.48±14.10) µm), and the differences were statistically significant. The diagnostic efficiencies of the overall average, superior quadrant, and inferior quadrant RNFL thicknesses, and a combined index of superior and inferior quadrant RNFL thicknesses were similar, and the AUCs were 0.739 (95% confidence interval (CI) 0.635-0.826), 0.683 (95% CI 0.576-0.778), 0.755 (95% CI 0.652-0.840), and 0.773 (95% CI 0.672-0.854), respectively. The diagnostic sensitivity of RNFL thickness in the superior quadrant reached 93.33%.

CONCLUSIONS

The thickness of the RNFL in the optic disc can be used as a diagnostic method for DPN.

Regional analysis of segmented-macular structure in patients with myopic anisometropia

PURPOSE

To compare intraretinal layers between the eyes in patients with myopic anisometropia, and evaluate the relationship between the layers with spherical equivalent (SE) and axial length (AL).

METHODS

In this retrospective study, the more myopic (MM) and fellow (F) eyes of 41 patients with myopic anisometropia, and 38 emmetropic (± 0.50 diopter) control (C) eyes were inclueded. Intraretinal layer segmentation was performed by optical coherence tomography. Global volumes of retinal layers and their thicknesses in nine macular regions were compared. Correlation analysis was used to determine the relationship with SE and AL in each layer.

RESULTS

Total retinal, ganglion cell (GCL), inner nuclear (INL), and outer plexiform (OPL) layer volumes in MM eyes were less than in C eyes, while INL and OPL were less than in F eyes. There was no difference in the fovea, except for the retinal pigment epithelium. In MM eyes, only INL and OPL were thin in at least one perifoveal and parafoveal quadrant compared to F eyes. Only INL and OPL thicknesses were significantly correlated with both SE and AL in all perifoveal quadrants. In contrast to the thinning found in MM eyes, the only layer in which thickening was detected to compare to C eye was nerve fiber layer (NFL), which correlated positively with SE and negatively with AL.

CONCLUSION

While the fovea is less affected by myopia, thinning becomes remarkable in the perifoveal quadrants. Despite thinning in many layers, especially INL and OPL, NFL thickening may be seen due to myopia.

Retinal Neurodegeneration in Diabetic Peripheral Neuropathy by Optical Coherence Tomography: A Systematic Review and Meta-analysis

PURPOSE

The optical coherence tomography (OCT) has been used to evaluate the changes of retinal degeneration in patients with diabetic peripheral neuropathy (DPN) in recent years, but the results of previous studies were controversial. Therefore, systematic review and meta-analysis were performed to evaluate the degree of retinal neurodegeneration in DPN measured by OCT.

METHODS

A comprehensive search of PubMed, Embase, Web of Science, Scopus, China Biomedical Literature (CBM), China National Knowledge Infrastructure (CNKI), VIP, and Wanfang databases were performed to identify studies that evaluate retinal neurodegeneration in DPN by using OCT. The included studies were critically reviewed and meta-analyses were performed to evaluate differences of the OCT-derived parameters between the DPN and non-DPN patients.

RESULTS

Twelve studies were included in the final meta-analysis, involving a total of 1,807 eyes (573 in the DPN group and 1,229 in the non-DPN group). The mean peripapillary retinal nerve fiber layer (pRNFL) thickness was significantly lower in the DPN group than in the non-DPN group (weighted mean difference [WMD] = -8.37 μm; 95% CI: -11.00, -5.74). The reduction of pRNFL thickness was the most pronounced in the inferior quadrant, and the differences in the nasal and temporal quadrants were also statistically significant, with WMD (95% CI) being -4.63 μm (-7.51, -1.76) and -3.92 μm (-6.86, -0.98), respectively. Similar results were observed for macular parameters, with WMD and 95% CI being -1.0 μm (-1.5, -0.5) for macular retinal nerve fiber layer (mRNFL), -2.7 μm (-10.7, -5.3) for macular ganglion cell-inner plexiform layer (mGCIPL), and -2.2 μm (-4.4, -0.04) for macular ganglion cell complex (mGCC), respectively.

CONCLUSIONS

Patients with DPN present with significant retinal neurodegeneration, with reduced pRNFL, mRNFL, mGCIPL, and mGCC thickness. Measurements of OCT parameters may serve as a biomarker for diagnosing and monitoring DPN.

Correlation between corneal and retinal neurodegenerative changes and their association with microvascular perfusion in type II diabetes

PURPOSE

The pathophysiology of diabetic neurodegeneration and microvasculopathy remains controversial. Neurosensory layer thickness and corneal nerve fibre loss represent potential biomarkers of neuropathy. The purpose of this cross-sectional study was to determine the correlation between these neurodegenerative features and their association with retinal microvascular integrity in patients with type II diabetes without retinopathy.

METHODS

Nerve fibre length (NFL), density (NFD) and branch density (NBD) were assessed using corneal confocal microscopy. Spectralis optical coherence tomography (OCT) was used for peripapillary retinal nerve fibre layer (RNFL), and macular RNFL, ganglion cell (GCL), inner plexiform (IPL) and inner nuclear layer (INL) thicknesses. Parafoveal vessel density (PVD) was determined using OCT angiography.

RESULTS

We analysed 118 eyes of 61 patients. Peripapillary RNFL, macular RNFL, GCL, IPL and INL were 101 ± 8, 29 ± 3, 43 ± 4, 36 ± 3 and 36 ± 3 μm. NFL, NFD and NBD were 12.3 ± 4.4 mm/mm² , 17.8 ± 7.4/mm² and 26.7 ± 15.2/mm² . Corneal nerve fibre variables were neither associated with inner retinal thicknesses nor PVD. A significant positive correlation was found between macular GCL, IPL and peripapillary RNFL with deep capillary plexus PVD (p ≤ 0.05).

CONCLUSION

Our results indicate that corneal and retinal neurodegeneration are independent changes early in type II diabetes and that distinct retinal, but not corneal neurodegenerative features, are associated with retinal microvascular perfusion.