Type 2 Diabetes, Fasting Glucose, Hemoglobin A1c Levels and Risk of Primary Open-Angle Glaucoma: A Mendelian Randomization Study

Insulin resistance in the retina: possible implications for certain ocular diseases

Insulin resistance (IR) is becoming a worldwide medical and public health challenge as an increasing prevalence of obesity and metabolic disorders. Accumulated evidence has demonstrated a strong relationship between IR and a higher incidence of several dramatically vision-threatening retinal diseases, including diabetic retinopathy, age-related macular degeneration, and glaucoma. In this review, we provide a schematic overview of the associations between IR and certain ocular diseases and further explore the possible mechanisms. Although the exact causes explaining these associations have not been fully elucidated, underlying mechanisms of oxidative stress, chronic low-grade inflammation, endothelial dysfunction and vasoconstriction, and neurodegenerative impairments may be involved. Given that IR is a modifiable risk factor, it may be important to identify patients at a high IR level with prompt treatment, which may decrease the risk of developing certain ocular diseases. Additionally, improving IR through the activation of insulin signaling pathways could become a potential therapeutic target.

Possible Causal Association between Type 2 Diabetes and Glycaemic Traits in Primary Open-Angle Glaucoma: A Two-Sample Mendelian Randomisation Study

Existing literature suggests a controversial relationship between type 2 diabetes mellitus (T2D) and glaucoma. This study aimed to examine the potential causal connection between T2D and glycaemic traits (fasting glucose [FG] and glycated haemoglobin [HbA1c] levels) as exposures to primary open-angle glaucoma (POAG) in multi-ethnic populations. Single-nucleotide polymorphisms associated with exposure to T2D, FG, and HbA1c were selected as instrumental variables with significance (p < 5.0 × 10-8) from the genome-wide association study (GWAS)-based meta-analysis data available from the BioBank Japan and the UK Biobank (UKB). The GWAS for POAG was obtained from the meta-analyses of Genetic Epidemiology Research in Adult Health and Aging and the UKB. A two-sample Mendelian randomisation (MR) study was performed to assess the causal estimates using the inverse-variance weighted (IVW) method, and MR-Pleiotropy Residual Sum and Outlier test (MR-PRESSO). Significant causal associations of T2D (odds ratio [OR] = 1.05, 95% confidence interval [CI] = [1.00-1.10], p = 0.031 in IVW; OR = 1.06, 95% CI = [1.01-1.11], p = 0.017 in MR-PRESSO) and FG levels (OR = 1.19, 95% CI = [1.02-1.38], p = 0.026 in IVW; OR = 1.17, 95% CI = [1.01-1.35], p = 0.041 in MR-PRESSO) with POAG were observed, but not in HbA1c (all p > 0.05). The potential causal relationship between T2D or FG and POAG highlights its role in the prevention of POAG. Further investigation is necessary to authenticate these findings.

Neuroprotective Effects of Anti-diabetic Drugs in the Treatment of Patients with Diabetes and Glaucoma or at High Risk for Glaucoma

There is an association between glaucoma and several risk factors and metabolic diseases, such as type 2 diabetes mellitus. Diabetes mellitus leads to neurodegenerative changes, both peripherally and in the brain. This might be a shared pathophysiology and etiology for both glaucoma and diabetes. It is interesting that drugs for the treatment of diabetes seem to have neuroprotective properties independent of their blood sugar reduction. Although prospective, randomized, clinical studies are still missing, particularly metformin and glucagon-like peptide receptor agonists (GLP 1 RA) seem to have neuroprotective effects. Sulphonylureas (e.g., glibenclamide, glimepiride) are still used. They frequently potently reduce blood pressure but may be less neuroprotective. In the present review, the evidence for neuroprotective effects of the different antidiabetic drugs is presented and a possible differential therapy for patients with diabetes and glaucoma, or at high risk of glaucoma, will be discussed.

Rates of choroidal loss and ganglion cell-inner plexiform layer thinning in type 2 diabetes mellitus and healthy individuals: a 2-year prospective study

AIMS

To investigate longitudinal choroid and ganglion cell-inner plexiform layer (GCIPL) changes in type 2 diabetes mellitus (T2DM) patients and healthy populations across 2 years.

METHODS

This prospective cohort study included T2DM patients and healthy controls. T2DM patients were divided into mild non-proliferative diabetic retinopathy (NPDR) or non-DR (NDR) groups. Macular choroidal and GCIPL thickness was measured using swept-source optical coherence tomography at baseline and follow-up after 2 years. A linear-mixed effect model compared rates of change in choroidal and GCIPL thicknesses between the three groups.

RESULTS

895 T2DM patients (770 in the NDR group and 125 in the NPDR group) and 847 healthy controls were included. Following 2 years, choroidal thinning occurred at a rate of -7.7±9.2 µm/year, -8.1±8.7 µm/year and -5.2±8.1 µm/year in NDR, NPDR and control groups, respectively (p<0.001). GCIPL loss occurred quickest in NPDR patients (-0.97±0.97 µm/year), followed by NDR (-0.91±0.89 µm/year) and the control group (-0.04±0.55 µm/year) (p<0.001). Following multivariate adjustment, choroidal thinning was -2.04 µm/year (95% CI: -4.05 to -0.03; p=0.047) and -1.95 µm/year (95% CI: -3.14 to -0.75; p=0.001) faster in NPDR and NDR groups than in the control group, respectively, and GCIPL thinning was -1.02 µm/year (95% CI: -1.19 to -0.84; p<0.001) and -0.88 µm/year (95% CI: -0.98 to -0.78; p<0.001) faster in the NPDR and NDR groups than in the control group, respectively.

CONCLUSION

Progressive choroidal and GCIPL thinning occurs in healthy individuals and T2DM patients; however, T2DM undergoes accelerated choroidal and GCIPL loss in NPDR patients.

Dissecting causal associations of type 2 diabetes with 111 types of ocular conditions: a Mendelian randomization study

Background

Despite the well-established findings of a higher incidence of retina-related eye diseases in patients with diabetes, there is less investigation into the causal relationship between diabetes and non-retinal eye conditions, such as age-related cataracts and glaucoma.

Methods

We performed Mendelian randomization (MR) analysis to examine the causal relationship between type 2 diabetes mellitus (T2DM) and 111 ocular diseases. We employed a set of 184 single nucleotide polymorphisms (SNPs) that reached genome-wide significance as instrumental variables (IVs). The primary analysis utilized the inverse variance-weighted (IVW) method, with MR-Egger and weighted median (WM) methods serving as supplementary analyses.

Results

The results revealed suggestive positive causal relationships between T2DM and various ocular conditions, including "Senile cataract" (OR= 1.07; 95% CI: 1.03, 1.11; P=7.77×10-4), "Glaucoma" (OR= 1.08; 95% CI: 1.02, 1.13; P=4.81×10-3), and "Disorders of optic nerve and visual pathways" (OR= 1.10; 95% CI: 0.99, 1.23; P=7.01×10-2).

Conclusion

Our evidence supports a causal relationship between T2DM and specific ocular disorders. This provides a basis for further research on the importance of T2DM management and prevention strategies in maintaining ocular health.

Causal factors in primary open angle glaucoma: a phenome-wide Mendelian randomisation study

Primary open angle glaucoma (POAG) is a chronic, adult-onset optic neuropathy associated with characteristic optic disc and/or visual field changes. With a view to identifying modifiable risk factors for this common neurodegenerative condition, we performed a 'phenome-wide' univariable Mendelian randomisation (MR) study that involved analysing the relationship between 9661 traits and POAG. Utilised analytical approaches included weighted mode based estimation, the weighted median method, the MR Egger method and the inverse variance weighted (IVW) approach. Eleven traits related to POAG risk were identified including: serum levels of the angiopoietin-1 receptor (OR [odds ratio] = 1.11, IVW p = 2.34E-06) and the cadherin 5 protein (OR = 1.06, IVW p = 1.31E-06); intraocular pressure (OR = 2.46-3.79, IVW p = 8.94E-44-3.00E-27); diabetes (OR = 5.17, beta = 1.64, IVW p = 9.68E-04); and waist circumference (OR = 0.79, IVW p = 1.66E-05). Future research focussing on the effects of adiposity, cadherin 5 and angiopoietin-1 receptor on POAG development and progression is expected to provide key insights that might inform the provision of lifestyle modification advice and/or the development of novel therapies.

Ankylosing spondylitis and glaucoma in European population: A Mendelian randomization study

Background

The relationship between ankylosing spondylitis (AS) and glaucoma in the European population remains unclear. In the present study, we applied a two-sample Mendelian randomization (MR) method to investigate their causal relationship.

Methods

MR analysis was conducted to validate the causal associations between AS with glaucoma using summary statistics from the genome-wide association studies of AS (9,069 cases and 13,578 control subjects) and glaucoma (8,591 cases and 210,201 control subjects). The inverse variance weighting method was performed to evaluate the causal relationship. The MR-Egger regression approach was applied to assess pleiotropy, while Cochran's Q test was used to analyze heterogeneity. Subgroup analysis was performed according to primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

Results

The results of the MR study reveal a risk-increasing causal relationship between AS and glaucoma among European populations (OR = 1.35, 95%CI = 1.16-1.57, P = 8.81 × 10^-5). Pleiotropy and heterogeneity were not found in our study. In the subgroup analysis, AS was also causal with POAG (OR = 1.48, 95%CI = 1.17-1.86, P = 8.80 × 10^-4) and PACG (OR = 1.91, 95%CI = 1.03-3.51, P = 3.88 × 10^-2).

Conclusion

The results of the MR analysis suggested a causal relationship between AS and glaucoma in the European population. Further studies are needed to identify the specific mechanism between these two diseases.

Blood cell traits and risk of glaucoma: A two-sample mendelian randomization study

Importance: Glaucoma is the second leading cause of blindness in the world. The causal direction and magnitude of the association between blood cell traits and glaucoma is uncertain because of the susceptibility of observational studies to confounding and reverse causation. Objective: To explore whether there is a causal relationship of blood cell traits including white blood cell (WBC) count (WBCC) and its subtypes [basophil cell count (BASO), monocyte cell count (MONO), lymphocyte cell count (LYMPH), eosinophil cell count (EOS), neutrophil cell count (NEUT)], red blood cell (RBC) count (RBCC), red blood distribution width (RDW), platelet count (PLT), and plateletcrit (PCT) on glaucoma risk. Methods: A two-sample Mendelian randomization (MR) analysis was conducted. Genome-wide significant single nucleotide polymorphisms (SNPs) from published genome-wide association studies (GWAS) on human blood cell traits were utilized as exposure instruments and the dataset for outcome was from the GWAS summary data of glaucoma. In the univariable MR analysis, we examined the association between genetic evidence of blood cell traits and glaucoma. To further investigate the potential causal mechanisms underlying the observed association, we performed multivariable MR analysis with three models, taking into account the mediator effect of inflammation and oxidative stress. According to Bonferroni-corrected for the 10 exposures in 3 methods, the MR study yielded a statistically significant p-value of 0.0017. Results: Genetically BASO, PCT, LYMPH, and PLT were potentially positively associated with glaucoma in the European ancestry [BASO: Odds ratio (OR) = 1.00122, 95% confidence interval (CI), 1.00003-1.00242, p = 0.045; PCT: OR = 1.00078, 95% CI, 1.00012-1.00143, p = 0.019; LYMPH: OR = 1.00076, 95% CI, 1.00002-1.00151, p = 0.045; PLT: OR = 1.00065, 95% CI, 1.00006-1.00123, p = 0.030], There was insufficient evidence to support a causal association of MONO, NEUT, EOS, WBCC, RBCC and RDW (MONO: OR = 1.00050, p = 0.098; NEUT: OR = 1.00028, p = 0.524; EOS: OR = 1.00020, p = 0.562; WBCC: OR = 1.00008, p = 0.830; RBCC: OR = 0.99996, p = 0.920; RDW: OR = 0.99987, p = 0.734) with glaucoma. The multivariable MR with model 1, 2, and 3 demonstrated that BASO, PCT, LYMPH, and PLT were still potentially genetically associated with the risk of glaucoma. Conclusion: Our study reveals a genetic predisposition to higher LYMPH, BASO, PLT, and PCT are associated with a higher risk of glaucoma, whereas WBCC, MONO, EOS, NEUT, RBCC, and RDW are not associated with the occurrence of glaucoma. This finding also supports previous observational studies associating immune components with glaucoma, thus provide guidance on the predication and prevention for glaucoma.