Genetic Correlations Between Diabetes and Glaucoma: An Analysis of Continuous and Dichotomous Phenotypes

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.

Polygenic risk score-based phenome-wide association for glaucoma and its impact on disease susceptibility in two large biobanks

BACKGROUND

Glaucoma is a leading cause of worldwide irreversible blindness. Considerable uncertainty remains regarding the association between a variety of phenotypes and the genetic risk of glaucoma, as well as the impact they exert on the glaucoma development.

METHODS

We investigated the associations of genetic liability for primary open angle glaucoma (POAG) with a wide range of potential risk factors and to assess its impact on the risk of incident glaucoma. The phenome-wide association study (PheWAS) approach was applied to determine the association of POAG polygenic risk score (PRS) with a wide range of phenotypes in 377, 852 participants from the UK Biobank study and 43,623 participants from the Penn Medicine Biobank study, all of European ancestry. Participants were stratified into four risk tiers: low, intermediate, high, and very high-risk. Cox proportional hazard models assessed the relationship of POAG PRS and ocular factors with new glaucoma events.

RESULTS

In both discovery and replication set in the PheWAS, a higher genetic predisposition to POAG was specifically correlated with ocular disease phenotypes. The POAG PRS exhibited correlations with low corneal hysteresis, refractive error, and ocular hypertension, demonstrating a strong association with the onset of glaucoma. Individuals carrying a high genetic burden exhibited a 9.20-fold, 11.88-fold, and 28.85-fold increase in glaucoma incidence when associated with low corneal hysteresis, high myopia, and elevated intraocular pressure, respectively.

CONCLUSION

Genetic susceptibility to POAG primarily influences ocular conditions, with limited systemic associations. Notably, the baseline polygenic risk for POAG robustly associates with new glaucoma events, revealing a large combined effect of genetic and ocular risk factors on glaucoma incidents.

Background polygenic risk modulates the association between glaucoma and cardiopulmonary diseases and measures: an analysis from the UK Biobank

AIMS

To assess whether associations of cardiopulmonary conditions and markers with glaucoma differ by background genetic risk for primary open angle glaucoma (POAG).

METHODS

We constructed a POAG polygenic risk score (PRS) using genome-wide association study summary statistics from a large cross-ancestry meta-analysis. History of glaucoma (including self-report and codes for POAG, 'other glaucoma' or unspecified glaucoma), history of common cardiopulmonary conditions and cardiopulmonary measures were assessed in the UK Biobank. Stratifying by PRS decile 1 (lowest risk) versus decile 10 (highest risk), separate multivariable models were estimated to assess the associations of cardiopulmonary diseases or factors with glaucoma, adjusting for age, sex, smoking and medication use. A Bonferroni correction was used to adjust p values for multiple comparisons.

RESULTS

Individuals in POAG PRS decile 1 (417 cases, 44 458 controls; mean age 56.8 years) and decile 10 (2135 cases, 42 413 controls; mean age 56.7 years) were included. Within decile 1, glaucoma cases had significantly higher glycated haemoglobin (38.5 vs 35.9 mmol/mol) and higher prevalence of diabetes (17.5% vs 6.5%), dyslipidaemia (31.2% vs 18.3%) and chronic kidney disease (CKD) (6.7% vs 2.0%) than controls (adjusted p<0.0013 for each). Within decile 10, glaucoma was associated with higher prevalence of dyslipidaemia (27.7% vs 17.3%, p=6.9E-05). The magnitude of association between glaucoma and diabetes, CKD and glycated haemoglobin differed between deciles 1 and 10 (contrast test p value for difference <0.05).

CONCLUSION

The relations between systemic conditions and glaucoma vary by underlying genetic predisposition to POAG, with larger associations among those who developed glaucoma despite low genetic risk.

Appraising the Effects of Metabolic Traits on the Risk of Glaucoma: A Mendelian Randomization Study

Metabolic traits are associated with the risk of developing glaucoma in observational studies. To assess whether theses associations reflect causality, we conducted a Mendelian randomization (MR) study. Our study included up to 20,906 glaucoma cases and 438,188 controls. Genetic instruments associated with the concerned 11 exposures at the genome-wide significance level were selected from corresponding genome-wide association studies. Summary-level data for glaucoma were obtained from the UK Biobank, the GERA study, and the FinnGen consortium. Univariable and multivariable MR analyses were conducted separately in two populations. Our results showed that higher genetic liability to type 2 diabetes (T2D) was causally and independently associated with an increased risk of glaucoma (odds ratio [OR], 1.11; 95% confidence interval [CI], 1.06-1.16; p = 4.4 × 10-6). The association for T2D persisted after multivariable adjustment. In addition, higher genetically predicted systolic blood pressure (SBP), fasting glucose (FG), and HbA1c, were also suggestively associated with glaucoma risk. The OR was 1.08 (95% CI, 1.01-1.16; p = 0.035) for SBP, 1.24 (95% CI, 1.05-1.47; p = 0.011) for FG, and 1.28 (95% CI, 1.01-1.61; p = 0.039) for HbA1c. No evidence was observed to support the causal effects of body mass index and blood lipids for glaucoma. This study suggests a causal role for diabetes, as well as possible roles for higher SBP, FG, and HbA1c in the development of glaucoma. Further validation is needed to assess the potential of these risk factors as pharmacological targets for glaucoma prevention.

Association of Diabetes Medication With Open-Angle Glaucoma, Age-Related Macular Degeneration, and Cataract in the Rotterdam Study

Importance

Recent studies suggest that the diabetes drug metformin has a protective effect on open-angle glaucoma (OAG) and age-related macular degeneration (AMD). However, studies have not addressed the critical issue of confounding by indication, and associations have not been evaluated in a large prospective cohort.

Objective

To determine the association between diabetes medication and the common eye diseases OAG, AMD, and cataract and to evaluate their cumulative lifetime risks in a large cohort study.

Design, Setting, and Participants

This cohort study included participants from 3 independent cohorts from the prospective, population-based Rotterdam Study between April 23, 1990, and June 25, 2014. Participants were monitored for incident eye diseases (OAG, AMD, cataract) and had baseline measurements of serum glucose. Data on diabetes medication use and data from ophthalmologic examinations were gathered.

Exposures

Type 2 diabetes (T2D) and the diabetes medications metformin, insulin, and sulfonylurea derivatives.

Main Outcomes and Measures

Diagnosis and cumulative lifetime risk of OAG, AMD, and cataract.

Results

This study included 11 260 participants (mean [SD] age, 65.1 [9.8]; 6610 women [58.7%]). T2D was diagnosed in 2406 participants (28.4%), OAG was diagnosed in 324 of 7394 participants (4.4%), AMD was diagnosed in 1935 of 10 993 participants (17.6%), and cataract was diagnosed in 4203 of 11 260 participants (37.3%). Untreated T2D was associated with a higher risk of OAG (odds ratio [OR], 1.50; 95% CI, 1.06-2.13; P = .02), AMD (OR, 1.35; 95% CI, 1.11-1.64; P = .003), and cataract (OR, 1.63; 95% CI, 1.39-1.92; P < .001). T2D treated with metformin was associated with a lower risk of OAG (OR, 0.18; 95% CI, 0.08-0.41; P < .001). Other diabetes medication (ie, insulin, sulfonylurea derivates) was associated with a lower risk of AMD (combined OR, 0.32; 95% CI, 0.18 to 0.55; P < .001). The cumulative lifetime risk of OAG was lower for individuals taking metformin (1.5%; 95% CI, 0.01%-3.1%) than for individuals without T2D (7.2%; 95% CI, 5.7%-8.7%); the lifetime risk of AMD was lower for individuals taking other diabetes medication (17.0%; 95% CI, 5.8%-26.8% vs 33.1%; 95% CI, 30.6%-35.6%).

Conclusions and Relevance

Results of this cohort study suggest that, although diabetes was clearly associated with cataract, diabetes medication was not. Treatment with metformin was associated with a lower risk of OAG, and other diabetes medication was associated with a lower risk of AMD. Proof of benefit would require interventional clinical trials.

Prevalence Rates and Risk Factors for Primary Open Angle Glaucoma in the Middle East

Glaucoma is a multifactorial disease and a leading cause of irreversible blindness worldwide. Current data has demonstrated the approximate distribution of primary open-angle glaucoma (POAG) in patients of European, African, Hispanic, and Eastern Asian descent. However, a significant gap in the literature exists regarding the prevalence of POAG in Middle Eastern (ME) populations. Current studies estimate ME POAG prevalence based on a European model. Herein we screened 65 total publications on ME prevalence of POAG and specific risk factors using keywords: "glaucoma", "prevalence", "incidence", "risk factor", "Middle East", "Mideast", "Persian", "Far East", as well as searching by individual ME countries through PubMed, Embase, Ovid, Scopus, and Trip searches with additional reference list searches from relevant articles published up to and including March 1, 2021. Fifty qualifying records were included after 15 studies identified with low statistical power, confounding co-morbid ophthalmic diseases, and funding bias were excluded. Studies of ME glaucoma risk factors that identify chromosomes, familial trend, age/gender, socioeconomic status, lifestyle, intraocular pressure, vascular influences, optic disc hemorrhage, cup-to-disc ratio, blood pressure, obstructive sleep apnea, and diabetes mellitus were included in this systematic review. We conclude that the prevalence of POAG in the ME is likely higher than the prevalence rate that European models suggest, with ME specific risk factors likely playing a role. However, these findings are severely limited by the paucity of population-level data in the ME. Well-designed, longitudinal population-based studies with rigorous inclusion and exclusion criteria are ultimately needed to accurately assess the epidemiology and specific mechanistic risk factors of glaucoma in ME populations.

Non-drug interventions in glaucoma: Putative roles for lifestyle, diet and nutritional supplements

Glaucoma is a major ocular neurodegenerative disease characterized by progressive retinal ganglion cells degeneration and sight loss. Current treatment options have been limited to reducing intraocular pressure (IOP), known as the leading risk factor for this disease; however, glaucoma can develop even with low or normal IOP and progress despite controlling IOP values. Lifestyle, dietary habits, and supplementation may influence some of the risk factors and pathophysiological mechanisms underlying glaucoma development and progression; thus, the role of this complementary and alternative medicine in glaucoma has received great interest from both patients and ophthalmologists. We provide a summary of the current evidence concerning the relationship between lifestyle, dietary habits, and effects of supplements on the incidence and progression of glaucoma and their targets and associated mechanisms. The data suggest the existence of a therapeutic potential that needs to be further explored with both preclinical and rigorous clinical studies.

Association Between Diabetes, Diabetic Retinopathy, and Glaucoma

PURPOSE OF REVIEW

The strength of the relationship between diabetes, diabetic retinopathy (DR), and glaucoma remains controversial. We review evidence supporting and refuting this association and explore mechanistic pathological and treatment relationships linking these diseases.

RECENT FINDINGS

While studies have shown diabetes/DR may increase the risk for glaucoma, this remains inconsistently demonstrated. Diabetes/DR may contribute toward glaucomatous optic neuropathy indirectly (either by increasing intraocular pressure or vasculopathy) or through direct damage to the optic nerve. However, certain elements of diabetes may slow glaucoma progression, and diabetic treatment may concurrently be beneficial in glaucoma management. Diabetes plays a significant role in poor outcomes after glaucoma surgery. While the relationship between diabetes/DR and glaucoma remains controversial, multiple mechanistic links connecting pathophysiology and management of diabetes, DR, and glaucoma have been made. However, a deeper understanding of the causes of disease association is needed.

Intraocular Pressure, Glaucoma, and Dietary Caffeine Consumption: A Gene-Diet Interaction Study from the UK Biobank

PURPOSE

We examined the association of habitual caffeine intake with intraocular pressure (IOP) and glaucoma and whether genetic predisposition to higher IOP modified these associations. We also assessed whether genetic predisposition to higher coffee consumption was related to IOP.

DESIGN

Cross-sectional study in the UK Biobank.

PARTICIPANTS

We included 121 374 participants (baseline ages, 39-73 years) with data on coffee and tea intake (collected 2006-2010) and corneal-compensated IOP measurements in 2009. In a subset of 77 906 participants with up to 5 web-based 24-hour-recall food frequency questionnaires (2009-2012), we evaluated total caffeine intake. We also assessed the same relationships with glaucoma (9286 cases and 189 763 controls).

METHODS

We evaluated multivariable-adjusted associations with IOP using linear regression and with glaucoma using logistic regression. For both outcomes, we examined gene-diet interactions using a polygenic risk score (PRS) that combined the effects of 111 genetic variants associated with IOP. We also performed Mendelian randomization using 8 genetic variants associated with coffee intake to assess potential causal effects of coffee consumption on IOP.

MAIN OUTCOME MEASURES

Intraocular pressure and glaucoma.

RESULTS

Mendelian randomization analysis did not support a causal effect of coffee drinking on IOP (P > 0.1). Greater caffeine intake was associated weakly with lower IOP: the highest (≥232 mg/day) versus lowest (<87 mg/day) caffeine consumption was associated with a 0.10-mmHg lower IOP (Ptrend = 0.01). However, the IOP PRS modified this association: among those in the highest IOP PRS quartile, consuming > 480 mg/day versus < 80 mg/day was associated with a 0.35-mmHg higher IOP (Pinteraction = 0.01). The relationship between caffeine intake and glaucoma was null (P ≥ 0.1). However, the IOP PRS also modified this relationship: compared with those in the lowest IOP PRS quartile consuming no caffeine, those in the highest IOP PRS quartile consuming ≥ 321 mg/day showed a 3.90-fold higher glaucoma prevalence (Pinteraction = 0.0003).

CONCLUSIONS

Habitual caffeine consumption was associated weakly with lower IOP, and the association between caffeine consumption and glaucoma was null. However, among participants with the strongest genetic predisposition to elevated IOP, greater caffeine consumption was associated with higher IOP and higher glaucoma prevalence.

Genome-wide meta-analysis identifies 127 open-angle glaucoma loci with consistent effect across ancestries

Primary open-angle glaucoma (POAG), is a heritable common cause of blindness world-wide. To identify risk loci, we conduct a large multi-ethnic meta-analysis of genome-wide association studies on a total of 34,179 cases and 349,321 controls, identifying 44 previously unreported risk loci and confirming 83 loci that were previously known. The majority of loci have broadly consistent effects across European, Asian and African ancestries. Cross-ancestry data improve fine-mapping of causal variants for several loci. Integration of multiple lines of genetic evidence support the functional relevance of the identified POAG risk loci and highlight potential contributions of several genes to POAG pathogenesis, including SVEP1, RERE, VCAM1, ZNF638, CLIC5, SLC2A12, YAP1, MXRA5, and SMAD6. Several drug compounds targeting POAG risk genes may be potential glaucoma therapeutic candidates.

Relationships of diabetes and hyperglycaemia with intraocular pressure in a Japanese population: the JPHC-NEXT Eye Study

Although a meta-analysis previously suggested a positive relationship between diabetes and intraocular pressure (IOP), the interrelationships among diabetes, IOP, and other ocular biometric parameters remain unclear. The present study investigated the relationships of diabetes, haemoglobin A1c (HbA1c), and serum glucose with IOP and ocular hypertension (IOP > 21 mmHg) in non-glaucomatous Japanese adults living in Chikusei City. Diabetes was defined as a self-reported history of diabetes, the use of antidiabetic medication, or HbA1c levels ≥6.5%. Among 6,786 enrolled participants aged 40 years and above, 734 were classified as diabetic (10.8%). After adjusting for several confounders, the IOP values were significantly higher in participants with diabetes than in those without diabetes (14.4 ± 0.1 vs. 13.9 ± 0.1 mmHg, P < 0.001) and were also significantly increased in those with elevated HbA1c and serum glucose levels (both P < 0.001). Moreover, diabetes was significantly related to ocular hypertension (multivariable-adjusted odds ratio, 1.75; 95% confidence interval, 1.09–2.81; P < 0.05). The positive influence of diabetes with ocular hypertension was consistent even after adjustment for central corneal thickness. In conclusion, diabetes, elevated HbA1c, and increased serum glucose are significant contributing factors for elevated IOP.