Clinical and experimental links between diabetes and glaucoma

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.

Retinal Neurodegeneration in an Intraocular Pressure Fluctuation Rat Model

Increased intraocular pressure (IOP) is the most important risk factor for glaucoma. The role of IOP fluctuation, independently from elevated IOP, has not yet been confirmed in glaucoma. We investigated the effects of IOP fluctuation itself on retinal neurodegeneration. Male rats were treated with IOP-lowering eyedrops (brinzolamide and latanoprost) on Mondays and Thursdays (in the irregular instillation group) or daily (in the regular instillation group), and saline was administered daily in the normal control group for 8 weeks. The IOP standard deviation was higher in the irregular instillation group than the regular instillation group or the control group. The degree of oxidative stress, which was analyzed by labeling superoxide, oxidative DNA damage, and nitrotyrosine, was increased in the irregular instillation group. Macroglial activation, expressed by glial fibrillary acidic protein in the optic nerve head and retina, was observed with the irregular instillation of IOP-lowering eyedrops. Microglial activation, as indicated by Iba-1, and the expression of TNF-α did not show a significant difference between the irregular instillation and control groups. Expression of cleaved caspase-3 was upregulated and the number of retinal ganglion cells (RGCs) was decreased in the irregular instillation group. Our findings indicate that IOP fluctuations could be induced by irregular instillation of IOP-lowering eyedrops and this could lead to the degeneration of RGCs, probably through increased oxidative stress and macrogliosis.

Risk of cataract and glaucoma among older persons with diabetes in India: a cross-sectional study based on LASI, Wave-1

According to the International Diabetes Federation-2019 estimates, India is home to 77 million diabetic individuals which is projected to grow up to 147.2 million by 2045. Diabetes being a progressive health disorder leads to multiple morbidities and complications including eye diseases and visual impairments. As the burden of diabetes mellitus is increasing, eye problems like cataracts and glaucoma are commonly cited problems among the older adults. In this context, this study aims to provide the public health evidences on diabetes associated burden and risk of developing cataracts and glaucoma among older adults aged 60 and above in India. The analytical sample of this cross-sectional study comprised of 31,464 individuals aged 60 and above. Bivariate cross-tabulation and chi-square test were performed to understand the differential in the prevalence of cataracts and glaucoma by diabetes mellitus including the socio-economic and demographic characteristics of the individuals. Binary logistic regression estimation was executed to estimate the adjusted odds ratio for each of the outcome variables within a multivariate framework. The cataract problem affects more than one-fifth of the older people, while glaucoma affects 2% of them. The prevalence of cataract and glaucoma is 29% among diabetic older adults compared to 22% among non-diabetic persons. In terms of gender, the cataract prevalence is comparatively higher among females (25%) than males (21%). It is important to note that while adjusting for socio-economic and demographic characteristics, the likelihood of cataract (AOR 1.495; p-value < 0.01) and glaucoma (AOR 1.554; p-value < 0.01) is significantly higher among older adults with diabetes than among their counterparts. Medical practitioners should conduct prognosis for diabetic eye problems among patients and raise awareness about the potential risks of developing vision loss, such as cataracts and glaucoma, which are more prevalent among individuals with diabetes.

Diabetes more than retinopathy, it’s effect on the anterior segment of eye

Diabetes mellitus (DM) is one of the chronic metabolic noncommunicable diseases that has attained worldwide epidemics. It threatens healthy life around the globe, with mild-to-severe secondary complications and leads to significant illness including nephropathy, neuropathy, retinopathy, and macrovascular abnormalities including peripheral vasculopathy, and ischaemic heart disease. Research into diabetic retinopathy (DR), which affects one-third of persons with diabetes, has made considerable strides in recent years. In addition, it can lead to several anterior segment complications such as glaucoma, cataract, cornea, conjunctiva, lacrimal glands and other ocular surface diseases. Uncontrolled DM also caused gradual damage to corneal nerves and epithelial cells, which raises the likelihood of anterior segment diseases including corneal ulcers, dry eye disease, and chronic epithelial abnormalities. Although DR and other associated ocular complications are well-known, the complexity of its aetiology and diagnosis makes therapeutic intervention challenging. Strict glycaemic control, early detection and regular screening, and meticulous management is the key to halting the progression of the disease. In this review manuscript, we aim to provide an in-depth understanding of the broad spectrum of diabetic complications in the anterior segment of the ocular tissues and illustrate the progression of diabetes and its pathophysiology, epidemiology, and prospective therapeutic targets. This first such review article will highlight the role of diagnosing and treating patients with a plethora of anterior segment diseases associated with diabetes, which are often neglected.

Evaluation of the lamina cribrosa in different stages of diabetic retinopathy

PURPOSE

To evaluate the relationship of the peripapillary retina nerve fiber layer (RNFL) and lamina cribrosa (LC) with diabetic retinopathy (DR) in type 2 diabetes mellitus (DM) cases.

STUDY DESIGN

Prospective comparative study.

METHODS

This study included 50 non-DR (Group 1), 55 non-proliferative diabetic retinopathy (NPDR) (Group 2), 28 DM cases with proliferative diabetic retinopathy (PDR) (Group 3) and 45 healthy volunteers (Group 4). All participants were evaluated with visual acuity, intraocular pressure (IOP) with Goldman applanation tonometry, anterior segment biomicroscopy, 24 - 2 visual field testing, and dilated fundus examination. Retinal nerve fiber layer (RNFL) thickness, lamina cribrosa thickness (LCT) and anterior lamina cribrosa depth (ALCD) were examined by spectral-domain optical coherence tomography (OCT).

RESULTS

There was no difference between the groups in terms of age and gender. Visual acuity (p < 0.001) was significantly different between the groups, while IOP (p = 0.068) was similar. Mean (p = 0.010), superior-temporal (p = 0.024), and superior-nasal (p = 0.011) RNFL thickness decreased significantly in correlation with the stage of DR. LCT decreased significantly as the stage of DR progressed in both vertical and horizontal radial OCT scans (p < 0.001). ALCD was not different between groups (p = 0.954 for horizontal scan, p = 0.867 for vertical scan).

CONCLUSION

Peripapillary RNFL and LCT significantly decreases as the DR stage progresses. The biomechanical effects of the LC may also be responsible for diabetes-induced neurodegeneration.

Mendelian randomization analyses in ocular disease: a powerful approach to causal inference with human genetic data

Ophthalmic epidemiology is concerned with the prevalence, distribution and other factors relating to human eye disease. While observational studies cannot avoid confounding factors from interventions, human eye composition and structure are unique, thus, eye disease pathogenesis, which greatly impairs quality of life and visual health, remains to be fully explored. Notwithstanding, inheritance has had a vital role in ophthalmic disease. Mendelian randomization (MR) is an emerging method that uses genetic variations as instrumental variables (IVs) to avoid confounders and reverse causality issues; it reveals causal relationships between exposure and a range of eyes disorders. Thus far, many MR studies have identified potentially causal associations between lifestyles or biological exposures and eye diseases, thus providing opportunities for further mechanistic research, and interventional development. However, MR results/data must be interpreted based on comprehensive evidence, whereas MR applications in ophthalmic epidemiology have some limitations worth exploring. Here, we review key principles, assumptions and MR methods, summarise contemporary evidence from MR studies on eye disease and provide new ideas uncovering aetiology in ophthalmology.

Visual Acuity Outcomes in Diseases Associated with Reduced Visual Acuity: An Analysis of the National Health Insurance Service Database in Korea

Visual acuity declines with age, and disease-related visual acuity changes vary. We evaluated factors affecting visual acuity and age-related visual acuity in diseases associated with reduced visual acuity such as hypertension, diabetes mellitus (DM), glaucoma, and diabetic retinopathy (DR). The Korean National Health Insurance Service 2015–2016 data were analyzed for age-related visual acuity changes and prevalence of diseases associated with reduced visual acuity. Among 993,062 participants, the prevalence rates of hypertension, DM, glaucoma, and DR were 27.0%, 15.1%, 13.8%, and 2.7%, respectively. Despite having the lowest prevalence, DR alone or DR with hypertension and glaucoma resulted in low visual acuity. Correlation analysis between disease frequency and mean age-related visual acuity revealed higher positive correlations in DR and hypertension than in DM and glaucoma, indicating lower visual acuity. Odds ratios for low visual acuity in cases including one disease such as hypertension, DM, glaucoma, and DR were 1.73, 1.23, 1.04, and 1.52, respectively. The prevalence and number of diseases associated with reduced visual acuity increased with age, and visual acuity decreased. The leading causes of vision loss were DR as a single disease and hypertension as a concomitant disease. Therefore, age-related vision management, through periodic eye examination and correction with age, should be performed along with management of diabetes and hypertension.

Bivariate Survival Copula Analysis of Glaucoma Patients during Blindness: Glaucoma Cases at Alert Hospital in Addis Ababa City of Ethiopia

BACKGROUND

Glaucoma is a worldwide problem that causes vision loss and even blindness, with a prevalence rate ranging from 1.9% to 15%. In Ethiopia, glaucoma is the fifth cause of blindness. This study aimed to explore the dependence between blindness of the right and the left eyes of glaucoma patients and assess the effects of the covariates under the dependence structure.

STUDY DESIGN

A retrospective cohort study.

METHODS

The study population included the glaucoma patients at Alert hospital from January 1, 2018, to December 30, 2021. The copula model was used to estimate the time to the blindness of the right and the left eyes of the glaucoma patients by specifying the dependence between the event times.

RESULTS

Out of 537 glaucoma patients, 224 (41.71%) became blind at least in one eye during the follow-up period. The results of the Clayton copula model revealed that factors, such as age, residence, diabetes mellitus, stage of glaucoma, and hypertension are considered the most prognostic factors for blindness in glaucoma patients. The findings also revealed that there was a strong dependence between the time to the blindness of the right and the left eyes in the glaucoma patients (τ = 0.43).

CONCLUSION

Based on the obtained results, high age, urban residence, hypertension, diabetes mellitus, and higher stage of glaucoma were factors associated with time to the blindness in the glaucoma patients. There was also a dependence between the right and the left eyes of the glaucoma patients. The results revealed that the Clayton Archimedean copula model was the best statistical model for accurate description of glaucoma patients' datasets.

Risk of Glaucoma Associated with Components of Metabolic Disease in Taiwan: A Nationwide Population-Based Study

PURPOSE

This retrospective cohort study was conducted to determine the glaucoma risk associated with metabolic disease (MetD) using insurance claims data of Taiwan.

METHODS

From the database, we identified patients with newly diagnosed hypertension, diabetes and/or hyperlipidemia from the years 2000 to 2002 as the MetD cohort (N = 42,036) and an age-gender-diagnosis-date matched control cohort without MetD with a two-fold sample size than that of the MetD cohort. Both cohorts were followed until the development of glaucoma, death, or withdrawal, until 31 December 2013. The incidence of glaucoma, and the Cox method estimated hazard ratio (HR) of glaucoma were calculated. Results showed that the incidence of glaucoma was two-fold higher in the MetD cohort than in the controls (1.99 versus 0.99 per 1000 person-years), with an adjusted HR of 1.66 (95% CI: 1.50-1.85). The glaucoma incidence was higher in patients with diabetes than those with hypertension and hyperlipidemia (2.38 versus 1.95 and 1.72 per 1000 person-years, respectively). The incidence increased to 5.67 per 1000 person-years in patients with all three comorbidities, with an aHR of 4.95 (95% CI: 2.35-10.40). We also found higher incidence rates of primary open-angle glaucoma and primary angle-closure glaucoma with aHRs of 2.03 and 1.44, respectively. It was concluded that glaucoma risk increased with the number of MetD. Health providers need to monitor patients with MetD to prevent glaucoma.

Systemic diseases and their association with open-angle glaucoma in the population of Stockholm

Objective

We aimed to study open-angle glaucoma in association with somatic comorbidities in the total population of adults in Region Stockholm.

Methods

The study population included all living persons aged 19 years and above who resided in Stockholm County, Sweden, on 1 January 2017 (N = 1 703 675). Subjects with specified diseases were identified with data from all registered consultations and hospital stays during 2008–2019. As outcome, the risk of being associated with a diagnosis of open-angle glaucoma was identified during 2012–2018. Analyses were performed by gender, controlling for age and socio-economic status. Age-adjusted odds ratios (ORs) with 95% confidence intervals (95% CI) for women and men with open-angle glaucoma, using individuals without this as referents, were calculated. Socio-economic status was assessed based on the neighbourhood the subjects lived in.

Results

In total, 16,299 cases of open-angle glaucoma were identified during 2012–2018, 9204 women and 7095 men. Higher fully adjusted OR (95% CI) for risk of being associated with open-angle glaucoma was for women and men with diabetes 1.138 (1.074–1.207) and 1.216 (1.148–1.289), cancer 1.175 (1.120–1.233) and 1.106 (1.048–1.166), hypertension 1.372 (1.306–1.440) and 1.243 (1.179–1.311); and for women with thyroid diseases 1.086 (1.030–1.146), chronic lung diseases 1.153 (1.093–1.216), and inflammatory arthropathies 1.132 (1.006–1.275). Higher glaucoma incidence was observed in individuals residing in high socio-economic status neighbourhoods.

Conclusion

The risk of glaucoma is increased in some somatic diseases, especially in individuals with diabetes, hypertension and cancer; and in higher socio-economic neighbourhoods as compared to lower socio-economic neighbourhoods.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10792-021-02137-w.

Characteristics of Diabetic and Nondiabetic Patients With Thyroid Eye Disease in the United States: A Claims-Based Analysis

OBJECTIVE

Thyroid eye disease (TED) is a debilitating autoimmune disease characterized by ocular and periorbital tissue inflammation, proptosis, and visual impairment. The known risk factors for TED include radioactive iodine therapy, female sex, and smoking. The risk factors for severe TED include hyperthyroidism, male sex, smoking, and diabetes; however, little is known about how diabetes mellitus (DM) influences TED. This claims-based analysis examined TED characteristics in patients with and without diabetes.

METHODS

Symphony database (2010-2015 U.S. claims) was mined for patients with ≥1 Graves' disease diagnosis code and ≥1 TED-associated eye code, including proptosis, strabismus, diplopia, lid retraction, exposure keratoconjunctivitis, and optic neuropathy (ON). DM status was determined based on type 1 or type 2 diabetes coding. Sight-threatening TED was defined as ≥1 ON or exposure keratoconjunctivitis code.

RESULTS

A total of 51 220 patients were identified. Of them, 2618 (5.1%) and 12 846 (25.1%) had type 1 and type 2 DM, respectively. Patients with and without DM had similar characteristics, but patients with DM were more often men (type 1: 30.3%, type 2: 28.7% vs no DM: 20.5%; both P < .001) and older at the first TED code. In patients with DM, strabismus (25.4%, 22.6% vs 19.9%) and diplopia (38.6%, 37.9% vs 29.9%) occurred more often but proptosis occurred less often (42.3%, 46.3% vs 58.5%; all P < .001). Sight-threatening TED occurred more often in patients with DM because of higher ON rates.

CONCLUSION

Patients with TED and DM may have more extraocular muscle involvement. Furthermore, the higher prevalence of severe TED stemmed from higher ON rates, possibly associated with diabetes-related vasculopathies. These hypothesis-generating data warrant further exploration.

Association of metformin use among diabetics and the incidence of primary open-angle glaucoma - The Chennai Eye Disease Incidence Study

Purpose

Studies have reported the usage of metformin being associated with the reduced risk of progression of glaucoma. The current study aims to determine the association of metformin usage among subjects with diabetes mellitus and the six-year incidence of primary open-angle glaucoma (POAG).

Methods

In this prospective cohort study, subjects who did not have glaucoma at the baseline and had a follow-up after a six-year interval were included. Details such as medical and drug history, applanation tonometry, gonioscopy, pachymetry, optic disc evaluation, and automated perimetry were collected. Incident POAG was defined as subjects who do not have glaucoma at baseline and developed glaucoma as classified International Society of Geographical and Epidemiological Ophthalmology Classification at the follow-up. The association between the subjects who were on metformin for treatment of diabetes mellitus and development of incident POAG was assessed.

Results

Among the 4302 eligible participants, 128 (3%) had incident POAG. There were 905 (21.0%) subjects who had diabetes mellitus of which 142 (15.7%) were using metformin. Of the subjects with POAG, 92 (71.9%) were nondiabetics and 36 were diabetics (28.1%). Among the diabetics, the incidence of POAG among those on metformin was 5.6% (8 participants) and those not on metformin was 3.6% (28 participants). There was no difference in the incidence of POAG in subjects with diabetes mellitus, with and without metformin use (P = 0.25). Logistic regression showed no association of metformin use with the incidence of POAG (OR: 1.33, 95 CI: 0.58-3.04, P = 0.49) after adjusting for age, gender, and place of residence.

Conclusion

The current study did not find any association between the effects of metformin on the incidence of POAG.

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.

Peripapillary Retinal Nerve Fiber Layer and Microvasculature in Prolonged Type 2 Diabetes Patients Without Clinical Diabetic Retinopathy

Purpose

The purpose of this study to identify the effects of prolonged type 2 diabetes (T2DM) on the peripapillary retinal nerve fiber layer (pRNFL) and peripapillary microvasculature in patients with prolonged T2DM without clinical diabetic retinopathy (DR).

Methods

Subjects were divided into 3 groups: controls (control group; 153 eyes), patients with T2DM < 10 years (DM group 1; 136 eyes), and patients with T2DM ≥ 10 years (DM group 2; 74 eyes). The pRNFL thickness and peripapillary superficial vessel density (VD) were compared. Linear regression analyses were performed to identify factors associated with peripapillary VD in patients with T2DM.

Results

The mean pRNFL thicknesses of the control group, DM group 1, and DM group 2 were 96.0 ± 7.9, 94.5 ± 0.9, and 92.2 ± 8.2 µm, respectively (P < 0.001). The VDs were 18.24 ± 0.62, 17.60 ± 1.47, and 17.15 ± 1.38 mm⁻¹ in the control group, DM group 1, and DM group 2, respectively (P < 0.001). In multivariate linear regression analyses, visual acuity (B = −2.460, P = 0.001), axial length (B = −0.169, P = 0.008), T2DM duration (B = −0.056, P < 0.001), and pRNFL (B = 0.024, P = 0.001) were significant factors affecting the peripapillary VD in patients with T2DM.

Conclusions

Patients with T2DM without clinical DR showed thinner pRNFL and lower peripapillary VD and perfusion density (PD) compared with normal controls, and such damage was more severe in patients with T2DM ≥ 10 years. Additionally, peripapillary VD was significantly associated with best-corrected visual acuity (BCVA), axial length, T2DM duration, and pRNFL thickness in patients with T2DM.

Diabetes Exacerbates the Intraocular Pressure-Independent Retinal Ganglion Cells Degeneration in the DBA/2J Model of Glaucoma

Purpose

Glaucoma is a multifactorial disease, causing retinal ganglion cells (RGCs) and optic nerve degeneration. The role of diabetes as a risk factor for glaucoma has been postulated but still not unequivocally demonstrated. The purpose of this study is to clarify the effect of diabetes in the early progression of glaucomatous RGC dysfunction preceding intraocular pressure (IOP) elevation, using the DBA/2J mouse (D2) model of glaucoma.

Methods

D2 mice were injected with streptozotocin (STZ) obtaining a combined model of diabetes and glaucoma (D2 + STZ). D2 and D2 + STZ mice were monitored for weight, glycemia, and IOP from 3.5 to 6 months of age. In addition, the activity of RGC and outer retina were assessed using pattern electroretinogram (PERG) and flash electroretinogram (FERG), respectively. At the end point, RGC density and astrogliosis were evaluated in flat mounted retinas. In addition, Müller cell reactivity was evaluated in retinal cross-sections. Finally, the expression of inflammation and oxidative stress markers were analyzed.

Results

IOP was not influenced by time or diabetes. In contrast, RGC activity resulted progressively decreased in the D2 group independently from IOP elevation and outer retinal dysfunction. Diabetes exacerbated RGC dysfunction, which resulted independent from variation in IOP and outer retinal activity. Diabetic retinas displayed decreased RGC density and increased glial reactivity given by an increment in oxidative stress and inflammation.

Conclusions

Diabetes can act as an IOP-independent risk factor for the early progression of glaucoma promoting oxidative stress and inflammation-mediated RGC dysfunction, glial reactivity, and cellular death.

Ophthalmic Sensors and Drug Delivery

Advances in multifunctional materials and technologies have allowed contact lenses to serve as wearable devices for continuous monitoring of physiological parameters and delivering drugs for ocular diseases. Since the tear fluids comprise a library of biomarkers, direct measurement of different parameters such as concentration of glucose, urea, proteins, nitrite, and chloride ions, intraocular pressure (IOP), corneal temperature, and pH can be carried out non-invasively using contact lens sensors. Microfluidic contact lens sensor based colorimetric sensing and liquid control mechanisms enable the wearers to perform self-examinations at home using smartphones. Furthermore, drug-laden contact lenses have emerged as delivery platforms using a low dosage of drugs with extended residence time and increased ocular bioavailability. This review provides an overview of contact lenses for ocular diagnostics and drug delivery applications. The designs, working principles, and sensing mechanisms of sensors and drug delivery systems are reviewed. The potential applications of contact lenses in point-of-care diagnostics and personalized medicine, along with the significance of integrating multiplexed sensing units together with drug delivery systems, have also been discussed.

Is Diabetes Mellitus a Blessing in Disguise for Primary Open-angle Glaucoma?

Although numbers of studies have addressed this question, the relationship between diabetes mellitus and primary open-angle glaucoma is still unclear. This article discusses progress in understanding the complex relationship between these 2 entities and recent shifts in perspective that challenge the traditional dogma regarding diabetes mellitus and primary open-angle glaucoma. There are still many unanswered questions.

Therapeutic Ophthalmic Lenses: A Review

An increasing incidence of eye diseases has been registered in the last decades in developed countries due to the ageing of population, changes in lifestyle, environmental factors, and the presence of concomitant medical conditions. The increase of public awareness on ocular conditions leads to an early diagnosis and treatment, as well as an increased demand for more effective and minimally invasive solutions for the treatment of both the anterior and posterior segments of the eye. Despite being the most common route of ophthalmic drug administration, eye drops are associated with compliance issues, drug wastage by lacrimation, and low bioavailability due to the ocular barriers. In order to overcome these problems, the design of drug-eluting ophthalmic lenses constitutes a non-invasive and patient-friendly approach for the sustained drug delivery to the eye. Several examples of therapeutic contact lenses and intraocular lenses have been developed, by means of different strategies of drug loading, leading to promising results. This review aims to report the recent advances in the development of therapeutic ophthalmic lenses for the treatment and/or prophylaxis of eye pathologies (i.e., glaucoma, cataract, corneal diseases, or posterior segment diseases) and it gives an overview of the future perspectives and challenges in the field.

Intraocular pressure fluctuation and neurodegeneration in the diabetic rat retina

BACKGROUND AND PURPOSE

Early retinal neurodegeneration occurs as one of the complications of diabetes even before clinically detectable diabetic vascular retinopathy. The pathogenesis of retinal diabetic neuropathy is still not well understood. We investigated the serial changes or fluctuations in intraocular pressure (IOP) and examined their roles in the pathogenesis of neuronal degeneration in diabetic retina.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats with streptozotocin-induced diabetes were treated with ophthalmic preparations of brinzolamide, latanoprost, both drugs (combined treatment) or saline for 8 weeks. IOP was measured daily under general anaesthesia using a rebound tonometer. Antegrade axoplasmic flow in the optic nerve was assessed with a fluorescent substrate. Immunohistochemical staining, TUNEL assays and western blots were also used.

KEY RESULTS

The fluctuation of IOP was higher in the diabetes group than in the normal control or the combined treatment group. Diabetes-induced apoptosis of retinal ganglion cells was decreased by combined treatment. Increased expression of glial fibrillary acidic protein or Iba-1 in the retina or optic nerve head, induced by diabetes, was attenuated only by the combined treatment. Intercellular adhesion molecule-1 was increased in diabetic rats but not in the combined treatment group. Diabetes-induced loss of antegrade axoplasmic transport was partially relieved with combined treatment.

CONCLUSION AND IMPLICATIONS

Elevated IOP fluctuations seemed to be associated with the gliosis, neuroinflammation, and neurodegeneration induced by diabetes. The loss of retinal ganglion cells might be relieved by IOP-lowering medication. The improvement of unstable perfusion pressure could play a role in neuroprotection in the diabetic retina.

Potential of Lipoprotein-Based Nanoparticulate Formulations for the Treatment of Eye Diseases

Lipoproteins are naturally occurring nanoparticles and their main physiological function is the promotion of lipid metabolism. They can be prepared in vitro for use as drug carriers, and these reconstituted lipoproteins show similar biological activity to their natural counterparts. Some lipoproteins can cross the blood-retinal barrier and are involved in intraocular lipid metabolism. Drug-loaded lipoproteins can be delivered to the retina for the treatment of posterior eye diseases. In this review, we have discussed the therapeutic applications of lipoproteins for eye diseases and introduced the emerging animal models used for the evaluation of their therapeutic effects.

Spectrum of Eye Disease in Diabetes (SPEED) in India: A prospective facility-based study. Report # 4. Glaucoma in people with type 2 diabetes mellitus

Purpose

To estimate the proportion of people with type 2 diabetes mellitus (T2DM) and glaucoma in a facility-based cross-sectional observational study in India.

Methods

All people received a comprehensive eye examination. Glaucoma-specific examinations included applanation tonometry, optic disc and cup evaluation, and stereo biomicroscopy in all people; gonioscopy and visual field testing in glaucoma suspects. The International Society of Geographic and Epidemiologic Ophthalmology guidelines were used to diagnose and classify glaucoma.

Results

The study recruited 11,182 people (average age: 58.2 ± 10.6; range 39-96 years). Glaucoma was diagnosed in 4.9% (n = 547) people. About 76.8% (n = 420) of those with glaucoma had bilateral disease, and 98.7% (n = 540) were >40 years. Among people with bilateral disease, 94.5% (n = 397) had primary glaucoma - open angle in 59.3% (n = 228) and angle closure in 40.2% (n = 169). Diabetes duration was ≤10 years in 71.5% (n = 300) people. On linear regression, the following were associated with glaucoma: advancing age [compared with < 40 years age group; odds ratio [OR] in 50-60 year age group: 1.36 [95% confidence interval (CI): 1.01-1.8], P < 0.035); >60 years age group (OR: 2.05, 95% CI: 1.57-2.67; P < 0.001), and diabetic neuropathy (OR: 2.62, 95% CI: 1.35-5.10, P < 0.003). Glycemic control did not have significant association (P = 0.425).

Conclusion

Presence of glaucoma in people with T2DM in this cohort was similar to the general population prevalence studies in India. Glaucoma was invariably bilateral. A comprehensive eye examination in people age 40 years and older with diabetes and/or glaucoma is beneficial.

Detailed Evaluation of Possible Ganglion Cell Loss in the Retina of Zucker Diabetic Fatty (ZDF) Rats

A thinning of the inner retina is one of the earliest potential markers of neuroretinal damage in diabetic subjects. The histological background is uncertain; retinal ganglion cell (RGC) loss and changes in the structure or thickness of the inner plexiform layer (IPL) have been suspected. Studies conducted on animal models on RGC pathology gave contradictory results. Hereby we present RGC numbers, distribution patterns and IPL thickness from Zucker Diabetic Fatty (ZDF) rats. After labelling RGCs on retinal whole mounts, isodensity maps were constructed, RGC numbers and distribution patterns analysed using a custom-built algorithm, enabling point-by-point comparison. There was no change in staining characteristics of the antibodies and no significant difference in average RGC densities was found compared to controls. The distribution patterns were also comparable and no significant difference was found in IPL thickness and stratification or in the number of apoptotic cells in the ganglion cell layer (GCL). Our results provide a detailed evaluation of the inner retina and exclude major RGC loss in ZDF rats and suggest that other factors could serve as a potential explanation for inner retinal thinning in clinical studies. Our custom-built method could be adopted for the assessment of other animal or human retinas.

Neovascular glaucoma regulation by arylsulfonyl indoline-benzamide (ASIB) through targeting NF-kB signalling pathway

The present study investigated the effect of arylsulfonyl indoline-benzamide (ASIB) on neovascular glaucoma in the mice model in vivo. In the mice model of glaucoma, ASIB treatment significantly (P < 0.05) increased PDGF-B-positive cell count in the corneal tissues. ASIB treatment at 5, 10, 15 and 20 mg/kg doses raised the level of PDGF-B mRNA in the mice cornea by 2.3-, 3.8-, 5.4- and 5.5-fold, respectively. Pre-treatment of the glaucoma mice with ASIB leads to inhibition of TNF-α and IL-6 production. In the glaucoma mice, treatment with ASIB leads to a marked decrease in the level of NOD2 mRNA and protein. ASIB treatment caused a significant decrease in the glaucoma-induced up-regulation of NF-κB p65 activation. The phosphorylation of NF-κB p65 was almost completely inhibited in the glaucoma mice on treatment with 15 mg/kg dose of ASIB. ASIB exhibited inhibitory effect on glaucoma-induced inflammatory cytokine and oxidative factor damage in the mice. It caused up-regulation of PDGF expression and down-regulated NF-κB activation. Therefore, ASIB can be of therapeutic significance for neovascular glaucoma treatment. However, more studies need to be performed to fully understand the molecular mechanism of ASIB in glaucoma treatment.

All roads lead to glaucoma: Induced retinal injury cascades contribute to a common neurodegenerative outcome

Glaucoma describes a distinct optic neuropathy with complex etiology and a variety of associated risk factors, but with similar pathological endpoints. Risk factors such as age, increased intraocular pressure (IOP), low mean arterial pressure, and autoimmune disease, can all be associated with death of retinal ganglion cells (RGCs) and optic nerve head remodeling. Today, IOP management remains the standard of care, even though IOP elevation is not pathognomonic of glaucoma, and patients can continue to lose vision despite effective IOP control. A contemporary view of glaucoma as a complex, neurodegenerative disease has developed, along with the recognition of a need for new disease modifying retinal treatment strategies and improved outcomes. However, the distinction between risk factors triggering the disease process and retinal injury responses is not always clear. In this review, we attempt to distinguish between the various triggers, and their association with subsequent key RGC injury mechanisms. We propose that distinct glaucomatous risk factors result in similar retinal and optic nerve injury cascades, including oxidative and metabolic stress, glial reactivity, and altered inflammatory responses, which induce common molecular signals to induce RGC apoptosis. This organization forms a coherent disease framework and presents conserved targets for therapeutic intervention that are not limited to specific risk factors.

Progression of Primary Open-Angle Glaucoma in Diabetic and Nondiabetic Patients

PURPOSE

To compare the rates of visual field (VF) loss and retinal nerve fiber layer (RNFL) thinning in primary open-angle glaucoma (POAG) patients with or without type 2 diabetes mellitus (DM).

DESIGN

Cohort study.

METHODS

A total of 197 eyes (55 eyes of 32 POAG patients with DM in POAG/DM group and 142 eyes of 111 age-matched POAG patients without DM in POAG/DM- group) were included from the Diagnostic Innovations in Glaucoma Study (DIGS). Type 2 DM participants were defined by self-report of DM history and use of antidiabetic medication. The rates of VF loss and RNFL loss were compared in POAG eyes with and without DM using univariate and multivariable mixed-effects models.

RESULTS

The median (interquartile range) follow-up was 5.7 years (4.0, 6.4). The mean rate of global RNFL loss in the POAG/DM group was 2-fold slower than in the POAG/DM- group overall (-0.40 μm/year vs -0.83 μm/year, respectively P = .01). Although a slower rate of VF mean deviation and pattern standard deviation loss was found in the POAG/DM group compared to the POAG/DM- group, the difference was not statistically significant.

CONCLUSIONS

POAG patients with treated type 2 DM, who had no detectable diabetic retinopathy, had significantly slower rates of RNFL thinning compared to those without diagnosed DM.

σ-1 receptor stimulation protects against pressure-induced damage through InsR-MAPK signaling in human trabecular meshwork cells

The purpose of the present study was to investigate the protective effect of the σ-1 receptor (Sig-1R) agonist (+)‑pentazocin (PTZ) on pressure-induced apoptosis and death of human trabecular meshwork cells (hTMCs). The expression levels of Sig‑1R and insulin receptor (InsR) were examined in hTMCs. Cells were cultured under a pressure of 0, 20, 40, 60 and 80 mmHg for 48 h, and under 80 mmHg for 44 h, after which the cells were treated with (+)‑PTZ (20 µM), N-(2-(3,4-dichlorophenyl)ethyl)-N‑methyl-2‑(dimethylamino) ethylamine (BD‑1063; 20 µM) administered 30 min prior to (+)‑PTZ, or BD‑1063 (20 µM) and then exposed to 80 mmHg again until the 48 h time‑point. The changes of the cells were observed by optical and electron microscopy, the apoptosis and death of hTMCs were detected by ethidium bromide/acridine orange dual staining assay and the expression of Sig‑1R and InsR by reverse transcription‑quantitative polymerase chain reaction and western blot analysis. The phosphorylation of extracellular signal‑regulated kinase (ERK), an important downstream protein of the InsR‑mitogen‑activated protein kinases (MAPK) signaling pathway, was also detected by western blot analysis when (+)‑PTZ and BD‑1063 were added to the 80 mmHg‑treated cells. Sig‑1Rs and InsRs were expressed in hTMCs. The apoptosis and death of hTMCs increased from 40 mmHg with 50% cell death when the pressure was at 80 mmHg and the structure of the cells noticeably changed. The expression of Sig‑1R and InsR increased along with the elevation of pressure. (+)‑PTZ decreased the apoptosis and death of hTMCs and increased the expression of Sig‑1R and InsR, and the phosphorylation of ERK. Such effects were blocked by BD‑1063. The present study suggested that Sig‑1R agonist (+)‑PTZ can protect hTMCs from pressure‑induced apoptosis and death by activating InsR and the MAPK signal pathway.

Effects of diabetes mellitus on biomechanical properties of the rabbit cornea

To investigate the effects of diabetes on the biomechanical behavior of cornea in alloxan-induced diabetic rabbits. Diabetes mellitus (DM) was induced in 20 rabbits using alloxan, while another 20 age- and weight-matched non-diabetic rabbits served as controls. Eyes were enucleated after 8 weeks of inducing diabetes and the whole cornea was removed with a 3 mm wide scleral ring and tested under inflation conditions with an internal pressure range of 2.0-30.0 mmHg to determine their stress-strain behavior using an inverse analysis process. The blood glucose level (BG), advanced glycosylation end products (AGEs), central corneal thickness (CCT) and intraocular pressure (IOP) increased significantly in the DM group. There were statistically significant correlations between BG and AGEs (r = 0.768, p = 0.00), and between AGEs and CCT variation upon induction of DM (r = 0.594, p = 0.00). The tangent modulus (Et) of the cornea at four stress levels (1-4 kPa, equivalent to approximately IOP of 7.5, 15, 22.5 and 30 mmHg, respectively) was significantly higher in diabetic rabbits than in the control group (p < 0.05). Further, Et at stress of 2 kPa (which corresponded to the average IOP for the control group) was significantly correlated with BG (r = 0.378, p < 0.05), AGEs (r = 0.496, p < 0.05) and CCT variation upon induction of DM (r = 0.439, p < 0.05). IOP, as measured by contact tonometry, was also significantly correlated with both CCT (r = 0.315, p < 0.05) and Et at 2 kPa (r = 0.329, p < 0.05), and even after correcting for the effects of CCT and Et, IOP still significantly increased with both AGEs (r = 0.772, p = 0.00) and BG (r = 0.762, p = 0.00). The cornea of diabetic rabbits showed a significant increase in mechanical stiffness as evidenced by increases in corneal thickness and tangent modulus. The Et increase may be explained by a non-enzymatic cross-linking of collagen fibrils mediated by AGEs due to the high blood glucose levels in diabetes. The study also found significant IOP increases with higher blood glucose level even after controlling the effects of both corneal thickness and tangent modulus.

Presence and Risk Factors for Glaucoma in Patients with Diabetes

Diabetes mellitus represents a growing international public health issue with a near quadrupling in its worldwide prevalence since 1980. Though it has many known microvascular complications, vision loss from diabetic retinopathy is one of the most devastating for affected individuals. In addition, there is increasing evidence to suggest that diabetic patients have a greater risk for glaucoma as well. Though the pathophysiology of glaucoma is not completely understood, both diabetes and glaucoma appear to share some common risk factors and pathophysiologic similarities with studies also reporting that the presence of diabetes and elevated fasting glucose levels are associated with elevated intraocular pressure-the primary risk factor for glaucomatous optic neuropathy. While no study has completely addressed the possibility of detection bias, most recent epidemiologic evidence suggests that diabetic populations are likely enriched with glaucoma patients. As the association between diabetes and glaucoma becomes better defined, routine evaluation for glaucoma in diabetic patients, particularly in the telemedicine setting, may become a reasonable consideration to reduce the risk of vision loss in these patients.

A histopathological investigation of Tenon's capsule in diabetic eyes

The aim of this study is to investigate the histopathological features of Tenon's capsule in eyes with diabetic macular oedema and to compare them between diabetic eyes and healthy subjects. The study included 26 eyes with diabetic oedema and 17 healthy eyes as healthy controls. Tenon's capsule biopsy specimens were processed with the routine electron microscopic analysis technique. Type I and III collagen fibres were labelled immunohistochemically to determine the amounts of predominating collagen fibres. Leica Q-Win program was used to calculate the amounts of collagen fibres type I and type III and independent-t test was utilized to compare the obtained results between the groups. Statistical significance was set at p < 0.05. Demographic characteristics of both groups were similar (p > 0.05). Collagen type I and type III immunoreactivity was observed both in the control and the diabetic groups. The Amounts of collagen fibres type I and type III were significantly higher in the diabetic group than in the control group (mean collagen type I area: 13.410 ± 0.99 and mean collagen type III area: 23.692 ± 0.17 in the control group; mean collagen type I area: 25.270 ± 6.48 and mean collagen type III area: 28.192 ± 0.82 in the diabetic group. p = 0.0037 for type I and p = 0.0000 for type III). In light of the findings of this study, it can be assumed that diabetes mellitus may engender increased amounts of collagen in Tenon's capsule. This alteration affecting the success of filtration surgery should be kept in mind especially in diabetic eyes with glaucoma.

Diabetes Mellitus as a Risk Factor in Glaucoma's Physiopathology and Surgical Survival Time: A Literature Review

Glaucoma is a multifactorial condition under serious influence of many risk factors. The role of diabetes mellitus (DM) in glaucoma etiology or progression remains inconclusive. Although, the diabetic patients have different healing mechanism comparing to the general population and it has a possible-negative role on surgical outcomes. This review article attempts to analyze the association of both diseases, glaucoma and DM, before and after the surgery. The epidemiological studies, based mainly in population prevalence analyzes, have shown opposite outcomes in time and even in the most recent articles also the association remains inconclusive. On the contrary, the experimental models based on animal induced chronic hyperglycemia have shown an important association of both diseases, explained by common neurodegenerative mechanisms. Diabetic patients have a different wound healing process in the eye viz-a-viz other organs. The healing process is more and it results in lower surgical survival time, higher intraocular pressure (IOP) levels and, therefore, these patients usually need more medication to lower the IOP. Both randomized and nonrandomized retrospective and experimental molecular studies have shown the association between DM and glaucoma. Further studies are needed to get better explanations about outcomes on more recent surgical procedures and with the exponential use of antifibrotics. How to cite this article: Costa L, Cunha JP, Amado D, Pinto LA, Ferreira J. Diabetes Mellitus as a Risk Factor in Glaucoma's Physiopathology and Surgical Survival Time: A Literature Review. J Curr Glaucoma Pract 2015;9(3):81-85.

Vascular Dysfunction in Diabetes and Glaucoma: A Complex Relationship Reviewed

Open-angle glaucoma (OAG) is a multifactorial disease characterized by progressive retinal ganglion cell death and visual field loss. Intraocular pressure, ocular perfusion pressure, and systemic vascular irregularities have all been identified as contributing factors for glaucoma onset and progression. Focal and systemic vascular abnormalities have also been well documented in diabetic patients. The relationship between diabetes mellitus and OAG remains enigmatic in the literature. As the pathogenesis of both diabetes mellitus and OAG involves compromised vascular regulation, this review was undertaken to further investigate their precise relationship. A literature review of published population-based studies was performed, with a focus on studies regarding blood flow abnormalities. Although current studies support the role of vascular contributions to both diseases, the association between glaucoma and diabetes yields contrasting results.

The Role of Systemic Arterial Stiffness in Open-Angle Glaucoma with Diabetes Mellitus

PURPOSE

To investigate the role of systemic arterial stiffness in glaucoma patients with diabetes mellitus (DM).

DESIGN

Retrospective, cross-sectional study.

PARTICIPANTS

DM subjects who underwent brachial-ankle pulse wave velocity (baPWV) were recruited.

METHODS

Glaucoma patients (n = 75) and age-matched control subjects (n = 92) were enrolled. Systemic examination including BaPWV and detailed eye examination were performed. The glaucoma group was divided into subgroups of normal tension glaucoma (NTG, n = 55) and primary open-angle glaucoma (POAG) based on an IOP of 21 mmHg. BaPWV was used to stratify the population into 4 groups based on the rate. Stepwise multiple logistic regression analysis by baPWV quartiles was used to compare the glaucoma group with the control group.

MAIN OUTCOME MEASURES

BaPWV in glaucoma with DM patients.

RESULTS

Faster baPWV was positively associated with glaucoma (odds ratio: 3.74; 95% CI: 1.03-13.56, stepwise multiple logistic regression analysis) in patients with DM. Increasing baPWV was also positively associated with glaucoma (p for trend = 0.036). The NTG subgroup showed similar results to those of the glaucoma group.

CONCLUSIONS

In this study, increased arterial stiffness was shown to be associated with glaucoma and may contribute to the pathogenesis of glaucoma in DM patients.

Chronic intraocular pressure elevation impairs autoregulatory capacity in streptozotocin-induced diabetic rat retina

PURPOSE

To assess ocular blood flow responses to acute IOP stress following 4 weeks of chronic IOP elevation in streptozotocin (STZ)-induced diabetic and control rats. We hypothesise that chronic IOP elevation for 4 weeks will further impair blood flow regulation in STZ-induced diabetic rats eyes.

METHODS

Two weeks following citrate buffer or STZ-injections chronic IOP elevation was induced in Long Evans rats via fortnightly intracameral injections of microspheres (15 μm) suspended in 5% polyethylene glycol. IOP was monitored daily. Electroretinography (ERG, -6.79-2.07 log cd s m(-2) ) was undertaken at Week 4 to compare photoreceptor (RmPIII ), ON-bipolar cell (Vmax ) and ganglion cell dominant ERG [scotopic threshold response (STR)] components. 4 weeks post-chronic IOP induction, ocular blood flow (laser Doppler flowmetry) was measured in response to acute IOP challenge (10-100 mmHg, in 5 mmHg steps, each 3 min).

RESULTS

Four weeks of chronic IOP (mean ± S.E.M., citrate: 24.0 ± 0.3 to 30.7 ± 1.3 and STZ-diabetes: 24.2 ± 0.2 to 31.1 ± 1.2 mmHg) was associated with reduced photoreceptor amplitude in both groups (-25.3 ± 2.2% and -17.2 ± 3.0%, respectively). STZ-diabetic eyes showed reduced photoreceptor sensitivity (citrate: 0.5 ± 1.8%, STZ-diabetic: -8.1 ± 2.4%). Paradoxically ON-bipolar cell sensitivity was increased, particularly in citrate control eyes (citrate: 166.8 ± 25.9%, STZ-diabetic: 64.8 ± 18.7%). The ganglion cell dominant STR was not significantly reduced in STZ-diabetic rats. Using acute IOP elevation to probe autoregulation, we show that STZ-diabetes impaired autoregulation compared with citrate control animals. The combination of STZ-diabetes and chronic IOP elevation further impaired autoregulation.

CONCLUSIONS

STZ-diabetes and chronic IOP elevation appear to be additive risk factors for impairment of ocular blood flow autoregulation.

DBA/2J mice are susceptible to diabetic nephropathy and diabetic exacerbation of IOP elevation

Some pathological manifestations of diabetes in the eye include retinopathy, cataracts and elevated intraocular pressure (IOP). Loss of retinal ganglion cells (RGCs) in non-proliferative stages of diabetic retinopathy and small increases in IOP in diabetic patients has raised the possibility that diabetes affects the development and progression of ocular hypertension and glaucoma. The Ins2Akita mutation is known to cause diabetes and retinopathy on a C57BL/6J (B6) background by as early as 3 months of age. Here, the impact of the Akita mutation on glaucoma was assessed using DBA/2J (D2) mice, a widely used mouse model of ocular hypertension induced glaucoma. In D2.Ins2Akita/+ mice, the contribution of diabetes to vascular permeability, IOP elevation, RGC loss, and glaucoma development was assessed. D2.Ins2Akita/+ mice developed a severe diabetic nephropathy and early mortality between 6-8 months of age. This agrees with previous reports showing that the D2 background is more susceptible to diabetes than the B6 background. In addition, D2.Ins2Akita/+ mice had vascular leakage, astrocyte reactivity and a significant increase in IOP. However no RGC loss and no anterograde axonal transport dysfunction were found at 8.5 months of age. Therefore, our data show that despite severe diabetes and an increased IOP compared to controls, RGCs do not lose axon transport or degenerate. This may be due to a DBA/2J-specific genetic modifier(s) that could provide novel and important avenues for developing new therapies for diabetic retinopathy and possibly glaucoma.

Intraocular surgery in a large diabetes patient population: risk factors and surgical results

The prevalence of diabetes is on the increase in developed countries. Accordingly, the prevention and treatment of vision-threatening diabetic eye complications is assuming greater importance. The overall aim of this thesis is to analyse risk factors for intraocular surgery in a large diabetes population and to report surgical results. The specific objectives are to (1) estimate the incidence of diabetic vitrectomy and analyse risk factors (Study I), (2) report long-term results, prognostic factors and incidence of cataract surgery after diabetic vitrectomy (Study II), (3) report results and prognostic factors after cataract surgery in diabetes patients (Study III) and (4) analyse risk factors for diabetic papillopathy with emphasis on metabolic control variability (Study IV). All studies are based on a close-to-complete national surgery register and a large, closely followed diabetic retinopathy screening population. Study I (cohort study, 3980 type 1 diabetes patients) illustrates that diabetic vitrectomy is rarely required in a diabetes patient population with varying degrees of diabetic retinopathy. The risk of reaching diabetic vitrectomy increases fourfold with poor metabolic control, defined as glycosylated haemoglobin A1c > 75 mmol/mol (~9%), which points to good metabolic control as an important preventive measure. Study II (cohort study, 167 diabetes patients) shows that most diabetic vitrectomy patients stand to gain visual acuity ≥0.3 after surgery. Visual acuity is stable after 1 year, and the stability is maintained through 10 years of follow-up. The use of silicone oil for endotamponade is a consistent long-term predictor of low vision after surgery. The risk of requiring cataract surgery after diabetic vitrectomy is substantial, and the risk increases if silicone oil is used. Study III (cohort study, 285 diabetes patients) shows, on the other hand, that diabetes patients can expect a significant improvement in visual acuity after cataract surgery, regardless of the degree of diabetic retinopathy. Poor preoperative visual acuity, a high degree of diabetic retinopathy and advanced age are predictors of a poor visual acuity after surgery. The risk of diabetic macular oedema after surgery is 4%. Finally, Study IV (case-control study, 2066 type 1 diabetes patients) demonstrates that diabetic papillopathy shares characteristics with diabetic retinopathy. The risk of experiencing diabetic papillopathy increases markedly with a drastic, recent reduction in glycosylated haemoglobin A1c and a small optic disc. This lends support to the theory that diabetic eye complications may occur in anatomically predisposed patients in response to metabolic control variability. Overall, results after intraocular surgery in diabetes patients are favourable. Surgery, however, is associated with costs to society, patient discomfort and risk of complications. This thesis provides an analysis of risk factors for intraocular surgery and identifies prognostic factors for visual acuity after surgery, which can be used for preventive purposes, surgical decision-making and patient counselling.

Salvia miltiorrhiza extracts protect against retinal injury in a rat glaucoma model

Glaucoma is a serious progressive degenerative disorder of the eye that leads to the continuous loss of retinal ganglion cells. Traditional Chinese medicine provides an important source for new drug screening and identification. The present study used Salvia miltiorrhiza (Danshen) extracts to examine the potential neuroprotective effects for the eye in a rat model of experimental glaucoma. The results of the study indicated that Salvia miltiorrhiza extracts were unable to prevent intraocular pressure increase in the laser-induced glaucoma model, but the treatment did reduce cell loss during glaucoma progression. Therefore, the results provide the basis for the development of a novel therapeutic agent that exhibits neuroprotective effects against glaucoma. In the future, further studies are required to purify the extracts and determine the effective bioactive components of Salvia miltiorrhiza.

Comparison of the nerve fiber layer of type 2 diabetic patients without glaucoma with normal subjects of the same age and sex

BACKGROUND

The retinal nerve fiber layer (RNFL) thickness in patients with diabetes mellitus type 2 was compared to normal subjects of similar age and sex, having first excluded any risk factors for glaucoma. The correlation between the RNFL thickness and the severity of diabetic retinopathy was investigated at its primary stages and with other ocular and diabetic parameters.

METHODS

A prospective, case series study was carried out. Twenty-seven diabetic patients without diabetic retinopathy, 24 diabetic patients with mild retinopathy, and 25 normal, age-matched subjects underwent a complete ophthalmological examination and imaging with scanning laser polarimetry for the evaluation of the RNFL. Multivariate analysis was applied in order to investigate the correlation between RNFL and diabetic parameters, such as age, duration of diabetes, insulin therapy, levels of glycosylated hemoglobin; and ocular parameters, such as cup to disc ratio, levels of normal intraocular pressure, and central corneal thickness.

RESULTS

The mean inferior average of RNFL and the temporal-superior-nasal-inferior-temporal standard deviation were statistically significantly lower in both diabetic groups, and the nerve fiber index was higher (P=0.04) compared to the normal group. There was no statistically significant difference between the diabetic groups. The factor analysis showed no significant correlation between the RNFL and the previously mentioned diabetic and ocular parameters.

CONCLUSION

The existence of diabetes should be seriously considered in evaluating the results of scanning laser polarimetry. Multivariate analysis for RNFL was used for the first time.

The influence of retinal blood flow on open-angle glaucoma in patients with and without diabetes

PURPOSE

To evaluate the impact of retinal blood flow on optic nerve head (ONH) morphology in patients with open-angle glaucoma (OAG) with and without diabetes mellitus (DM).

METHODS

A total of 66 patients with OAG (14 with DM, 52 without DM) were assessed at baseline and 3-year follow-up for retinal capillary blood flow using confocal scanning laser Doppler and ocular structure using Heidelberg retinal tomography and optical coherence tomography.

RESULTS

Change in retinal tissue with zero blood flow in the superior and inferior retina was found to have a strong correlation with ONH changes in diabetic patients (r≥0.90, p≤0.03); however, no relation was found in the nondiabetic cohort. There were also significant changes in inferior mean flow that strongly correlated with changes in cup area (r = 0.97, p = 0.0029), cup/disc area ratio (r = 0.96, p = 0.0070), linear cup/disc ratio (r = 0.93, p = 0.0172), rim area (r = -0.97, p = 0.0036), and rim volume (r = -0.95, p = 0.0084) in diabetic patients only, while changes in the superior mean flow were only significantly associated with cup area (r = -0.30, p = 0.0498), cup volume (r = -0.36, p = 0.0178), and rim volume (r = 0.35, p = 0.0193) in nondiabetic patients.

CONCLUSIONS

In this cohort of patients with OAG, changes in retinal capillary blood flow correlated more strongly with changes in ONH morphology in patients with DM than in those without DM. These data suggest that changes in retinal blood flow may play a larger role in glaucomatous ONH progression in patients with OAG with DM.

Myopia and diabetes mellitus as modificatory factors of glaucomatous optic neuropathy

Myopic deformation of the eye and metabolic alterations of the nerve tissue of patients with diabetes may modify glaucomatous optic neuropathy (GON). Blockage of axonal transport of neurotrophic factors (NTFs) is the event crucial to understanding the factors that affect GON. The primary, but not sole, blockage site is at the lamina cribrosa (LC). Other than this primary site of damage at the LC, 7 other factors may explain atypical nerve fiber layer (NFL) defects and the vulnerability of the nerve fibers in eyes with high myopia and glaucoma: a second point of blockage at the edge of the posterior scleral foramen; ectatic strain on the NFL; ectasia and distortion of the LC; association of a hypoplastic optic disc; thin and weak collagen fibers; peripapillary chorioretinal atrophy; and myopic neuropathy. Among diabetic patients, diabetic neuropathy in the retinal NFL is present initially, and increased resistance to aqueous outflow leads to ocular hypertension. Superimposition of GON on diabetic neuropathy and ocular hypertension in patients with diabetes may enhance their susceptibility to nerve damage. Results of a meta-analysis study suggested a positive association between diabetes mellitus and glaucoma whereas other reports suggested that leakage of vascular endothelial growth factor, a survival mechanism of ischemic neural tissue, and enhanced stiffness of the LC as a result of diabetic glycation may protect neurons from apoptosis. Thus, modification of GON as a result of diabetes remains controversial.

Exclusion of aldose reductase as a mediator of ERG deficits in a mouse model of diabetic eye disease

Streptozotocin (STZ)-induced diabetes is associated with reductions in the electrical response of the outer retina and retinal pigment epithelium (RPE) to light. Aldose reductase (AR) is the first enzyme required in the polyol-mediated metabolism of glucose, and AR inhibitors have been shown to improve diabetes-induced electroretinogram (ERG) defects. Here, we used control and AR -/- mice to determine if genetic inactivation of this enzyme likewise inhibits retinal electrophysiological defects observed in a mouse model of type 1 diabetes. STZ was used to induce hyperglycemia and type 1 diabetes. Diabetic and age-matched nondiabetic controls of each genotype were maintained for 22 weeks, after which ERGs were used to measure the light-evoked components of the RPE (dc-ERG) and the neural retina (a-wave, b-wave). In comparison to their nondiabetic controls, wildtype (WT) and AR -/- diabetic mice displayed significant decreases in the c-wave, fast oscillation, and off response components of the dc-ERG but not in the light peak response. Nondiabetic AR -/- mice displayed larger ERG component amplitudes than did nondiabetic WT mice; however, the amplitude of dc-ERG components in diabetic AR -/- animals were similar to WT diabetics. ERG a-wave amplitudes were not reduced in either diabetic group, but b-wave amplitudes were lower in WT and AR -/-diabetic mice. These findings demonstrate that the light-induced responses of the RPE and outer retina are disrupted in diabetic mice, but these defects are not due to photoreceptor dysfunction, nor are they ameliorated by deletion of AR. This latter finding suggests that benefits observed in other studies utilizing pharmacological inhibitors of AR might have been secondary to off-target effects of the drugs.