Diabetic retinopathy and its relation to errors of refraction

Positive and Negative Associations of Myopia with Ocular Diseases in Population-Based Studies

PURPOSE

Prevalence of myopia and vision impairment due to myopic macular degeneration and myopia-related optic neuropathies have markedly increased worldwide. We evaluated whether myopia is associated with other ocular disorders.

DESIGN

Population-based studies conducted in Russia, China, and India.

PARTICIPANTS

The Russian Ural Eye and Medical Study (UEMS) and the Beijing Eye Study (BES) included 5899 individuals and 4439 individuals (all aged 40+ years), respectively, and the Central India Eye and Medical Study (CIEMS) consisted of 4711 individuals aged 30+ years. The studies were conducted in rural and urban regions in Bashkortostan/Russia, Nagpur/India, and Beijing/China.

METHODS

The participants underwent a series of ophthalmological and general medical examinations.

MAIN OUTCOME MEASURES

Axial length as a surrogate for myopia and prevalence of diabetic retinopathy (DR), age-related macular degeneration (AMD), angle-closure glaucoma (ACG), and open-angle glaucoma (OAG).

RESULTS

In the UEMS, DR prevalence (odds ratio [OR], 0.73), AMD prevalence (OR, 0.85), and ACG prevalence (OR, 0.72) decreased, and OAG prevalence (OR, 1.65) increased with longer axial length in multivariable analyses. In the CIEMS, lower AMD prevalence (OR, 0.81) and lower ACG prevalence (OR, 0.55), and higher OAG prevalence (OR, 1.45) were associated with longer axial length. Diabetic retinopathy prevalence (0.33%) was too low for statistical analysis in the CIEMS. In the BES, prevalence (OR, 0.64) and 10-year incidence of DR (OR, 0.48) and prevalence (OR, 0.83) and 5-year incidence of AMD (OR, 0.996) decreased, and prevalence (OR, 1.35) and 10-year incidence of OAG (OR, 1.40) increased with longer axial length. In all 3 studies, the association between higher OAG prevalence and longer axial length was nonlinear with a slight increase for the moderate myopia range and a steep increase in the highly myopic range.

CONCLUSIONS

Myopia is associated with a lower prevalence of DR, AMD, and ACG and a lower incidence of DR and AMD, whereas high myopia more than moderate myopia is associated with a higher prevalence and incidence of OAG. Future studies may assess whether in myopia (in particular, in moderate myopia), the myopia-related advantages, that is, lower prevalence of DR, AMD, and ACG, may outweigh the increased risks for OAG and other myopia-related disorders.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

The relationship between refractive error and the risk of diabetic retinopathy: a systematic review and meta-analysis

Purpose

This meta-analysis was conducted to collect all available data and estimate the relationship between refractive error and the risk of diabetic retinopathy (DR) in patients with diabetes, and to assess whether vision-threatening DR (VTDR) is associated with refractive error.

Methods

We systematically searched several literature databases including PubMed, Embase, Cochrane Library, Web of Science, CNKI, CBM, Wan Fang Data, and VIP databases. Pooled odds ratios (OR) and 95% confidence intervals (CI) were calculated using fixed or random effects models. Four models were developed to assess the relationship between refractive error and the risk and DR, VTDR: hyperopia and DR, VTDR; myopia and DR, VTDR; spherical equivalent (SE per D increase) and DR, VTDR; and axial length (AL per mm increase) and DR, VTDR. The included literature was meta-analyzed using Stata 12.0 software, and sensitivity analysis was performed. Publication bias in the literature was evaluated using a funnel plot, Begg's test, and Egger's test.

Results

A systematic search identified 3,198 articles, of which 21 (4 cohorts, 17 cross-sectional studies) were included in the meta-analysis. Meta-analysis showed that hyperopia was associated with an increased risk of VTDR (OR: 1.23; 95% CI: 1.08-1.39; P = 0.001), but not with DR (OR: 1.05; 95% CI: 0.94-1.17; P = 0.374). Myopia was associated with a reduced risk of DR (OR: 0.74; 95% CI: 0.61-0.90; P = 0.003), but not with VTDR (OR: 1.08; 95% CI: 0.85-1.38; P = 0.519). Every 1 diopter increase in spherical equivalent, there was a 1.08 increase in the odds ratio of DR (OR: 1.08; 95% CI: 1.05-1.10; P<0.001), but not with VTDR (OR: 1.05; 95% CI: 1.00-1.10; P = 0.06). AL per mm increase was significantly associated with a decreased risk of developing DR (OR: 0.77; 95% CI: 0.71-0.84; P<0.001) and VTDR (OR: 0.63; 95% CI: 0.56-0.72; P<0.001). Analysis of sensitivity confirmed the reliability of the study's findings.

Conclusion

This meta-analysis demonstrates hyperopia was associated with an increased risk of VTDR in diabetes patients. Myopia was associated with a reduced risk of DR. AL is an important influencing factor of refractive error. Every 1 mm increase in AL reduces the risk of DR by 23% and the risk of VTDR by 37%.

Systematic review registration

identifier: CRD42023413420.

Axial myopia, a protective factor for diabetic retinopathy-role of vascular endothelial growth factor

Long axial length is one of the ocular protective factors in development of diabetic retinopathy (DR). In this study we examined the effect of axial length (AL) on aqueous humor vascular endothelial growth factor (VEGF) levels in patients with diabetes mellitus with or without DR. Forty-eight eyes of 48 participants were divided into three groups of 16 each. Group A consisted of non-diabetic patients, Group B had diabetic patients without DR, and Group C had diabetic patients with treatment-naive non-proliferative DR (NPDR). The groups were further subdivided based on axial lengths i.e., AL ≤ 23.30 mm (A1, B1, C1) and AL > 23.30 mm (A2, B2, C2). Undiluted aqueous humor was obtained during cataract surgery to measure the VEGF levels. We observed significant decrease in VEGF concentration in patients with AL ≥ 23.30 mm as compared with AL ≤ 23.30 mm in non-diabetic as well as diabetic patients. As the eye elongates, there is less secretion of VEGF in non-diabetics as well in diabetics with or without DR. Our findings strengthened the concept that an increase in AL leads to less VEGF in diabetic eyes, thus leading to less severe DR changes.

Tilted disc syndrome (TDS): New hypotheses for posterior segment complications and their implications in other retinal diseases

Tilted disc syndrome (TDS) is considered a congenital anomaly due to a delayed closure of the embryonic fissure. It is characterized by an oblique orientation of the axis of the optic disc, associated with other posterior pole anomalies such as inferior crescent, situs inversus and inferior staphyloma. The aim of this review was to summarize the data supporting the current hypotheses for the pathogenesis of TDS, and its anatomical and functional clinical consequences. Recent imaging techniques, such as magnetic resonance imaging, wide-field fundus imaging, and 2- and 3-D optical coherence tomography have provided a new perspective on TDS and its complications. Different abnormalities have previously been reported, both in the anterior and posterior segments. The focus was on vision-threatening chorioretinal changes or complications, including choroidal neovascularization and serous retinal detachments and their therapeutic options. Based on clinical observations, assumptions were proposed to understand the occurrence of complications such as chorioretinal degenerative changes, choroidal neovascularization and polypoidal choroidal vasculopathy, macular serous retinal detachment, myopic foveoschisis and chorioretinal folds. These hypotheses could be referred to as the curvature "breaking point" hypothesis, the uneven growth "tractional" hypothesis, the "container-content" imbalance hypothesis, and the "choroidal funnel" hypothesis. Because these complications could also occur in other contexts, understanding the pathogenesis of TDS complications could help to understand their pathophysiology.

Refractive Error and Retinopathy Outcomes in Type 1 Diabetes: The Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study

PURPOSE

To determine the relationship between refractive error and diabetic retinopathy (DR).

DESIGN

Clinical trial.

PARTICIPANTS

Type I diabetes individuals with serial refractive error and DR stage measurements over 30 years in the Diabetes Control and Complications Trial (DCCT) and Epidemiology of Diabetes Interventions and Complications (EDIC) follow-up study.

METHODS

Stage of DR was measured every 6 months from standard fundus photographs, and refractive error was measured annually during the 6.5 years of DCCT; then, both were staggered every fourth year during EDIC with the full cohort measured at EDIC years 4 and 10. Outcomes of DR were 2- or 3-step progression, presence of proliferative DR (PDR), clinically significant macular edema (CSME), diabetic macular edema (DME), or ocular surgery. Myopia, emmetropia, and hyperopia were defined as a spherical equivalent of ≤-0.5, >-0.5 and <0.5, and ≥0.5, respectively.

MAIN OUTCOME MEASURES

For each outcome separately, Cox proportional hazard (PH) models assessed the association between the refractive error status and the subsequent risk of that outcome, both without and with adjustment for potential risk factors.

RESULTS

Hyperopia was associated with a higher risk of 2-step progression (hazard ratio [HR], 1.29; 95% confidence interval [CI], 1.05-1.59), 3-step progression (HR, 1.35; 95% CI, 1.05-1.73), and PDR (HR, 1.40; 95% CI, 1.02-1.92) compared with emmetropia in unadjusted models. These associations remained significant after adjustment for DCCT treatment group, cohort, age, sex, smoking, duration of diabetes, systolic and diastolic blood pressures, pulse, low-density lipoprotein, high-density lipoprotein, triglycerides, albumin excretion rate, and DCCT/EDIC mean updated hemoglobin A1c (HbA1c) (2-step progression: HR, 1.28; 95% CI, 1.03-1.58; 3-step progression: HR, 1.30; 95% CI, 1.00-1.68; PDR: HR, 1.38; 95% CI, 1.00-1.90). Myopia was not associated with any of the 5 DR outcomes in the unadjusted models and only marginally associated with 2-step progression (HR, 1.11; 95% CI, 1.00-1.24) in the adjusted models.

CONCLUSIONS

Myopia is not associated with DR progression risk. Hyperopia is an independent risk factor for 2-step and 3-step DR progression and PDR.

Refractive Errors, Ocular Biometry and Diabetic Retinopathy: A Comprehensive Review

Purpose: To summarize the association between diabetic retinopathy and refractory status as well as ocular biometric parameters; To review the theories of the protective effect of high myopia against diabetic retinopathy. Methods: A comprehensive literature search on MEDLINE, EMBASE, Web of Science and Scopus databases as well as reference list search, and systematic review of relevant publications.  Results: Myopia may delay the onset and progression of diabetic retinopathy. Increased axial length in myopia is associated with reduced risk of any diabetic retinopathy and vision-threatening diabetic retinopathy. The possible mechanisms for the protective effect of myopia against diabetic retinopathy may include posterior vitreous detachment, change in retinal blood flow and oxygen demand, choroidal thinning and altered cytokine profiles.  Conclusions: High myopia may be a protective factor against the onset and progression of diabetic retinopathy. Further studies about the mechanisms of how myopia, axial length and ocular biometrics influence the onset and progression of DR are needed.

Ocular Axial Length and Diabetic Retinopathy: The Kailuan Eye Study

Purpose

To examine the role of ocular axial length as an ocular parameter for the prevalence and severity of diabetic retinopathy (DR).

Methods

The cross-sectional Kailuan Diabetic Retinopathy Study included patients with diabetes who participated in the community-based longitudinal Kailuan Study and who had undergone ocular fundus photography. The fundus photographs were graded using the Early Treatment of Diabetic Retinopathy Study criteria.

Results

The study included 1096 patients with diabetes (mean age: 60.8 ± 9.4 years; axial length: 23.37 ± 0.92 mm). In binary regression analysis, a higher DR prevalence was associated with shorter axial length (P = 0.007; odds ratio [OR]: 0.81; 95% confidence interval [CI]: 0.70, 0.95) after adjusting for longer known duration of diabetes (P = 0.02; OR: 1.13; 95%CI: 1.02, 1.24) and higher fasting blood glucose concentration (P < 0.001; OR: 1.38; 95%CI: 1.26, 1.52). A more severe DR stage was associated (regression coefficient r: 0.46) with shorter ocular axial length (P = 0.047; standardized regression coefficient β: -0.06) after adjusting for higher fasting blood glucose (P < 0.001; β: 0.41) and longer known duration of diabetes (P = 0.045; β: 0.07). Longer axial length was associated with a lower DR prevalence (P = 0.003; β: -0.10) after adjusting for younger age (P < 0.001), male sex (P < 0.001), higher body mass index (P = 0.016), and lower fasting blood glucose concentration (P = 0.036).

Conclusions

After adjusting for systemic risk factors, DR prevalence decreased by 19% (95%CI: 5, 30) for each millimeter increase in axial length. With longer axial length being a surrogate for axial myopia, the marked increase in myopia prevalence worldwide may lead to a relative decrease in the prevalence and incidence of DR in future.

Correlation of axial length and myopic macular degeneration to levels of molecular factors in the aqueous

To elucidate the molecular processes associated with the development of myopic macular degeneration (MMD), we measured the intraocular concentrations of molecular factors in emmetropic and myopic eyes. This is a retrospective clinic-based case-control study that included eyes undergoing routine cataract surgery whereby aqueous humour samples were obtained. We measured the concentrations of pigment epithelium derived factor(PEDF), matrix metalloproteinase 2(MMP-2), tissue inhibitor of metalloproteinase(TIMP-2), vascular endothelial growth factor isoform A(VEGF-A), interleukin 8(IL-8), interleukin 6(IL-6), C-reactive protein(CRP), angiopoietin 2(Ang2), and amphiregulin. 38 eyes (axial length (AL): 22.4–32.4 mm), including 12 highly myopic (HM) eyes (AL ≥ 26.5 mm) without MMD and 12 HM eyes with MMD but without neovascularization were included. Eyes with MMD were found to have significantly lower VEGF-A levels (p = 0.007) and higher MMP-2 levels (p = 0.02) than control eyes after adjusting for age and gender. MMP-2 levels correlated positively (r = 0.58, p = 0.002), while VEGF-A levels correlated negatively with longer axial length (r = −0.75, p < 0.001). Both the concentrations of VEGF-A (P = 0.25) and MMP-2 (P = 0.69) were not significantly associated with MMD after adjusting for AL. These findings suggest that the predominant mechanism underlying the development of non-neovascular MMD may be axial elongation, driven in part by MMP-2 related mechanisms.

Myopia and/or longer axial length are protective against diabetic retinopathy: a meta-analysis

PURPOSE

To evaluate the current evidence of the relationship between myopia, together with its structural and refractive component, and diabetic retinopathy (DR) risk.

METHODS

A systematic search was performed up to April, 2015. Summary odds ratios (ORs) and 95% confidence intervals (CIs) were calculated employing random-effects models. Three models were used to assess the association between myopia and risk of DR: axial length (AL) (per millimetre increase) and DR; myopia (myopia versus non-myopia) and DR; refractive error (RE) (per D decrease) and DR. Publication bias of the literature was evaluated using Begg's funnel plots and Egger's test.

RESULTS

A total of 11 studies that met the predefined criteria were included in this meta-analysis. Overall, longer AL (per millimetre increase) was associa-ted with a significantly decreased risk of DR (combined OR, 0.75; 95% CI, 0.65-0.86; p < 0.001); myopic eyes (myopia versus non-myopia) showed a lower risk of DR (combined OR, 0.70; 95% CI, 0.58-0.85; p < 0.001). A greater degree of myopic RE (per D decrease) also revealed a significantly decreased risk of DR (combined OR, 0.89; 95% CI, 0.85-0.93; p < 0.001). The sensitivity analyses and cumulative meta-analysis showed similar results. No publication bias was detected in any of the three models.

CONCLUSIONS

This meta-analysis suggests that both myopic refraction and longer AL are associated with a lower risk of DR. Further studies are needed to determine exact mechanisms underpinning the protective effect of myopia against DR.

Intracameral interleukin 1β, 6, 8, 10, 12p, tumor necrosis factor α and vascular endothelial growth factor and axial length in patients with cataract

Objective

To assess associations between the aqueous humour concentration of interleukin IL-1β, IL-6, IL-8, IL-10 and IL-12p, tumor necrosis factor α (TNF-α) and vascular endothelial growth factor (VEGF) and axial length in eyes with cataract.

Methods

The hospital-based investigation included patients who underwent cataract surgery between March 2014 and April 2014. Using aqueous humour collected at the start of cataract surgery, the interleukins IL-1β, IL-6, IL-8, IL-10 and IL-12p, TNF-α and VEGF were examined using a cytometric bead array. Axial length was determined by partial coherence laser interferometry (IOL Master).

Results

The study included 33 patients with cataract (33 eyes) with a mean age of 69.2±10.8 years (range:50–87 years) and a mean axial length of 24.7±1.9 mm (range:22.6–31.5 mm). Lower aqueous concentration of VEGF was significantly associated with longer axial length (VEGF concentration (pg/mL) = -5.12 x Axial Length (mm) + 163; correlation coefficient r = -0.41; P<0.001) and more myopic refractive error (VEGF concentration (pg/mL) = 1.27xspherical equivalent (diopters)+44.8; r = 0.383; P = 0.002). The aqueous concentrations of all other substances were not significantly (all P>0.10) associated with axial length or refractive error.

Conclusions

Higher intravitreal concentrations of VEGF were measured in eyes with a longer axial length, while the intraocular concentrations of IL-1β, IL-6, IL-8, IL-10, IL-12p and TNF-α were not correlated with axial length. The lower concentration of VEGF in axially elongated eyes may be one of the reasons for the lower prevalence of age-related macular degeneration and diabetic retinopathy in myopic eyes.

Diabetic retinopathy and pregnancy

Diabetes mellitus and pregnancy have reciprocal influences between them, therefore diabetes mellitus may complicate the course of pregnancy as well as pregnancy can worsen the performance of diabetes especially at the fundus oculi. Several factors seem to play a role in retinal neovascularization. Actually it's not possible to understand the mechanisms underlying this progression. Moreover chronic hyperglycemia leads to several events such as: the activation of aldose reductase metabolic pathway, the activation of the diacylglycerol-protein kinase C, the non-enzymatic glycation of proteins with formation of advanced glycation endproducts and the increase of hexosamines pathway. Although every structure of the eye can be affected by diabetes, retinal tissue, with all its vessels, is particularly susceptible. Pregnancy may promote the onset of diabetic retinopathy, in about 10 % of cases, as well as contribute to its worsening when already present. The proliferative retinopathy must always be treated; treatment should be earlier in pregnant women compared to non-pregnant women. Pregnancy can also cause macular edema; it spontaneously regresses during the postpartum and therefore does not require immediate treatment. In summary, collaboration between the various specialists is primary to ensure the best outcomes for both mother's health and sight, and fetus' health.

Exogenous endophthalmitis in diabetic patients: a systemic review

Diabetes mellitus is a systemic disease that increases the risk of infections. Exogenous endophthalmitis is an inflammatory disease to which diabetic patients are more predisposed to than nondiabetic patients undergoing any intraocular intervention. This might be because of the change in the immune and inflammatory factors that intervene in wound healing and in the bacterial flora of the ocular adnexa. We conducted a literature review to assess the risk of exogenous endophthalmitis in diabetic patients undergoing cataract extraction, pars plana vitrectomy, and intravitreal injections and to check whether its treatment differ from in non-diabetics. We found that diabetic patients are more predisposed to virulent organisms and that the incidence of ophthalmic symptoms was not substantially different in diabetic versus nondiabetic patients. Regarding treatment, all patients with light perception should receive pars plana vitrectomy, while those with hand motion and better vision should be given an intravitreal antibiotics injection. Some authors recommend vitrectomy to diabetic patients with even counting figure vision.

Modifying factors related to asymmetric diabetic retinopathy

PURPOSE

To identify the modifying factors related to the development of proliferative diabetic retinopathy (PDR).

METHODS

Thirty-eight eyes of 19 non-insulin-dependent diabetes mellitus (NIDDM) patients with maintained asymmetric PDR were retrospectively reviewed.

RESULTS

Five patients with ipsilateral carotid stenoses > or = 90% had PDR. Four patients with high myopia over 6 dioptres and 4 patients with optic atrophy and at least a quadrant defect in the visual field had non-proliferative diabetic retinopathy. Of 6 patients with unilateral asteroid hyalosis, 5 had no posterior vitreous detachment (PVD) and PDR.

CONCLUSION

Two factors reached statistical significance as factors modifying PDR: carotid occlusive disease and PVD. Optic atrophy and high myopia showed trends of being a protective influence.

Diabetic retinopathy in Down's syndrome

AIM

To determine the prevalence of diabetic retinopathy in patients with Down's syndrome and diabetes mellitus.

METHODS

Nine patients with Down's syndrome and diabetes mellitus were assessed. Factors recorded included type and duration of diabetes, level of diabetic control, blood pressure, urinalysis, and results of ophthalmological examination.

RESULTS

The duration of diabetes ranged from 8 to 41 years (mean 17.6 years). All had satisfactory glycaemic control and blood pressure measurements on the low side of normal (mean 106.6/70 mm Hg). One patient had early background diabetic retinopathy. The remainder had no evidence of diabetic retinopathy.

CONCLUSION

The low prevalence of diabetic retinopathy in these Down's syndrome patients, despite the long duration, is an interesting finding. It suggests some inherent protective factor against the development of diabetic retinopathy in this patient subgroup.

Long-term influence of insulin dependent diabetes mellitus on refraction and its components: a population based twin study

AIM

To study whether refraction of the eye, or some of its components is influenced by duration of insulin dependent diabetes mellitus.

METHODS

From the young cohort of the population based Danish Twin Register, containing 20,888 twin pairs born between 1953 and 1982, all twin pairs having one or both partners affected with IDDM were searched. Autorefraction, autokeratometry, and ultrasonic biometric measurements were carried out on 45 twin pairs: 16 monozygotic (MZ) twin pairs, 14 dizygotic twin pairs of same sex (DZss), and 15 dizygotic twin pairs of opposite sex (DZos). To obtain an estimate of the influence of duration of diabetes, the intrapair differences in duration of diabetes were correlated with intrapair differences in refraction and each of its components.

RESULTS

Refraction was statistically significantly negatively correlated with duration of diabetes in the DZss group, and axial length correspondingly positively correlated. Surprisingly, refraction and axial length in the MZ group, adjusted for confounding factors, were correlated with diabetes duration in the opposite direction than in the DZss group, although not reaching statistical significance. Lens thickness was statistically significantly positively correlated with duration of diabetes in both MZ and DZ twins. Anterior chamber depth was negatively correlated with duration of diabetes in all the zygosity groups.

CONCLUSIONS

Studies of relations between refraction and duration of diabetes show diverging results. In the MZ group, a tendency to reduced axial length and corresponding hyperopia with increasing duration of diabetes was found. However, in the DZ group of same sex the opposite tendency was found. Increasing lens thickness and decreasing anterior chamber depth with increasing duration of diabetes have been confirmed in this study.

Ocular factors in the incidence and progression of diabetic retinopathy

PURPOSE

To investigate the association of intraocular pressure (IOP), ocular perfusion pressure, and myopia with the incidence and progression of diabetic retinopathy.

METHODS

The design is a cohort study of a population-based sample (n = 1210) of persons with younger-onset diabetes (diagnosis was made before 30 years of age, and subjects were taking insulin) and a random sample (n = 1780) of persons with older-onset diabetes (diagnosis made after 30 years of age). Baseline and 4-year follow-up examinations were completed by 891 younger-onset and 987 older-onset persons. Retinopathy was graded from stereoscopic fundus photographs. Endpoints were incidence of retinopathy, progression of retinopathy, and progression to proliferative diabetic retinopathy (PDR). Ocular perfusion pressure was calculated from IOP and blood pressure. Myopia was a refractive error of -2 diopters or less.

RESULTS

In univariate analyses, ocular perfusion pressure was associated with incidence of retinopathy (P < 0.005), progression of retinopathy (P = 0.07), and progression to PDR (P < 0.001) in the younger-onset group but not in older-onset subjects taking or not taking insulin. Intraocular pressure and myopia were not associated with any endpoint in any group. Using logistic regression to control for covariates, ocular perfusion pressure was significantly associated only with incidence of retinopathy in younger-onset persons. The odds ratio for a 10-mmHg increase in ocular perfusion pressure was 2.13 (95% confidence interval, 1.30-3.50). Also, myopia was protective for progression to PDR in younger-onset persons with an odds ratio of 0.40 (95% confidence interval, 0.18-0.86).

CONCLUSIONS

These results suggest that pressure phenomena may be related to the development of retinopathy in younger-onset persons. This would have implications for treatments affecting both IOP and blood pressure.

Pathogenesis of diabetic retinopathy--the missing link?

Release of angiogenic factors in response to the ischaemic retina is currently the most favoured hypothesis for the pathogenesis of proliferative diabetic retinopathy. Reducing the stimulus for angiogenesis by destroying the ischaemic retina also forms the basis of the most effective treatment of diabetic retinopathy by photocoagulation. Though ischaemia is undoubtedly important for neovascularization, there is recent evidence which cast doubts on ischemia being the sole mechanism for diabetic retinopathy. Many clinical observations viz. the protective effects of glaucoma, myopia, unilateral carotid stenosis on diabetic retinopathy; and its worsening after cataract extraction are not adequately explained by the present hypothesis. Moreover, the recent in vitro culture studies on retinal pigment epithelial cells have suggested an alternative explanation for the effectiveness of photocoagulation in proliferative diabetic retinopathy. Furthermore, hyperglycemia has been strongly correlated with the incidence and progression of diabetic retinopathy, but has only been indirectly indicted in its pathogenesis. These facts can be integrated into a more plausible hypothesis for the pathogenesis of diabetic retinopathy. It is hypothesized that a relative reduction in intra-ocular pressure caused by persistent or intermittent hyperglycemia may be the missing link that induces certain morphological changes in the retinal pigment epithelium. These changes, in addition to the ischaemic retina, may be important for the pathogenesis of diabetic retinopathy. Such a hypothesis also explains most of the hitherto unexplained features of diabetic retinopathy.

Asymmetric retinopathy in patients with diabetes mellitus

We reviewed retrospectively the records of 57 diabetic patients with asymmetric retinopathy persisting for two years or more (mean, 4.8 years) to identify intraocular risk and protective factors for the development of proliferative retinopathy. For each patient in this series, the more severely affected eye had proliferative retinopathy and the fellow eye had either background diabetic retinopathy or no retinopathy. Branch vein occlusion (P = .016) was identified as a statistically significant risk factor for proliferative retinopathy and chorioretinal scarring (P = .031) was found to be a statistically significant protective intraocular factor. In 34 patients with long-standing asymmetric retinopathy, no intraocular risk or protective factors were identified.

Proteinuria and blood glucose levels in a population with diabetic retinopathy

In a population-based study of all insulin-treated diabetic patients on the Swedish island of Gotland, we compared the prevalence and severity of retinopathy with those of nephropathy as measured by proteinuria and serum creatinine levels. Of 365 diabetic patients, 66 (18%) had proteinuria. Of these 66, 39 (59%) had retinopathy. Proteinuria and serum creatinine correlated with increasing severity of retinopathy (P less than .001). Of 47 patients with proliferative retinopathy, 19 (40%) had proteinuria. Of 124 patients with retinopathy of other grades of severity, 20 (16%) had proteinuria. Visual acuity in the best eye was negatively correlated to proteinuria, which was present in 17 of 203 (8.4%) patients with a visual acuity of 20/20, compared with eight of 15 (53%) of those with a visual acuity of 20/200 or less. Blood glucose, determined two hours postprandially, was satisfactory (less than 10 mmol/l) in 162 patients (44%), unsatisfactory (10 to 14 mmol/l) in 89 (24%), and poorly regulated (greater than 14 mmol/l) in 114 (31%). Increasing mean blood glucose correlated to retinopathy (P less than .05).

Modern cataract surgery in a highly myopic population

A retrospective series of 117 highly myopic eyes with extracapsular cataract extractions and posterior chamber lens implants is presented. The results are analysed with reference to the current understanding of the complications anticipated. Of particular note is the use of low-powered posteriorly vaulted posterior chamber implants, with and without primary posterior capsulotomy. The results show a low retinal detachment rate (one eye, mean follow-up 12 months); low induced astigmatism (average 0.86 D); low myopic postoperative refraction (median -1.0 D); and high patient satisfaction.

Influence of HLA-DR phenotype and myopia on the risk of nonproliferative and proliferative diabetic retinopathy

The relationship between HLA-DR phenotype, refractive error, and risk of both nonproliferative and proliferative diabetic retinopathy was studied among 227 insulin-dependent diabetics participating in a case-control study of diabetic retinopathy. In the absence of myopia, risk of both proliferative and nonproliferative diabetic retinopathy was increased for HLA-DR phenotypes 4/0, 3/0, and X/X (HLA susceptible) compared to HLA-DR phenotypes 3/4, 3/X, and 4/X (HLA nonsusceptible). Odds ratios equalled 11.8 and 7.4 respectively. In the presence of myopia this increased risk associated with HLA status was abolished. Myopia decreased the risk of proliferative and nonproliferative diabetic retinopathy among HLA-susceptible individuals, odds ratio equalled .09 and .09, but had no protective influence among HLA-nonsusceptible individuals.

Multiple factors in the prediction of risk of proliferative diabetic retinopathy

To identify risk factors for the development of proliferative diabetic retinopathy, we compared 111 patients with longstanding insulin-dependent diabetes who had proliferative retinopathy (cases) with 81 patients with diabetes of similar duration (an average of 26 years) who did not have proliferative diabetic retinopathy (controls). The cases had diabetes that was more difficult to manage, as evidenced by their more frequent blood sugar levels above 200 mg per deciliter (11 mmol per liter) on routine clinic visits (odds ratio, 1.6 for each increment of 10 per cent in the relative frequency), and they expended less effort in managing their diabetes, as indicated by their less frequent testing of urine for sugar (odds ratio, 0.3). Among those who did not have myopia, the cases also had an excess of the HLA-DR phenotypes 4/0, 3/0, or X/X (odds ratio, 10.0). Among those with myopia, these phenotypes did not carry an increased risk of proliferative retinopathy. These results support a multifactorial model for the development of proliferative diabetic retinopathy; however, the mechanisms of action of the identified factors remain unknown.

Diabetic retinopathy in visual deprivation. A case report

A case of asymmetric retinal involvement in a diabetic patient who has long been exposed to visual deprivation on one eye is described. The question implied by this condition is if a relationship could exist between the distinct exposure of each eye to different visual excitations, and the outcome of the different retinal diabetic involvement. The possibility that the retina in a resting state might be less prone to develop diabetic retinopathy than usual, and a possible functional hypothesis on the pathogenesis of this diabetic complication, are questioned.