Diabetic Retinopathy: Focus on Minority Populations

Diabetic retinopathy is a major cause of blindness in the United States. With rise of the epidemic of obesity and diabetes in the USA and around the globe, serious and common diabetic complications are evolving as a major public health problem, particularly among minority populations. These populations are disproportionately affected by diabetes and 2-3 times more likely to develop visually signifi cant complications. In this highly illustrated review article, we discuss the diabetic epidemic, highlighting the biology and the pathophysiologic mechanisms of this disorder on the anatomy of the eye. We also discuss the risk factors and the implications for minority populations. For the health care providers, we provide cutting edge information and imminently relevant information to help evaluate, manage, and know when to refer their patients to a specialist in ophthalmology to quell the tide of the epidemic. Review Article Diabetic Retinopathy: Focus on Minority Populations Arpine Barsegian1, Boleslav Kotlyar1, Justin Lee2, Moro O Salifu2 and Samy I McFarlane2* 1Department of Ophthalmology, SUNY-Downstate Medical Center and Kings County Hospital, Brooklyn, NY 11203, USA 2Department of Medicine, SUNY-Downstate Medical Center and Kings County Hospital, Brooklyn, NY 11203, USA Dates: Received: 08 August, 2017; Accepted: 09 November, 2017; Published: 11 November, 2017 *Corresponding author: Samy I. McFarlane, MD, MPH, MBA, FACP, Distinguished Teaching Professor of Medicine and Endocrinology State University of New York-Downstate Medical Center, 450 Clarkson Avenue, Box 50, Brooklyn, New York, 11203, Tel: 718-270-3711; Fax: 718-270-6358; E-mail: https://www.peertechz.com


Introduction
Diabetes Mellitus types 1 and 2 can cause diabetic retinopathy and blindness. Diabetic retinopathy (DR) is the 3 rd leading source of overall blindness in the United States and the leading cause of new cases of legal blindness in working age Americans [1]. The total number of individuals worldwide with diabetes is expected to increase from 171 million in 2000 to 366 million in 2030 [2], and the concurrent rise in preventable visual dysfunction and quality adjusted life years is lamentable.
In the United States, an estimated 25.6 million people aged 20 or older have either been diagnosed or remain undiagnosed with diabetes mellitus (11% of people in this age group) [3].
The prevalence rate for retinopathy for all adults with diabetes over 40 years of age in the United States is 28.5% (4.2 million people), and worldwide it has been estimated at 34.6% (93 million people). Assuming similar prevalence of diabetes mellitus, 6 million Americans are projected to have diabetic retinopathy by the year 2020 [4,5].
The diabetes epidemic already disproportionately affects racial and ethnic minorities, who have higher rates of macro and microvascular complications of diabetes [6], and are more susceptible to known risk factors of DR [7][8][9]. The same groups may undergo screening less often than white patients for a variety of factors (including patient, provider, and system factors [10]); for this reason, it is important to understand the classifi cation scheme for both categories of DR, as each stage of disease necessitates a different screening, monitoring, and possibly, treatment schedule [11]. As the minority fraction of the total US population continues to grow, this will continue to evolve into a larger problem.

Biology
Diabetic retinopathy occurs through injury to the retinal microvasculature due to extended exposure to the metabolic modifi cations caused by diabetes. Without appropriate intervention, it progresses in a predictable fashion from mild to more severe stages. Non-proliferative diabetic retinopathy (NPDR) is characterized by superfi cial and deep retinal hemorrhages, microaneurysms, venous dilation, and cottonwool spots (signs of focal retinal nerve fi ber layer ischemia). and leading to persistent eye pressure elevations, otherwise known as neovascular glaucoma. Cataracts also occur at an earlier age, 2-5 times more frequently in patient with diabetes, compounding the issue of signifi cant visual decline [12,13].

Pathogenesis
The pathogenesis of diabetic retinopathy is thought to entail three factors: neovascularization caused by damage to blood vessels, infl ammation, and platelet abnormalities.
Diabetic retinopathy is characterized as a microangiopathy and its development is due to glucose injury to the microvasculature leading to increased permeability of the blood retinal barrier, with loss of pericytes and endothelial cells, and eventual occlusion of capillaries, vascular basement membrane thickening, and retinal neuronal and glial damage [14] ( Figure   1). In response to this injury and to relative focal areas of retinal ischemia, the retina and retinal pigment epithelium exude vasoproliferative factors, such as vascular endothelial growth factor (VEGF), which result in neovascularization. These effects also contribute to the formation of diabetic macular edema (DME). DME is the most common cause of vision loss in patients suffering from diabetes [15] Diabetic retinopathy also has an infl ammatory element that is caused by macrophage and complement activation. Deposition of complement factors 5b-9 and fi bronectin have been described in the connective tissue matrix of the choriocapillaris.
Complement activation causes increased neutrophil activation, and eventually endothelial injury. Damaged capillaries leak lipids and proteins, and the complement cascade infl uences nearby cells, causing a thickened choriocapillaris and Bruch's membrane. Therefore, infl ammation also exacerbates macular edema; in fact, it is believed that long-standing DME may be related to infl ammation more than to neovascularization and responds signifi cantly to steroids [22].
Lastly, platelet abnormalities and increased viscosity also lead to focal capillary occlusion and focal regions of ischemia in the retina, further aggravating diabetic retinopathy.    and very severe. In general, treatment of NPDR consists of managing systemic risk factors, and improving blood glucose control, while maintaining close follow-up with ophthalmology to catch progression of disease into the proliferative stage. The Diabetes Control and Complications Trial (DCCT) showed that patients with type 1 diabetes who tightly controlled their blood glucose level (with four measurements daily) had a 76% reduction in the rate of development of any retinopathy, and a 54% reduction in progression of pre-existing retinopathy [23]. In fact, DCCT showed that for every 1% decrease in HbA1C level, the incidence of DR decreased by 28%. The Epidemiology of Diabetes Intervention and Complications observational study of the DCCT cohort showed continued benefi t for the tight glucose control cohort over conventional treatment (once daily blood glucose measurement) despite normalization of glucose control even after seven years of follow-up [24]. Intensive management of glycemic level and blood pressure in people with type 2 diabetes was explored in the 1998 United Kingdom Prospective Diabetes Study (UKPDS), revealing 21% reduction in the one year rate of progression of retinopathy [25]; this highlights the decrease in need for intensive treatment of diabetic retinopathy. There was no evidence of glycemic threshold for any of the microvascular complications above normal glucose levels (HbA1C > 6.2%).

The Classifi cation and Treatment of Diabetic Retinopathy
Proliferative Diabetic Retinopathy is defi ned as any of the following: retinal neovascularization of the disc (within 1 disc diameter of the optic disc), neovascularization elsewhere (further than 1 disc diameter from the optic disc), vitreous hemorrhage, and/or fi brous tissue proliferation. High-risk PDR is defi ned as at least 1/3 disc area of disc neovascularization  • Cotton wool spots commonly present.

Severe NPDR
Review in 4 months. PDR in up to 50%. High risk PDR in up to 15% within a year.
• Signifi cant venous beading in 2 or more quadrants.
• Moderate IRMA in 1 or more quadrants.

Very Severe NPDR
Review in 2-3 months. High risk PDR in up to 45% within a year. Two or more of the criteria for severe NPDR.

Mild-moderate PDR
Consider treatment according to severity of signs, stability, systemic factors, patient reliability of attendance for review. If not treated review in up to 2 months.
New vessels on the disc (NVD) or new vessels elsewhere (NVE) but extent insuffi cient to meet high-risk criteria.

High Risk PDR
Treatment advised -see text. Should be performed immediately when possible, especially if symptomatic presentation with good retinal view.
DOI: http://dx.doi.org/10.17352/ijcem.000027 was 16.3% in untreated eyes, but only 6.4% in treated eyes, showing that photocoagulation reduced the 2 year risk of blindness by about 60%. On the basis of the high statistical signifi cance, the study design was changed more than 3 years prior to the planned termination date of the DRS, and photocoagulation was used on initially untreated eyes which at that time point or anytime in the future would fulfi ll the characteristics of what is now called high risk PDR, as defi ned above. Furthermore, although the principal goal of PRP was to prevent visual loss, not to improve vision, some eyes showed evidence of recovery (vision improving to better than 5/200). The percentage of eyes with evidence of recovery at post-laser month 4, 8, and 12 were 28.6%, 12.2%, and 7.7% in untreated eyes, compared to 48.8%, 28.6%, and 20.8% in treated eyes, respectively. This seems to show that visual acuity recovered more frequently in treated eyes [26]. Benefi ts of treatment of proliferative diabetic retinopathy were also illustrated by ETDRS, which showed that after 7 years of follow-up, 25% of eyes that received PRP developed high risk PDR as compared to 75% in which PRP was deferred until high risk PDR features developed.
PRP is achieved through 360 degree photocoagulation of ischemic retina with a few thousand noncontiguous small burns, generally peripheral to the major retinal blood vessels. Laser energy is absorbed and converted to thermal energy causing denaturation of tissue proteins leading to local retinal cell death and coagulative necrosis. Over time, these damaged tissues form heavily pigmented laser scars at the level of the retinal pigment epithelium. By destroying the largely unused, ischemic extramacular retina, PRP reduces total production of vasoproliferative factors in the eye and the impetus for neovascularization [27]. As with any treatment, the benefi ts must always be balanced against the risk of therapy. Currently, most commonly followed treatment paradigms maintain close patient follow-up with systemic diabetic control, and reserve the use of PRP until eyes reach proliferative or even high-risk PDR stages due to the laser's damaging permanent effects on peripheral vision, overall decrease in light sensitivity (affecting night vision most notably), and similar effects on fi ne color vision differentiation. The procedure itself may also be uncomfortable and is usually broken up into multiple sessions until suffi cient areas of retina are covered with laser marks. Other common therapies directly target and aim to decrease the level of vasoproliferative factors in the eyes, most signifi cantly with the anti-VEGF class of intravitreal injectable medicines, and corticosteroids. Despite the demonstrated improvements in vision and degree of retinopathy, the intravitreal injections frequently require repeat administration, as often as every month, increasing the burden on both patients and healthcare systems.
When diabetic retinopathy damages the macula, it is called diabetic maculopathy. The vascular seepage and eventual swelling of the macula is called diabetic macular edema. Although DME can develop at any stage during the progression of retinopathy, it is most commonly seen during the later phases, after advanced vascular and neural injury [28,29]. This maculopathy may be further classifi ed as central or noncentral, depending on the involvement of the fovea; focal or diffuse, depending on the extent of the edema, and ischemic or non-ischemic, depending on the extent of occlusion of the perifoveal capillary network [14]. Additionally, clinically signifi cant macular edema (CSME), is a distinct entity that requires particularly aggressive treatment. It was defi ned by the ETDRS as one or more of the following: retinal thickening within 500 microns of the center of the macula, exudates within 500 microns of the center of the macula (if associated with retinal thickening, the thickening itself may be outside the 500 microns), or retinal thickening 1 disc area (1500 microns) or larger, any part of which is within 1 disc diameter of the center of the macula [11]. Furthermore, diabetic maculopathy may be named tractional or non-tractional, depending on whether traction from an incompletely detached posterior hyaloid or pre-retinal neovascularization is involved.

Diabetic Retinopathy in Minorities
Many studies have investigated disparities in the incidence, prevalence, screening, and treatment of diabetic retinopathy in minorities. In the Salisbury Eye evaluation, African Americans  [30][31][32]. Furthermore, even with limited studies, the reported prevalence of diabetic retinopathy in some Native American tribes is as high as 45.3% [30,33,34].
The Hispanic population makes up the largest ethnic or racial minority in the United States, and is growing as a fraction of the US total. As of July 1, 2015, there were 56.6 million Americans of Hispanic descent, which constituted 17.6% of the nation's total population [35]. For adults over 18 years of age, the age adjusted prevalence of diagnosed diabetes in 2006 was 10.5% for Hispanic or Latino individuals compared with 6.8% for non-Hispanic whites [36]. Over the four-year enrollment period, 34% of Latinos who had diabetes developed DR, with Latinos aged 40 to 59 having the highest rate. Though increasing age did not play a role, Latinos with a longer duration of diabetes were more likely to develop the disease. In fact, 42% of Latinos with diabetes for more than 15 years developed diabetic retinopathy. Also, among participants who had diabetic retinopathy at the beginning of the study, 39% showed worsening of the disease four years later [37].
Proyecto VER (Vision Evaluation and Research) also highlighted these disparities; this was a diabetic retinopathy prevalence study of 4774 Hispanic adults over the age of 40 living in Arizona; the prevalence of diabetes in this population was 22%, with 15% of these being made up of patients undiagnosed prior to study enrollment. Of the newly diagnosed patients, 23% had some retinopathy, with 9% already in moderate to severe stages. The prevalence of diabetic retinopathy in Hispanics was 48%, which was almost twice that of Caucasians [38], and very similar to the 46.9% prevalence rate seen in LALES.
The disparities in prevalence of DR may be associated with delayed diagnosis, access to care, comorbidities such as hypertension, and inequality of screening for diabetic retinopathy. Not surprisingly, inadequate access to healthcare in low socioeconomic populations is frequently cited as a reason for health-related disparities in minority groups. For example, the LALES showed that Latinos with less education and without health insurance were less probable to be screened than those with more education and health insurance [39].
Interestingly, the severity of DR, rather than its presence, was found to aggregate in type 2 diabetes affl icted families in a study of Mexican-American siblings of individuals with DR [40]; this implies a possible genetic component to the severity of DR in Mexican-Americans [41].

Risk Factors
Duration of diabetes is a major risk factor associated with development of diabetic retinopathy. In the 1370 patients presumed to have type 2 diabetes, 40% of those taking insulin and 24% of those not taking insulin had retinopathy, when known duration of diabetes was less than 5 years. These rates increased to 84% and 53%, respectively, when the duration of diabetes had been documented for up to 19 years. PDR developed in 2% of type 2 patients who had diabetes less than 5 years, and in 25% of patients who had diabetes for 25 years or more.
The rate of development of diabetic retinopathy in a patient with no previous retinopathy on exam one year prior is reported to be between 5 and 10%.
LALES and Proyecto VER showed that 18% of patients with diabetes of more than 15 years duration had PDR, with no difference in percentage of PDR in type 1 vs type 2 diabetes [34,38].

Risk Factors for Proliferative Diabetic Retinopathy in African Americans and Latinos
In the US, African Americans not only have a high prevalence of type 2 diabetes, but they also seem to be at high risk for consequent microvascular disease, including nephropathy and retinopathy [47]. Some studies have concluded that African Americans have an increased risk of developing DR when compared with Caucasians [7,48-51]. As an example, the prevalence of moderate NPDR or worse was elevated for African American veterans over Caucasian veterans in the Veterans Affairs Diabetes Trial of type 2 diabetes even after adjusting for clinical risk factors [51].
In general, the following risk factors have been consistently found to be associated with DR: longer diabetes duration, hyperglycemia, hyperlipidemia, and hypertension [52]. In regards to hyperlipidemia, there is evidence that total cholesterol and low-density lipoprotein cholesterol are associated with the presence of hard exudates, a fi nding in the primary stages of DR; furthermore, the severity of DR is inversely associated with systemic apolipoprotein A1, and positively associated with ApoB and the ApoB-to-ApoA1 ratio; thus, the role of lipid-lowering medication in the control of DR should not be underestimated [53]. Risk factors for progression to proliferative diabetic retinopathy are especially valuable for selected subsets, such as African Americans, due to the risk of life-changing vision loss in these patients. A prospective, non-interventional, cross sectional case control study by Penman et al. analyzed 380 African Americans with type 2 diabetes [54]. PDR was associated with increased systolic blood pressure (OR 1.65, P<0.001), insulin use (OR 6.65, P<0.001), and a prolonged duration of diabetes (odds ratio OR 1.62, P<0.001); surprisingly, HbA1c was not a signifi cant risk factor in the multivariate analysis, though it did achieve statistical signifi cance in the univariate analysis. This exact same result was seen in a parallel PDR study in a Latino patient population [55]. The correlation between HbA1c and DR may decline with more severe retinopathy and explain differences in results of this study compared to UKPDS and DCCT. One possible reason for this is that patients with PDR may become inspired to improve their glycemic control, lowering their HbA1c which is no longer refl ective of their glycemic control for most of the duration of their diabetes. There is also contradictory evidence as to whether retinopathy starts to appear at lower HbA1c levels in African Americans [56,57]. This may be because these population-based trials on cultural changes in HbA1c have concentrated on prevalence of any DR, as opposed to advanced DR. It is still unclear as to whether or not these ethnic differences infl uence the relationship between HbA1c and PDR in African-Americans.
The association with insulin may be due to the fact that participants with poorly controlled diabetes are more likely to use more insulin. It is important to note that although HbA1c was not found to be signifi cant in the multivariate analysis, the HbA1c was based on a 1 time draw of blood, not on the average levels over an extended period of time. In this Penman cohort, African Americans had a 65% increased chance of progressing to PDR for every 10 mmHg increase in systolic blood pressure. This further highlights the need for patient education among African Americans regarding the value of hypertension management in preventing diabetes related visual loss. Importantly, prospective randomized controlled trials in patients with type 2 diabetes have demonstrated the advantage of blood pressure control on development of retinopathy in general [25,58]. Even though these trials were carried out in mostly Caucasian patients, one study included 30% non-white patients, including African Americans and other non-white ethnic minorities [59]. Another study performed in African Americans with type 2 diabetes also noted that hypertension, renal disease, and poor glycemic control are associated with PDR [59]. The following factors have not been noted to infl uence progression of PDR: age, sex, diastolic blood pressure, serum lipid levels, BMI, waist circumference, or smoking status. Importantly, randomized clinical trials in patients with type 2 diabetes have established that glycemic control is vital to decreasing the risk of DR development [25,58].
A parallel prospective case control study conducted in a Latino American patient population by Nittala et al. also found the following risk factors to be associated with an increased risk of PDR in a multivariate analysis (p<0.05): male gender, insulin treatment, high creatinine levels, and hypertension. Surprisingly, obesity, total cholesterol, and HbA1c were not associated with PDR; if anything, obese patients were less likely to have PDR. Those with a history of smoking also demonstrated a decreased risk of developing PDR, although the risk of PDR was greater in those who smoked a higher number of cigarettes daily. Patients with a greater than 25 year diagnosis of DM were at increased risk when compared to patients with a 10 to 15 year diagnosis of diabetes mellitus [55].

The Importance of Blood Pressure
Many studies have shown the protective infl uences of blood pressure control on the progression of diabetic retinopathy. The United Kingdom Prospective Diabetes Study showed that patients with tighter control of blood pressure were much less likely to experience advancement of their DR [60,61]. In addition, the META-EYE study demonstrated that patients with normal blood pressure were less likely to demonstrate DR development compared to those with hypertension (BP >140/90 mmHg) or those already taking anti-hypertensive drugs [52]. A study by Silva et al. even suggested that episodes of systemic hypertension can aggravate the initiation and development of retinopathy [62]. For this reason, patients with diabetes may benefi t from the earlier use of anti-hypertensive medications such as angiotensin-converting enzyme inhibitors and angiotensin-2 receptor blockers [63]. Hypertension as a risk factor in diabetic retinopathy progression was likewise noted in studies specifi cally looking at African American and Hispanic-American populations [54,55]. Thus, prompt and aggressive treatment of hypertension likely helps in management of diabetic retinopathy.

Macular Edema in Minorities
A comparative study between ethnic groups showed that Hispanic and Latino Americans have higher risks of clinically signifi cant macular edema [4]. Prevalence of CSME was 8.63% DOI: http://dx.doi.org/10.17352/ijcem.000027 in the Beaver Dam Eye Study, twice that reported in the white population [64][65][66]. LALES reported over 10% of participants with diabetes had macular edema, 60% of these warranting laser therapy.
Similarly, the Veterans Affair Diabetes Trial reported that 15.6% of African Americans had CSME, compared to 6.3% of Non-Hispanic Whites [51] and Multi-Ethnic Study of Atherosclerosis showed that the risk of CSME is approximately 5 times higher in African-Americans than in white patients (11.1 % vs 2.7%) [9]. It is unclear why minority populations have a higher risk of CSME; it may be due to delayed detection and screening, varieties in the pathogenesis of diabetic retinopathy in these patients, or simply a vulnerability to CSME. Regardless, given the increased risk of permanent vision loss in these patients, it is important to diagnose and treat them in a timely fashion. Hispanics, showed statistically signifi cant decreased rates of eye examinations [82].

Disparities in Diabetic Retinopathy Screening
CDC data for 2010 showed that 64% of both African Americans and Non-Hispanic whites with diabetes had received a dilated eye exam in the past year, as compared to 55% of Hispanic subjects [83]. Sloan and Orr have both noted that African Americans are less probable to be screened for DR than whites [77,84]. A recent observational study also showed lower rates of dilated eye examinations among ethnic minorities compared with non-Hispanic white patients with diabetes [85,86].

Barriers to Screening
Patient factors: These include a lack of understanding of diabetic retinopathy and the importance and accessibility to treatment [78,80,87]. The following have all been mentioned as obstacles to routine screening: economic issues, spirituality, absence of time and transportation, and no desire to make follow-up appointments [26,78,80,84,[87][88][89]. LALES reported that patients with lower socioeconomic status were at higher risk of not obtaining preventive care; those with no health care were twice as likely to not have had an eye exam or a visit to the doctor in the prior year [34]. In addition, health literacy, the extent to which patients can receive, process, and comprehend the simple health information and services they require to make proper health decisions [90], has been demonstrated to affect diabetes management, results, and knowledge [91,92]. Language barriers for non-English-speaking Hispanic patients, lack of access to specialty physicians, and a lack of health insurance have also been described as impediments to screening [82]. Other factors that may play a role are rejection of services, lack of timely care, and a general distrust of the medical system [79,82]. Walker et al. conducted a cross sectional study through telephone interview to assess the knowledge and health beliefs preventing African-Americans from undergoing regular screening for DR. In this patient group, "retinopathy" had the lowest level of perceived risk (30%), and only 21% of the sample believed there were effi cacious treatments for retinopathy. 87% believed that "diabetic eye problems have symptoms." 36% of the sample had heard of retinopathy, and of these, only 8% described it accurately. Obstacles mentioned by patients included: fear, spirituality (faith and hope), economic or logistical factors, and priorities [80].
Interventions concentrated on patients can help improve diabetic retinopathy screening. Culturally specifi c screening efforts [93], patient reminders [94], and educating patients about the importance of DR screening [80,87] have all demonstrated positive effect in some settings [78,80,87,89,[94][95][96]. In addition, personalized follow-up and patient reminders, and diabetes management programs that enhance self-management skills can all lead to improved screening rates. Language barriers and health literacy can be addressed by interventions to mend any disparities in patient-provider communication [92,[97][98][99].
Provider factors: These include insuffi cient patient education [79,80], patient-physician interaction [87], and increase in contact may allow more time for proper education and interaction with the patient [97,101]. Even an increase of 1 monthly visit to the PCP escalated the odds of screening by 28% [10].
Provider-level interventions such as educating primary care providers about screening guidelines and diabetic retinopathy may improve screening rates [102]. Also, training to aid providers in increasing their quality of screening and helping them track their adherence to guidelines may also be effi cacious [103,104]. In addition, cultural competency can also play a role in increasing the number of ethnic minority patients who are screened [105,106]. System-level interventions can be undertaken to improve screening rates as well. These include patient registries and diabetes collaboratives to improve the quality of diabetes care [102][103][104]107], provider reminders (such as prompts in electronic medical records) [108,109], to aid providers in tracking which patients have missed screening appointments, population-based screening programs [110], diabetes management programs, including those that have been undertaken by HMOs [93,111,112], and community based diabetes management and DR screening programs [93]. Telemedicine [113,114], mobile screening [114][115][116][117][118][119][120][121], and the placement of diabetic retinopathy screening equipment in primary care offi ces may also help decrease the number of cases of DR that progress to visionthreatening complications; this is particularly valid in populations with limited health care access, including rural Native American tribes and various other rural communities. Importantly, retinal imaging in primary care offi ces has been quite successful in eradicating some of the obstacles that impede diabetic patients from undergoing diabetic retinopathy screening [113,122,123,125,126]. Patients with diabetic retinopathy (or ungradeable disease) noted on photographs may be referred to ophthalmologists for further evaluation and treatment; this may eventually lower the number of overall screening referrals to ophthalmology for disease not warranting treatment, thus allowing more resources for evaluation of patients with ungradeable pathology on photos or treatment of those with clearly noted disease [124]. The ubiquitous nature of smartphones and their ever increasing quality of cameras also opens new avenues for screening without the need for expensive equipment. Building databases that integrate machine learning algorithms can further decrease the amount of photos and exams that need to be performed by an ophthalmologist [127]. International efforts to combat vision loss from diabetic retinopathy are beginning to make a difference. Between 2003 and 2008, England and Wales introduced nationwide diabetic retinopathy screening services, which annually screen almost 2 million people. A comparison of reasons for blindness certifi cations in England and Wales in working age adults for 2009-2010 showed diabetic retinopathy dropping to second place, for the fi rst time in over fi fty years [128].

Conclusion
Diabetic retinopathy is a signifi cant public health issue that is projected to only increase in impact in the coming years. Minority populations are particularly vulnerable to macro and microvascular complications of diabetes, particularly retinopathy. Their vulnerability combined with insuffi cient screening is a recipe for many vision-threatening complications. The authors seek to raise awareness and provide a review of many aspects of diabetic retinopathy with reminders of the social implications of DR, especially in regard to minority populations, focusing on pathogenesis, risk factors, classifi cation, and treatment options for this condition. With greater awareness, increased screening, and encouragement, we are hopeful that diabetic retinopathy will no longer be the number one cause of new cases of blindness in adults in the United States.