**2. Magnitude of blindness due to diabetic eye disease**

Reports on the vision loss attributable to diabetes in the 1980s and 1990s vary greatly in their methodology—some have derived clinical information from hospital series, and others have reviewed the registry forms of certified disabled persons

from the records of societies of the blind; there are reviews on patients referred to low vision rehabilitation centers and finally some present data from populationbased observational studies. Each source has its shortcomings. Definitions in registry databases depend on the national disability legislation and often differ from the categories for blindness and low vision in the International Classification of Diseases (ICD)—Ninth and Tenth Revisions—that were in use at that time. Many authors stress on the difficult task of identifying the onset and the main cause of vision loss in diabetic patients with multiple ophthalmic comorbidities, especially in their final stages. For a long period, well into the 1980s, non-ophthalmic professionals were allowed to certify blind persons for registration that raises reservations regarding the accuracy of the cause. A common concern is the inability to determine the number of underreported and unregistered diabetic persons with vision loss as registration is voluntary, and it depends on clinical, social, and cultural factors; many authors have noted a rise in the incidence rates of DR with the arrival of more consultants in the area, after upgrade in the financial benefits and social support for legally blind or following campaigns to improve public awareness and reduce stigmatization.

Hospital series analyze clinical data collected in specialized diabetic units over long periods in a consistent manner and provide reliable estimate on the severity and progression of vision loss; however, extrapolations of their findings for the population beyond their urban region are seldom possible.

Publications from the UK, Denmark, and Sweden demonstrate a decrease in the incidence of new blindness from DR in the 1980s and 1990s [2–5]; however it remained unchanged between 1967 and 1991 in Italy and Avon, UK [6, 7]. In their review on the trends in blindness in Singapore, See et al. [8] present a sharp increase in the prevalence of diabetes in the age between 15 and 69 from 1.99% in 1975 to 8.6% in 1992 and a rise in the proportion of blindness from diabetic complications from 5% in the 1950s to 47.3% in the 1980s.

Global data on blindness [9, 10], a review report of the WHO programme for prevention of blindness, summarized available information from population-based assessment of visual loss and its causes. DR was not among the four major causes for blindness and low vision globally and ranked between the first and fourth only in Western Europe, the former socialist economies of Europe, North America, Latin America, and Oceania. The authors note the lack of relevant epidemiological data for some specific causes of blindness; however they emphasize that this disease is "generally recognized to be the leading cause of blindness among those in working age in developed countries and rapidly emerging in urban areas of the developing world."

An update on the estimates of global and regional blindness and low vision was published in 2004 presenting results of new population-based studies and other sources of information. The proportion of DR rose to 4.8% globally, and it was ranked fifth as a cause of blindness, with significant regional variations reaching 17% for North America and Australia, 17–15% in Europe, and 3–7% in the rest of the world where the majority of vision loss was due to cataract, glaucoma, and corneal opacities as complications of trachoma [11].

A meta-analysis of all available population-based studies performed worldwide from 1990 to 2010 [12] estimated that 833,690 people were blind and 3.7 million were visually impaired globally in 2010 due to DR. The highest number of blind diabetic patients was in South Asia, 295,000; North Africa/Middle East, 108,000; Eastern sub-Saharan Africa, 50,000; and Western sub-Saharan Africa, 66,000. The age-standardized prevalence of blindness from diabetic retinopathy in people over the age of 50 years was 0.05% globally, reaching 0.19% in Western

**227**

*Diabetic Retinopathy and Blindness: An Epidemiological Overview*

sub-Saharan Africa, 0.16% in North Africa/Middle East, 0.14% in Eastern sub-Saharan Africa, and 0.12% in Southeast and East Asia. Moderate and severe vision impairment due to DR affected 3174 million, and the largest number of them were in South Asia, 1450 million, followed by North Africa/Middle East, 336,000; Eastern Asia, 279,000; Western Europe, 225,000; Western sub-Saharan Africa, 193,000; Eastern Europe, 166,000; Eastern sub-Saharan Africa, 128,000; and Central Latin America, 109,000. The age-standardized prevalence of moderate and severe vision impairment due to DR in people over the age of 50 years was 1.9% globally and was highest—0.51%—in South Asia, 0.50% in Western sub-Saharan Africa, 0.44% in North Africa/Middle East, 0.36% in Southern Latin America, 0.33% in Central sub-Saharan Africa, 0.32% in Andean Latin America, 0.31% in Eastern sub-Saharan Africa, and 0.26% in Oceania [13]. From 1990 to 2010, the number of blind diabetics had increased by 27% and those with visual impairment by 64% globally. Globally, age-standardized prevalence of blindness and vision impairment of diabetics over the age of 50 years was relatively unchanged in the course of these 20 years. It reduced by half in high-income Pacific Asia, Europe, Australasia, and North America; however it remained high in large, densely populated regions of Africa and Asia with rapidly increasing

A continuation of this systematic review and meta-analysis of data from 261 population-based studies published till 2014 [14] observed that while blindness to all causes reduced between 1990 and 2015, DR was the only one with prevalence that increased by 7.7% for blindness and by 28.6% for impairment. The proportion of vision loss attributable to diabetes ranked seventh in 2015 at 1.06% (0.15–2.38) globally and was highest in Eastern Europe, 4.91%, followed by Australasia, high-income North America, high-income Pacific Asia, and Central Asia. The contribution of DR to moderate and severe vision impairment was 1.30% (0.20–2.93) and reached 5.06% in Eastern Europe, followed by Australasia, high-income North America, high-income Pacific Asia, and Central Asia. The same regions were leading in the percentage of blindness and low vision due to DR for people over the age of 50 years. The age-standardized prevalence of blindness from DR across all ages was relatively low, in the range of 0.00–0.01 (0.00– 0.02), and was considerably higher for vision impairment, 0.03% (0.00–0.13), with Eastern Europe ranking first at 0.11%, Central Asia, 0.09%; Southern Latin America, 0.08%; and North Africa/Middle East and Australasia, 0.07%. The agestandardized prevalence of blindness of diabetics over the age of 50 was 0.02% (0.00–0.07) and was highest in North Africa/Middle East, Eastern Europe, and Central Asia. The age-standardized prevalence of low vision in the same age group was 0.13% (0.01–0.48), and the same regions were most affected. For the first time, this report presented data on the gender differences in the cause and magnitude of vision loss and demonstrated that the relative risk of blindness and vision impairment in diabetic women as compared to men was 2.52. The number of people with blindness due to diabetic retinopathy was estimated at 400,000 (0–1.5 million) and low vision 2.6 million (0.2 million—9.9 million), both almost doubled since 1990. The projections for diabetic complications for 2020 are for further increase, and the largest number of people are expected to reside in North Africa/Middle East, 73,000 blind and 4,480,000 with low vision; Eastern Europe, 47,000 blind and 362,000 with low vision; Western Europe, 46,000 blind and 422,000 with low vision; East Asia, 41,000 blind and 400,000 with low vision; and Southeast Asia, 30,000 blind and 216,000 with low vision. The authors point out that the prevalence of any DR and sight-threatening DR was similar in men and women, whereas their analysis suggested female preponderance for

*DOI: http://dx.doi.org/10.5772/intechopen.88756*

prevalence of diabetes.

*Visual Impairment and Blindness - What We Know and What We Have to Know*

from the records of societies of the blind; there are reviews on patients referred to low vision rehabilitation centers and finally some present data from populationbased observational studies. Each source has its shortcomings. Definitions in registry databases depend on the national disability legislation and often differ from the categories for blindness and low vision in the International Classification of Diseases (ICD)—Ninth and Tenth Revisions—that were in use at that time. Many authors stress on the difficult task of identifying the onset and the main cause of vision loss in diabetic patients with multiple ophthalmic comorbidities, especially in their final stages. For a long period, well into the 1980s, non-ophthalmic professionals were allowed to certify blind persons for registration that raises reservations regarding the accuracy of the cause. A common concern is the inability to determine the number of underreported and unregistered diabetic persons with vision loss as registration is voluntary, and it depends on clinical, social, and cultural factors; many authors have noted a rise in the incidence rates of DR with the arrival of more consultants in the area, after upgrade in the financial benefits and social support for legally blind or following campaigns to improve public awareness and reduce

Hospital series analyze clinical data collected in specialized diabetic units over long periods in a consistent manner and provide reliable estimate on the severity and progression of vision loss; however, extrapolations of their findings for the

Publications from the UK, Denmark, and Sweden demonstrate a decrease in the incidence of new blindness from DR in the 1980s and 1990s [2–5]; however it remained unchanged between 1967 and 1991 in Italy and Avon, UK [6, 7]. In their review on the trends in blindness in Singapore, See et al. [8] present a sharp increase in the prevalence of diabetes in the age between 15 and 69 from 1.99% in 1975 to 8.6% in 1992 and a rise in the proportion of blindness from diabetic complications

Global data on blindness [9, 10], a review report of the WHO programme for prevention of blindness, summarized available information from population-based assessment of visual loss and its causes. DR was not among the four major causes for blindness and low vision globally and ranked between the first and fourth only in Western Europe, the former socialist economies of Europe, North America, Latin America, and Oceania. The authors note the lack of relevant epidemiological data for some specific causes of blindness; however they emphasize that this disease is "generally recognized to be the leading cause of blindness among those in working age in developed countries and rapidly emerging in urban areas of the developing

An update on the estimates of global and regional blindness and low vision was published in 2004 presenting results of new population-based studies and other sources of information. The proportion of DR rose to 4.8% globally, and it was ranked fifth as a cause of blindness, with significant regional variations reaching 17% for North America and Australia, 17–15% in Europe, and 3–7% in the rest of the world where the majority of vision loss was due to cataract, glaucoma, and

A meta-analysis of all available population-based studies performed worldwide from 1990 to 2010 [12] estimated that 833,690 people were blind and 3.7 million were visually impaired globally in 2010 due to DR. The highest number of blind diabetic patients was in South Asia, 295,000; North Africa/Middle East, 108,000; Eastern sub-Saharan Africa, 50,000; and Western sub-Saharan Africa, 66,000. The age-standardized prevalence of blindness from diabetic retinopathy in people over the age of 50 years was 0.05% globally, reaching 0.19% in Western

population beyond their urban region are seldom possible.

from 5% in the 1950s to 47.3% in the 1980s.

corneal opacities as complications of trachoma [11].

**226**

world."

stigmatization.

sub-Saharan Africa, 0.16% in North Africa/Middle East, 0.14% in Eastern sub-Saharan Africa, and 0.12% in Southeast and East Asia. Moderate and severe vision impairment due to DR affected 3174 million, and the largest number of them were in South Asia, 1450 million, followed by North Africa/Middle East, 336,000; Eastern Asia, 279,000; Western Europe, 225,000; Western sub-Saharan Africa, 193,000; Eastern Europe, 166,000; Eastern sub-Saharan Africa, 128,000; and Central Latin America, 109,000. The age-standardized prevalence of moderate and severe vision impairment due to DR in people over the age of 50 years was 1.9% globally and was highest—0.51%—in South Asia, 0.50% in Western sub-Saharan Africa, 0.44% in North Africa/Middle East, 0.36% in Southern Latin America, 0.33% in Central sub-Saharan Africa, 0.32% in Andean Latin America, 0.31% in Eastern sub-Saharan Africa, and 0.26% in Oceania [13]. From 1990 to 2010, the number of blind diabetics had increased by 27% and those with visual impairment by 64% globally. Globally, age-standardized prevalence of blindness and vision impairment of diabetics over the age of 50 years was relatively unchanged in the course of these 20 years. It reduced by half in high-income Pacific Asia, Europe, Australasia, and North America; however it remained high in large, densely populated regions of Africa and Asia with rapidly increasing prevalence of diabetes.

A continuation of this systematic review and meta-analysis of data from 261 population-based studies published till 2014 [14] observed that while blindness to all causes reduced between 1990 and 2015, DR was the only one with prevalence that increased by 7.7% for blindness and by 28.6% for impairment. The proportion of vision loss attributable to diabetes ranked seventh in 2015 at 1.06% (0.15–2.38) globally and was highest in Eastern Europe, 4.91%, followed by Australasia, high-income North America, high-income Pacific Asia, and Central Asia. The contribution of DR to moderate and severe vision impairment was 1.30% (0.20–2.93) and reached 5.06% in Eastern Europe, followed by Australasia, high-income North America, high-income Pacific Asia, and Central Asia. The same regions were leading in the percentage of blindness and low vision due to DR for people over the age of 50 years. The age-standardized prevalence of blindness from DR across all ages was relatively low, in the range of 0.00–0.01 (0.00– 0.02), and was considerably higher for vision impairment, 0.03% (0.00–0.13), with Eastern Europe ranking first at 0.11%, Central Asia, 0.09%; Southern Latin America, 0.08%; and North Africa/Middle East and Australasia, 0.07%. The agestandardized prevalence of blindness of diabetics over the age of 50 was 0.02% (0.00–0.07) and was highest in North Africa/Middle East, Eastern Europe, and Central Asia. The age-standardized prevalence of low vision in the same age group was 0.13% (0.01–0.48), and the same regions were most affected. For the first time, this report presented data on the gender differences in the cause and magnitude of vision loss and demonstrated that the relative risk of blindness and vision impairment in diabetic women as compared to men was 2.52. The number of people with blindness due to diabetic retinopathy was estimated at 400,000 (0–1.5 million) and low vision 2.6 million (0.2 million—9.9 million), both almost doubled since 1990. The projections for diabetic complications for 2020 are for further increase, and the largest number of people are expected to reside in North Africa/Middle East, 73,000 blind and 4,480,000 with low vision; Eastern Europe, 47,000 blind and 362,000 with low vision; Western Europe, 46,000 blind and 422,000 with low vision; East Asia, 41,000 blind and 400,000 with low vision; and Southeast Asia, 30,000 blind and 216,000 with low vision. The authors point out that the prevalence of any DR and sight-threatening DR was similar in men and women, whereas their analysis suggested female preponderance for

vision-impairing DR. They attribute this discrepancy to the use of aggregated data for both genders combined in some of the studies and highlight the need for further research into the gender differences. There are considerable regional variations in the blindness and low vision due to DR, and they are related to the prevalence of diabetes in the population and the life expectancy of the diabetic patients. In the Middle East, Kuwait, for example, the prevalence of diabetes has reached 20–25% of the whole population and over 50% after the age of 60 years. In some regions, in particular in South Asia, the life expectancy of diabetic individuals is reduced, they do not have the chance to develop retinopathy as sequela of the disease, and the prevalence of debilitating retinopathy is low despite the high proportion of diabetes.

A detailed meta-analysis of the trends in vision loss in high-income countries in Pacific Asia, Australasia, North and Latin America and Western Europe, as well as Central and Eastern Europe from 1990 to 2015 [15] presented a relatively low and stable prevalence of blindness due to DR for all ages in the range of 0.01–0.02% in the whole super-region; however the rates for moderate and severe visual impairment varied in the range from 0.6–0.7% in most of the high-income countries to 1.6% in Eastern Europe and Australasia. The crude prevalence of blindness among diabetics over 50 years was in the range of 0.02–0.03% in the high-income countries, 0.04% in Central Europe, and 0.06–0.07% in Eastern Europe, and visual impairment was lowest in Western and Central Europe and Pacific Asia, followed by North America and Australasia and highest in Eastern Europe. The projections for 2020 were for stable or slightly reduced prevalence of blindness and gradual increase of patients with visual impairment in the super-region.

Vision loss in the multiethnic population of Singapore over the age of 40 years was investigated in a series of population-based studies that demonstrated relatively high prevalence of diabetes in the sample—29.5%; DR was the second leading cause of vision impairment and blindness, and Indians and Malays were more affected than the Chinese. The authors point out that DR-related blindness in these three ethnicities in Singapore was less than the mainland Southern Indians, mainland Han Chinese, and peninsula Malays, and they attribute this to better access to qualified eye screening and care in Singapore. Diabetes was a significant contributing factor for visual impairment generally and increased the risk by 2.96 for people below the age of 60 years and 12.70 times for those over 60, particularly for females and patients with cognitive impairment and deafness, a tendency that was consistently observed across Malays, Indians, and Chinese. Diabetes in combination with other comorbidities, hypertension, hyperlipidemia, cardiovascular, or renal disease, was associated with higher risk of vision loss, up to 9.51 for people younger than 60 years and 26.56 for those older than 60, particularly for Indians, and an interaction effect for concomitant diabetes and renal diseases [16].

Vision-threatening DR (VTDR) is a compound term used in the literature for the presence of proliferative disease grading over level 60 by EDTRS scale and its modification and/or macular edema in its various stages [17, 18], and its magnitude is essential for planning the life-long management of these patients and prevention of blindness. The prevalence and risk factors of VTDR were estimated in a large meta-analysis of 38 population-based studies from Australia, the USA, Europe, and Asia involving 42,091 participants from 20 to 79 years with diabetes. There was no discernible sex difference in the age-standardized prevalence of VTDR, 11.7%; it was highest among African Americans, 16.89%; followed by Caucasians, 15.45%; and Hispanics, 10.35, and was lowest in South Asians—5.2%. Duration of diabetes (DM) was associated with rapidly increasing prevalence from 3.53% for DM less than 10 years to 17.78% for 10–20 years and up to 87% for more than 20 years.

**229**

*Diabetic Retinopathy and Blindness: An Epidemiological Overview*

the studies with assessment of the patients after 2000.

health awareness, and individual income.

**3. Social and economic risk factors**

Metabolic control, estimated by the levels of HbA1c, directly affected the extent of VTDR—the disease doubled in patients with levels between 7.1 and 8.0% and tripled among those with more than 9.0%. Elevated blood pressure over 140/90 and hypercholesterolemia over 4.0 mMol/L elevated the risk of VTDR twice, particularly for macular edema. Individuals with type 1 diabetes for more than 20 years were 15 times more likely to have proliferative diabetic retinopathy (PDR) (15.3 [11.3–20.8]), 5 times more likely to have DME (4.83 [3.71–6.30]), and 8.7 times more likely to have VTDR (8.69 [7.10–10.63]) than those with type 2 diabetes for less than 10 years. On a positive note, the prevalence of VTDR reduced from 15.62% in studies where the fundus photographs were taken before the year 2000 to 7.86% in

This pivotal work highlighted the importance and cutoff levels of the systemic factors associated with progression of DR to sight-threatening stage and the need for close collaboration with the treating diabetology team. It outlined the profile of the patients at risk of vision loss with their features—type and duration of diabetes, levels of metabolic control, hypertension, and hypercholesterolemia. The role of ethnicity was limited to the populations studied, and the authors note the absence of studies from Middle East, Africa, and South America that could affect the accuracy of their global estimates. The differences in the rates of VTDR in the various populations could be due to both genetic factors and access to health care. Ethnicity itself is multidimensional, and it may not be possible to differentiate its effect from the risk associated with remoteness, urbanization, lifestyle, education,

Social and economic factors have a fundamental impact on the visual prognosis of diabetic eye disease. A number of studies have investigated the negative influence of deprivation on the prevalence of diabetes, access to evaluation and care, level of metabolic control, and rate of complications and were reported in systematic reviews for type 1 [19] and type 2 diabetes [20]. Remoteness [odds ratio (OR) 2.02] and diabetes in combination with never having had an eye examination (OR 14.47) were among the main risk factors for vision loss in indigenous Australians, and blindness prevalence was 2.8 times higher among them than in non-indigenous

Australians after age and gender adjustment [21]. The presence of PDR was associated with low income (OR = 3.6 for developing PDR if income was less than \$20000) in the Proyecto VER Study in the USA involving 4774 Hispanics over the age of 40, after controlling for other factors [22]. Deprivation, as a comprehensive measure of income, employment, health and disability, education, crime, barriers to housing, services, and living environment at the level of small geographic areas, was developed in the UK as a numerical index per residential code and used in a large national database study of 79,775 diabetic patients to highlight its effect on visual acuity and need for early treatment at first hospital presentation [23]. The OR of presenting with "sight impairment" at first visit to the hospital eye service was gradually decreasing from 1.29 in the most deprived group to 0.77 in the least deprived one, and OR for "severely sight impaired" was 1.17 in the most deprived decile versus 0.88 in the least deprived one. The risk of sight-threatening maculopathy and vitreous hemorrhages showed little variations across the deprivation range, and tractional retinal detachment was less likely in the two least deprived deciles. The large scale of the study and use of "real-world" multicenter in-hospital dataset provided statistical strength to the conclusion that the impact of deprivation extends to late presentation of retinopathy, significant loss of vision at presentation,

*DOI: http://dx.doi.org/10.5772/intechopen.88756*

#### *Diabetic Retinopathy and Blindness: An Epidemiological Overview DOI: http://dx.doi.org/10.5772/intechopen.88756*

*Visual Impairment and Blindness - What We Know and What We Have to Know*

increase of patients with visual impairment in the super-region.

high proportion of diabetes.

vision-impairing DR. They attribute this discrepancy to the use of aggregated data for both genders combined in some of the studies and highlight the need for further research into the gender differences. There are considerable regional variations in the blindness and low vision due to DR, and they are related to the prevalence of diabetes in the population and the life expectancy of the diabetic patients. In the Middle East, Kuwait, for example, the prevalence of diabetes has reached 20–25% of the whole population and over 50% after the age of 60 years. In some regions, in particular in South Asia, the life expectancy of diabetic individuals is reduced, they do not have the chance to develop retinopathy as sequela of the disease, and the prevalence of debilitating retinopathy is low despite the

A detailed meta-analysis of the trends in vision loss in high-income countries in Pacific Asia, Australasia, North and Latin America and Western Europe, as well as Central and Eastern Europe from 1990 to 2015 [15] presented a relatively low and stable prevalence of blindness due to DR for all ages in the range of 0.01–0.02% in the whole super-region; however the rates for moderate and severe visual impairment varied in the range from 0.6–0.7% in most of the high-income countries to 1.6% in Eastern Europe and Australasia. The crude prevalence of blindness among diabetics over 50 years was in the range of 0.02–0.03% in the high-income countries, 0.04% in Central Europe, and 0.06–0.07% in Eastern Europe, and visual impairment was lowest in Western and Central Europe and Pacific Asia, followed by North America and Australasia and highest in Eastern Europe. The projections for 2020 were for stable or slightly reduced prevalence of blindness and gradual

Vision loss in the multiethnic population of Singapore over the age of 40 years

Vision-threatening DR (VTDR) is a compound term used in the literature for the presence of proliferative disease grading over level 60 by EDTRS scale and its modification and/or macular edema in its various stages [17, 18], and its magnitude is essential for planning the life-long management of these patients and prevention of blindness. The prevalence and risk factors of VTDR were estimated in a large meta-analysis of 38 population-based studies from Australia, the USA, Europe, and Asia involving 42,091 participants from 20 to 79 years with diabetes. There was no discernible sex difference in the age-standardized prevalence of VTDR, 11.7%; it was highest among African Americans, 16.89%; followed by Caucasians, 15.45%; and Hispanics, 10.35, and was lowest in South Asians—5.2%. Duration of diabetes (DM) was associated with rapidly increasing prevalence from 3.53% for DM less than 10 years to 17.78% for 10–20 years and up to 87% for more than 20 years.

was investigated in a series of population-based studies that demonstrated relatively high prevalence of diabetes in the sample—29.5%; DR was the second leading cause of vision impairment and blindness, and Indians and Malays were more affected than the Chinese. The authors point out that DR-related blindness in these three ethnicities in Singapore was less than the mainland Southern Indians, mainland Han Chinese, and peninsula Malays, and they attribute this to better access to qualified eye screening and care in Singapore. Diabetes was a significant contributing factor for visual impairment generally and increased the risk by 2.96 for people below the age of 60 years and 12.70 times for those over 60, particularly for females and patients with cognitive impairment and deafness, a tendency that was consistently observed across Malays, Indians, and Chinese. Diabetes in combination with other comorbidities, hypertension, hyperlipidemia, cardiovascular, or renal disease, was associated with higher risk of vision loss, up to 9.51 for people younger than 60 years and 26.56 for those older than 60, particularly for Indians, and an interaction effect for concomitant diabetes and renal

**228**

diseases [16].

Metabolic control, estimated by the levels of HbA1c, directly affected the extent of VTDR—the disease doubled in patients with levels between 7.1 and 8.0% and tripled among those with more than 9.0%. Elevated blood pressure over 140/90 and hypercholesterolemia over 4.0 mMol/L elevated the risk of VTDR twice, particularly for macular edema. Individuals with type 1 diabetes for more than 20 years were 15 times more likely to have proliferative diabetic retinopathy (PDR) (15.3 [11.3–20.8]), 5 times more likely to have DME (4.83 [3.71–6.30]), and 8.7 times more likely to have VTDR (8.69 [7.10–10.63]) than those with type 2 diabetes for less than 10 years. On a positive note, the prevalence of VTDR reduced from 15.62% in studies where the fundus photographs were taken before the year 2000 to 7.86% in the studies with assessment of the patients after 2000.

This pivotal work highlighted the importance and cutoff levels of the systemic factors associated with progression of DR to sight-threatening stage and the need for close collaboration with the treating diabetology team. It outlined the profile of the patients at risk of vision loss with their features—type and duration of diabetes, levels of metabolic control, hypertension, and hypercholesterolemia. The role of ethnicity was limited to the populations studied, and the authors note the absence of studies from Middle East, Africa, and South America that could affect the accuracy of their global estimates. The differences in the rates of VTDR in the various populations could be due to both genetic factors and access to health care. Ethnicity itself is multidimensional, and it may not be possible to differentiate its effect from the risk associated with remoteness, urbanization, lifestyle, education, health awareness, and individual income.
