Around the world, most people are identified with ethnic and/or racial characteristics at birth. Aside from extrinsic environmental factors, biologic and cultural associations play a key role in many disease processes among various ethnic backgrounds.

This article provides further insight into the prevalence of various ocular conditions, disparities in disease presentation, and differences in treatment and management among members of different ethnic subgroups.

 

African-Americans

Primary open-angle glaucoma (POAG). Glaucoma affects more than 67 million people in the world and leads to blindness in 10% of those affected.1 POAG affects more than 2.25 million people in the United States, and it is projected to increase to 3.4 million people by the year 2020.2

Large population-based U.S. studies, such as the Baltimore Eye Survey, have estimated POAG to be up to 4.3 times more prevalent in blacks than in whites.3 POAG in blacks also has an earlier age of onset, is more advanced when initially diagnosed, and progresses more rapidly after diagnosis.

Also, evidence suggests that blacks dont respond as well to glaucoma treatment (both medically and surgically) as whites do.4 One likely reason: Drugs bind to the heavy ocular melanin found in blacks and may require a higher concentration of the medication to have the same effect as in whites. In addition, blacks have thinner corneas than whites (an average 23m thinner), which can lead clinicians to underestimate measured IOP and cause a delay in diagnosis and treatment.5

Literature suggests physiologically larger cup-to-disc ratios and thinner retinal nerve fiber layer (RNFL) among blacks, which has implications of a lack of structural support and subsequent bowing of the lamina cribrosa leading to further damage of neuronal axons.6

Eye-care practitioners should be aware of these differences as well as the presence of other risk factors, such as family history, diabetes and hypertension for early detection, treatment and management in this patient population.

Hypertension and hypertensive retinopathy. In the U.S., hypertension and hypertensive retinopathy are more prevalent in blacks than in whites.7 Hypertension not only shows up at an earlier age in blacks, but also is much higher than in whites and results in severe complications with increased risk of mortality. Stage 3 hypertension (>180/110mm Hg) is 8.5% more prevalent in blacks than whites.8 In the U.S., hypertensive retinopathy is twice as common in blacks than whites.9 Mortality due to hypertension and its complications is four to five times more likely in blacks than in whites.8

Compared to whites, blacks have been shown to have salt-sensitive hypertension, which results from a delayed ability to get rid of excess salt.8,10 The Dietary Approaches to Stop Hypertension (DASH) trial demonstrated that a diet low in sodium, sugars and red meat, with lower total and saturated fats and cholesterol, led to significantly lower blood pressure in people with and without hypertension.11 Lifestyle modifications, such as incorporating dietary changes and exercise, are crucial in this population to decrease the risk of complications and mortality from uncontrolled hypertension.

 

Whites

Age-related macular degeneration (AMD). In the developed world, AMD is the leading cause of irreversible blindness in older whites. And, as baby boomers age, the number of people who have AMD is expected to rise. An estimated 8 million Americans currently have intermediate or unilateral advanced AMD, and up to 3 million will have geographic atrophy (GA) or choroidal neovascularization (CNV) by the year 2015.12

In this disease process, age and race are two big risk factors in progression from early to the more advanced stages of AMD. Data from the Salisbury Eye Evaluation (SEE) project suggest evidence of significant funduscopic differences within the 1,500m macular zone of black and white individuals.13 Although small drusen (64m) were seen equally among white and black participants in this study, large drusen (>125m) were more common in whites than in blacks. Also, drusen larger than 250m, confluent drusen, or a large area of drusen was more commonly seen among whites.

This data suggests that blacks may have a protective mechanism for AMD, at least in the central macula. Specifically, the increased melanin in the retinal pigment epithelial (RPE) cells of blacks may have antioxidant properties that act as a free radical scavenger and help protect the RPE cells.14 RPE lipofuscin, which has been associated with breakdown of the RPE and thus implicated in the pathogenesis of AMD, has not only been shown to be increased with age, but also is disproportionately higher in whites than in blacks.15

Uveal melanoma. Uveal melanoma is the most common ocular melanoma and is of serious consequence if it is medium to large in size.16 There is a significant difference in the incidence of uveal melanoma among ethnic and racial groups. Uveal melanomas are very rare in black patients. The estimated black:white ratio of uveal melanoma is anywhere from 1:10 to 1:50.17 Results of larger population-based studies among different ethnic backgrounds have estimated the relative risk of uveal melanoma to be 1.2 for Asian and Pacific Islanders, 5.4 for Latinos and 19.2 for non-Latino whites, as compared with blacks.18 The degree of uveal pigmentation in blacks is a possible protective factor from ultraviolet radiation because the higher levels of melanin in the ciliary body and choroid of blacks may suppress oxidative species associated in the pathogenesis of malignant tumors.19

 

Latinos

Diabetes and diabetic retinopathy. The Latino population is the largest minority group in the U.S., comprising 12.5% of the population, according to the 2000 census. By 2020, Latinos are projected to account for 17.8% of the U.S. population.20 Of all Latinos in the U.S., individuals of Mexican origin comprise about 60%, making them the largest ethnic subgroup of this population.21

According to the National Health and Nutrition Examination Survey (NHANES), the prevalence of type 2 diabetes is twice as high in blacks and Mexican-Americans than in non-Hispanic whites.22 There is a higher likelihood of proliferative diabetic retinopathy and clinically significant macular edema in this populationboth account for moderate to severe visual impairment.21,23 Some studies have identified socioeconomic conditions and access to care as major risk factors for diabetes to be undetected or detected at a later stage.23 Other studies have identified younger age of onset, poor glycemic control, American Indian ancestry and/or greater waist-hip ratio as predictors of diabetic retinopathy.23,24

Traditional Hispanic beliefs suggest that experiencing intense emotions, such as fright, anger or sadness, could trigger diabetes.25 Homeopathic therapies, such as prickly pear cactus and aloe vera, have also been used by this population as a means of controlling diabetes.

So, from a public health perspective, it is important that health care providers be culturally aware in order to properly understand, educate, treat and manage this growing patient population.

Pterygium. Pterygium, initially thought to be a degenerative or inflammatory ocular condition, is now known to be proliferative in nature, resulting from increased exposure to ultraviolet (UV) B radiation.26,27 An increased prevalence of pterygium has been noted in latitudes known as the pterygium beltcountries between 37 north and south of the equator, where UV radiation is the strongest.26

Other risk factors include increasing age, male gender and certain occupations that cause increased UV exposure. Occupational studies suggest a significantly higher prevalence of pterygium in welders, sawmill workers and farmers.26,28,29 There are 4.2 million farm workers in the U.S., and the majority of them are Mexican. The prevalence of pterygium in this population is 23.3%.29

Genetic and other environmental factors, such as abnormal expression of p53 protein and the presence of the human papilloma virus (HPV), have been linked to the possible pathogenesis of pterygium.30 Future population-based studies with larger sample sizes would be beneficial in understanding the prevalence and risk factors of this condition in countries around the world.

 

Asians

Primary angle-closure glaucoma (PACG). PACG is the most common form of glaucoma among East Asians (Chinese from Singapore or Hong Kong, and Japanese).31 The Inuit people of Alaska, Canada and Greenland are believed to be descendants of East Asians who have the highest rates of narrow angles and angle-closure glaucoma in the world.32 In China, the worlds most populous country, PACG is the leading cause (91%) of bilateral irreversible blindness.31 This condition is quite rare in the white population of Europe and North America. Traditionally, PACG has been divided into four clinical types: acute, subacute, intermittent and chronic.33 The majority of patients in Asian countries have the asymptomatic chronic form, with the exception of Singapore, where reported incidence is highest for acute primary angle-closure glaucoma.34

Anatomic differences in the anterior chamber angle as well as increased formation of peripheral anterior synechiae have been reported in this patient population. Anterior chamber depth (ACD) is significantly shallow in the Chinese. Also, the iris tissue of Chinese people is thick and heavily pigmented.35 Additionally, eyes with chronic angle-closure glaucoma have irides with less collagen and less elasticity, which makes it harder for argon and Nd:YAG lasers to penetrate the iris tissue.36 With such a high prevalence of a disease that leads to severe visual morbidity, important screening mechanisms should be in place to detect it earlier.

Vogt-Koyanagi-Harada (VKH) syndrome. VKH is an autoimmune disorder associated with severe, bilateral panuveitis along with specific neurologic, auditory and integumentary components.37 It is more common in certain darkly pigmented individuals, such as East and Southeastern Asians, Native Americans, Hispanics and Middle Easterners. It is very rare to see in the white population and, interestingly, in people of African descent. So, skin pigmentation may not be the only factor at play in the pathogenesis of this disease.

In Japan, VKH is responsible for more than 8% of all cases of uveitis.38 In the U.S., it accounts for just 1% to 4% of all uveitis cases.37 The racial distribution of VKH has been noted to differ even within the U.S., with Asians primarily affected in northern California and Hispanics in southern California.

A genetic mechanism has been strongly linked with VKH and this association has been found in various groups, such as East and Southeast Asians, Native Americans and Hispanics.39 Aggressive systemic steroids are the mainstay of initial VKH therapy, but non-steroidal immunomodulatory therapy is essential to treat recalcitrant cases.

 

While we sometimes forget that race can often mask many social and economic factors that influence health status and health care delivery, we should still be mindful that ethnicity and race can also suggest very important clues to disease diagnosis and treatment. As always, consider the patients individual condition in light of your knowledge and experience.

Dr. Mani is a clinical assistant professor of optometry at the Pennsylvania College of Optometry at Salus University.

 

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