Glaucoma and Population Health
Glaucoma leads as the cause of irreversible blindness across the world. It remains particularly worrisome because estimates have shown that about half of people with the disease do not know it and will not experience symptoms until they begin to lose their vision. According to the National Eye Institute (NEI), in the United States, primary open-angle glaucoma, which is the most common form, affects up to 3 percent of the population aged 40 and over, which equates to about 2.7 million Americans. By the year 2030, the NEI expects this number will increase to more than 4 million.
Providers caring for people with glaucoma must approach detection and treatment of the disease from a population health perspective because it does not affect all Americans equally. In particular, rates of glaucoma are much higher among African American and Hispanic populations.
Higher Glaucoma Incidence Among African Americans
According to research conducted by the NEI in 2012, approximately 520,000 Americans with open-angle glaucoma are African American, which makes the condition the leading cause of irreversible blindness in this population. The finding was not surprising. One of the landmark studies of open-angle glaucoma among African Americans, “Racial variations in the prevalence of primary open-angle glaucoma: The Baltimore Eye Survey,” was published in the Journal of the American Medical Association in July 1991. The study, led by James Tielsch, MD, showed African Americans were approximately four to five times more likely to receive a diagnosis of glaucoma as compared to Caucasian patients. Furthermore, the researchers found that the disease seems to begin at an earlier age for African Americans.
A number of researchers have asked why African Americans experience a higher incidence of glaucoma as compared to Caucasians, but no clear conclusions have been made. One likely explanations relates to genetics and fundamental differences in anatomic structures, especially as they pertain to the optic nerve.
A recent study looked at the optic nerve structures of Americans from both African and European ancestry and found significant differences. The researchers, led by Alon Skaat, MD, and Carlos Gustavo De Moraes, MD, MPH, announced their findings in “The African Descent and Glaucoma Evaluation Study (ADAGES): Racial Differences in Optic Disc Hemorrhage and Beta-Zone Parapapillary Atrophy,” published in the July 2016 Ophthalmology, the journal of the American Academy of Ophthalmology. One of the findings of the study was that individuals of African descent tended to have larger optic nerve areas, which could actually lead to a misdiagnosis.
The study also found that African Americans have thinner corneas than people of European descent. Disease among African American tends to progress faster, although the researchers have not discovered why. Another notable difference between these two groups is glaucoma among African Americans tends to prove more refractory to treatment, perhaps because of its quicker progression.
Increased Risk of Open-Angle Tension Among Hispanics
Hispanics also have an increased risk of developing open-angle glaucoma, as found by the Los Angeles Latino Eye Study (LALES), led by Rohit Varma, MD, MPH. The majority of patients included in the study were of Mexican descent. The rate of glaucoma in this population was found to be roughly equivalent to that among African Americans, although 75 percent of patients with the disease had not previously been diagnosed, a sharp increase from the rate of 50 percent among both African Americans and Caucasians. This finding may relate to a lack of access to care stemming from high uninsured rates. LALES connected many of the glaucoma cases among Hispanics to high blood pressure. Hypertension remains one of the major risk factors for developing open-angle glaucoma. The study also showed Hispanics tend to have thinner corneas than Caucasians, similar to African Americans.
Another study focused on glaucoma as a population health issue projected Hispanics will carry the largest burden of open-angle glaucoma by the year 2050, and especially Hispanic men. This finding emphasizes the importance of designing interventions to identify people most at risk for glaucoma, providing screening, and then connecting them to treatment when necessary.
Unique Risks Faced by Asian Americans
While African Americans and Hispanics have a higher risk of open-angle glaucoma, there is a segment of the American population at high risk of angle-closure glaucoma. While this form of glaucoma is not as common, it represents a true medical emergency and can lead to blindness quickly if not addressed. Angle-closure glaucoma accounts for approximately 90 percent of blindness in China, and Asian Americans are at particular risk of developing the condition. Often, this condition relates to having a narrow angle for the drainage of aqueous fluid from the eye. This angle refers to the space between the cornea and the iris. People of Vietnamese, Chinese and Pakistani heritage have the highest risk of a narrow angle and thus angle-closure glaucoma.
Notably, Asian American populations may also have rates of open-angle glaucoma similar to those of Hispanics and African Americans, according to one study. Researchers believe this increased risk may also be due to eye anatomy, which reflects genetics. Another form of glaucoma is known as normal-tension glaucoma in which eye pressure is never elevated. For this reason, it is difficult to diagnose this form of the disease. Studies show Japanese Americans, as well as Native Americans and Alaskan Natives, have a higher prevalence of normal-tension glaucoma.