Racial differences in chronic disease care have been documented for decades, with White people more likely to receive better quality care than minority populations. How does race impact eye disease? In the journal Missouri Medicine, two Washington University professors discuss potential genetic and physiologic links between race and glaucoma.*

Glaucoma and race

Internal eye (intraocular) pressure, or IOP, is the only known modifiable glaucoma risk factor, and high IOP is the only factor currently approved for treatment. Lowering IOP requires consistency with therapies and medical appointments. 

Large population studies have shown that Black and Latino people have higher rates of glaucoma than other racial groups, as well as lower rates of disease screening and follow-up, and greater issues with:

• Healthcare cost, access, and health literacy
• Surgical undertreatment and surgical failure
• Lower racial representation among ophthalmologists (less than 2% are Black or Latino)

Primary open-angle glaucoma (POAG) is the leading cause of blindness in Black Americans, and Black populations in other countries have shown similar trends.

Biological considerations

Scientists are still searching for the exact mechanisms of POAG development, since there are a variety of possible disease pathways, as well as genetic and environmental factors. 

Vascular disease

Compared to Whites, Black people have a higher risk of blood vessel (vascular) issues, like high blood pressure inside the arteries, which can create problems with blood vessels in the eye. 

In Barbados, however, research showed that lower systolic blood pressure was linked to increased POAG risk, mostly in Black participants. 

In short, the relationship between blood pressure, eye pressure, and glaucoma is still unclear.

Genetics

Genetics appear to play a role in glaucoma risk, though the exact nature remains elusive. Large population studies have variously found:

• Several gene mutations linked to glaucoma, but only in a small proportion of cases
• Genetic contribution in POAG risk
• Associations between Latinos and certain glaucoma risk factors, such as vertical cup-disc ratio and central corneal thickness, but much is still unknown, and further research is required

The large, ongoing Primary Open-Angle African-American Glaucoma Genetics study is gaining valuable data on family history, sex, and genetic variants in this population group. 

Trabecular meshwork

The trabecular meshwork (TM) is part of the eye’s drainage system for maintaining normal eye pressure. TM samples from Black and White glaucoma patients show differences in gene expression, seen most prominently in genes encoding for mitochondria (microscopic structure inside the nucleus of a cell, where energy is made). In Black people, gene expression was largely increased, which the authors say points to mitochondrial dysfunction in Black patients. 

Oxidation and glaucoma

Oxidative stress is involved in many eye diseases, and is higher in Blacks than Whites after adjusting for outside factors. Researchers believe that oxidative stress is a major contributor to TM cell degeneration in glaucoma. 

They think this stress could be from elevated oxygen levels in the frontal eye chamber, which the authors found in Black glaucoma and cataract patients. They also found elevated oxygen in people with thinner corneas, a risk factor for POAG, which is seen more often in Black patients than in White ones.

Race and social determinants of health

Evidence shows that POAG is strongly influenced by race and social determinants of health. The authors say it is incumbent upon healthcare providers and researchers to better understand how socioeconomics, health literacy, community, and cultural sensitivity influence differences in disease outcomes.

More extensive research on these differences must be done, they add, and should include people from diverse backgrounds to better determine individual risk and disease mechanics. Only then can more people benefit from new therapies.

*Siegfried, C. J. & Shui, Y.-B. (2022, Jan-Feb). Racial Disparities in Glaucoma: From Epidemiology to Pathophysiology. Missouri Medicine, 119(1). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9312450