A recent study published in the American Journal of Ophthalmology evaluated the relationship between body mass index (BMI) and primary open-angle glaucoma (POAG) in a cohort of Black American patients.
To note: All participants were part of the Primary Open-Angle African American Glaucoma Genetics (POAAGG) study.
What is the POAAGG study?
Although POAG disproportionately affects Black American patients, most genetic studies on POAG have focused on patients with European or Asian ancestry.
To address this gap in information: The National Eye Institute funded the POAAGG study in 2014 to better understand the genetic architecture of POAG in African-American patients.
Tell me more.
The POAAGG population consists of 10,255 patients of African ancestry (Black, Afro-Caribbean, or African American) who are aged 35+ and recruited from the greater Philadelphia area.
Since then, researchers have conducted genome-wide association studies (GWAS), whole-exome sequencing, and whole-genome sequencing to identify the genes involved in glaucoma in Black American patients.
Bring it back to this study.
While obesity is often considered a risk factor for various systemic health conditions, previous studies have suggested that patients who are underweight (i.e., have a low BMI), in fact, have a higher risk of POAG.
- Consequently: Researchers sought to elucidate the association between BMI and POAG in Black American patients.
Now talk about the study.
In this retrospective comparison study, investigators included 2,977 cases and 3,657 controls for a total of 6,634 POAAGG study subjects.
They collected ocular and demographic information from on-site examinations, standardized interviews, and electronic medical records (EMRs).
BMI was calculated and categorized as:
- Low <18.5 kg/m2
- Moderate 18.5-24.9 kg/m2
- High 25.0-29.9 kg/m2
- Very high ≥30 kg/m2
How did they measure POAG progression?
Structural and functional POAG progression were assessed by annual rate of change in retinal nerve fiber layer (RNFL) thickness and visual field (VF) mean deviation, respectively, using a mixed-effects model.
Findings?
Lower BMI was associated with increased POAG risk (adjusted odds ratio [aOR] 1.02, 95% confidence interval [CI] 1.007-1.023, per kg/m2 decrease in BMI, p = 0.0003).
Low BMI was associated with a larger cup-to-disc ratio (p = 0.007) and worse visual acuity (VA, p = 0.04).
Fast functional POAG progressors had a significantly lower mean BMI than slow progressors (25.7 vs. 30.0 kg/m2, p = 0.04).
Expert opinion?
The study authors noted several potential explanations for the association between low BMI and POAG, including:
- Lower BMI is linked with faster functional progression and other variables that may result in more severe glaucoma that requires surgical intervention
- These findings support previous reports that low BMI increases POAG risk due to a deficiency in vitamins and nutrients that potentially have neuroprotective benefits
- Cerebrospinal fluid pressure may affect the translaminar pressure gradient
- This leads to increased VF defects and deformation of the lamina cribrosa as well as a decrease in neuroretinal rim area.
- Activation of G protein-coupled estrogen receptors has demonstrated neuroprotective effects against retinal ganglion cell (RGC) damage
- Meaning: Patients with less body fat (i.e., the dominant site of estrogen production) could be at greater risk for glaucoma.
Limitations?
These results could have been impacted by comorbid conditions often found in glaucoma patients, including:
- Diabetes
- Obstructive sleep apnea
Take note: Both are linked with high BMI.
Take home.
These findings suggest that low BMI was associated with an increased POAG risk in a cohort of Black American patients.
Specifically: POAG patients with low BMI were more likely to have signs of more severe glaucoma, such as:
- Larger cup-to-disc ratios
- Worse VA
- Faster functional progression