The Gut of the Matter: AMD

In the past several years, the topic of gut health has gained incredible traction in almost every aspect of disease. The eye is no exception. Here, we look at how gut health manifests in age-related macular degeneration (AMD).

AMD, IN BRIEF

AMD, a leading cause of visual impairment and vision loss in the elderly, occurs as a result of a disruption in the metabolism of the photoreceptor cells caused by the thickening of Bruch membrane, accumulation of lipofuscin, and development of drusen within the retina.^1,2 Oxidative damage and chronic inflammation, resulting from the infiltration of the immune cells to clear up the toxic debris and drusen, cause changes in the choroidal vascularization and, ultimately, the development of AMD.

Various factors (eg, age, sex, race, diet, smoking, and genetics) contribute to the changes that precede AMD, as do systemic conditions relating to cardiovascular and metabolic, hormonal and reproductive, and ocular and visual health.³ Common risk factors include obesity, atherosclerosis, hypertension, hyperlipidemia, and diabetes.⁴

THE GUT MICROBIOME

The gut microbiome is home to several trillion microorganisms, or microbes. These digestive tract-associated microbes play a significant role in modulating every system and organ in the body, including digestive, immune, cardiovascular, nervous, endocrine, lymphatic, reproductive, muscular, urinary, integumentary, and ocular. Some of the gut microbiome’s functions include breaking food down into nutrients, synthesizing necessary enzymes, training the immune system to identify pathogens, and creating neurotransmitters and hormones. Approximately 80% of our immune system lives in the gut.⁵

Alteration in the human microbiome leads to gut dysbiosis, or imbalance, eventually causing inflammation, which becomes chronic and results in systemic conditions, such as inflammatory bowel disease, cancer, autoimmunity, allergy, obesity, diabetes, hypertension, and cardiovascular disease.⁶ Other resulting conditions include mood disorders, skin issues, neurodegenerative decline, fatigue, pain, nutrient deficiencies, and ocular disease, to name a few.⁷

CONNECTING THE TWO

Studies have found that the composition of the gut microbiome in patients with AMD differs from that of healthy individuals. One such study reported that Anaerotruncus, Oscillibacter, Ruminococcus torques, and Eubacterium ventriosum were elevated in patients with AMD, and, conversely, Bacteroides eggerthii was elevated in controls.⁸ AMD patients also had significantly lower levels of Firmicutes and relatively higher levels of Proteobacteria and Bacteroidota compared with controls.⁸ Other evidence showed that patients with AMD had a higher level of Negativicutes, whereas controls had a higher level of Oscillibacter and B. eggerthii.^9,10

Yet another set of studies discovered that intestinal dysbiosis results in an enhanced abundance of Prevotella, Holdemanella, and Desulfovibrio but a reduced abundance of Oscillospira, Blautia, and Dorea in patients with AMD compared with controls.^11,12 These findings have concluded that gut dysbiosis and potential subsequent increased intestinal permeability causes chronic low-grade inflammation with elevated production of proinflammatory cytokines and vascular endothelial growth factor, ultimately exacerbating the pathological angiogenesis characteristic of AMD.^8-12

OPTIMIZING GUT HEALTH

One of the most effective ways to improve gut health is through balanced nutrition.¹³ It is essential to educate patients on the importance of following a diet rich in fiber with colorful fruits and leafy green vegetables, as well as fermentable foods, while reducing sugar and processed food consumption. Reducing stress, exercising regularly, implementing a consistent eating and sleeping schedule, minimizing chemical and medication intake, and incorporating targeted dietary supplementation are also key factors in a healthy gut.¹⁴

KNOWLEDGE IS POWER

Optometrists have a unique vantage point in health care and owe it to our patients to consider all parts of the whole. The gut microbiome is at the intersection of genetic and environmental factors in AMD. It is imperative that key players in the industry strengthen their knowledge of the intricately complex interplay between genetics, the gut, and lifestyle, as this information will be crucial in developing novel treatment approaches for AMD.