Link Between Gut Microbiome and Vision Loss Uncovered

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Gut Bacteria and Eye Health

A groundbreaking study published in Frontiers of Medicine has uncovered a significant link between the gut microbiome and vision loss, particularly in inherited retinal diseases (IRDs), a group of disorders that cause progressive photoreceptor cell loss and blindness. The research of Richard Lee, MBBS, BSc, DIC, MSc, PhD, FRCOphth, at University College London, demonstrates that gut bacteria can influence eye health through a mechanism dubbed the gut-retina axis.

In experiments with mice engineered to mimic IRDs, antibiotics reduced harmful gut bacteria, lowering retinal inflammation and cell death, thus preserving vision for longer than untreated mice. The study pinpointed Morganella morganii, a gut bacterium producing indole toxins, as a key contributor to retinal damage when it leaks into the bloodstream and crosses the blood-retina barrier. Conversely, restoring beneficial bacteria via fecal transplants from healthy mice also slowed vision loss, suggesting a protective role for a balanced microbiome. In humans, blood samples from patients with IRDs showed higher indole levels, reinforcing the gut-eye connection.

This discovery challenges the view of IRDs as solely genetic, highlighting environmental factors such as gut health as potential modifiers. The findings open the door to novel treatments, such as probiotics or antibiotics, that can help delay vision loss, although clinical applications remain years away, pending further research. Experts emphasize the complexity of translating these insights into therapies, given the microbial differences between species. Nonetheless, this research marks a paradigm shift, offering hope for managing a condition that affects more than 2 million people worldwide. (Read more here.)

My Two Cents

I started to look closer at the connection between the gut biome and the eye when I had an engaging conversation with Andrew Royer, OD, at a conference in Nashville. He has a wealth of knowledge about the gut biome and its connection to the body as a whole. I firmly believe we will start seeing more research and publicity regarding the gut’s connection to the eye and its proper functioning. It seems logical that the connection would ring true, especially with the tear film. Let’s hope more research follows this regarding all areas of the human eye, from tear film to retina!

OUTSIDE THE LANE

Can the Shingles Vaccine Stave Off Dementia?

A recent study published in Nature highlights a potential link between the shingles vaccine and a reduced risk of dementia. The analysis leveraged a natural experiment in Wales, Great Britain, where eligibility for the herpes zoster vaccine (Zostavax, Merck) was determined by birthdate (those born before September 2, 1933, were ineligible, while those born on or after that date were offered the vaccine).

Examining health records of more than 200,000 individuals, the study found that vaccinated individuals had a 20% lower risk of dementia over 7 years compared with their unvaccinated counterparts. This reduction surpasses the effects of any other known intervention, suggesting the vaccine may suppress the varicella-zoster virus, which has been implicated in the development of dementia.

The research employed a regression discontinuity design borrowed from economics to establish causality rather than mere correlation, showing no significant differences in other health factors across the eligibility cutoff. While the vaccine’s protective mechanism remains unclear, possibly involving viral suppression or immune system modulation, the findings align with growing evidence linking herpes viruses to cognitive decline.

Experts caution that randomized controlled trials are needed to confirm these results and to explore optimal vaccination strategies. If validated, this could position shingles vaccination as a cost-effective public health measure with dual benefits: to delay dementia, a condition affecting millions globally, alongside its primary role in preventing shingles. (Read more here.)

My Two Cents

This is yet one more reason to recommend the shingles vaccine to your patients—as if witnessing or treating a patient with shingles isn’t enough on its own! Almost 9 years ago (April 9th, 2016), I was thrust into the role of being a shingles expert (see below for the full, ridiculous story).

CAN YOU RELATE

Speaking of shingles … sometimes, you become an unexpected expert in something you have no interest in. Nine years ago, I got married on April 8th, 2016. My now ex-wife, who I get along with and co-parent with exceptionally well, is a particularly high-strung and type-A pharmacist. She was so stressed out the days leading up to and the day of our wedding that she gave herself an awful case of shingles. The morning after our wedding, she awoke with the tell-tale shingles blisters on one side of her face and noticeable discomfort. After going through the differential diagnoses and dragging her into the clinic on the weekend to make sure she didn’t have any ocular side effects, I started her on standard valacyclovir (Valtrex), and we headed to St. Lucia for our once-in-a-lifetime honeymoon.

Well, as I’m sure most of you are aware, although extremely safe and tolerable, oral antivirals such as valacyclovir can make patients extremely sensitive to the sun and bright lights, thus increasing their risk of sunburns. Add to that, the fact that she had sensitive, fair skin to begin with, so instead of spending the week lying on the beach sipping frozen drinks loaded with sugar, we spent most of our time inside, away from the sun’s harmful rays. (As a pharmacist, she followed those colorful little stickers they put on the pill bottles exactly as written.)

I used my time inside researching the herpes zoster virus and its effect on the human body, notably the ocular surface, while she slept off the pain. I decided that I would attempt to learn as much as I could learn about this bizarre virus that had affected my then 30-year-old bride. Although not ideal, it was one of those situations that allowed me to focus exclusively on one thing and be productive rather than sit and mope around. I’m sure many of you have been in a similar situation. If not, remember that in the right situation, you can always take lemons and make lemonade!