A 'surprising link' between gut bacteria and vision loss

A new study has found that gut bacteria may cause vision loss in some cases of eye disease.

Researchers from China and the United Kingdom found intestinal bacteria in affected areas of the eyes of mice, with mutations in the gene responsible for hereditary eye diseases Crumbs Homolog 1 (CRB1).

Study author, ophthalmologist Richard Lee, from University College London, said: “We found an unexpected link between the gut and the eye, which may be the cause of blindness in some patients. Our findings could have major implications for changing the treatment of CRB1-related eye diseases.”

Visual impairment associated with CRB1 begins at an early age, when the retina fails to develop its structure with thin layers of photoreceptor cells and becomes abnormally thick.

Researchers believe that the CRB1 mutation allows gut bacteria to reach the eyes, where they can contribute to vision loss. The Crb1 protein encoded by the CRB1 gene is only found in the brain and retinal pigment epithelium (RPE) (i.e. the outer blood-retinal barrier).

But the team discovered that the intestinal wall also genetically expresses this protein, which is vital for maintaining the barrier between the intestine, the rest of the body and the RPE. The CBR1 mutant does not express enough Crb1 protein, causing these two protective barriers to be compromised.

A genetic mutation in mouse models led to a defect in both of these barriers, allowing gut bacteria to pass through the bloodstream into the retina and cause damage. The researchers revealed that treatment with antibiotics reduced retinal damage and prevented vision loss.

The team was able to limit damage to the retina when natural Crb1 was introduced into the intestines of mice with a CRB1 mutation.

“We hope to continue investigating clinical studies to confirm whether this mechanism is indeed the cause of blindness in humans, and whether treatments targeting the bacteria can prevent blindness,” Lee says.

The research team explained that there is not enough evidence to know whether the same mechanism occurs in humans who suffer from the CRB1 mutation, which causes 4% of retinitis pigmentosa and thus loss of peripheral and night vision, and 10% of Leber’s congenital disease, which leads to complete blindness in about One third of the cases.

The study was published in the journal Cell.