Study finds COVID-19 virus can penetrate the blood-retinal barrier

The blood-retinal barrier safeguards our vision by blocking microbial pathogens from reaching the retina and causing inflammation that could lead to vision loss. However, researchers at the University of Missouri School of Medicine found that the COVID-19 virus can penetrate this barrier, posing potential long-term consequences for eye health.

The study was published in the journal PLoS Pathogens.

The global COVID-19 pandemic caused by SARS-CoV-2 affected millions worldwide, leading to significant morbidity and mortality. Apart from respiratory symptoms, the virus also demonstrated a tendency to affect ocular tissues, resulting in various complications such as conjunctivitis, dry eye, redness, tearing, itching, ocular pain, retinal hemorrhage, optic nerve edema, neuropathies, cerebral vein thrombosis, and glaucoma.

SARS-CoV-2, the virus responsible for COVID-19, can spread through mucosal surfaces like the nose, mouth, and eyes when exposed to infectious aerosols. The eye, being an immune-privileged organ, is susceptible to viral replication, making it a potential site for the virus to persist.

Studies have shown that SARS-CoV-2 can infect various cells in the eye, including photoreceptor and ganglion cells, conjunctival epithelial cells, scleral and limbal cells. Additionally, preclinical research has demonstrated that SARS-CoV-2 can invade the eyes via neuronal pathways after exposure through the nasal route.

In the study, researchers utilized a humanized ACE2 mice model, and discovered that SARS-CoV-2, the virus responsible for COVID-19, has the capability to infect the interior of the eyes, even if it doesn't initially enter the body through the eye's surface. Instead, their findings revealed that when the virus enters the body through inhalation, it not only targets organs like the lungs, but also manages to reach highly protected organs such as the eyes. This occurs through the blood-retinal barrier, where the virus infects the cells lining this protective barrier, allowing it to penetrate and potentially cause harm to the eyes.

“Earlier, researchers were primarily focused on the ocular surface exposure of the virus. However, our findings reveal that SARS-CoV-2 not only reaches the eye during systemic infection but induces a hyperinflammatory response in the retina and causes cell death in the blood-retinal barrier. The longer viral remnants remain in the eye, the risk of damage to the retina and visual function increases,” said Pawan Kumar Singh, PhD, an assistant professor of ophthalmology.

“While viruses and bacteria have been found to breach the blood-retinal-barrier in immunocompromised people, this research is the first to suggest that the virus that causes COVID-19 could breach the barrier even in otherwise healthy individuals, leading to an infection that manifests inside the eye itself. Immunocompromised patients or those with hypertension or diabetes may experience worse outcomes if they remain undiagnosed for COVID-19 associated ocular symptoms.”

Reference: Monu Monu; Faraz Ahmad; Rachel M. Olson; Vaishnavi Balendira, Pawan Kumar Singh; SARS-CoV-2 infects cells lining the blood-retinal barrier and induces a hyperinflammatory immune response in the retina via systemic exposure; PLoS Pathogens; https://doi.org/10.1371/journal.ppat.1012156