Blockages of arteries and veins that control bloodflow into and out of the retina are a common cause of vision impairment. Some case reports have described cases of retinal vascular occlusion (RVO) occurring within days of mRNA COVID-19 vaccination; however, it was unclear if this was coincidental.

Researchers at Case Western University and the Cleveland Clinic, both in Ohio, identified more than 3.1 million patients who had received mRNA vaccines in 2020-22 from a database of the anonymised health records of 103 million people. Of these, 104 individuals – or 3.4 per 100,000 – had a new RVO diagnosis within 21 days of receiving a first dose of mRNA vaccine.