Researchers suspected that covert mortality nodavirus (CMNV) might be the cause since patients with the condition consistently tested negative for common eye viruses such as herpes or shingles. And earlier investigations had identified unknown virus particles in the eye tissue of a few patients that looked similar in shape and size to CMNV.

To investigate further, scientists in China recruited 70 people diagnosed with the condition between January 2022 and April 2025.