Scientists have discovered that Pfizer's COVID-19 vaccine may cause changes to the eye’s cornea that could potentially affect vision over time, according to a new study published in the journal Ophthalmic Epidemiology.
The study, conducted by researchers in Turkey, examined the effects of the Pfizer-BioNTech vaccine on the corneal endothelium; the thin, inner layer of the cornea responsible for keeping it clear by pumping out excess fluid. Using 64 participants, researchers measured changes in the cornea before the first vaccine dose and approximately 75 days after the second dose.
Findings showed that the corneas had become slightly thicker, and the density of endothelial cells had decreased from an average of 2,597 to 2,378 cells per square millimeter, an eight percent drop. The cells also showed increased variation in size and a small reduction in the proportion maintaining their normal hexagonal shape, signs that could indicate cellular stress.
Researchers emphasized that while these short-term changes did not lead to noticeable vision problems in participants, they could pose risks for individuals with pre-existing eye conditions or those who have undergone corneal transplants.
“If these changes persist for years, they could lead to corneal swelling or vision disturbances, particularly in vulnerable individuals,” the study noted. A thicker cornea and reduced endothelial cell count are associated with eye diseases such as corneal edema and bullous keratopathy, which can cause irreversible vision loss if left untreated.
Specular microscopy, a tool that captures high-resolution images of the corneal endothelium—was used to assess the cell size, density, and structure. Additional tests measured corneal thickness and overall eye health to rule out other potential causes.
The study also found an increase in the coefficient of variation (a measure of size irregularity among cells) from 39 to 42, and a drop in healthy hexagonal cells from 50 percent to 48 percent. These signs further point to endothelial stress, though the researchers clarified that these early indicators did not yet imply long-term damage.
While the authors of the study did not recommend halting vaccinations, they urged careful monitoring in patients with low endothelial cell counts or a history of eye surgeries. “The endothelium should be closely monitored in those with a low endothelial count or who have had a corneal graft,” the researchers stated.
The findings add to growing scrutiny of COVID-19 vaccines. In May, the U.S. Food and Drug Administration (FDA) expanded warning labels on Pfizer and Moderna vaccines to highlight risks of heart inflammation in young men aged 16 to 25.
Researchers are calling for longer-term follow-up studies to determine whether the observed eye changes are temporary or indicative of more lasting effects. For now, they recommend that patients with existing eye vulnerabilities consult with an ophthalmologist before receiving the vaccine.
