A peer-reviewed study from Turkey has identified structural changes in the cornea following Pfizer-BioNTech COVID-19 vaccination, raising questions about potential ocular side effects of mRNA vaccines. The research, published in Ophthalmic Epidemiology, examined 64 individuals and found measurable alterations to corneal structure 75 days after completing the two-dose vaccination series.
Study Design and Methodology
Researchers evaluated 128 eyes using advanced imaging techniques including Sirius corneal topography and Tomey EM-4000 specular microscopy. Each participant underwent comprehensive ophthalmic evaluation, including visual acuity tests, intraocular pressure checks, and scans of the eye's anterior and posterior segments. Measurements were taken before vaccination and 75 days after the second Pfizer dose.
Key Findings
The study revealed several significant changes in corneal structure:
- Corneal thickness increased by 2% (from 528 to 542 micrometers)
- Endothelial cell density decreased by 8% (from 2,597 to 2,378 cells/mm²)
- Hexagonally shaped cells dropped from 50% to 48%
- Coefficient of variation in cell size rose from 39 to 42
These changes indicate increased variability in cell size and shape within the corneal endothelium, the innermost layer responsible for maintaining corneal clarity by pumping out excess fluid.
Clinical Implications
While no participants reported impaired vision during the short follow-up period, researchers warned that the observed changes may signal stress or inflammation in the cornea. The endothelium consists of cells that do not regenerate, making any loss or dysfunction potentially significant for long-term eye health.
"The endothelium should be closely monitored in those with a low endothelial count or who have had a corneal graft," the authors cautioned in their paper.
The researchers explained that "healthy endothelial cells are usually shaped like hexagons, which allows them to fit together tightly, like a honeycomb. When cells die, nearby cells stretch to fill the gaps, leading to bigger differences in size."
Risk Assessment for Vulnerable Populations
The study emphasizes particular concern for high-risk groups, including individuals with:
- Prior eye surgery
- Fuchs' dystrophy
- Corneal grafts
- Low baseline endothelial cell counts
For these populations, the observed changes could potentially lead to conditions such as corneal edema, bullous keratopathy, or corneal decompensation if the effects persist long-term.
Study Limitations and Future Research
The researchers acknowledged that the two-month post-vaccination observation period may not fully capture long-term effects. They emphasized that follow-up studies are required to determine whether these structural changes are temporary or progressive.
The scientists noted that although the observed trends were unlikely to be due to random anomalies, the study does not recommend against vaccination. Instead, it calls for enhanced monitoring protocols for at-risk populations.
Broader Context
These findings contribute to the growing understanding of rare side effects associated with mRNA vaccines. The U.S. Food and Drug Administration has previously expanded warning labels on Pfizer and Moderna vaccines to include myocarditis and pericarditis, particularly in males aged 16 to 25.
The Turkish research team concluded that "changes in corneal endothelium occur in the short term after two doses of the Pfizer-BioNTech (BNT162b2) COVID-19 mRNA vaccine," emphasizing the need for continued surveillance and monitoring of vaccine recipients with pre-existing ocular vulnerabilities.
