A new study from Turkey has raised questions about the potential effects of the Pfizer-BioNTech COVID-19 vaccine on eye health, revealing changes in the cornea’s inner layer that may signal stress or early signs of damage in certain individuals.
The research, conducted on 64 people and published in the journal Ophthalmic Epidemiology, tracked changes in the eye’s endothelium — a thin layer of specialized cells lining the inner surface of the cornea. Researchers took detailed measurements before participants received their first Pfizer dose and again roughly 75 days after their second.
Their findings revealed that after the full two-dose regimen, participants’ corneas became slightly thicker, experienced a measurable drop in endothelial cell density, and showed signs of increased cell variation in shape and size — all indicators that could point to temporary weakening of this vital eye layer.
The corneal endothelium plays a crucial role in keeping the cornea clear by pumping out excess fluid. These cells do not regenerate once damaged, making their health especially important. In this study, the average thickness of participants’ corneas increased from 528 micrometers to 542 micrometers — about a two percent change. While not immediately dangerous, sustained thickening can lead to issues such as blurred vision, especially in people with pre-existing eye conditions.
More concerning was the eight percent drop in endothelial cell density. The number of these critical cells fell from 2,597 to 2,378 cells per square millimeter. While still within the normal range (2,000–3,000 per mm² for healthy adults), the reduction could pose a risk for individuals who already have a lower count due to prior surgeries, eye disease, or trauma.
Study Links Pfizer COVID-19 Vaccine to Subtle Yet Concerning Eye Changes
Additionally, researchers observed that the endothelial cells were becoming less uniform. The “coefficient of variation” — a metric indicating how similar the cells are in size — increased from 39 to 42. At the same time, the proportion of healthy, hexagon-shaped cells fell from 50% to 48%. Hexagonal cells typically interlock tightly like honeycomb, contributing to the integrity and transparency of the cornea. When these cells begin to lose their shape and structure, it may be a response to physiological stress or early signs of dysfunction.
“These results don’t necessarily mean people should avoid the vaccine,” said one of the study’s authors, “but they do highlight the importance of continued monitoring — particularly in people with pre-existing corneal conditions or those who’ve had corneal transplants.”
People with low endothelial cell counts may be more vulnerable to complications such as corneal edema, bullous keratopathy, or decompensation — all of which can result in permanent vision damage if left untreated.
An ophthalmologist can assess a patient’s endothelial cell health using a non-invasive imaging test known as specular microscopy. This is often recommended for individuals experiencing unexplained blurry vision, discomfort, or who have a known history of eye surgeries or conditions like Fuchs’ dystrophy.
The Turkish research team conducted a battery of tests to arrive at their findings. These included full eye exams, vision acuity testing, pressure checks, and corneal scans. They used advanced tools such as the Sirius corneal topography machine to assess thickness and shape, and the Tomey EM-4000 specular microscope to closely examine the endothelial cells.
Despite the observed changes, the study’s authors emphasized that no participants reported any noticeable deterioration in their vision during the follow-up period. However, the researchers warned that if such subtle changes persist over time, they may become clinically relevant, especially among high-risk groups.
The study adds to a growing body of literature investigating potential adverse effects tied to COVID-19 vaccines. In May, the U.S. Food and Drug Administration (FDA) updated its guidance for Pfizer and Moderna vaccines, expanding warning labels related to rare cases of myocarditis and pericarditis — two types of heart inflammation that appear more frequently in younger males between the ages of 16 and 25.
While those warnings focus on cardiovascular risks, the new data from Turkey suggest that the eyes, particularly the corneal endothelium, may also be sensitive to vaccine-related immune responses in some cases. Researchers hypothesize that these eye changes might stem from a temporary inflammatory reaction or mild immune-mediated stress.
The team stopped short of advising against vaccination, noting that COVID-19 vaccines continue to be crucial tools in controlling the pandemic. They stressed, however, that longer-term studies are essential to determine whether these early corneal changes persist, worsen, or resolve over time.
In conclusion, while the Pfizer-BioNTech vaccine remains safe for the vast majority of recipients, this study serves as a reminder that ongoing research and robust post-vaccination surveillance are vital — not just for tracking known side effects, but also for identifying unexpected ones in vulnerable populations. Those with existing eye conditions should consult their doctors before vaccination and consider additional eye monitoring if necessary.
