The researchers focused on the corneal endothelium, the innermost layer of the cornea responsible for maintaining corneal clarity by pumping out excess fluid. Using specialized tools such as specular microscopy and Sirius corneal topography, they observed changes in corneal thickness, a decline in endothelial cell count and alterations in cell size and shape — indicators of stress or damage to this delicate structure.
Specifically, corneal thickness increased by approximately 14 micrometers (a 2 percent rise), which in itself is not harmful but could signal inflammation or fluid retention. More concerning was the eight percent drop in endothelial cell density — from 2,597 to 2,378 cells per square millimeter — still within the safe range for healthy individuals, but potentially risky for those with already compromised eye health.
The study also found that the vaccine led to increased variability in cell size, known as the coefficient of variation, which rose from 39 to 42. This suggests some cells may have died and others stretched to fill the gaps, a typical response to stress. Additionally, the percentage of hexagon-shaped cells, which are vital for maintaining a healthy endothelial layer, dropped slightly from 50 percent to 48 percent.
Although none of the participants reported noticeable vision issues during the two-month follow-up, scientists caution that these microstructural changes could have long-term consequences, especially for people with existing eye problems or a history of eye surgeries such as corneal grafts. If the damage to the endothelium is permanent or worsens over time, it could result in conditions like corneal edema, bullous keratopathy or corneal decompensation — disorders that may lead to chronic vision impairment or even blindness if untreated.
Despite these findings, the researchers did not advise against COVID-19 vaccination. They emphasized the need for ongoing monitoring and further long-term studies to determine if the observed changes persist or resolve over time. Importantly, the study confirmed a high likelihood that the changes were directly associated with the vaccine and not random occurrences.
This research adds to a growing list of safety concerns surrounding COVID-19 vaccines. In May, the U.S. Food and Drug Administration expanded warning labels on Pfizer and Moderna vaccines to more clearly highlight the risk of myocarditis and pericarditis, particularly in young men aged 16–25.
While the short-term effects of the Pfizer vaccine on eye health appear to be mild, the study underscores the importance of ongoing post-vaccination surveillance and personalized medical care for individuals at risk. As evidence continues to evolve, health agencies and physicians may need to consider more tailored guidance for those with existing ocular conditions.
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