Covid shot linked to vision loss in rare cases
It found that Pfizer 's vaccine can adversely affect the cornea, which allows light to enter the eye.
At its worst this could lead to corneal swelling or blurry vision, especially in those who already suffer from eye problems or have had a cornea transplant.
In 64 people, scientists in Turkey measured changes in the cornea's inner layer, called the endothelium, before taking the first Pfizer dose and two months after receiving the second.
Results revealed that taking both doses of the vaccine led to thicker corneas, fewer endothelial cells in the eye and more variation in size of these specialized cells that form the endothelium.
In the short term, these changes suggest the Pfizer vaccine may temporarily weaken the endothelium, even though patients didn't suffer clear vision problems during the study.
For people with healthy eyes, these small changes likely won't affect vision right away.
However, if scientists find that these changes last for years, they could lead to corneal swelling or blurry vision, especially in those with pre-existing eye problems or people who have had a cornea transplant.
A thicker cornea and reduced cell density could contribute to eye conditions like corneal edema, bullous keratopathy, or corneal decompensation, which can all cause permanent vision loss in severe cases, especially if left untreated.
The researchers warned in the study, published Wednesday in the journal Ophthalmic Epidemiology: 'The endothelium should be closely monitored in those with a low endothelial count or who have had a corneal graft.'
An eye doctor can use a special microscope called specular microscopy to find out if someone has a low endothelial cell count.
If you have blurry vision or eye discomfort, this test can also check if your cornea's cells are healthy.
A low count can be the result of aging, eye diseases like Fuchs' dystrophy, eye surgeries, injuries, or infections. These factors damage the cells that keep your cornea clear, and they don't grow back.
Specifically, the team found that the Pfizer-BioNTech vaccine caused a patient's cornea to go from 528 to 542 micrometers in thickness, or roughly 0.0208 inches to 0.0213 inches. This is a roughly two-percent increase in micrometers.
A slightly thicker cornea isn't automatically harmful. The cornea can thicken temporarily due to inflammation, fluid buildup, or stress on the endothelium from minor illnesses or injuries to the eyes.
If it stays too thick for months or years, however, it could make the cornea less clear, potentially affecting vision.
The team did not recommend against vaccination and will still need to conduct long-term testing on patients to see if these changes continue to appear months and years after taking the shots.
The average number of endothelial cells, which keep the cornea clear by pumping out excess fluid, dropped from 2,597 to 2,378 cells per square millimeter in the study, a loss of about eight percent.
Normal endothelial cell counts range from 2,000 to 3,000 cells per square millimeter in healthy adults, so 2,378 is still within a safe range for most people.
However, for someone with a low cell count to start with, due to a previous eye surgery, infection, or disease, this loss could be riskier for their vision.
Researchers also discovered that these cells became less uniform after the vaccination, with their coefficient of variation - each cell's difference in size - increasing from 39 to 42.
When cells die, nearby cells stretch to fill the gaps, leading to bigger differences in size.
This could mean the endothelium is less healthy. If this trend continued for years, it could affect the cornea's clarity.
After vaccination, the study found fewer cells kept their healthy six-sided shape, with the total dropping from 50 to 48 per cent of the cells in the eye.
Healthy endothelial cells are usually shaped like hexagons, which allows them to fit together tightly, like a honeycomb.
Although the two per cent drop was not a direct sign of damage, it suggested to the team that the cells might be reacting to some sort of stress over those two months to three months.
Researchers said their results also showed evidence that the changes had a high likelihood of being directly linked to taking the vaccine, meaning it wasn't just a random anomaly in the testing.
If the signs of stress and inflammation drop off shortly after receiving the Pfizer shot, the impact of these minor changes would not be overly harmful.
To find these results, the team studied 128 eyes, 64 pairs in total, before each person received their Covid vaccinations.
They followed up with the group approximately 75 days after they got their second dose of the Pfizer-BioNTech vaccine.
The team used a machine called Sirius corneal topography to measure the corneas' thickness and shape, and another device, the Tomey EM-4000 specular microscope, to take detailed pictures of the endothelial cells to check their number, size and shape.
Each participant also took a full eye exam, including tests for vision sharpness, eye pressure and scans of the eye's front and back parts to ensure overall eye health.
By comparing the measurements taken before vaccination to those after, the researchers could see if the Pfizer vaccine was influencing the health of the eyes.
The new data on potentially harmful side-effects linked to Pfizer's Covid vaccine added to a growing list of concerns the Trump Administration has highlighted.
In May, the US Food and Drug Administration (FDA) forced Pfizer and Moderna to use expanded warning labels about the risks of heart damage tied to Covid-19 vaccines.
The shots previously included warning labels about the rare chance of patients suffering myocarditis, inflammation of the heart muscle, and pericarditis, inflammation of the sac-like lining surrounding the heart.
The new labels expanded that warning to certain age groups, particularly men between the ages of 16 and 25.
Researchers found that this seemingly healthy group appeared to be at the highest risk of the rare complications.
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