Can you catch an eye infection from a camera viewfinder, and how should you clean it?

Yes, there is some risk if multiple people share a camera, especially if someone has something contagious like conjunctivitis and puts their eye close to the eyepiece. The viewfinder itself does not create infections, but it can transfer germs.

In most cases, germs that cause common eye infections do not survive very long away from a human host, so simply letting the camera sit unused for a while can reduce risk. To be more cautious, clean the outside eyepiece/viewfinder area carefully with lens cleaner; many lens cleaners are alcohol-based and can help disinfect. Avoid harsh cleaning methods and focus on the exterior surfaces that contact skin.

If you are sharing the camera with many people, a practical precaution is to have anyone with red or irritated eyes avoid the viewfinder and use the rear LCD instead. Also ask users to wash their hands before handling the camera.

So: the risk is possible but generally low, and basic hygiene plus careful cleaning of the eyepiece area is usually sufficient.