A common cause is simply eye strain from keeping one eye tightly closed while the other stays on the viewfinder for long periods. The easiest fix is to learn to shoot with both eyes open instead of squinting one shut.

Closing or squinting one eye for hours can fatigue the muscles around that eye and lead to soreness or headaches. Keeping both eyes open is often more comfortable and reduces that strain.

It can take practice at first, but many photographers adapt to it over time. If needed, take short breaks during the event to relax your eyes as well.

If the pain continues even after changing your technique, it may be worth discussing with an eye-care professional, since persistent eye pain isn’t something to ignore.