What's causing my 11 year old to have a constant sticky eye?

[IToldYouIWasFreaky]

My 11 year old DS seems to constantly have a problem with his eye. When he wakes up in the morning, it can be a bit crusty and the eyelid is swollen. If you ask him, he'll say it's itchy and it hurts but he doesn't complain about it a lot (and he can be a bit of a whinger when it comes to illness or injury!) so I don't think the discomfort is major. And it can look a bit unsightly first thing but the swelling soon goes down and once he's washed his face the gunk is gone. The eye is not red or constantly watering or oozing.
I buy over the counter eyedrops for infected eyes which clears it up for a while but it always comes back. It just seems to be a constant battle at the moment so I am wondering if there's an underlying cause?

Sounds like blepharitis. Warm compress and washing eyelids with baby shampoo should help.

Thank you! That picture looks exactly like DS's eyelid so I think that's what it is.
I have an appointment with the optician booked and I have started the warm compresses tonight.

@IToldYouIWasFreaky, how was the appointment with the optician?

Good, thanks! In general, his eyes are fine and it is definitely blepharitis. The warm compresses really helped before the appointment, but I have also bought some wipes and wash to deal with it properly now.
I had no idea how common it was! I had never heard of it before so thanks for thr advice