I suggest Naresuan University Hospital
Located in the town of Pitsanoluk within University grounds.
Bring a Thai speaker with you the first time at least, the registration procedures can be confusing and everything is in Thai. They don't see many foreigners.
Also bring patience and something to read, waist may be long.
Possible that the opthalmologist is nto there every day, you'll have to check.
I don't know what your problem is, but if anything seriouc or complicated, the best thing is to come to Bangkok and go to Rutnin Eye Hospital. But for routine things Naresuan should be OK.