We see a pead opthamologist too she diagnosed dd at 3 with a turn in her eye and long sighted and beacause we were already seeing her she checked ds at 18mths and he has glasses too. You don't have to wait until they can recognize letters, if we had waited that long dd would most likely have needed surgery. Dd used shapes to be tested, and with ds she used stickers on her nose and just followed his sight and reactions. If you are concerned ask for a referal, ours isn't cheap but has been fantastic when the mchn said dd was fine. We didn't have to see an optometrist first we just got a referal from our gp we didn't wait too long as she puts aside times for new patients.