change in eye rx

My son was diagnosed with amblyopia when he was 5 years old.  His right eye has perfect vision.  His left eye has poor vision and he has to wear glasses.  His glasses prescription has been the same for the last 3 years.  He is 8 1/2 years old now.  We just went to his yearly eye exam with his opthamologist and he did awful on his exam.  He did the exam with his glasses on and said every line was blurry.  I don't think he got 1 letter correct.  His doctor said maybe his eye got better and the glasses are too strong for him.  So she changed his rx and said to come back in 3 months.  If he still does bad then maybe his eye got worse.  
What I don't get is how does she not know if his eye got better or worse?  Why didn't she let him take the exam with another prescription lens?  Doesn't she have lenses there to try?  Is it because he is a kid?  And why does he go back in 3 months?  It sounds crazy to me.  
I just ordered glasses for $150 and might have to get another pair!  
I don't mean to ramble on but I'm so confused!!!!!
PLEASE HELP!!!

[Michael J Kutryb, MD]

Just make sure you are seeing a pediatric ophthalmologist.  Is your son has amblyopia - usually there is some type of patching of good eye or blurring of good eye with dilating drops to make weak eye stronger and of course have to have the right glasses prescription.  What kind of therepy has your son been getting and how much did his vision change?  You need to address your questions TO YOUR DOCTOR.  Your questions are legitimate.  If you are not satisfied with current doctor - see another.

MJK MD