IMO, u will do just fine with the eye examination in Singapore... The optometrists are all trained and certified.... with a professional diploma... not sure its equivalent here in the states... maybe like an associate degree???

Bring along a pair of your old glasses... They will determine the old prescription from there... and then continue with the routine eye-examination... If u are comfortable with your current prescription, go thru the test... and at the end of it, check with the optometrist if it is very different from the old ones.... if not, just tell him/her that u prefer to stick with the old prescription... something i do often... coz mine doesn't change much.. and hate to have my eyes adjust to the new prescription...

There are a few major franchises in singapore...
Paris Miki
Capitol Optical
Nanyang Optical

Oh, i just remembered one thing while checking the website for u... When u are in Singapore, either buying your eyeglasses or at a restaurant... Before paying with credit cards, ask if any major credit cards offer u a discount... For example, Paris Miki offer 10% discount on eye frames for citi cards holder... But i am not sure if they limit the promo to cards issue in Singapore only... But chances are, they wont be able to tell, given the vast number of expats working in Singapore....