I have been buying eyeglasses from Raymond Chan at Tai Kwong Optical in Kowloon for years. The quality and service are superb, and the prices are about 50-75% of what I'd pay in the US. I much prefer doing business with Raymond than with one of the franchise shops like the Optical Shop.
Tai Kwong Optical is on the corner of Mody Road and Hart Ave, midway between the Holiday Inn and the Shangri-La. (The address is 31 Mody Road, though the entrance is actually on Hart Ave.) If you stop there, please tell Raymond that Mister Donald, the big fellow from the States, says hello -- that might get you a few dollars off.