Had my 3rd pair of prescription sunglasses made 4/13 -- all have worked well and have been durable -- not the cheapest but certainly around half of what you would pay in US...

Peninsula Optical
Shop S06, Street Floor, The Elegance
At Sheraton Hotel, 20 Nathan Rd, Kowloon
Tel: 2730 5808 or 2385 5543
(it's under the FDX Kowloon Sheraton layover hotel)