If you are wanting to get cheap prescription glasses while in Bali, make sure you give your self 7-8 days from the time of ordering until they return. On our recent trip (16 May) went to each of the 3 places in Centro Discovery Mall in Tuban and each quoted 7 days at least. Each also quoted 475,000rp for the prescription + frames. Definately worthwhile getting them if you have the time to wait.
There were also qualified optometrists as all stores.