Mapusa market is on everyday but the "touristy" one takes place on Friday with a bit more "tat" than usual, but it's a round trip of 120kms from Cavelossim. Margao, the second city of Goa, is much closer and have heard there are some good opticians. Don't know any exact details but again the local taxi drivers will know for sure.

Tks very much, yep been to Margao market a couple of years ago. But thanks for your help anyway.