I've bought many pairs of glasses online and there are many reputable dealers online for such a thing. Be prepared, however, to wait a couple weeks for them to arrive, but you'll also find that the prices are WAY cheaper. I used to work at an in-store optical shop, and no matter what, the online prices were cheaper, and the glasses were better quality. It's sad but true. I use zennioptical.com, but I'm not sure they ship to Portugal. Just read the customer reviews, and hear what people around the internet are saying about the site. Use your best judgment, and just like the in-store optical shops, don't let them fool you into paying high prices for what should be a cheap commodity. I hope you find what you're looking for!