Generally speaking, when you do not need to wear your sunglasses, you have put them away getting rid of the dirt and dust, especially the branded sunglasses, like Smith brand. If now you want to clean your loved Smith sunglasses, I can tell you two options, and you can choose from them. The first way, also the easiest way, is that you can take your sunglasses to the authentic Smith shop because thery can clean them for you. Pls no worries, it will as free of charge as usual. Then, if you think the shop is far away from you and you want to clean them by yourself, now and here I can tell you some simple ways to make it. A much better idea is to clean the lenses with a microfiber or lint-free cloth, which will cost you less money and time.(pls note never clean them with regular towel, paper towel, or washcloth) Hope I can help you and your loved Smith sunglasses.
You may just use the clear water to wash the lenses. It will not damage the coating part which adopts the special materials. However, if there is the oil on the lenses, you may use the little amount of abluent to get the oil splash off. Last of all, use the clean cloth to dry them.
It would be washed by clean water. It's simple to clean the sunglass, washing it with clean water after wearing. Then softly wipe the water which remain in the glasses, put it in a ventilated place to blow dry. If there's some oil stain attached in the lenses, apply a little drop of liquid soap and use water to wash after it, which will be ok to get rid of it. But please pay attention that the dry cloth can not use to rub the surface of lenses to prevent from scratch and the increasing of blur area. Make sure the glasses are put in the shade and cool place other than under the blazing sun for quite a long time for the sake of deformation possibility. The resin lenses of sunglasses are not so durable, so the method of water washing is better than cloth rubbing. Thus the lenses would be clean and the scratching will be effectively avoided.