Frames and lenses

How do I choose the right frame size? How does the virtual try-on work? What if it doesn't open? What frame materials do you have? What is the difference between single-vision, distance, computer and reading glasses? What are progressive glasses? Are they right for me? What lens thinning options do you offer? What is a blue-light filter? Do I need one? What are photochromic lenses? Do you have prescription sunglasses? What is the difference between polarised and tinted lenses? Do you sell lenses only, or fit lenses into my own frames? Do you have collections for children or teenagers? Will the frames I want come back in stock? Do you have nickel-free frames? How do I clean my lenses? What is bridge width and how is it measured? Which frames have spring hinges? How do I measure my frames? Can the glasses handle heat and cold?