BIAL HD Horizontal Loon Glasses Refraction Glasses Bed Prism Spectacles Glasses - Size L Color Black material:K9 optical glass lens Have obvious effect in preventing and alleviating cervical spine, lumbar spine and shoulder fatigue and discomfort. Use optical principle and high quality optical materials, prism turns page 90, help people easy to read books, watch TV or do other things while lying flat. Simple use and maintenance, high quality, makes the user feel comfortable. Strict material selection and precision processing, internal reflection prism equivalent in glass plate, so there is no influence to the user's vision.