Thinnest bifocal on the market, made by Essilor. The high index 1.67 bifocal lenses for reading and distance vision viewing means that the reading area has a half moon shape with a "flat top", in the bottow area of the lens. The standard polycarbonate, flat top 235 bifocal has a reading area that is 35mm wide at the top. This is a good choice for prescriptions up to +/-8.00 sphere. This lens is available in the following range: -9.75 to +6.00 sphere, - 4.00 to +3.00 cylinder, and up to +3.00 add (prism and slab off excluded). This lens is also available in the Flat Top 28 style. For the Flat Top 28 style, the reading section is 28mm across thte top. Crystal Vision lenses are made by one of the world's largest lens company making top quality lenses. All Crystal Vision Lenses are made in the U.S., to exacting specifications, in an Essilor laboratory, and we are able to offer them at a great price point. This lens is a good choice for corrections up to +/-4.00, and it is available with a variety of options such as Transitions, UV protection, sunglasses or fashion tint, standard Anti-Reflective coating, and the top-quality Crizal Alize and Crizal Avance coatings.