About Our Free Standard Lenses
Video: Lens indexes explained.
When browsing our frame selection, you will notice that we say that standard lenses are included in the frame price. These standard lenses are a 1.57 index lens. 1.57 lenses are recommended for low to mid prescriptions with a power between -4 and +2 dioptre, although this is a very general guideline; much depends on your specific prescription, the orientation of your cylinder (if you have astigmatism), and the size and shape of your chosen frame.
If you aren't sure which lens to choose, please use our unique 3D lens viewer to compare available lenses and determine for yourself which lens offers you the best weight/thinness combination, based on your prescription and chosen frame.
Video: Lens materials recommended for rimless frames.
1.57 Lenses and Mechanical Properties
1.57 index lenses are an excellent mid-index lens. Unfortunately, the mechanical properties of this 1.57 index lens are somewhat poor. It is a great lens in a full rim frame where the lens is supported on all sides, but in a (semi) rimless frame the 1.57 material is prone to cracking over time.
You will find that most optical stores (and optical websites which truly understand lenses) do not recommend the 1.57 index lenses for rimless and semi rimless frames.The reasoning behind this is that the material loses tensile strength when making adjustments to the lens to accommodate these frame styles; a groove is edged into the lens to support the wire for semi rimless frames, and holes are drilled to mount rimless frames. Cracking and chipping can occur over time
around these modified areas, causing customer dissatifaction and possible safety hazards.
If you want to select a rimless or semi rimless frame, then we recommend you select an appropriate lens material for this frame style. We recommend any of our lens materials, except for the 1.57 or 1.50 index lenses.
Video: Shatter resistance and lens materials.
1.57 Lenses and Shatter Resistance
Our 1.57 index lenses comply with the FDA regulations regarding impact resistance (i.e. a 5/8" steel ball dropped from a 50 inch height). However, for sports activities or use by children, we recommend lens materials which have enhanced shatter resistance. The available lens materials are polycarbonate, Trivex and Xirm. 1.67 would also be reasonable option as it has shatter resistance significantly superior to 1.57, but not as good as polycarbonate, Trivex and Xirm.
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