The entire lens is same power throughout it, and may correct either Myopia (near-sightedness), Hyperopia (far-sightedness) or Astigmatism. Single Vision lenses correct for a single point of focus whether it be Distance, Intermediate, or Near.
This type of multifocal contains 2 different powers in the lens. Standard Bifocals typically come in a Flat Top 28(FT28), Flat Top 35(FT35) or Executive. 28 and 35 represent how wide the bifocal is from side to side and Executive represents that the bifocal goes across the entire lens.
This type of multifocal contains 3 different powers. Typically the top power is for distance, the middle power is for intermediate, and the bottom power is for reading. Trifocals also come in 7 x 28, 8 x 35, and Executive.
Instead of having just 2 or 3 lens powers like bifocals or trifocals, progressive lenses provide a seamless progression of many lens powers for all viewing distances. Progressive lenses also have more cosmetic appeal due the invisible zones and no harsh lines like bifocal and trifocals.
|( Thickest to Thinnest )||PRO's||Con's|
Index:1.498 Abbe: 58
|Clarity - Less Expensive Lightweight||Breakable - Heavy|
Index:1.52 Abbe: 59
|Highest Abbe||Heavy Easily Breakable|
Index:1.54 Abbe: 45
|Impact Resistant Blocks 100% UV - Lightest Higher Abbe than Polycarbonate||Thicker than Poly|
Index:1.586 Abbe: 30
|Lighter than Hi-Index Blocks 100% UV||Lower Abbe|
Index:1.67 Abbe: 32
|Thick and Light Blocks 100% UV||Lower Abbe|
Index:1.74 Abbe: 45
|Thinnest Lens Available Blocks 100% UV||Thicker than Poly|
Index of Refraction
The index of refraction (also called the Refractive index) is a measure of how efficiently a lens material can bend light. The index of refraction of eyeglass lens materials usually ranges from 1.50 (regular plastic) to 1.74 (on variety of high index plastic.) In other words, the thickness of the lens.
In optics and lens design, the Abbe number, also known as the V-number or constringence of a transparent material, is a measure of the material’s dispersion (variation of refractive index versus wavelength), with high values of V indicating low dispersion. In other words, the clarity of the lens.