Welcome to a little background on spectacle lenses including types available and variations.
- Single vision lenses have just one focus throughout the whole lens i.e. lenses ‘only for near’ would be reading glasses and ‘only for driving’ would be distance glasses.
- Bifocals and Trifocals are older styles of lenses though still occasionally used. They have 2 focuses and 3 focuses respectively separated by lines.
- Progressives or Multifocals have many focuses with no lines visible on the lens. The focus ‘progresses’ from distance to near with every distance in between. They look better and are easier to walk in (no lines) and provide excellent results for most patients.
- Extended Focus Lenses belong to the same family as progressives but have an emphasis on the near strength. These are often called Vocational or Occupational lenses as they are excellent for computer and office work.
- High Index Material describes a denser material that doesn’t need much thickness to produce the same prescription. They are used to create thinner and lighter lenses. Standard CR39 resin material has a refractive index of 1.5. Higher Index materials are most commonly 1.6, 1.67 or 1.74 though do come as high as 1.91.
- Aspheric Design uses asphericity to produce a flatter lens surface design resulting in less optical distortion & thinner lenses.
- Photochromatic materials are used to produce lenses with a tint that reacts to sunlight. Generically they are called photochromatic though are more commonly known by their brand names e.g. Transitions, SunSensor, Photofusion
- Anti-Reflective Coatings (AR Coats) greatly reduce reflections on lenses increasing invisibility of lenses from only about 90% to over 99% visible light transmission. They have cosmetic advantages (easier to see patients eyes) and practical advantages as you see clearer through these lenses and they minimise glare from headlights when night driving.