A Single vision lens is a lens with one strength/power throughout the lens i.e. either for distance vision or reading.
A Bifocal lens has two separate viewing areas within one lens, the top part for distance vision and the bottom for reading. The most commonly used bifocal design is the flattop bifocal, where the reading area looks like a sideways D.
A progressive lens has a strength/power for every distance the wearer would want to look at i.e. distance, intermediate (arm’s length) and near (reading). Progressive lenses are commonly called Multifocals, because of the different viewing areas in the lens. A progressive lens has no lines to separate the different viewing areas and is thus cosmetically much more appealing (looks like a single vision lens).
Progressive lenses are advanced lenses and require very precise measurements and regular adjustments (to the frame) by your Optometrist or Optical Dispenser. These lenses have mild to medium (depending on the laboratory design e.g. Zeiss, BBGR etc) distortion (blur) areas to the sides of the lenses. These distortions are however minimized by regular fitting and adjustments to the frame.
A few adaptation tips
Most wearers adapt virtually immediately to progressive lenses, but some patients need a short adaptation period to get used to the progressive lens. The quickest and surest way to get used to progressive lenses, is frequent adjustment at the practice you purchased your spectacles, as the Optometrist or Dispensing Optician knows your history. Secondly to wear the spectacles constantly and to follow some simple exercises as described in the following points:
Tip 1: Distance Vision
The distance area of a progressive lens is the top of the lens, so if you hold your head in the normal upright position and look straight ahead, you will be looking through the correct area and your distance vision will be clear. In other words point your nose at that which you would like to see, and look through the top portion of the lens.
Tip 2: Intermediate Vision
Objects in your intermediate vision area are at arms length i.e. your computer screen or an item on a shelf. Choose an item to focus on, point your nose at it and move your head slowly up and down until the object comes into focus. This is the intermediate zone of the progressive lens. With practice you will soon automatically find the correct area of the lens to look through in order to get objects in focus.
Tip 3: Near vision (reading)
Hold a book at your normal reading distance; keep your head in a comfortable position, as you would normally read, as this is the way the lens measurements for the specific reading area were taken by the Optometrist and/or Optical Dispenser. Now move your eyes up and down, keeping your head and reading matter still, at some point the reading matter will come into focus. You will need to move your head from side to side more than what you where used to before progressives, in order to keep clarity from one side of a page to the other.
Human beings are amazingly adaptive and you will be surprised at how soon these “tips” become a part of life.
Lens coatings or treatments
Lens coatings can be used to enhance performance and lifespan of your lens. These coatings include anti-reflection coating, scratch resistant coating, tints and ultra violet blocking coatings.
Scratch resistant coating
Light-weight plastic lenses can be more easily scratched than glass lenses. However, special hard coatings have been developed to help protect your lenses from scratching and wear and tear caused by everyday use. The small additional cost for scratch protection is a prudent investment as it will lengthen the lifetime of your lenses.
Ultraviolet rays in sunlight pose potential harm to your eyes as it does to your skin. We protect our skin with many different “UV protection” products, and we can also protect our eyes by having a UV protection coating applied to our plastic lenses. Unfortunately this coating cannot be applied to a glass lens.
The coating will block out the hazardous UV rays without visibly tinting the lenses. Michele Hlava Optometrists have an instrument that can test all types of lenses for transmittance of UV rays as well as Infra-red rays.
We strongly suggest all persons have a UV coating on lenses, as UV damage to the eye is irreversible.
Special anti-reflective coatings, similar to those used for “fine” camera lenses are available for spectacle lenses. These coatings are particularly effective for reducing eye fatigue for computer operators, and for driving at night. Anti-reflective coatings also enhance the appearance of eyewear by removing all distracting reflections from white paper, magazine paper and computer screens etc.