Understanding Varifocals and Bifocals
A varifocal is designed for people who need both a reading and distance correction but also use an intermedidate distance, ie computers .
The top part of the lens holds your distance perscription, just below eye level the power is adapted to suit a range of 60 cm which is perfect for computer use. The bottom part of the lenses is used for reading.
Due to the manufacturing process a varifocal will always have a small amount of distortion on the edge of the lens. This means that your best vision is in the centre.
In order for you to use your Varifocal effectively there are a few simple rules!
- Always look directly at what you want to see, eg if you are driving and need to look at your mirror, turn your head towards it as opposed to looking through the side of the lenses.
- When walking down steps drop your head so that you are looking through your distance corection instead of your reading area.
- When reading, lift your head slightly and look through the end of the lens.
This may all seem a little complicated but after a day or two it will come naturally to you and will be alot better than having two or three pairs of glasses lying around your desk!
A bifocal differs from a varifocal as it only holds prescriptions. The top half of the bifocal is your distance prescription and blended onto the lens is a reading segment. The bifocal is easily identifiable as it has a line across it seperating the two prescriptions. The reading segments come in many styles the most popular being the flat top in the bottom of the lens.
While the bifocal has less distortion than a varifocal it does not work for computer use and is cosmetically less attractive.
High Index Lenses Explained
Most Lenses are made from an optical plastic material called 1.499.
The 1.499 means the refractive index of the lens i.e. the thickness of the lenses. This lens can look quite thick and curved in high prescriptions. In order for us to reduce the thickness and weight of your lenses we use materials with a higher refractive index such as a 1.6, 1.67 and a 1.74. The higher the index of the lens the thinner and flatter it will be.
Not all prescription require High Index lenses. So here is what we recommend:
- For prescriptions of +/- 3DS, a 1.499 standard anti-reflective coating is suitable.
- For prescriptions of +/- 3.50DS to 5DS a 1.6 or a 1.67 would reduce both weight and thickness of the lenses
- For prescriptions of +/- 5.50 to 8DS then a 1.74 lens is the index best suited.
Do remember that the bigger the frame the bigger the lenses that will need to be ordered, this can increas the thickness of the lenses!
Do not hesitste to contact our Optician with any queries regarding lens seletion.
Anti-Reflective Coatings for Glasses
The anti-reflective coating was originally designed for night time driving and computer use as they have the highest instances of glare.
When used for night time driving they reduce the glare from on coming traffic. The coating is also perfect for office use and is highly reccomended for computer users.
The other benefit of this coating is its cosmetic apperance. The coating makes the lenses look completly clear and reduce image distortion in higher prescriptions.
All our Anti-reflective lenses also have a layer of scratch-resistant coatings. This coating protects your glasses from general day to day scratches, but remember, while the lenses are scratch resistant, no plastic lens is completly scratch-proof!