High Index Lenses For My Glasses?
What Are the Benefits of High Index Lenses For My Glasses and What Should I Choose?
High index lenses offer a better cosmetic look to your glasses and can be from 20% to 45% thinner depending on the index that you choose.
Nearsighted people (myopia) will require a divergent lens which is thinner in the middle and thicker at the edges. Farsighted people (hyperopia) will require a convergent lens which is thicker in the middle and thinner at the edges.
Choosing a thinner lens will generally reduce the thickness of the lenses and be far more comfortable to wear.
The index of the lens will indicate its refractive index and how refractive that lens is. You can select a 1.6 index, 1.67 index, and 1.74 index.
The higher the index the more the lens will bend or refract the light and is the ratio of the speed of light passing through the air compared to the speed of light passing through the lens.
A 1.60 index will give you approximately a 20% thinner lens, a 1.67 index will give you 30% thinner, and a 1.74 index gives a 45% thinner lens.
Standard plastic lenses will have an index of 1.5 and glasses about 1.52.
High index lenses will range from 1.6 to 1.74 (some specialist lenses will offer an index of up to 1.9 but these are rare and highly expensive).
There are other factors which will affect your lens thickness such as the overall lens diameter: the larger the lens the thicker it will be. And also your PD value and the type of frame chosen.
For best results, choose a small frame and if you have a higher power then a plastic frame will do a good job of hiding the lens thickness.
We would usually advise prescriptions over +2.5 to +5.00 should consider a 1.60 index or above.
Those with a prescription over +/-5.00 should consider a fully rimmed frame with a 1.74 index.
High index lenses will reflect more light than standard index lenses by about 50% so they should always have an anti-reflective coating applied which allows 99.5% of light to be transmitted through the lens and all the lenses at Glasses2You have this coating as standard.
For further research see: http://en.wikipedia.org/wiki/Corrective_lenses
Written by: Russell Andrew, Director