With the advancements in the lens making technology lenses that are lighter in weight are very common these days. The glass lenses were heavy and they have the problem of shattering. The plastic lenses were then introduced as they are shatter proof. The optical quality of plastic lenses was also good.
People who wear prescription glasses for vision correction used glass lenses. The vision correction is obtained by bending the light rays to the required extent. This bending depends on the index of refraction (IOR) of the lenses. To bend the rays, higher IOR is needed and the glass lenses were thick enough to bend the rays. But people wearing thick correction glasses started feeling being pushed out of the fashion world.
Then plastic lenses were used as corrective lenses but they were suitable for weak prescriptions. For a strong prescription thicker lenses were only used to reach a high index of refraction. Depending on the eyesight problem such as myopia or hypermetropia the lenses were thick either in the middle or at the edges. These people were waiting to wear the trendy flat thin glasses that can correct their vision too. The high index plastic material was used to make lenses keeping the thirst of these people in mind.
High index plastic lenses have a higher index of refraction and hence lesser material is sufficient to reach the required bending of light rays. The curves in the lenses were flat and they provide corrective vision.
The index refers to the amount of bending achieved. This can range anywhere from 1.50 to 1.74. The high index lenses with 1.74 IOR are very flat, very thin and very trendy. These lenses include the current anti reflective treatments to reflect off excess light.
These high index 1.74 lenses are perfect for fashion conscious people who want to be at the pinnacle of fashion. It is for people who want to get rid of their thick corrective glasses which hide the natural beauty of their eyes. These glasses can be used for even strong prescriptions.
The curves of high index 1.74 lenses are flat and due to the extremely flat curves off-axis vision may be blurred. To eliminate this problem aspheric lens technology is incorporated into these lenses. These extremely flat, thin light weight high index 1.74 lenses are sure to add a touch of style to your face but they cost more and they are worth it.