1) The advantages of the 1.56
Lenses with a 1.56 index are considered the most cost effective lens on the market. They possess 100% UV protection and are 22% thinner than CR39 lenses.
1.56 lenses can cut to fit the frames perfectly, and these lenses with knife edge finishing would suit those irregular frame sizes (small or large) and would make any pair of glasses look thinner than ordinary.
1.56 single vision lenses have higher Abbe value, can offer wearers excellent wearing comfort.
2) What are bifocal glasses.
● Bifocals are two prescriptions combined into a single lens. Trifocals are three prescriptions combined into one lens.
● Bifocals were originated by Benjamin Franklin in the 18th century when he cut the halves of two spectacle lenses and fitted them into one frame.
● Bifocals are needed because the distance glasses do not suffice to focus sufficiently for near. As age increases, (in India 38-40 years is the presbyopic age) reading glasses are required to read at a comfortable distance. Rather than taking out the distance glasses and putting on near glasses
3)The advantages of the bifocal lenses.
With a bifocal, distance and near are clear but the intermediate distance (between 2 and 6 feet) is blurred. Where intermediate is essential for a patient a trifocal or varifocal is required.
Take the instance of a piano player. He can see distance and near, but the music notes he has to read are too far away. Hence, he has to have an intermediate section to see them.
A lady who plays cards, can see the cards in her hand but cannot see the cards laid on the table.