High Refractive Index Plastic Optical Materials

Abstract

[Master of Philosophy thesis]. Although, glass was the only lens material for over 600 years, today plastic lenses used for prescription eyewear and sunglasses requiring high abrasion resistance and high quality optical properties have been developed. These first plastic lenses, like CR-39" with a 1.498 refractive index, could not compete with the high index glasses known as flints.

High index plastic lenses are a new lens category, having refractive index from 1.54 (SOLA Spectralite) to even thinner 1.71 high index (Hoya Teslalide). Recently, much interest has been shown in development of new
high index polymeric materials. Main target of all these efforts of course is the production of lenses with a very good optical performance. This performance includes high refractive index, low constrigence, good light transmission and UV absorption. Obviously, the outstanding factors defining this performance are refractive index and chromatic aberration.

The refractive index can easily be measured using a light source or a laser beam and computing the minimum deviation angle after the beam refraction through a prism of the material. The chromatic aberration can be determined by evaluating the optical performance of the material itself.

Nowadays, ophthalmic lenses of plastic have become very popular because they are inexpensive, lighter in weight and more resistant to shattering than glass. However plastic lenses generally have less surface hardness and wear resistance, especially materials such as polycarbonate, polyethylmethacrylate, and polyallyldiglycol carbonate which have to be
improved by surface coatings and processes such as hard-coating.

At all times we have to consider that spectacle lenses have a psychological function. In that way, what is better for the consumer is not always what is best for the researcher. In order to check out this factor, is essential to look into the performance of these plastic materials in front of the consumer's eye.

Experimental work included testing and estimating refractive index and
chromatic performance of various plastic lenses. On one hand, we had to
verify and confirm the index of new materials in ophthalmic lenses market
and on the other hand to compare different plastic materials about the chromatic dispersion, transparency and yellowness.

Date of Award	May 2003
Original language	English
Awarding Institution	Aston University