Chromatic Performance of High Index Plastic Optical Materials

Purpose: The aim of this study was the evaluation of different plastic optical materials and determination of their behaviour in front of the eye. The study was not for clinical screening but mainly for material determination purposes, where the contrast sensitivity function is inefficient and difficult to interpret.

Methods: Thirty male and female subjects with no ocular or reported systemic abnormality were selected. Twenty-two lenses of +6.00D power, made from 8 different plastic materials following requested: specifications; were edged to round shape and decentred in order to produce a 9∆ prism in front of the subjects’ eye. Measurements of every subject were repeated four times on Bailey-Lovie and Pelli Robson charts, for each lens used in the experiment

Results: A significant decline of visual acuity in correlation to higher index plastic lenses was observed. Also we observed a similar visual acuity decline concerning aspheric design lenses, but with a little better performance than non-aspheric design lenses of the same index material.

Conclusion: The hypothesis of this work was that the higher the index the more the chromatic aberration. The conclusion is that this hypothesis is quite correct. However, the measurement of visual performance is not a very easy task. The wearer may simply experience blur through the periphery of the lens without realising the cause, and therefore the symptoms described to the optician can be confusing.