Double torsion testing of prescription lenses

✍ Scribed by P. J. McAuliffe; R. W. Truss

• Publisher: Springer
• Year: 1995
• Tongue: English
• Weight: 505 KB
• Volume: 6
• Category: Article
• ISSN: 0957-4530
• DOI: 10.1007/bf00123442

✦ Synopsis

In previous work, a modified double torsion test was developed to measure the fracture toughness of polymeric ophthalmic lenses with parallel surfaces. The method used production lenses so that the toughness of the manufactured articles could be measured directly. This method has now been extended to measure the K~c of powered lenses in which the thickness of the sample varied with both Xand Ycoordinates instead of being constant. A computer model of the sample's breaking load was constructed and the predicted values from this were compared to experimental results and a good correlation was obtained. In addition, the computer-generated correction factors were validated using the more rigorous compliance curve technique.