Influence of contact lenses power on Young's modulus

Abstract

Purpose: The modulus of a material describes its ability to keep its shape and resist deformation. The modulus of a contact lens (CL) is measured using Young’s modulus and is defined as the capacity of a lens material to align to the ocular surface and its resistance to being deformed and can influence comfort and ocular health. The aim of this study was to compare the Young's modulus of different CL power. Methods: One bi-weekly and one daily disposable CL, Senofilcon A and stenfilcon A, with powers of: +6.00D, +3.00D, -0.50D, -3.00D, -6.00D and -9.00D were characterized by their Young Modulus using the Linkam TSS 350 System with LNP95 and the Dualcope® MP0R. Two samples of each CL were tested right after the lenses were taken out of the original pack. For the calculation of the Young Modulus (in MPa), the area, diameter and thickness of the CL were considered. Results: The mean value of Modulus (in MPa) registered for Senofilcon A was 0,68± 0,24. When the power was considered, the values ranged between 0.24± 0.13 and 0.88± 0.17. The mean value registered for Stenfilcon A was 0.24 ±0.09. When the power was considered, the values ranged between 0.13± 0.09 and 0.37± 0.01.

Conclusion: The results show that there is a variation in modulus with power of the CL evaluated which indicates that the stiffness of a CL can also be dependent on its power and thickness.