Ready-made readers vs CR-39: A study of refractive index, clarity, and scratch resistance

Background: Columbia Resin 39 (CR-39) is a plastic polymer widely recognised in the ophthalmic industry for the production of spectacle lenses. This material is known for its superior optical qualities and higher scratch resistance compared to other materials. Ready-made reading spectacles (RMRS) offer a cost-effective and readily accessible option for vision correction. Aim: This study aimed to compare lenses used in RMRS to CR-39 lenses, specifically in terms of refractive index, image quality and scratch resistance. Setting: This study was conducted at the University of the Free State, Bloemfontein, South Africa. Methods: In this comparative study, 12 RMRS lenses were evaluated against three CR-39 lenses. A spectrometer was used to determine the refractive index by quantifying the percentage of light transmission. Image quality was assessed using an optical tract that projected images of line pairs through the 15 lenses, utilising a monochromatic light filter. The scratch resistance was measured by counting the number of scratches on the lenses produced by an anti-scratch coating device. Results: A statistically significant difference in the refractive indices was found. No statistically significant correlation was found in image quality. However, practically, CR-39 demonstrated superior image quality and exhibited less susceptibility to scratching. Conclusion: When prioritising practical implications of image quality and scratch resistance, CR-39 lenses exhibit superior performance compared to RMRS lenses. Contribution: This study offers the public community and the ophthalmic industry insights into the differences in optical and physical quality between RMRS and CR-39 materials.