The optical possibilities of gelatin

Abstract

Contact lenses have traditionally been manufactured using a variety of plastics: polymers for soft lenses and acrylic or polymethyl methacrylate for hard lenses. There is emerging interest in the use of gelatin for lenses to increase malleability, water solubility, and sustainability as a non-plastic. A predicted difficulty in the use of gelatin is the reduced refractive index (RI). We looked at how acrylic or gelatin changes the RI and focal length in order to see how gelatin lenses would have to be altered for more severe prescriptions. We tested the refractive rays of gelatin and acrylic with both convex and concave lens types to investigate which produced smaller angles of refraction and correspondingly greater focal length. The average RI of the biconvex and biconcave acrylic without Pam, acrylic with Pam, and gelatin were 1.47, 1.496 and 1.36, respectively. Gelatin’s lesser angles of refraction produced a longer focal length. The lower RI of the gelatin (0.11–0.136 less than acrylic) directly correlated with its lesser angles of refraction, which produced an overall greater focal length (3.51– 4.38 more than acrylic). Gelatin needs to be thickened, increased in curvature, or mixed with crosslinkers to strengthen the lens. Lens makers will face similar challenges with the switch to gelatin lenses, so they may need to incorporate a larger percentage of solid gelatin concentrate or a plastic alloy in the gelatin to increase the RI, decrease the focal length, and improve the stability of the gelatin.