FROM THE BIRTH of glass contact lenses in the late 1800s to the evolution of polymethyl methacrylate (PMMA) in the late 1930s, the primary obstacle facing the contact lens industry was not manufacturing or lens design; instead, it was always the non-oxygen-transmitting materials. The lack of oxygen permeability of both glass and PMMA dramatically limited many patients’ wearing times due to the onset of hypoxia-induced corneal clouding.

If contact lenses were to ever achieve wide acceptance, the industry would need to develop an oxygen-permeable material. This led to the industry’s first rigid GP lens material: cellulose acetate butyrate (CAB).

Cellulose acetate (from wood pulp) was first processed into a synthetic plastic in 1865 by the French chemist Paul Schützenberger (Plastic Historical Society [PHS], 2015). In 1894, the first industrial process for its manufacture was patented by Charles Frederick Cross and Edward John Bevan in the U.K. (PHS, 2015).

In the early 1900s, the Swiss brothers Henri and Camille Dreyfus used this process for manufacturing lacquer and photo film (PHS, 2015). At the outbreak of World War I, the brothers established a factory in England to manufacture a cellulose acetate fabric that was stiff and waterproof for the wings of WWI aircraft.

In 1938, a more durable and dimensionally stable plastic (CAB) became a commercial product (Bowden, 2009). In the early 1970s, petroleum chemist and bioengineer Irving Fatt suggested that CAB might have modest oxygen permeability properties, making it a possible material for contact lenses (Bowden, 2009). Early CAB-based contact lenses were manufactured by Ben Parrish, an optometrist from Tennessee, because there was a factory near his office that used CAB plastic to make screwdriver handles (Bowden, 2009).

CAB had a number of positive characteristics, making it superior to PMMA for many patients. It had better on-eye wetting properties and some oxygen permeability, with a Dk that ranges from 3.75 to 5.90 x ^10(-11) (Pearson, 1978). This modest Dk allowed many patients to be edema-free throughout their wearing schedules. However, CAB was often dimensionally unstable at the thin configuration of a corneal lens, could not be tinted, and was more difficult to manufacture.

In 1970, Titmus Eurocon of Germany launched the Persecon GP lens made from CAB (Lamb and Bowden, 2019). Around this same time, Rynco Scientific of New York began producing a CAB contact lens under the name of Rx 56 (Basile, 1976).

Because the material had not gone through the appropriate approval procedures, in August 1975 the plant was inspected by the U.S. Food and Drug Administration (FDA), which seized all of the material stock as well as the names and addresses of all of the Rynco customers supplied with Rx 56 (Basile, 1976). Reluctantly, Rynco agreed to seek FDA approval and in 1978 CAB was approved by the FDA as the first GP contact lens material (Bennett and Grohe, 1986).

Soon after the approval, Danker & Wohlk Inc. (Meso) and Barnes-Hind (CABCurve) joined Rynco (Rx 56) in manufacturing CAB lenses in the U.S. CAB dominated the custom (made to order) GP lens market from 1978 until the approvals of the silicone/acrylate materials Boston II and Paraperm O2 in 1982 (Schifrin et al, 1984).

Few plastics can boast such a long pedigree as cellulose acetate. Today, it continues to be used in certain spectacle frames to achieve special color effects not possible using injection molding. CLS

References

1. Plastic Historical Society. Cellulose Acetate. 2015. Available at plastiquarian.com/?page_id=14227 . Accessed June 14, 2023.
2. Bowden TJ. Contact Lenses the Story: A Historical Development of Contact Lenses. Bower House Publications. 2009:205-206.
3. Pearson RM. Dimensional stability of lathe cut C.A.B. lenses. J Am Optom Assoc. 1978 Aug;49:927-929.
4. Lamb J, Bowden T. History of Contact Lenses. 2019. Available at eu-ireland-custom-media-prod.s3-eu-west-1.amazonaws.com/UKMEAEU/eSample/9780702071683-sample-chapter.pdf . Accessed June 14, 2023.
5. Basile DS. Eyeball to Eyeball With the F.D.A. New York Times. 1976 Jun 27. Available at nytimes.com/1976/06/27/archives/eyeball-to-eyeball-with-the-fda-rynco-gets-legislative-lift-for-a.html . Accessed June 14, 2023.
6. Bennett ES, Grohe RM. Rigid Gas-Permeable Contact Lenses. Professional Press Books, Fairchild Publications New York. 1986:34-40.
7. Schifrin LG., with Rich WJ. The Contact Lens Industry: Structure, Competition, and Public Policy (Health Technology Case Study 31). Washington, DC: U.S. Congress, Office of Technology Assessment. 1984 Nov.