SPECTRAL TRANSMITTANCE OF UV-ABSORBING SOFT AND RIGID GAS-PERMEABLE CONTACT-LENSES

Increasing evidence of acute and chronic ocular effects of ultraviolet (UV) radiation has prompted some manufacturers to develop UV-absorbing rigid and soft contact lens materials. Currently, eight different lenses containing UV-absorbing agents are available in Canada. The spectral transmittance of a sample of these UV-absorbing contact lenses was measured in order to determine if all of them provide adequate protection from wavelengths in the UV spectrum. The sample consisted of 1 lens of each type: Cibasoft Ultrabloc; Permaflex UV; Boston RXD and Equalens; Alberta S; FluoroPerm 30, 60, and 92. A Philips single beam spectrophotometer was used. The lens under test was placed in a silica wet cell filled with unpreserved saline. Spectral transmittance was measured at 0.8-nm intervals over the waveband 200 to 800 nm. The results were recorded by a microcomputer interfaced to the spectrophotometer. The repeatability of spectral transmittance measurements of contact lenses using this method varied between 0% and +/-1.55% of transmission depending on lens material and wavelength studied. The results showed that none of the rigid gas permeable (RGP) lenses, except the Alberta S, transmitted more than 0.1% (the sensitivity limit of the spectrophotometer) up to 380 nm. The Alberta S exhibited transmittance windows in the UV spectrum with peaks at 270 nm (23%) and 318 nm (29%). The Cibasoft Ultrabloc transmitted less than 1% up to 344 nm, whereas the Permaflex UV had a transmittance window in the waveband 240 to 316 nm with a maximum of 17% at 270 nm. The level of protection afforded by each lens was assessed by the computation of protection factor (PF) and safe exposure duration (SED). All lenses studied, including the five for which transmittance curves have not been published earlier, provide a better level of protection from normal environmental UV exposure than lenses without UV-absorber, although the Alberta S is the least effective among all the lenses studied. The clinical significance of these results will be discussed.