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-absorbin g rigid and soft contact lens materials. Currently, eight different le nses containing UV-absorbing agents are available in Canada. The spect ral transmittance of a sample of these UV-absorbing contact lenses was measured in order to determine if all of them provide adequate protec tion from wavelengths in the UV spectrum. The sample consisted of 1 le ns of each type: Cibasoft Ultrabloc; Permaflex UV; Boston RXD and Equa lens; Alberta S; FluoroPerm 30, 60, and 92. A Philips single beam spec trophotometer was used. The lens under test was placed in a silica wet cell filled with unpreserved saline. Spectral transmittance was measu red at 0.8-nm intervals over the waveband 200 to 800 nm. The results w ere recorded by a microcomputer interfaced to the spectrophotometer. T he repeatability of spectral transmittance measurements of contact len ses using this method varied between 0% and +/-1.55% of transmission d epending on lens material and wavelength studied. The results showed t hat none of the rigid gas permeable (RGP) lenses, except the Alberta S , transmitted more than 0.1% (the sensitivity limit of the spectrophot ometer) 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 Ciba soft Ultrabloc transmitted less than 1% up to 344 nm, whereas the Perm aflex 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 saf e 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 effect ive among all the lenses studied. The clinical significance of these r esults will be discussed.