Recently we were faced with the task of obtaining accurate transmission curves in the visible and ultraviolet spectral regions of intraocular lenses (IOL) containing various UV absorbing materials. These aspheric lenses are generally made from polymethylmethacrylate, are about 6 mm in diameter, and have focal lengths in the range 1 to 2 cm. Simply placing the lens in the masked, sample beam of a spectrophotometer is not satisfactory, owing to the possibility of large photometric errors arising from the strong refractive effects of the lens on the sampling beam. The use of specific commercial spectrophotometers in which the detector is positioned close to the sample will reduce the errors but not necessarily eliminate them. In this note we describe a different method that we believe offers several advantages for the simple and accurate measurement of the absorption properties of IOLs and other items of irregular configuration made from polymethylmethacrylate (pMMA). Refractive effects are virtually eliminated, and in addition no reflection loss corrections are needed. The results may be of general interest in regard to optical studies employing components fabricated from pMMA or for other light-handling problems.
Leigh B. Clark and David G. Kaplan, "The Measurement of UV/VIS Transmission Characteristics of Intraocular Lenses," Appl. Spectrosc. 41, 334-336 (1987)