In 1978, Stone reported an astute clinical observation that whilst fluorescein pattern of corneal lenses made from new could be seen using blue filter on a slit-lamp microscope, there was an apparent lack of peripheral clearance using a Burton type lamp. She attributed this difficulty to the existence of a UV inhibitor in lens material. It was subsequently ascertained that this problem had, in fact, been confined to one material, Hydropoly (Neefe Optical Lab.), which had been supplied by several laboratories under different names. This material was a variety of poly (methyl methacrylate) (PMMA)which was claimed to exhibit better surface wetting than conventional PMMA. In an account of fitting of bifocal corneal lenses published by Focus Contact Lens Laboratory in 1983, it was recommended that Physical fit is checked with fluorescein, preferably using a slit lamp and blue filter (as opposed to UV), because of characteristics of some new types of materials used in lens manufacture. The purpose of present investigation was to explore validity of this assertion that use of fluorescent examination lamps of Burton type is contra-indicated when fitting hard lenses made from recently developed materials. As an introduction to this problem, a brief review is presented of basis of fluorescein pattern inspection. Fluorescein Fluorescein was first synthesized by von Baeyer in 1871 (Norn, 1974) and in 1877 he was able to trace course of a river using fluorescein due to fact that even in very low dilutions, such as one part in 200 million parts of water, its fluorescent emission of light is visible (DeMent, 1945). A solution containing 10 kilograms of fluorescein was sunk in River Danube near its head springs and some 60 hours later, characteristic luminescence appeared in a small river which emptied into Lake Constance and then into River Rhine. It is of interest to those engaged in ophthalmic field to note that finorescein was used to detect epithelial defects by Pfluger in 1882 and Straub in 1888 (Passmore and King, 1955). In 1899, Bihler used a 5 per cent solution following instillation of cocaine in order to detect endothelial defects (Anderson, 1949). The applications of fluorescein in ophthalmological diagnosis have subsequently developed particularly in technique of angiography. Fluorescein sodium (C20H10OsNa2), also known as uranin, is a yellow dye which on exposure to light absorbs certain exciting wavelengths and then emits fluorescent light of longer wavelengths and lower relative intensity. For dilute concentrations of fluorescein in aqueous solution, light with a wavelength between 485 to 500nm permits maximal absorption and resultant emitted light of highest intensity at a wavelength between 525 and 530nm (see Fig. 1). Fluorescent UV Examination Lamps Ultra-violet examination lamps of Burton type used by contact lens practitioners are generally fitted with a pair of 4 watt Blacklight miniature tubular fluorescent lamps. Wavelengths emitted by such a source range approximately from 305 to 410nm in wavelength and are predominantly within UV-A band of long-wave UV radiation (which spans 315 to 400rim) with maximum emission at 350nm (see Fig. 2). Blue Filters in Slip-lamp Microscopes The slit-lamp microscope incorporates a cobalt blue filter which can be introduced, when required, into illumination system in order to achieve excitation of fluorescein. Absorbance/transmission characteristics of two such filters are illustrated in Fig. 3. The Topcon data were provided by manufacturer for blue filter which is employed in slit-lamp models 1D, 2D, 3D and 5D and is stated to have a thickness of 1.50mm. Transmissions of this filter appears to be maximal at a wavelength of 390nm. A blue filter of type used in Kelvin slit-lamps was supplied to author who determined its spectral