SCATTERING PROPERTIES OF BAGOLINI LENSES AND THEIR EFFECTS ON SPATIALVISION

The effect of a Bagolini lens on spatial vision was investigated by st udying its far-field diffraction pattern as produced by a coherent bea m of laser light, and its effect on the contrast sensitivity function (CSF) in human subjects. For lenses of the main type studied, which we re crossed by a series of slightly-irregular striated bands, each cons isting of fine, parallel, etched lines of various widths and separatio ns, the diffraction pattern consisted of undiffracted light giving a b right central spot and wide-angle, diffracted light giving a dim strea k. The latter was due to the sum of the diffraction patterns associate d by the irregular fine etched lines. The streak produced by a single striated band was modulated by a series of regular maxima and minima r elated to the width of the band. Analysis of this pattern gave the wid th of the band as 0.6 mm, in close agreement with direct microscopical measurements. When four bands were illuminated by a beam of about 3 m m diameter, similar to the diameter of the photopic pupil, the diffrac tion pattern showed no obvious maxima and minima, due to irregularity in the width and separation of the bands. The central spot contained m ore than 90% of the total light in the diffraction pattern. Thus the B agolini lens, with its relatively weak far-field diffraction pattern l acking regular maxima and minima when areas greater than or equal to 3 mm in diameter were used, was expected to have only a small effect on the apparent contrast of the targets in CSF experiments. This was con firmed by the measurements: Bagolini lenses showed no significant effe ct on either the monocular or binocular CSF, Further similar measureme nts with lenses of slightly different design from another manufacturer confirmed these findings. Therefore Bagolini lenses do not disrupt vi sion when they are used to determine the presence of suppression and a nomalous retinal correspondence, (C) 1998 The College of Optometrists. Published by Elsevier Science Ltd. All rights reserved.