Abstract
Purpose:
Negative dysphotopsia (ND) remains a clinical phenomenon whose understanding is not to date materialized in an ameliorated intraocular lens (IOL) design. In this context, the current study describes the development and initial results of an in-vitro method for measuring dysphotopsia.
Methods:
For the theoretical evaluation of the photic events, a Zemax Non-Sequential model eye (OpticStudio 14, Zemax LLC) was developed in which the IOL was implemented as a 3D CAD object with a complete geometry (optics, edges, haptic system). The irradiance was mapped on the entire image plane as a function of object angle (0 - 85o), pupil size (3, 6 mm), wavelength and IOL effective position and orientation. Additionally, the image heights of the glare secondary images were computed. For the measurements, an off-axis MTF bench with a 12-bit CCD camera was used (Image Master HR, Trioptics). An anatomical physical eye model with a population average cornea was designed and manufactured. The measurements were performed in photopic light. The measurements output were image frames which were processed off-line by the means of a Matlab script (R2013, The MathWorks Inc.). The figures of merit were frames, average intensities as well as areas under the intensity curves. For benchmarking, both silicone and PMMA IOLs with unfrosted and frosted edges respectively were measured. Finally, IOLs designed to reduce negative dysphotopsia were tested.
Results:
Both positive dysphotopsia (PD) and ND were captured by simulation and measurement results. All IOLs produced different levels of PD and ND under the conditions tested in this study. PD was observed more for small to medium light incident angles for IOLs without edge frosting and was more visible when the pupil was larger. ND was observed and measured at larger light incident angles and more obvious for smaller pupil sizes. Objective measures show the potential for dysphotopsia occurrences for varying types of lenses. IOLs with optimized geometries were proposed and shown to reduce the incidence of dysphotopsia.
Conclusions:
The study proposed a dysphotopsia measurement method based on a combined theoretical and experimental approach. This enables a quantitative mapping in order to better understand the origins of the IOL dysphotopsia including how these relate to a given IOL geometry and implantation position.