Wide-angle Point Spread Function and Straylight of Intraocular Lenses

Investigative Ophthalmology and Visual Science
Augusto Arias, Pablo Artal
Purpose:Although current intraocular lenses (IOLs) have a good optical quality, new designs and manufacture processes may cause an increase of straylight that is often unnoticed. In this study, we evaluated the wide-angle point-spread function (PSF) and straylight for two IOLs in vitro.
Methods: The optical integration method (Ginis et al., JoV, 2012) was implemented to measure the wide-angle PSF and the angular course of the straylight for IOLs immersed in saline solution in a cell. In this metholodgy, uniform disks with different radii were imaged through the IOL to record their intensity at the center. The wide-angle (up to 5.1 degrees) PSF was calculated from the angular derivative of these central intensity data. Then the straylight was quantified as the product of the PSF by the squared angle. Two lenses were evaluated: (1) the AcrySoft IQ SN60WF (monofocal) and (2) the Tecnis Symfony ZRX000 (diffractive with extended depth of focus). Moreover, the straylight generated by the used optical system (i.e., relay lenses, mirrors and the cell) was measured as baseline. Units of the reported amounts of straylight are sr-1deg2.
Results: The straylight values between 1 to 5.1 degrees for the monofocal lens (1) (mean ± standard deviation, 8.5±2.8) were slightly higher than the baseline (7.3±2.6). However, in the case of the lens (2) those values are much higher (40.8±20) and a peak maximum value of 74 was found at around 1.8 degrees. This could be produced by micro-rings etched in its posterior surface whose period is smaller than the etching of the diffractive profile. The measured amount of straylight in lens (2) is significatively larger than what occurs in normal older subjects and would surely produce visual disturbances.
Conclusions: In vitro measurements of wide-angle PSF and straylight are useful to evaluate the quality of IOLs and their potential impact in visual discomfort of patients. As an example, one of the measured lens (Symfony) exhibits an amount of straylight several times larger than what is normal in older eyes.