Inhomogeneity in the aging crystalline lens and voids in intraocular lenses (IOLs) cause light to scatter and potentially may deteriorate quality of vision. We evaluated photographic diffusers filters mimicking micro vacuoles in IOLs. The impact of these filters on straylight level was measured using two methods.
Four photographic diffusers introducing different amount of light scattering (Pro-Mist Black ¼, ½, 1, and 2. The Tiffen Company, NY, USA) were first characterized in vitro. Subsequently, the increase of straylight that the filters induce when introduced in front of subjects’ eyes was measured by a psychophysical and an optical method. A straylight parameter was measured in six subjects using the compensation comparison method (C-Quant, OCULUS, Germany) with the glare source positioned at 7 degrees and at 2.5 degrees. Three of the same subjects were measured with an optical integrator method (Ginis et al., JOV, 2012) that reconstruct the eye’s point spread function with an angular extend of up to 8.1 degrees. An optical straylight parameter over the angular range from 3 to 7 degrees was determined for each filter.
The induced straylight parameter of the filters measured by the C-Quant ranged from 0.8 to 1.4 for the glare source at 2.5° and from 0.3 to 1.0 at 7°. The induced average straylight level measured by the optical method increased as the filters becomes more diffuse and ranged from 0.2 to 0.7. These results indicate that filters ¼ and ½ represent values for the condition of micro-vacuoles present in IOLs and filters 1 and 2 produce values resembling cataract. An undesired side effect was the different absorption levels of the filters that may impact retinal illuminance.
Both methods showed on average an increase in straylight induced for each filter. These results indicate that the diffuser filters are helpful in quantifying the straylight effect for ocular conditions ranging from microvacuoles in IOLs to cataract.