Pseudophakic photopsia – Optical simulations with a model eye to evaluate IOL design and material

Abstract

AbstractPurpose Photopic phenomena (photopsia) gain in relevance and may become key problems after modern cataract surgery. The purpose of this study is to evaluate potential influencing factors for these optical phenomena using ray tracing techniques in a model eye.Methods A schematic model eye was used for simulations with professional optic design software (ASAP). The crystalline lens was replaced by an intraocular lens implant. We varied the lens’ edge design (edge radius from 0.00 mm (0.05 mm) 0.15 mm), refractive index (1.55 and 1.46), axial and lateral position (each ±0.5 mm), as well as the pupil diameter (2.5, 3.5 and 4.5 mm). Retinal illuminance was simulated for a Ganzfeld perimeter sphere (d=300 mm, 250° field of view) with 107 rays emitting in a Lambertian distribution.Results Positive photopsia could be observed at the central and paracentral nasal visual field originating from total internal reflection at the lens’ optics edge, which becomes more intense with higher refractive index and smaller edge radius or larger peripheral thickness of the lens. Negative photopsia was seen at the far temporal visual field as a gap in illuminance originating by a gap between overlaying light pathways of primary image and direct path. Photopsia is less pronounced with larger pupil size and axial or lateral displacement of the lens.Conclusion Photopsia is not a new phenomenon in pseudophakic eyes, but with lenses with a high refractive index (smaller incision) and sharp optic edges (for prevention of secondary cataract) the intensity of artificial light phenomena and gaps photopsia might become the main reason for patient dissatisfaction after cataract surgery.