Purpose: Negative dysphotopsia (ND) is an entoptic phenomenon which affects pseudophakic eyes. In ND a shadow is a crescent-shaped perceived in the peripheral visual field. Several studies indicate the ND is caused by light transmitted through the gap between the intraocular lens (IOL) and the posterior surface of the iris, which is transmitted without being focused by IOL. The purpose of this study was to compare ND occurrence and severity between biconvex and meniscus lenses.
Methods: ND was investigated for two different types of IOLs (Acrysof SA60AT, Alcon, TX USA and ArtIOLs, Art25, Voptica SL, Murcia, Spain). A physical model of the pseudophakic eye was used together with an extended light source implemented using a computer screen. The eye model had a PMMA cornea (R=7.73mm, Q= -0.24) an iris at a depth of 3.55mm and an IOL holder introducing the IOL at a distance of 1.5mm from the pupil, simulating a pseudophakic anterior chamber depth (pACD) of 5.05 mm. The eye was filled with distilled water. A camera (72BUC02-ML, Imaging Source, Germany) in a water-tight container was used to record the retinal images. To evaluate dysphotopsia a horizontal bar (5ο vertical x 15ο horizontal) was presented at the peripheral field of view (70ο to 85ο). Images at the retinal plane were assessed with respect to the occurrence and severity of a shadow near the edge of the visual field. Measurements were done for 3 and 6 mm pupil diameters.
Results: A characteristic ND shadow appeared on the retinal image with the biconvex IOL, being more pronounced for 3 mm than for 6 mm pupil diameter. The shadow did not occur with the meniscus shaped IOLs with either pupil diameter.
Conclusion: Negative dysphotopsia can be reduced or eliminated using a meniscus shaped IOL. Meniscus shape IOL has an inherently narrower gap in the periphery between IOL’s optic and the posterior surface of the iris. Consequently, it is less likely to cause negative dysphotopsia. This finding is consistent with OpticStudio (ANSYS, Inc, Canonsburg, USA) non-sequential modelling.