Author: Eleni Papadatou, University of Valencia
Implantation of multifocal intraocular lenses (MIOLs) has been proved a successful method of refractive surgery in order to restore satisfactory the quality of vision after cataract removal. Toric MIOLs aim to provide good near vision with distance correction and correct also the astigmatism. Innovations in both lenses construction and surgery techniques have optimized the surgical procedure (e.g. smaller incisions). Nevertheless, phenomena related with the stabilization of the lens postoperatively occur and may affect the visual outcome. In the labs of GIO we examine in vitro the optical quality of bifocal and trifocal diffractive toric MIOLs in simulated conditions of decentration, tilt and rotation under photopic and mesopic conditions. The evaluation is performed by means of Modulation Transfer Function (MTF) that is an internationally approved method for testing the optical quality of an optical element (ISO 11979-2, ISO 11979-9).
Image: diffractive bifocal toric MIOL.
The results so far demonstrate that decentration and tilt have a gradual impact on the optical quality of the lenses that can be interpreted as deterioration of the visual performance. Moreover, the power of the IOL has an inverse relationship with decentration tolerance limit. That means the higher the power of the lens is the lower the amount of decentration that does not decay the optical quality of the lens. Tilt, seems to have a greater impact in optical quality than decentration. It is important to take into account that these phenomena happen at the same time when the lens is implanted. In future, the next step is to examine the effect of rotation, which we expect to have the greatest impact on toric MIOLs optical quality.
Figure: Through focus MTF curves of bifocal toric MIOL, at centered, decentered and tilted positions for a 3mm aperture.