Influence of Add Power on the Optical Characteristics of Diffractive Multifocal IOLs
Narrative Responses:
Purpose
The purpose of this study is to determine how various optical characteristics of diffractive multifocal intraocular lenses (IOLs) are influenced by a change in add power.
Methods
Various optical properties were determined for three diffractive multifocal IOLs with add powers of 2.75, 3.25 and 4.0 diopter (D).
The through-focus MTF was measured on an optical bench in an eye model that reproduces the spherical and chromatic aberration of an average pseudophakic eye. Testing was done using varying aperture sizes. Additionally, straylight was measured. Finally, using computer-based model eyes, defocus curves were simulated for visual acuity.
By comparing all results and performing a theoretical evaluation, the optical outcomes were correlated with add power. Additionally the results were compared to other multifocal IOLs designed to improve intermediate vision.
Results
The MTF values in white light for a 3mm pupil were between 0.25 and 0.30 for all models for both foci. Only the distance between the near and far focus peak differed, corresponding to the add power differences. Similar trends are found for other conditions.
Simulated visual acuity curves show little or no change in the in-focus values between IOLs with different add powers. However, lower add power improves simulated intermediate vision. As add power is reduced the straylight peaks are also reduced and move closer to the optical axis. Similar trends are observed for other multifocal IOL designs.
Conclusion
Lowering the add power has no effect on in-focus vision. A difference in peak scatter intensity and location as well as improved intermediate vision may be expected with reduced add power. The expected in vivo reading distance changes from 33cm for the 4.0D add to 50cm for the 2.75D add.