Purpose: : Implanting two different multifocal IOLs, one refractive and the other diffractive, in the two eyes of a patient is a widely used surgical approach. It is often referred as mix-and-match and appears to provide patients with reasonable quality of vision for both distance and near objects. Some clinical experience suggests that visual performance in these patients tends to improve with time. The underlying causes of this improvement, with special emphasis in the possible role of neural adaptation, are evaluated.
Methods: : From a population of bilaterally implanted cataract patients, we selected a group with mix-and-match (Tecnis/Rezoom, AMO) (MM_group) and another with the same type of diffractive IOL (Acrilisa, Zeiss) in each eye (DD_group). They were fully evaluated one and six months after the surgeries. Best corrected visual acuity (BCVA) at far (10 m) and at reading distance (30 cm) were measured both monocularly and binocularly. A custom method for measuring visual acuity was used with a tumbling E projected on a micro-display. The optical properties of the implanted eyes were controlled in both visits. Ocular aberrations were evaluated with a Hartmann-Shack sensor and the transparency and ocular scattering were tested by using a double-pass based instrument (OQAS, Visiometrics SL) and slit-lamp imaging.
Results: : In the patients finally selected (five in each group), the optical properties in the eye were nearly constant over the 6-months time. Aberrations and scatter were stable suggesting that the quality of the retinal image was unchanged. This assured us that there were not significant modifications in the optics over time. One month after surgery, the average values of the binocular far and near BCVA (expressed in LogMAR) were similar for both groups: MM: -0.08±0.06, DD: -0.09±0.05; MM: 0.09±0.06, DD: 0.08±0.13. After six months, binocular distance BCVA did not change for both IOLs configurations: MM: -0.10±0.08, DD-0.07±0.03. However, binocular VA for the near target improved for the mix-and-match configuration (MM: -0.01±0.04) but not for the other group with two diffractive lenses (DD: 0.10±0.13).
Conclusions: : Binocular near vision acuity improved after six months in patients implanted with the mix-and-match approach. In patients with two diffractive IOLs, visual acuity did not change with time. Considering that there were not optical changes and differences found between the two IOLs combinations, some particular type of binocular interaction of neural adaptation appears as the main reason for visual improvement.