ACCOMMODATION

Observed changes in wavefront aberrations between near, intermediate and far vision in patients implanted with the WIOL-CF accommodative IOL (Medicem, Czech Republic) offer objective evidence of accommodation and insight about its mechanisms, said Ioannis G Pallikaris MD, PhD, at the XXXI ESCRS Congress in Amsterdam.

“Obtaining objective proof of accommodation with ‘accommodating’ IOLs is a major challenge. We used quantitative analysis of optical aberrations to help us understand what is happening with the WIOL-CF IOL during the accommodation process,” said Dr Pallikaris, professor of ophthalmology, Institute of Vision and Optics, University of Crete Medical School, Heraklion, Greece.

“Our findings show that the WIOL-CF has at least 0.8 D of real accommodation that is driven by a change in defocus. In addition, there are also changes in higher order aberrations that result in an increase in depth of focus. Combined, this information provides at least partial justification for the satisfactory near vision achieved in patients implanted with the WIOL-CF.”

Described as a “bioanalogic lens”, the WIOL-CF IOL is designed to mimic key properties of the natural crystalline lens. It has a large diameter (~9mm) polyfocal optic and is made of a flexible hydrogel material so that it is able to change shape in response to ciliary muscle contraction and relaxation, leading to changes in refractive power.

Wavefront aberrations

To evaluate accommodation with the WIOL-CF IOL, changes in wavefront aberrations were measured at three years postoperatively in 15 patients who had undergone uneventful cataract surgery with binocular implantation of the WIOL-CF IOL. The patients had a mean age of 65 years with a range between 53 and 83 years.

Zernike coefficients from second to fourth order were obtained using a raytracing unit (iTrace, Tracey Technologies) that has a view-through device allowing wavefront capture at different distances. The measurements were performed at the natural pupil diameter under photopic conditions with patients looking at an illuminated target at three different distances: far (4m), intermediate (60cm) and near (33cm). All measurements were performed twice with the same pupil size and centred first on the pupil and then at the visual axis. Differences maps were generated from measurements obtained at far and intermediate and from far and near.

Myopic shift

The results for defocus showed there was a myopic shift in all patients with the change from the far to intermediate distance stimulus (mean -1.02 D, range -0.24 D to -2.15 D) and from the far to near distance stimulus (mean -0.87 D, range -0.4 to -1.58 D).

The shifts from far to intermediate and from far to near were also associated with changes in third and fourth higher order aberrations whether the measurements were performed with centration on the pupil or the visual axis, although the changes were more pronounced with pupil centration. For the latter measurements, the mean (+-standard deviation) change in vertical coma was 0.04 Â}0.07 microns with the shift from far to near and 0.08Â}0.09 microns. The shift from far to intermediate; spherical aberration showed negative shifts with changes of -0.05Â}0.03 microns from far to near and -0.03+-0.03 microns from far to intermediate.