The latest version of an accommodating IOL provides increased depth of field for better near vision performance than predecessor versions.
"Studies investigating previous versions of the [lens] showed accommodation was the result of a combination of factors," said Dr. Hovanesian, clinical instructor, Jules Stein Eye Institute, University of California, Los Angeles.
"Optic translation may occur," he said. "However, increased vitreous pressure resulting from ciliary muscle contraction also causes central steepening of the lens optic, a phenomenon described as accommodative arch and that has been demonstrated using wavefront studies."
"The [accommodating IOL] was developed to take advantage of this optic change to. . . improve visual function [further]," he said. "Laboratory studies' clinical trial data show that the new modified optic achieves its goal in providing better near vision without degrading contrast sensitivity."
The optic change involved a 3-µm increase in thickness to the 1.5-mm central diameter that shortens the spherical radius and imparts some negative spherical aberration to the mid-peripheral zone of the lens. Optical bench evaluations at an independent laboratory showed that at 1 D of defocus, the modified optic had a flatter overall wavefront and lower total RMS value compared with the predecessor lens (Crystalens AT-45, Bausch & Lomb) (360 versus 570 µm) and a greater depth of field.
In addition, objective evaluation of contrast sensitivity based on modulation transfer function analyses showed some improvement with the accommodating IOL relative to the predecessor lens (0.29 versus 0.51, respectively) although the difference was not statistically significant.
The FDA study compared 60 eyes with the accommodating IOL implanted and 60 eyes with the predecessor lens implanted.
In monocular testing of near uncorrected visual acuity (UCVA), the results at all thresholds favored the accommodating IOL for providing better near vision.
J3 or better near UCVA was achieved by 100% of eyes with the accommodating IOL implanted compared with only 78% of eyes with the predecessor lens, and J2 or better near UCVA was achieved by 80% of eyes with the accommodating IOL compared with only 55% of eyes with the predecessor lens.
"However, measurement of monocular near VA with distance correction is a better measure of accommodation, and the results for this testing also consistently favored the [accommodating IOL] over the [predecessor lens]," Dr. Hovanesian said.
In the accommodating IOL group, distance corrected near VA was J3 or better in 90% of eyes, J2 or better in 70% of eyes, and J1 or better in 33% of eyes. These different levels of vision were achieved at rates of 65%, 32%, and 13%, respectively, in the predecessor lens group.
Contrast sensitivity was tested with and without glare, and the results were slightly better in patients who received the latest version of the accommodating IOL, but not significantly different between the two lens groups.
"Certainly there was no evidence that the optic modification led to worsening of contrast sensitivity," Dr. Hovanesian concluded.