Laser ablation profile corrects presbyopia by manipulating spherical aberration

Induced spherical aberration compensates for the loss of accommodation, preserving quantity and quality of vision, investigator says.

ByMichela Cimberle

FLORENCE – A new laser ablation profile based on the modification of spherical aberration seems to effectively address presbyopia in a significant number of cases with no loss in quantity and quality of vision and no induced diffractive phenomena, according to an investigator.

The treatment creates a new aspheric corneal profile that increases the depth of focus and recovers about 2 D of near acuity in the presbyopic eye, Ocular Surgery News Europe/Asia-Pacific Edition Editorial Board Member José L. Güell, MD, said at the Florence Symposium.

“The key point is spherical aberration,” he said.

The starting point

A previous study by Franco Bartoli, MD, demonstrated that spherical aberration is zero or slightly negative in the nonaccommodating eye, while during accommodation the center of the anterior surface of the lens vaults forward and induces positive spherical aberration. Dynamic wavefront analysis quantified both accommodation and induced spherical aberration.

As a consequence, it was found that in presbyopic eyes, the loss of accommodation produces a loss of the ability to induce spherical aberration, Dr. Güell said.

Based on these discoveries, Dr. Bartoli, in collaboration with Carl Zeiss Meditec, developed new software for wavefront-guided ablation. The treatment was aimed at inducing a certain amount of spherical aberration to compensate for the loss of accommodation in presbyopic eyes. This software was first used with the WASCA aberrometer and Zeiss MEL 70 excimer laser, and has now been modified and updated to the MEL 80. A multicenter study in Europe is currently evaluating the results of the Bartoli-Zeiss ablation profile in both ametropic and emmetropic presbyopic eyes.

Figure 1. Common bifocal profile design. Superimposition of a standard correction profile (myopic in this example) with a small diameter hyperopic profile in the center.
Source: Güell JL

Figure 2. The Bartoli-Zeiss method creates a negative spherical aberration. Superimposition of a standard correction profile (myopic in this example) creates an increased spherical aberration.

Advantages

According to Dr. Güell, this treatment works better than other laser-based presbyopic treatments, which are normally aimed at creating a multifocal cornea with specific refractive zones for near and distance vision.

“As we know, multifocality requires a variable period of adaptation and is not equally well accepted by all patients. In addition, the light scattering from transition zones produces a loss of contrast sensitivity, and the contour changes between refractive zones might require a long period of epithelial healing which, at the same time, may reduce the initial effect. In the worst cases, these treatments could be responsible for a series of distressing complications, such as diplopia, regression, glare, halos and ghost images, as well as the loss of visual acuity and contrast sensitivity,” he said.

A treatment that basically maintains the monofocal aspheric profile of the cornea and spreads contour changes over the entire optical zone has, theoretically, no risk of any of these complications, he explained.

“The smooth contour of an intended spherical aberration is integrated into the profile design,” Dr. Güell said.

Encouraging results

In the first stage of the study, Dr. Güell evaluated the results of the treatment in 17 eyes of 13 patients, with mean age of 45 years. Three of these eyes were myopic, eight were hyperopic, and six were pseudophakic, with residual myopia in three of the cases and residual hyperopia in three cases. Uncorrected and best corrected vision at both distance and near as well as near vision with distance correction were evaluated. Asphericity changes were measured with the WASCA aberrometer, and modulation transfer function (MTF), point spread function (PSF) and amplitude of accommodation were measured with the double-pass Visiometrics OQAS (Optical Quality Analysis System).

A standard myopic or hyperopic treatment was combined with aberrometric correction of a fourth-order aberration to obtain the desired increase in spherical aberration.

“The treatment proved to be safe, with no loss of high- or low-contrast visual acuity in any of the patients. No problems with glare, halos, ghosting or double vision were reported. The efficacy on near vision was remarkable in most cases, without any loss of distance vision quantity and quality,” Dr. Güell said.

Subgroup analysis showed that near vision with distance correction improved in the myopic eyes, was stable in the hyperopic eyes and had a marked increase in the pseudophakic eyes, both myopic and hyperopic. The need for spectacle correction decreased in the pseudophakic group and in the myopic group, while no substantial change was seen in the small group of hyperopic eyes. Best corrected near visual acuity was unchanged, except for the hyperopic group where a small improvement was measured.

Measurements with the WASCA aberrometer showed that, as Dr. Güell expected, spherical aberration increased in all groups, especially in the hyperopic group, where it almost doubled.

Figure 3. The smooth contour of an intended spherical aberration is integrated into the ablation profile design.
Image: Carl Zeiss Meditec

Clinically nonsignificant but important data came from the OQAS analysis. The MTF showed a slight decrease in the hyperopic and myopic group, but not in the pseudophakic eyes. The slight decrease in optical quality did not affect the pseudophakic patients. Amplitude of accommodation increased between 1.25 D and 2.25 D and was again particularly notable in the pseudophakic eyes. The increased depth of focus improved the PSF.

“Following these results, we are trying to establish who are the best candidates for this treatment. On the whole, we were satisfied with most of our cases, and this approach appears so far to be the easiest and safest of all known techniques for improving presbyopia at the corneal level and at the same time correcting pre-existing refractive errors,” Dr. Güell said.

For Your Information:

José L. Güell, MD, can be reached at I.M.O., c/Munner 10, 08022 Barcelona, Spain; +34-93-2531500; fax: +34-93-4171301; e-mail: guell@imo.es. Dr. Güell is a consultant to Carl Zeiss Meditec and Visiometrics. He has a direct financial interest in the Visiometrics OQAS system.

The Florence Symposium was the 10th Annual Joint Meeting of Ocular Surgery News, the Italian Association of Cataract and Refractive Surgery, the Italian Society of Ophthalmology and the International Society of Refractive Surgery held on May 12 and 13, 2005.

Carl Zeiss Meditec can be reached at 5160 Hacienda Drive, Dublin, CA 94568; +1-925-557-4100; fax: +1-925-557-4101.

Michela Cimberle is an OSN Correspondent based in Treviso, Italy.