LASIK corrects high hyperopia out to 2 years

ORLANDO, Fla. — Results from a study involving 798 eyes of 651 patients indicate that the Mel 80 excimer laser can safely apply large zone hyperopic ablation totaling up to +9.50 D, with stable results out to 2 years.

Timothy J. Archer, MA, DipCompSci, and colleagues reported in a poster here at the Association for Research in Vision and Ophthalmology meeting results of their retrospective analysis of patients with target maximum hyperopic meridian of at least +4.00 D, preoperative corrected distance visual acuity of 20/20 or better and a minimum follow-up of 1 year. Patients were a mean of 51 years (range: 18 to 70 years).

The Mel 80 excimer laser (Carl Zeiss Meditec) was used with either the Hansatome microkeratome (Bausch + Lomb) or VisuMax femtosecond laser (Carl Zeiss Meditec).

The researchers reported that the primary procedure was performed as an intentional partial correction in 160 eyes, and 81 of those have undergone a second treatment. Six hundred thirty-eight eyes were intended for full correction, and 220 of those have undergone re-treatment. A re-treatment was performed if the maximum ablation site’s predicted residual stromal thickness was greater than 250 µm and epithelial thickness, measured by Artemis (ArcScan) very high-frequency digital ultrasound, was thick enough to safely allow the further thinning associated with the intended associated increase in stromal surface curvature to be induced by re-treatment.

The mean target spherical equivalent was +4.69 ± 1.03 D for all primary procedures, according to the abstract. Postoperatively, the spherical equivalent refraction after all procedures relative to the intended target was +0.10 ± 0.69 D. There were small shifts in spherical equivalent over time, with 0.00 D at 3 months, +0.11 D at 6 months, +0.24 D at 1 year and +0.43 D at 2 years. However, the change between 3 months and 2 years was shown to be lenticular given that over this time period the average simulated keratometry showed virtually no change.

Mean refractive astigmatism went from 1.04 ± 0.86 D preoperatively to 0.77 ± 0.58 D postoperatively. Mean average keratometry went from 43.3 ± 1.5 D preoperatively to 46.7 ± 1.9 D postoperatively.

Postoperatively, uncorrected distance acuity was 20/20 or better in 76% of eyes and 20/40 or better in 98%, according to the abstract.

“Results are comparable to clear lens exchange,” co-author Dan Z. Reinstein, MD, MA, FRCSC, DABO, FRCOphth, FEBO, told Ocular Surgery News. “We avoid the albeit unusual but potential catastrophic complications of intraocular surgery, and we have the advantages of centering the flap and ablation on the coaxially sighted corneal light reflex and inducing spherical aberration in this location to increase the depth of field, which gives presbyopes improved near, intermediate and distance vision.

“This can’t be done with standard LASIK techniques,” he continued. “You need a laser that treats a large optical zone — a minimum of 6.5 mm and preferably 7 mm — with a large transition zone outside of that. The laser must enable centration of the ablation on the visual axis instead of the pupil.”

Reinstein noted that surgeons should not base their treatment capability on the eye’s keratometry.

“It can be misleading in hyperopic treatment when assessing whether further steepening can be safely performed,” he said.

“After a primary hyperopic procedure, the cornea can be still keratometrically flat and deemed suitable for re-treatment, but the epithelium may already have a minimal epithelial thickness too thin for further steepening,” Reinstein said. “It’s also possible to have a steep cornea with thick epithelium at the vertex, meaning that further steepening can be safely performed. Such cases would otherwise have been rejected for re-treatment based purely on keratometry.”

He said that the safety of the procedure depends on the diagnostics of epithelial thickness and the ability to measure the thinnest point on the residual stroma under the flap.

“As a back-up, you need the capability of topography-guided treatment, so if there’s a centration issue or optical aberration issue, you can repair it,” Reinstein noted. “It cannot be adequately done by entrance pupil-centered wavefront-guided treatment.”

Reference:

Reinstein DZ, et al. J Refract Surg. 2010;doi:10.3928/1081597X-20091105-02.

Disclosure: Archer and Gobbe have no relevant financial disclosures. Reinstein has a financial interest in ArcScan Inc. and is a consultant to Carl Zeiss Meditec.