LASIK with aspheric ablation profile treats myopia with astigmatism

Higher-order aberrations, spherical aberration and coma increased slightly, but contrast sensitivity remained mostly unchanged at 6 months.

LASIK performed with a non-wavefront-guided aspheric ablation profile offered positive visual outcomes in treating myopia with astigmatism, according to a study.

The procedure was predictable and improved overall visual acuity despite slightly increased corneal aberrations.

The Amaris flying-spot excimer laser was used with the Customized Ablation Manager software package (both Schwind), which generated an aberration-free aspheric ablation algorithm.

“Treatment of myopia with astigmatism using the Schwind Amaris excimer laser is safe, efficacious and predictable and maintains visual quality,” Maria Clara Arbelaez, MD, the lead author, told Ocular Surgery News in a subsequent e-mail interview.

Maria Clara Arbelaez

The ablation algorithm is designed to maintain preoperative levels of corneal higher-order aberrations using a sophisticated pattern that encompasses sphere, cylinder and orientation. The software calculates the size of the optimal transition zone, depending on preoperative refraction and optical zones, Dr. Arbelaez said.

“Aspheric treatments aiming for preservation of the preoperative higher-order aberrations show their strengths in patients with preoperative [best corrected visual acuity] of 20/20 or better, or in patients in whom the visual degradation cannot be attributed to the presence of clinically relevant higher-order aberrations,” she said.

Study data were published in the Journal of Refractive Surgery.

Parameters and procedure

The prospective, international multicenter study included 358 eyes of 179 patients who underwent bilateral LASIK for myopia and astigmatism. Mean patient age was 28 years. Mean preoperative manifest refraction spherical equivalent (MRSE) was –3.47 D, mean sphere was –3.13 D and mean cylinder was –0.69 D. Cylinder ranged from –5 D to 0 D.

Investigators preoperatively assessed uncorrected visual acuity, best corrected visual acuity, MRSE, contrast sensitivity, corneal topography, corneal wavefront, ultrasound corneal pachymetry, pupillometry, and slit lamp and dilated fundus images. These measurements, except dilated fundus imaging, pupillometry and contrast sensitivity, were also performed at 1 week and at 1, 3 and 6 months after surgery.

The Carriazo-Pendular microkeratome (Schwind) was used to create flaps with a superior hinge. The Amadeus microkeratome (Ziemer) was used to create flaps with a nasal hinge. An infrared 1,050-Hz eye tracker fixed on the pupil was used to attain proper alignment.

The laser’s 500-Hz repetition rate enabled safe and rapid treatment.

“The use of a 500-Hz repetition rate created no postoperative complications,” Dr. Arbelaez said. “The use of a particle aspirator coupled with random placement of the laser spots in this study seems to efficiently speed up the treatment without increasing the thermal load in the cornea.”

Results and observations

At 6 months after surgery, mean MRSE was –0.21 D; 96% of eyes had MRSE within 0.5 D of the targeted value, and 73% of eyes had MRSE within 0.25 D.

Also at 6 months, mean sphere was –0.12 D, and mean postop cylinder was –0.17 D. UCVA was 20/20 or better in 98% of eyes. No eyes lost two or more lines of BCVA.

Results showed statistically significant, but not clinically relevant, increases in total corneal higher-order aberrations (0.09 µm, P < .01), spherical aberration (0.08 µm, P < .01) and coma (0.04 µm, P = .02).

“The increase in spherical aberration can be partially explained by the biomechanical response and corneal epithelial remodeling,” Dr. Arbelaez said. “Biomechanical changes after myopic astigmatism treatments contribute to an oblate contour, increasing spherical aberration and shrinking the effective optical zone.”

Photopic and mesopic contrast sensitivity showed no statistically significant change at 6 months.

“The mild induction of higher-order aberrations, spherical aberration and coma may explain the maintenance of visual quality postoperatively found in the current study,” Dr. Arbelaez said. “For example, at 6 months postoperatively, there was negligible change in photopic and mesopic contrast sensitivity. This outcome may indicate that the induction of higher-order aberrations reported here may require less neural adaptation, if any at all.”

The study data were comparable to those on wavefront-guided and non-wavefront-guided ablation profiles, Dr. Arbelaez said.

“Compared to other studies using non-wavefront-guided profiles, we found less amounts of induced higher-order aberrations in our sample,” she said. “Compared with other studies of ocular wavefront-guided LASIK treatment for myopia with astigmatism that found wavefront-guided LASIK to be safe and effective, the outcomes of the present study are better.” – by Matt Hasson

Reference:

• Arbelaez MC, Aslanides IM, Barraquer C, et al. LASIK for myopia and astigmatism using the Schwind Amaris excimer laser: an international multicenter trial. J Refract Surg. 2010;26(2):88-98.

• Maria Clara Arbelaez, MD, can be reached at Muscat Eye Center, P.O. Box 938 PC, 117 Wadi al Kabir, Muscat, Oman; +96-824-691-414; fax: +96-824-601-212; e-mail: drmaria@omantel.net.om. Dr. Arbelaez receives occasional travel expenses from Schwind.