Wavefront-Guided, Wavefront-Optimized, and Topography-Guided Ablations
Conventional excimer laser ablation treats lower-order, or spherocylindrical, aberrations such as myopia, hyperopia, and astigmatism. These lower-order aberrations constitute approximately 90% of all aberrations. Higher-order aberrations make up the remainder; such aberrations cannot be treated with glasses. Some ophthalmologists feel that small amounts of higher-order aberrations, which are commonly found in patients with excellent uncorrected vision, may not adversely affect their vision. Higher-order aberrations are also a by-product of excimer laser ablation. Some higher-order aberrations can cause symptoms—such as loss of contrast sensitivity and nighttime halos and glare—that decrease the quality of vision. The aberrations most commonly associated with these visual concerns are spherical aberration and coma. See Chapter 1 for more detailed discussion of higher-order aberrations.
In an effort to reduce preexisting aberrations and minimize the induction of new aberrations, wavefront-guided ablation creates ablation profiles that are customized for individual patients. In addition to addressing higher-order aberrations, wavefront-guided treatments can correct the lower-order aberrations of spherical error and astigmatism.
Wavefront-optimized lasers do not use patient-specific wavefront data. Instead, they adjust the ablation profile of conventional treatments to create a more prolate shape with the additional peripheral ablation in the myopic patient, thereby reducing spherical aberration; however, they have no effect on other higher-order aberrations.
Compared with conventional excimer laser ablation, wavefront-guided ablations and wavefront-optimized ablations appear to offer better contrast sensitivity and induce fewer postoperative higher-order aberrations. Although advances in aberrometry and registration systems have led to improved outcomes, patients who undergo photoablation may still have more higher-order aberrations postoperatively than they did preoperatively. Wavefront-guided ablations in general remove more tissue than conventional ablations.
Wavefront-guided ablation appears to have clear-cut benefit compared with wavefront-optimized ablation only for patients with significant preoperative higher-order aberrations. The procedure is not suitable for all patients and may be inappropriate for use after cataract surgery, particularly with multifocal intraocular lenses. Intraocular lenses, especially multifocal intraocular lenses, interfere with capturing the wavefront scan and could result in the delivery of an inaccurate treatment. In addition, wavefront data may be impossible to obtain in highly irregular corneas or in eyes with small pupils.
Topography-guided ablations have recently been approved by the US Food and Drug Administration (FDA). Topography-guided systems use corneal topography data to create ablation profiles that treat existing corneal shape irregularities and optimize corneal curvature. Topography-guided ablations have gained traction outside the US in the treatment of corneas with irregular surfaces, such as those with small or decentered optical zones from prior excimer ablations, LASIK flap complications, or post-RK corneal irregularities. Data from a recent FDA clinical trial, demonstrated that topography-guided ablations may result in excellent outcomes for even routine laser vision correction cases in previously unoperated eyes.
Nuijts RM, Nabar VA, Hament WJ, Eggink FA. Wavefront-guided versus standard laser in situ keratomileusis to correct low to moderate myopia. J Cataract Refract Surg. 2002;28(11): 1907–1913.
Stonecipher KG, Kezirian GM. Wavefront-optimized versus wavefront-guided LASIK for myopic astigmatism with the ALLEGRETTO WAVE: three-month results of a prospective FDA trial. J Refract Surg. 2008;24(4):S424–S430.
Stulting RD, Fant BS PharmD; T-CAT Study Group. Results of topography-guided laser in situ keratomileusis custom ablation treatment with a refractive excimer laser. J Cataract Refract Surg. 2016;42(1):11–18.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.