Poor visual quality and reduced contrast sensitivity can be attributed to optical aberrations in the eye.1,2 Although the two main contributors to optical aberrations are the cornea and lens, an abnormal tear film or vitreous can also cause an increase in aberrations.
Conventionally, aberrations are divided into lower-order (sphere and cylinder) and higher-order (spherical aberration, coma, and trefoil). Laser vision correction has been extremely successful at treating lower-order aberrations (LOAs); however, a minority of patients experience visual degradation as a result of higher-order aberrations (HOAs).
AN ABERRATION-NEUTRAL APPROACH
With the maturing of excimer laser technology and the ability to routinely achieve good postoperative visual acuity, attention has turned to improving visual quality by treating existing ocular aberrations or minimizing their induction during laser vision correction. Techniques that focus on minimizing induced aberrations have been demonstrated to be safe, predictable, and efficacious.3,4
Patients with a preoperative BCVA of 20/20 or better do not have significant HOAs that degrade visual quality. This group represents the majority of patients who present for laser vision correction, and in these patients it is more appropriate to focus attention on performing an aberration-neutral procedure. The goals are to achieve an excellent refractive outcome and to preserve visual quality by not inducing glare and reduced contrast sensitivity.
The aspheric aberration-free ablation profiles created by the Schwind Amaris 750S excimer laser system (Schwind eye-tech-solutions) result in excellent refractive outcomes and minimize induction of HOAs. These profiles include large optical zones, multidynamic aspheric transition zones, compensation for aberration and focus shift caused by tissue removal, pseudomatrix-based spot positioning, and intelligent thermal effect control. The randomized flyingspot ablation pattern and local repetition rate controls minimize the thermal effect of tissue removal to produce a smooth ablation with no risk of thermal damage.
Currently we use the Amaris’ aberration-free profile for myopic femtosecond LASIK (femto-LASIK) treatments in eyes with up to -10.00 D of sphere and -5.00 D of cylinder. We recently reviewed 2,862 consecutive cases with complete pre- and postoperative data at 3 months (Table 1). Our retrospective analysis omitted exclusion criteria that would limit enrollment in a prospective study.
Manifest refractive spherical equivalent (MRSE).
We found a close relationship between attempted and achieved MRSE (Figure 1). Additionally, 79% of patients achieved a UCVA of 20/20 or better and 26% achieved 20/16 or better; all patients achieved the United Kingdom Driving Standard of 20/40.
Refractive outcomes. In our study, 95% of patients were within ±0.50 D of emmetropia, and 100% were within ±1.00 D (Figure 2). No eye lost more than 2 lines of BCVA (Figure 3), 26% gained 1 line, and 1% gained 2 lines. The outcomes were stable through 3 months (Figure 4).
Corneal wavefront aberrations. We compared pre-and postoperative mean HOAs, spherical aberration, and coma. The root-mean-square (RMS) HOAs did not change significantly from pre- to postoperatively (preoperative: 0.30 ±0.12 μm; range, 0.15–0.84 μm; postoperative: 0.35 ±0.13 μm; range, 0.13–0.85 μm). Pre- and postoperative mean spherical aberration were 0.16 ±0.07 μm (range, 0.03–0.40 μm) and 0.18 ±0.10 μm (range, 0.02–0.49), respectively. Mean pre- and postoperative coma were 0.18 ±0.11 μm (range, 0.03–0.75 μm) and 0.21 ±0.12 μm (range, 0.03–0.75), respectively.
Our results demonstrated that the aberration-free aspheric ablation profiles of the Schwind Amaris750S were indeed aberration-neutral.
Achieving good refractive outcomes with high levels of safety and patient satisfaction is crucial. The speed of laser treatments with the aberration-neutral profiles of the Schwind Amaris 750S provides an exceptional patient experience, and we have yet to receive a complaint of glare and halos due to the large optical treatment zones and resultant prolate corneas. The laser’s 6-dimensional tracking function has also ensured accurate treatments, with no evidence of decentration thus far.
Amir Hamid, BMedSci, FRCOphth, is Medical Director of Ultralase Optimax Eye Surgery Specialists in London. Dr. Hamid states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: email@example.com.
Arif Sokwala, BSc (Hons), is the Head Optometrist at Ultralase Optimax Eye Surgery Specialists, London. Mr. Sokwala states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: firstname.lastname@example.org.
- Liang J, Grimm B, Goelz S, Billie JF. Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor. J Op Soc Am A Opt Image Sci Vis. 1994;11:1949-1957.
- Mastropasqua L, Toto L, Zuppardi E, et al. Photorefractive keratectomy with aspheric profile of ablation versus conventional photorefractive keratectomy for myopia correction; six month controlled clinical trial. J Cataract Refract Surg. 2006;32:109-116.
- Arbelaez MC, Mosquera SA. The Schwind Amaris Total-Tech Laser as an all-rounder in refractive surgery. Middle East Afr J Ophthalmol. 2009;16(1):46-53.
- Arbalaez MC, Vidal C, Mosquera SA. Six-month clinical outcomes in LASIK for high myopia with aspheric “aberration neutral” ablations using the AMARIS laser system. Journal of Emmetropia. 2010;1:111-116.