Evaluating Ocular Aberrometic Outcomes

We evaluated the visual, refractive and ocular aberrometric outcomes after wavefront-guided (WFG) laser in situ keratomileusis (LASIK) for the correction of myopia using an excimer laser platform with Iris Registration (IR) technology (STAR S4IR excimer laser, Abbott Medical Optics, Santa Ana, CA, USA) and combined with a new Hartmann-Shack wavefront sensor (iDesign aberrometer, Abbott Medical Optics, Santa Ana, CA, USA) capturing 1250 data points from a 7.0-mm pupil and using Fourier reconstruction for aberration data. Specifically, we conducted a prospective case series study including 92 eyes of 46 patients with ages between 22 and 46 years and undergoing WFG femto-LASIK for the correction of myopia and myopic astigmatism using the Advanced CustomVue platform that combines the excimer laser and the new Hartmann-Shack aberrometer as previously mentioned. Mean preoperative manifest sphere and cylinder were 2.81 ± 2.27 D (range, +0.75 to −10.25 D) and −1.22 ± 1.14 D (range, −4.00 to −0.12 D), respectively. In all cases, corneal flaps were created using the iFS femtosecond laser (Abbott Medical Optics, Inc). The visual, refractive and ocular aberrometric outcomes were evaluated during a 3-month follow-up period.

20/20 Vision 3 Month Post-Operative

At 3 months after surgery, the percentage of eyes that achieved 20/20, 20/25 and 20/40 uncorrected distance visual acuity were 90%, 92% and 99%, respectively (Fig. 1). Postoperative manifest spherical equivalent was within 0.5 D and 1.0 D of emmetropia in 96.7% and 100% of cases, respectively. There were no eyes with a loss of two or more lines of corrected distance visual acuity. These results are consistent with those reported recently by Schallhorn et al.1 using the same technology and also for myopic eyes. Likewise, our visual and refractive outcomes are similar and sometimes better than those reported for myopic WFG-LASIK by a great variety of authors with the last generation of excimer laser platforms.2,3 The combination of the STAR S4IR excimer laser with the new aberrometry technology used in the current series seems to optimize the efficacy and especially the predictability of WFG-LASIK compared to the previous version of such technology.2,4 It should be noted that this new aberrometer is the result of the refinement of a previous Hartmann-Shack wavefront sensor, the WaveScan, with a lower sampling ability and without Fourier data reconstruction.

Besides visual and refractive outcomes, ocular aberrometric changes were also evaluated. To date, this is the first study evaluating the aberrometric outcomes of WFG-LASIK using the evaluated technology. Mean change in higher order aberration (HOA) root mean square and primary spherical aberration (5-mm pupil) was +0.04 ± 0.09 μm (P < 0.01) and +0.01 ± 0.06 μm (P = 0.42), respectively. This change in primary spherical aberration was lower than that reported by some authors evaluating the aberrometric changes after WFG-LASIK for the correction of a similar range of myopic refractive errors and the same pupil of analysis.5,6 Khalifa and colleagues6 found in a sample of myopic eyes with spherical equivalent ranging from −6.63 to 0.00 D that the mean change in spherical aberration after WFG-LASIK using the STAR S4 excimer laser combined with a previous aberrometer version (Wavescan) was 0.18 μm (6-mm pupil).

In conclusion, WFG-LASIK using the STARS4 excimer laser platform with IR technology and combined with a new Hartmann-Shack wavefront sensor capturing 1250 data points from a 7.0-mm pupil and using Fourier reconstruction for aberration data is safe, predictable and efficacious for the correction of myopia or myopic astigmatism. This precise level of correction is combined with a preservation of the quality of ocular optics, maintaining postoperative HOA within a physiological range. A longer follow-up is necessary to study other aspects of surgery, such as refractive stability and change in visual symptoms with time.

Con N Moshegov FRANZCO1,2 and Sara Skaf BHlthSc MClinVisSc1
1Ophthalmology, Private Practice and 2University of Sydney, Sydney, New South Wales, Australia Received 17 September 2014; accepted 18 September 2014.

Eye Surgery References

1. Schallhorn S, Brown M, Venter J, Teenan D, Hettinger K, Yamamoto H. Early clinical outcomes of wavefrontguided myopic LASIK treatments using a newgeneration hartmann-shack aberrometer. J Refract Surg 2014; 30: 14–21.

2. Shaheen MS, Massoud TH, Ezzeldin H, Khalifa MA.
Four-year visual, refractive, and contrast sensitivity outcomes after wavefront-guided myopic LASIK using an advanced excimer laser platform. J Refract Surg 2013; 29: 816–22.

3. Feng Y, Yu J, Wang Q. Meta-analysis of wavefrontguided vs. wavefront-optimized LASIK for myopia.Optom Vis Sci 2011; 88: 1463–9.

4. Zhang J, Zhou YH, Li R, Tian L. Visual performance after conventional LASIK and wavefront-guided LASIK with iris-registration: results at 1 year. Int J Ophthalmol 2013; 6: 498–504.

5. Taneri S, Oehler S, MacRae SM. Aspheric wavefrontguided versus wavefront-guided LASIK for myopic astigmatism with the Technolas 217z100 excimer laser. Graefes Arch Clin Exp Ophthalmol 2013; 251: 609–16.

6. Khalifa MA, Allam WA, Shaheen MS. Visual outcome after correcting the refractive error of large pupil patients with wavefront-guided ablation. Clin Ophthalmol 2012; 6: 2001–11.

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A new technique being used to treat myopia is called SMILE. That stands for SMall Incision Lenticular Extraction. It is a little different to LASIK.

With LASIK a femtosecond laser is used to make a flap in the cornea which is semicircular and which is lifted up to expose the underling corneal stroma.

An excimer laser is then used to reshape the stroma before the flap is put back down over the treated area.

It is a procedure with a very long history of safety and accuracy making it most popular.

Furthermore…it is improving all the time.

How Small Incision Lenticular Extraction (S.M.I.L.E) Works

With SMILE the femtosecond laser is the only laser used. It outlines a lenticule (like a pancake) of stroma within the cornea and then makes a small incision at the side for the surgeon to open up. The lenticule (pancake) is then pulled out (extracted) through the small incision.

The purported advantages over SMILE are that there is no flap that could move, less weakening of the cornea and less dry eye compared to LASIK.

Already sturdies are coming out demonstrating no significant differences in dry eye symptoms between S.M.I.L.E and LASIK.

How Does S.M.I.L.E Compare with LASIK?

There has already been at least one report of corneal weakening (ectasia) following S.M.I.L.E and there will be more to come.

Indeed there is no flap that could, theoretically, be dislodged. However, there have been reports of wrinkles and inflammation within the stroma very similar to flaps in LASIK .

In other words, there is very little difference in the safety profile of the two procedures.

On the other hand, S.M.I.L.E can only treat myopia and astigmatism in association with it. Not astigmatism alone or longsightedness.

S.M.I.L.E cannot be used to retreat an eye (so called ‘enhancement’) if the vision is not quite right or if it deteriorates with time. Other techniques need to be employed to do that.

With S.M.I.L.E it takes longer for the vision to recover. That’s because the lenticule needs to be manipulated out of the cornea manually  and the tissues need a bit more time to recover.

That’s not so bad…if there was a real benefit to the patient.

S.M.I.L.E is still very new. LASIK has had time to incorporate refinements to give people optimal results.

With S.M.I.L.E there is no automated tracking of the pupil. The eye is just tightly held still while the laser is being applied.

With S.M.I.L.E there is no automated pupil centration. The surgeon just estimates the centre of the pupil when performing the procedure

With S.M.I.L.E there is no wavefront analysis or guidance in the procedure. It’s back to the original formula in calculating how much tissue needs to be removed to treat myopia.

However, marketing wizards tell us you need to DIFFERENTIATE yourself in competing for business. S.M.I.L.E is different to LASIK.

Perhaps S.M.I.L.E is enough to lure patients to a particular clinic. Because it’s ‘Different’!

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