Wavefront Results

Mixed astigmatism

Paolo Vinciguerra and Fabrizio I. Camesasca

Department of Ophthalmology, Istituto Clinico Humanitas, Milano, Italy

Correction of astigmatism

Until recently, the main goal in the treatment of astigmatism was complete refractive correction of the defect. The commonly adopted methods followed two main strategies: ablation on one meridian only, or split on to the two meridians of astigmatism, axis and power.

Treating all astigmatism on one meridian leads to marked corneal asymmetry, similar to the previous situation of astigmatism: asymmetry is merely moved from the center of the cornea towards the periphery. It is important to note that the shape of the cornea resulting from this correction is frequently oblate, very different from a physiological, normal, anastigmatic cornea (Fig. 1). When the pupil dilates even slightly, i.e., to 5 mm, eyes that received this type of treatment show an increase in aberrations, including spherical aberration, quadrafoil, and astigmatism in the periphery.

Presently available techniques for the correction of myopic astigmatism are adequate on the steepest meridian, but create overcorrection on the oblique meridians, which have a lower dioptric power. For example, if we treat for five negative diopters of cylindrical ablation with an optical zone (OZ) of 5 mm, we plan 30 m ablation on 126 axis. However, the actual ablation is 40 m, thus an overcorrection of 10 m. A standard ablation appears to be adequate on the steepest meridian, but actually overcorrects the oblique ones, leading to a hyperopic shift. Overcorrection is spherical and of about 20%, with an irregular ‘four-leaf’ astigmatism on the oblique meridians (Table 1, Fig. 2).

Perfect ablation for myopic astigmatism should completely correct the steepest meridian as well as the oblique ones in proportion to their curvature. The flattest meridian should remain unchanged. In order to avoid regression, a dioptrically progressive corneal shape is decisive.

Epithelial layering follows a superficial tension law.1 When it meets irregular surfaces, the corneal epithelium becomes thicker, in order to fill any gaps. A thicker epithelium induces scar tissue formation below. Therefore, corneal irregularities are partially compensated for by deposition of scar tissue. Unfortunately, this mechanism leads to regression of a given correction.2 Corneal scarring and epithelial thickening can also

Address for correspondence: Paolo Vinciguerra, MD, Via Ripamonti 205, 20110 Milan, Italy. e-mail: vincieye@tin.it

Wavefront and Emerging Refractive Technologies, pp. 27–37

Proceedings of the 51st Annual Symposium of the New Orleans Academy of Ophthalmology, New Orleans, LA, USA, February 22-24, 2002

edited by Jill B. Koury

© 2003 Kugler Publications, The Hague, The Netherlands

Fig. 2. 5 D myopic astigmatism.

lead to midperipheral flattening. In order to avoid regression and decrease of visual acuity, a regular and progressive change in corneal curvature is mandatory.

It is commonly thought that a large ablation diameter (i.e., 6.5 mm) is not associated with regression, while a small ablation diameter (i.e., 4 mm) is. This is not completely true: by studying topographical maps, we could see that, with large ablations as well, there are changes of the ablation edge due to scar tissue formation, and/or epithelial hyperplasia. Changes take place at the edge of the ablation and far away from the pupillary area, and thus the optical zone remains homogeneous and patients are asymptomatic. On the other hand, in small ablations, optical zone edge modifications are within the pupillary area, and thus the optical zone becomes non-homogeneous

Fig. 3. Oblique meridian overcorrection.

with multifocality and optical aberration: patients note night halos, visual loss, and glare. Regression leads to new myopic astigmatism on the steepest meridian (Fig. 3) and to a positive spherical equivalent because of hypercorrection on the oblique meridian. Eventually, we will have mixed astigmatism, which is more difficult to retreat.

Exactly the opposite situation can be observed in the correction of hypermetropic astigmatism. There is undercorrection on the oblique meridians: when regression takes place, mixed astigmatism occurs (Fig. 4).

In the 1990s, refractive surgeons had limited tools for the evaluation of results, i.e., only the axial algorithm was available for corneal topography. Nevertheless, it was rapidly understood that a monochromatic topographical map, corresponding to a regular keratoscopy, with rings that were symmetrical in width, a regular and reciprocal distance, was associated with better and more stable results, fewer halos, less glare, and greater patient satisfaction. Thus, in recent years, emmetropia as well as a regular corneal surface have been pursued when correcting astigmatism.

Correction of astigmatism on two meridians was then introduced, basically by means of two methods: the amount of correction split either evenly or unevenly between the two main meridians. Starting from the analysis of nomograms which showed that residual astigmatism was left on the untreated meridian, Chayet et al. introduced an asymmetrical correction split onto the two astigmatism meridians.1 He deserves much credit for his clever approach, even though an asymmetrical correction still has the limitation of creating an asymmetrical corneal surface, thus with possible aberrations. In a thorough analysis of the different methods available, Azar and Primack recom-

Fig. 4. 5 D hyperopic astigmatism.

mended correction on the hyperopic meridian only, with the advantage of removing even less cornea than with any other technique.4 However, in this case too, treatment leads to corneal surface asymmetry, even if on a different meridian, with the possible induction of aberrations.

We must keep in mind that, nowadays, patients do not simply ask that the need for spectacles be eliminated, at times still a difficult target, but usually for improved vision. Therefore, our real target is improved visual quality. Frequently, a patient’s discontent is not caused by a limited residual refractive defect, but by an increase in aberrations, with good acuity, but poor quality and frustrated expectations.

Correction astigmatism with crossed cylinders, besides requiring limited tissue ablation, leaves the cornea prolate and symmetrical, thus with a final shape closer to the normal prolate cornea, without inducing aberrations, i.e., coma. Corneal regularity, previously an almost intuitive concept, now can be described as maintaining its eccentricity within physiological limits, with a surface generating an aberration-free wave front.

Eccentricity can also be considered a way of expressing spherical aberration, measuring its shape, not the effect on vision. When the spherical aberration is high, the optical zone diameter is very close to the ablation zone diameter. Containing the spherical aberration within one or two diopters will provide a much wider optical zone than the ablation zone provided.

In the correction of astigmatism, the choice of the diameter of the optical zone was

normally related to the maximum diameter of the pupil. Now, the surgeon must choose the correction and ablation diameter in relation to the corneal changes in curvature from the center to the periphery (eccentricity).

The cross-cylinder technique can be reliably used for one or more diopters of astigmatism, and can be applied with all the last generation excimer lasers. Ablation zone diameters of positive and negative cylinders must be identical or very similar.

As mentioned above, the most frequently encountered limitation of a single meridian correction is that it results in a poor corneal profile on the uncorrected meridian. The critical point lies in the junction between treated and untreated meridians. Applying a myopic/hyperopic ablation pattern leads to a more gradual ray of curvature, with a better transition zone in the uncorrected meridian.

Corneal eccentricity

Our ideal postoperative target is a prolate cornea, which maintains corneal eccentricity. Eccentricity is the measure of corneal asphericity; therefore, it expresses the way the cornea changes from a flatter periphery to a more curved central portion. Normal eccentricity values (e values) range between +0.5 and +0.6 (normally prolate cornea: curved in the center, flat in the periphery).

Normal astigmatism correction provided to one meridian only, only leads to corneal symmetry centrally, with no change in the ray of curvature on the opposite meridian. Thus, ablation on one meridian only changes corneal asphericity: a negative cylinder flattens the corneal center (oblate cornea), a positive cylinder flattens the corneal periphery (excessively prolate cornea). Peripheral change in curvature is also important: the transition zone concentrates it in a limited area, with loss of physiological curvature leading to optical aberrations. Thus, if the two ablations are not symmetrical, an asymmetrical cornea, with high order aberrations and poor quality of vision, may be the final result. These aberrations negatively influence the quality of vision, even at different pupil diameters, more than aberrations originating from symmetrical changes (i.e., coma), and the patients often complain of monocular double vision.

Mixed astigmatism

Recent advancements in the correction of mixed astigmatism include the pursuit of a postoperative corneal surface that is as symmetrical as possible, centrally as well as in the periphery.3 Mixed astigmatism can be classified as regular, showing the typical bow-tie shape with lobes symmetrical in shape, dioptrical power, laying on the same axis. Irregular astigmatism, not showing these features and presently regarded as resulting from high order optical aberrations, will ideally need custom ablation for proper correction.

With regard to regular astigmatism, it is important to remember that a large or a small bow-tie seen on axial topography does not directly relate to the size of the corneal area involved in astigmatism. The size of the bow-tie is an expression of the change in curvature, greater in the large bow-tie, smaller in the small one. The ray of curvature changes rapidly from center to periphery in small bow-ties (e values of more than 0.5), and more gradually in large ones (e values of less than 0.5) (Figs. 5 to 10).

Cross-cylinder technique

The cross-cylinder ablation technique is our method of choice for astigmatism.5-8 The cornerstone of this treatment is the division of the cylinder power into two symmetric parts. Its main advantages are preservation of the mean corneal ray of curvature, and therefore of corneal eccentricity. A further advantage of this technique, as well as of other techniques, i.e., a positive cylinder, is a reduction in the quantity of ablated tissue.

Small bow-ties are less critical as far as the transition zone is concerned, while large ones require larger transition zones. Classically, small bow-ties provide better results with the usual techniques and small optical zones, correcting only the center of the cornea. Large bow-ties, with a more gradual change in curvature, when treated with a small optical zone, show a sharper postoperative change in curvature. Since the corneal epithelium follows the laws of superficial tension, during the healing process, sharper curvature changes induce, in both PRK and LASIK, epithelial hyperplasia and consequent regression. Therefore, high-power astigmatism with a large bow-tie can be complex. The cross-cylinder technique can be adopted with recent-generation excimer lasers that permit ablation with both negative and positive cylinders.

Diameters of ablation and transition zones

Ablation zones (AZ) and transition zones (TZ) must be symmetrical, i.e., a 6.5 AZ with a 1.0 TZ for a positive cylinder, and a 6.5 AZ and a 1.0 –9.5 TZ for a negative cylinder. In this way, the mean corneal curvature ray is unchanged and maintains the physiological shape.

Variable formulas

Variable formulas change the percentage of the cylindrical correction provided, according to the amount of sphere to be corrected. This variable pattern makes the postoperative shape unpredictable, giving the result a variable quality, since treated corneas will show variable asymmetry, with variable eccentricity values.

Example 1

With the cross-cylinder technique, a mixed astigmatism of +2.00 sph and -4.00 (180) cyl will be treated by ablating a +2.00 (90) cyl zone and a –2.00 (180) cyl zone. This is because we must take the spherical equivalent (SE) into account.

•The spherical equivalent of this defect is zero.

•According to the cross-cylinder formula, the amount of astigmatism must regularly be divided into two, half to be treated on the negative meridian and half on the positive meridian. Therefore, a –4.00 (180) cyl is divided into two –2.00 (180) cyl components, and one is transformed, taking the SE into account, into -2.00 sph +2.00 (90) cyl, while the other –2.00 (180) cyl remains unchanged.

•The –2.00 sph SE generated, converting the first half of the total cyl, nullifies the +2.00 sph of the defect: the SE of the original defect, zero, is thus respected.

•The resulting refractive defect correction is, as mentioned above, +2.00 (90) cyl and –2.00 (180) cyl. The mean ray of corneal curvature remains unchanged.

Example 2

+3.00 sph –3.00 (80) cyl

•The spherical equivalent of this defect is +1.50 sph.

•The –3.00 (80) cyl is divided into two –1.50 (80) cyl components, and taking the SE into account, one is transformed into –1.50 sph +1.50 (170) cyl, while the other –1.50 (80) cyl remains unchanged.

•The –1.50 sph SE generated, converting the first half of the total cyl plus the +3.00 sph of the defect, leads to a residual +1.50 sph: the SE of the original defect, +1.50

sph, is thus respected.

CThe resulting refractive defect correction is +1.50 sph +1.50 (170) cyl and –1.50 (80) cyl.

References

1.Chayet AS, Montes M, Gomez L, Rodriguez X, Robledo N, McRae S: Bitoric laser in situ keratomileusis for the correction of simple myopic and mixed astigmatism. Ophthalmology 108:303-308, 2001

2.Dierick HG, Missotten L: Is the corneal contour influenced by a tension in the superficial epithelial cells? Refract Corneal Surg 8:54-59, 1992

3.Krueger RR, Binder PS, McDonnell PJ: The effects of excimer laser photoablation on the cornea. In: Salz JJ, McDonnell PJ, McDonald MB (eds) Corneal Laser Surgery. St Louis, MO: CV Mosby 1995

4.Azar DT, Primack JD: Theoretical analysis of ablation depths and profiles in laser in situ keratomileusis for compound hyperopic and mixed astigmatism. J Cataract Refract Surg 26:1123-1136, 2000

5.Vinciguerra P, Epstein D, Azzolini M: Ablation of both meridians in LASIK and PRK: a new tissue-saving strategy for correcting astigmatism. Invest Ophthalmol Vis Sci 40:S782, 1999

6.Vinciguerra P: Cross-cylinder ablation for the correction of myopic or hyperopic astigmatism. In: Gimbel HV, Anderson Penno EE (eds) Refractive Surgery: A Manual of Principles and Practice, pp 105-113. Thorofare, NJ: Slack Ed 2000

7.Epstein D, Vinciguerra P, Prussiani A, Camesasca FI: Cross-cylinder ablation in LASIK and PRK: a new tissue-sparing, accuracy-enhancing strategy for correcting astigmatism. Invest Ophthalmol Vis Sci 41:S690, 2000

8.Vinciguerra P, Epstein D, Camesasca FI, Prussiani A: A new splitting technique to improve optical zone curvature in astigmatism correction in LASIK and PRK. Invest Ophthalmol Vis Sci 41:S688, 2000

Wavefront results

Bausch-Lomb clinical data

Stephen G. Slade

University of Texas, Houston, TX, USA

Abstract

Global results with the Zyoptics wavefront laser system from Bausch & Lomb are promising. Comparative studies show an improvement over Plano scan results.

The laser system

Currently, we are studying wavefront ablation results for the standard Bausch & Lomb 217 Technolas excimer laser, which uses 2-mm and 1-mm spot truncated gaussian beams.

The system is a 50 Hz scanning laser, which uses a 2-mm spot for the masses of tissue removal. The 2-mm is four times faster than the 1-mm spot, which is used for fine-tuning. The laser system has an eye tracker with a fast reaction time. In addition, the set-up is easy.

In the near future, Bausch & Lomb plans to integrate a torsional eye tracker, which is an important element of customized ablation. The customized system uses an Orbscan topographer integrated with a Shack-Hartmann device, called the Zywave.

The Orbscan topographer maps out the thickness of the cornea and screens for any pathology. It is our hope that, in the future, it will give input to the aberration treatment. The standard screen details the higher order aberrations, total aberrations, and then a series of point-spread functions showing the uncorrected image, a predicted standard correction, and a predicted customized correction.

As the operator progresses through the system, a series of screens allows for selection of the subjective correction, and it allows the operator to choose the sphere and cylinder, either based upon the wavefront or upon the subjective refraction that can be blended. The system also allows for the input of any nomogram option. Furthermore, the exact zone can be selected and the surgeon can sculpt the multi-zone as desired in order to obtain the full single zone.

Address for correspondence: Stephen G. Slade, MD, FACS, 3900 Essex, Suite 101, Houston, TX 77027, USA

Wavefront and Emerging Refractive Technologies, pp. 39–41

Proceedings of the 51st Annual Symposium of the New Orleans Academy of Ophthalmology, New Orleans, LA, USA, February 22-24, 2002

edited by Jill B. Koury

© 2003 Kugler Publications, The Hague, The Netherlands

Global results

In order to explain the results in context, we will compare the Bausch & Lomb 217 Technolas excimer laser custom results with the current Plano scan results. This is the algorithm that is currently used, and it is approved up to –1.00 to –7.00 D.

In the FDA trial, results show that nearly 90% of patients (–1.00 to –7.00 D with up to 4 D of cylinder) were at 20/20, and almost 100% were at 20/40.

For the preoperative versus the postoperative questionnaire, no increase in night vision difficulties was observed when comparing the total percentage of responders. There was a very low number of best-corrected visual acuity lines lost. Overall accuracy was good.

The Bausch & Lomb 217 Technolas excimer laser is currently being used in more than 55 centers throughout the world. The global data have been culled from 35 centers using Zyoptics on myopic patients with up to –12.00 and up to 6 D of cylinder. Our research showed an improvement with the global Plano scan data and the global dioptrics data.

When comparing the preoperative best-corrected visual acuity against the postoperative best-corrected visual acuity, almost 47% of patients were corrected at 20/16 at three months. There was a lag, but at three months, an improvement was observed and seemed to stabilize. In addition, an improvement of about a line in efficacy data was noted over the excellent Plano scan results.

Therefore, the procedure appears to be stable over time. However, there is a one-month period in which most of the changes occur. Even though changes are noted up to one month, at least by three months they appear to be stable.

Results in the USA

The data for the USA study results include studies from our site, as well as those from other investigators: Daniel S. Durrie, MD, director of refractive surgery at the Hunkeler Eye Centers in Kansas City, and Scott M. MacRae, MD, professor of ophthalmology and visual sciences, University of Rochester, NY.

More than 200 eyes have been treated. Today, I will report data on the first 60 eyes. These were masked and controlled, with one eye of the patient being randomly assigned to the Plano scan and the other to the Bausch & Lomb Zyoptics system. For the US data, the study included patients with up to 7 D and those with only up to 3 D of cylinder.

The US data over time were very flat, and yielded very stable spherical equivalents over time. For a comparison, we put the Plano scan US data, the Plano scan global data, and the Zyoptics US and global data together. With regard to efficacy, the results had significantly improved over time and were all significantly better than the original non-custom results. With regard to safety measures, there were also improvements in all the groups over the original.

By means of the study, we learned that, with the wavefront ablation, less tissue is used. This phenomenon is probably a function of using a 1-mm spot to carry out a portion of the blending, rather than using a 2-mm spot for the entire procedure. When comparing Plano scan patients with Zyoptics patients for ablation depth, many more of the Zyoptics patients had less tissue removed than the Plano scan group. We concluded that this technique saves about 20% of tissue in depth.

In addition, we also found that there seems to be (at least in our first algorithm), a ‘sweet spot’ as far as the results with optical zones are concerned, both regarding safety and the efficacy ratios. When we go out beyond that ‘sweet spot’, say, for smaller pupils or smaller treatment zones, there is a drop-off effect. Although the numbers are less, it seems to be a better treatment with better results in this area.

For our study, we used a tightly controlled one-eye Plano scan, and one-eye Zyoptics in fairly high myopic patients. All these analyses were significant and were performed for a 6-mm pupil size. The Zyoptics preoperative sphere rose to 6-3/4 D, and the Plano scan rose to 8 D. The amount of cylinder – the maximum rose to 4 D and 3 D, respectively. The mean was low in the amount of cylinder.

We analyzed the aberrations in this particular study population. We were able to decrease the preoperative aberrations up to the fifth order. The Zyoptics patients resulted in much less RMS and higher order aberrations than preoperatively.

Patients were surveyed both preand postoperatively regarding quality of vision. There was a significant improvement in visual quality in all three of the light conditions tested, as well as a significant improvement in the patients’ night driving vision, even over the Plano scan, which did not induce any increase in the number of patients who had problems with night driving.

We also found that we achieved the greatest effect with the larger pupils, while with smaller pupil size, there tended to be less of an effect.

These data have been submitted to the FDA. The international accumulation of data is continuing.

The future

Our continued research is addressing the major problem of induced aberrations. This group of patients has more spherical aberrations after surgery than before. This affects their point-spread function.

We are evaluating numerous options, including LASEK or PRK, and spherical treatment with ICLs or keratophakia, in order to address this problem.

We have been doing laser keratectomies using an Intralase keratome to try to decrease the amount of aberrations that the flap induces. A double-masked study is under way, in which patients are assigned to either an Intralaser or a keratome flap group.

Finally, we are also analyzing the role of corneal topography in conjunction with wavefront technology.

The wavefront results

Alcon CustomCornea clinical data

Ronald R. Krueger

Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, OH, USA

With the advent of wavefront technology and its clinical use and application in ophthalmology, customized corneal ablation has become the chief investigational pursuit of laser vision correction. The following represents one commercial perspective of customized laser vision correction,using the Alcon LADARVision andLADARWave unit. The investigators contributing to the data gathered are Steve Brint, Daniel Durrie, Omar Hakim, Brock McGruder and Marguerite McDonald.

Before discussing the clinical outcomes, it is important to outline the platform for customized laser vision correction. The Alcon LADARVision 4000 laser offers a unique platform for customized laser treatment, which is superior to other laser vision correction platforms. It contains the essential features of a small, 0.8-mm scanning spot, with a gaussian beam profile, which is the best pulse shape for achieving a smooth correction. The closed loop active tracking system is the state-of-the-art in eye tracking, because it essentially eliminates the latency period from sampling to mirror adjustment and pulse placement. With a 4000-Hz sampling rate, this produces a space-stabilized image when the tracker is engaged, so that even the fastest and most abrupt movement of the eye can be fully tracked without delay, achieving a maximum position error of only 30 m. This powerful combination of scanning and tracking capabilities is optimized by the registration of the laser with the treated eye, based on the center of the undilated pupil and limbus alignment ring for all X and Y translation movement. Cyclotorsion movement can also be precisely registered by preoperative assessment of torsional changes from the upright position, where refractive information is gathered, to the supine position of laser treatment. These essential elements allow for any customized ablation pattern to be precisely applied to the eye with an appropriate blend zone for smooth optical correction.

The Alcon LADARWave unit for gathering wavefront information is a ShackHartmann sensor that measures approximately 200 wavefront spots within a 7-mm pupillary area. It has a large instantaneous dynamic range of up to 15 D of myopia, 6 D of hyperopia, and 6 D of astigmatism, and achieves a precise and natural refractive

Address for correspondence: Ronald R. Krueger, Cole Eye Institute, Cleveland Clinic Foundation, 9500 Euclid Ave/i32, Cleveland, OH 44195, USA (216)-445-8475 (FAX)

Wavefront and Emerging Refractive Technologies, pp. 43–46

Proceedings of the 51st Annual Symposium of the New Orleans Academy of Ophthalmology, New Orleans, LA, USA, February 22-24, 2002

edited by Jill B. Koury

© 2003 Kugler Publications, The Hague, The Netherlands

Fig. 2. Best-corrected visual acuity: custom eyes.

this same group, there are no eyes with a loss of best corrected lines of vision, with 55% gaining one line and 9% gaining two lines.

Further evidence of the improvement in vision can be seen when analyzing the gain in contrast sensitivity in the custom-treated eyes and comparing this to the same results intheconventionallytreatedeyesofthecontralateralstudy.Againofcontrastsensitivity ofgreaterthan0.3 logunits attwoor morespatial frequencieswasseen in 5% ofcustomtreated eyes compared to 0% of conventionally-treated eyes under photopic conditions. The same gain was seen in 32% of custom-treated eyes compared to 23% of conventionally treated eyes under mesopic conditions. In a similar manner, a comparative loss of contrast sensitivity was also analyzed, showing no loss of > 0.3 log units at two or more spatial frequencies under photopic conditions and a 5% loss in custom-treated eyes compared to a 9% loss in conventionally treated eyes under mesopic conditions.

Objective information on improvements in customized laser vision correction can beseeninthepercentagechangeofhigherorderaberrationsinthecontralaterallytreated patients. The conventional eyes in this cohort showed an average 27% increase in higher order RMS error from preto postoperation, compared to an average 7% increase in the custom-treated eyes. Here, the customized treatment induced four times less aberrations than that seen in conventionally treated LASIK eyes. This represents an actual reduction in postoperative high order aberrations in 36% of custom-treated eyes compared to their preoperative value. An ideal case example of a custom-treated eye can be seen in Figure 3 where the preoperative higher order RMS error is 0.233 m and the postoperative value is 0.084 m. Here, the best-corrected preoperative visual acuity of 20/16 is maintained postoperatively with a similar uncorrected vision.

However,thegreatestimprovementinhigherorderaberrationsisnotedinthechange in spherical aberration. In the contralaterally treated cohort, the customized eyes had 50% less spherical aberration than the conventionally treated eyes, which was found to be highly statistically significant (p = 0.001, Fig. 4). Here, 54% of customized eyes had reduced spherical aberration from preto postoperation, giving an average overall reduction in spherical aberration postoperatively. This compares to only 9% of conventionally treated eyes which showed such a reduction.

In summary, we can see that CustomCornea, using the LADARVision laser and LADARWave wavefront device, provides an optimal platform for wavefront-guided

Fig. 3. Effect on higher order aberrations.

Fig. 4. Spherical aberration.

treatment. It uses a small, gaussian, scanning spot, a very fast, closed-loop tracker, a highly accurate and reproducible wavefront device, and a space stabilized graphical user interface. This allows accurate registration of the wavefront image, laser tracker, and patient eye. It facilitates the excellent results of customized treatment to date, demonstrating improvements in uncorrected and best spectacle-corrected acuity, and more gain/less loss of mesopic contrast sensitivity. Even the higher order aberrations have not only shown less induction, but also actual reduction in 36% of customized eyes compared to preoperation. Furthermore, there is essentially no induced spherical aberration in the customized compared to the conventional eyes, where a doubling is noted. Finally, the overall uncorrected results of the CustomCornea eyes can be subject to additional improvements with adjustment of the nomogram to compensate for the slightundercorrection.Overall,theAlconCustomCorneaplatformshowsgreatpromise for the future of customized laser vision correction.