Refractive surgeons have faced challenges in effectively combining the treatment of refractive errors and presbyopia.1,2 Good near vision should be accompanied by minimal detrimental effect on the distance vision. Charman3 proposed that the main aim of presbyopia treatments was to extend the binocular depth of focus to yield adequate distance and near vision with good retinal contrast at lower spatial frequencies.
Surgical presbyopia corrections have seen several developments from the monovision and multifocal ablation techniques to the modern hybrid methods combining the benefits of several techniques. Monovision techniques4 usually involve correcting the dominant eye for distance, as opposed to crossed monovision5 where the dominant eye is corrected for near vision.
Multifocal ablations result in a pseudo-accommodative cornea realized in the form of either a peripheral near zone (concentric ring for near vision)6 or a central near zone (central disc for near vision).7 Schlote and Heuberger8 reported efficacy and safety of the varifocal excimer laser corneal ablation profile (SupraCor; Technolas Perfect Vision GmbH, Munich, Germany) in hyperopic presbyopia 1 year after laser treatment. They reported that uncorrected distance visual acuity (UDVA) and uncorrected near visual acuity (UNVA) improved markedly, photopic contrast sensitivity was in the normal age-correlated range, and 75% of patients were satisfied with the results. Similar promising results have been reported in other studies.9–11
In any presbyopic treatment, some myopic refraction postoperatively facilitates near vision, but at the cost of distance vision. Therefore, various manufacturers have incorporated a myopic target refraction (either symmetric in both eyes or asymmetric) into their presbyopia treatment protocol. With different ablation profiles and techniques offered by commercially available laser platforms to treat presbyopia, it is relevant to examine whether the spherical aberration induction through varifocal ablation profiles is sufficient to reach better near vision without diminishing distance vision (as previously reported using various approaches).12,13 This may be evaluated by comparing varifocal ablations targeting emmetropia to monofocal ablations, ideally using the same laser. However, even monofocal ablations may induce higher order aberrations, and in particular hyperopic ablations may induce negative spherical aberrations, resembling what varifocal ablations aim for.14,15
In this prospective study, we performed varifocal and monofocal LASIK in 15 consecutive patients with hyperopic presbyopia. Eight patients were bilaterally treated with varifocal ablations (SupraCor) and 7 patients were treated with monofocal parabolic nonaspheric ablations (TissueSaving; Bausch & Lomb, Rochester, NY) using the same laser.
Patients and Methods
Originally, the study was designed to include 35 patients. However, in view of the interim analysis after 15 patients, we decided to terminate this study for ethical reasons because no clinically significant difference between ablation profiles could be demonstrated. The patients were not masked and could opt for either SupraCor LASIK or TissueSaving LASIK (Zyoptix; Bausch & Lomb) because both software programs had already received the Conformité Européene (CE) mark and were commercially available. Therefore, an enquiry at the local ethics committee yielded that no formal approval was required. Informed consent was obtained from each patient, for both the treatment and use of their deidentified clinical data for publication. Investigation in this form is not subject to the Medical Research Involving Human Subjects Act (WMO).
Hyperopic patients older than 47 years (as recommended by the manufacturer for varifocal ablations) with corrected distance visual acuity (CDVA) of 20/25 or better in each eye were included in this study. Distance refraction had to be stable (< 0.50 diopters [D] change in mean spherical equivalent) for at least 1 year prior to the treatment with astigmatism between 0.00 and 2.50 D. A maximum difference between manifest and cycloplegic spherical equivalent of 0.50 D was allowed. All eyes were required to have normal keratometry and topography and a preoperative central corneal thickness of more than 500 µm. Angle kappa (ie, the difference between the pupillary and visual axis) had to be less than 10° in the Orbscan (Bausch & Lomb Technolas, Munich, Germany) examination. Patients who suffered from systemic illness or had previous ocular surgery were excluded from the study. Additional exclusion criteria were clinically relevant lens opacities or any signs of binocular vision anomalies, including (relative) amblyopia at distance or near.
Before preoperative evaluation, soft contact lenses had to be discontinued for at least 2 weeks and rigid lenses for at least 4 weeks. A full ophthalmologic examination was performed on all patients prior to surgery, including manifest refraction, cycloplegic refraction, keratometry, corneal topography, and central corneal thickness (Orbscan II; Bausch & Lomb Technolas). Monocular and binocular UNVA, distance-corrected near visual acuity (DCNVA), uncorrected intermediate visual acuity (UIVA) at 70 cm, UDVA, and CDVA were assessed. The corrected visual acuity was always assessed by the same examiner using the same automatic phoropter (Möller Wedel, Wedel, Germany). Low-contrast UDVA and CDVA were also assessed using retroilluminated Sloan charts (Bausch & Lomb Technolas) at a distance of 3 meters (because this is the distance the charts are designed for).
Patients were treated by the same surgeon (ST) in a standardized fashion, with either bilateral varifocal LASIK or bilateral monofocal LASIK.
The intended postoperative refraction was emmetropia in all eyes. In the varifocal ablations, the laser manufacturer's start-up nomogram as of May 2011 was used: if the manifest preoperative spherical equivalent (SEQ) was 1.00 to less than 1.75 D, then the sphere was adjusted by −0.25 D (SEQ: 1.75 to < 2.50 D, −0.50 D; 2.50 to < 3.50 D, and −0.75 D, respectively). There was no nomogram adjustment in the monofocal group.
The same laser (Technolas 217 Z 100, Software Keracor 4.5; Bausch & Lomb Technolas) and a XP microkeratome (Bausch & Lomb Technolas) with a 120-µm head and a 9.5-mm suction ring were used in all eyes. The optical treatment zone diameter was 6 mm for varifocal ablations (as recommended by the manufacturer) and 6.5 mm for monofocal ablations (as had been our standard).
Two drops of topical anesthetic (proximetacaine-hydrochloride, Proparakain-POS 0.5%; Ursapharm, Saarbrucken, Germany) were instilled immediately before surgery. A sterile drape covering the eyelashes was used to isolate the surgical field. An eyelid speculum with suction (52135; Storz Ophthalmic Instruments, Heidelberg, Germany) was inserted to allow maximum exposure of the globe.
Proper alignment of the ablation was achieved with the built-in automatic eye-tracking system with compensation of cyclotorsional movements in all eyes. The ablation was centered between the pupil center and the first Purkinje image (coaxially sighted corneal light reflex), as recommended by the laser manufacturer. Patients were instructed to look at a blinking red fixation light throughout the ablation.
Patients were prescribed antibiotic (ofloxacin, Floxal EDO; Bausch & Lomb) and corticoid (dexamethasone, Dexa EDO; Bausch & Lomb) eye drops four times a day for 5 days and ocular lubricants (hyaluronic acid) at least five times per day for 3 months.
Follow-up examinations were scheduled at 1 day, 1 week, 1 month, and 3 months postoperatively.
Visual acuity was measured in decimal scale, converted to logMAR units, and presented in Snellen equivalents for reporting comparability. The analysis comprised evaluating the change in binocular and monocular visual acuity, preoperatively and at each follow up. The paired and unpaired Student's t tests were used to evaluate the difference between preoperative and postoperative visual acuity and between groups, respectively. A P value of less than .05 was considered statistically significant.
The preoperative demographic and refractive data were similar in both groups except for SEQ and mesopic pupil diameter (Table 1). No intraoperative or postoperative complication occurred. Of the 15 patients enrolled in the study, 12 patients (6 in the varifocal ablation group and 6 in the monofocal ablation group) completed the 3-month follow-up period. The drop-outs were contacted but did not want to return for final examination because they were satisfied with their results. Refractive results at 3 months are summarized in Table 2 and as standard graphs in Figure 1.
Preoperative Demographic and Refractive Data
Postoperative Refractive Data at 3 Months
Refractive and visual acuity outcomes at 3 months of follow-up in 15 consecutive patients with hyperopic presbyopia treated with either bilateral varifocal (8 patients) or monofocal (7 patients) laser in situ keratomileusis (LASIK). UDVA = uncorrected distance visual acuity (in Snellen equivalent); CDVA = corrected distance visual acuity (in Snellen equivalent); SEQ = spherical equivalent refraction (in diopters [D]); Ast = astigmatism (in D); UNVA = uncorrected near visual acuity (in Snellen equivalent); CNVA = corrected near visual acuity (in Snellen equivalent)
The efficacy index of varifocal and monofocal LASIK was 0.9 and 0.88, respectively (no significant difference, P > .05). The distribution of monocular UDVA is presented in Figure 1A. At 3 months, 7 eyes (44%) achieved 20/20 or better monocular UDVA in the varifocal ablation group (no statistical difference from preoperative CDVA, P = .30), whereas 10 eyes (71%) achieved 20/20 or better monocular UDVA in the monofocal ablation group (no statistical difference from preoperative CDVA, P = .10), with no significant difference observed between the two groups (P = .20).
In terms of the difference between preoperative CDVA and postoperative UDVA (Figure 1B), monofocal ablations performed slightly better, with no eye losing more than one Snellen line, whereas 3 eyes (19%) lost two or more Snellen lines after varifocal ablations. However, this was not statistically significant (P = .09).
Monocular UNVA (Figure 1D) was not statistically different between groups (P = .40). The difference between preoperative CNVA and postoperative UNVA (Figure 1E) was not statistically different between groups (P = .50).
No eye lost one or more lines of monocular CDVA (Figure 1C). The safety index was 1.08 in the varifocal group and 1.125 in the monofocal group (no significant difference, P > .05). At 3 months of follow-up, no statistically significant difference was seen between the two groups in terms of change of CDVA (P = .07).
The refractive stability in terms of SEQ is presented in Figure 1F. The relationship between attempted and achieved SEQ is presented in Figure 1G. This scatter-gram shows a slightly better linearity of monofocal ablations compared to varifocal ablations (coefficient of determination, R2 = 0.81 and 0.63, respectively).
The accuracy of postoperative SEQ to the intended target SEQ showed a distinction between the two groups, with monofocal ablations approaching emmetropia, whereas varifocal ablations were more myopic (Figure 1H).
Predictability of refractive astigmatism (Figure 1I) was similar in both groups (P = .15).
Longitudinal Comparison of Visual Acuity
The longitudinal comparison of varifocal and monofocal LASIK in terms of mean monocular UDVA, binocular UIVA, monocular UNVA, monocular DCNVA, and monocular low contrast (Sloan chart) uncorrected and corrected visual acuity is presented in Figure 2 (in logMAR). Similar behavior of those different visual acuity metrics was seen between the two groups.
The longitudinal visual acuity outcomes in 15 consecutive patients with hyperopic presbyopia treated with either varifocal (8 patients; SupraCor; Technolas Perfect Vision GmbH, Munich, Germany) or monofocal laser in situ keratomileusis (LASIK) (7 patients; Zyoptix TissueSaving; Bausch & Lomb, Rochester, NY). Varifocal and monofocal ablations were comparable in terms of average monocular uncorrected distance visual acuity, uncorrected near visual acuity, distance-corrected near visual acuity, low contrast (Sloan chart) corrected and uncorrected distance visual acuity, and binocular uncorrected intermediate visual acuity. A similar progression over time of different visual acuity metrics was seen between the two groups, also confirmed by the overlapping error bars representing a single standard deviation in the metric. VA = visual acuity
No eyes were re-treated in the follow-up period.
Multifocal corneal ablation profiles have shown to provide a high level of spectacle independence for near vision in hyperopic presbyopic corneas, but are associated with diminished distance visual acuity.16,17 After multifocal ablations, a greater spread of surface powers is observed, often with a bimodal distribution, indicative of an apparent multifocal effect.18,19 These corrections are dependent on pupil size and use the central and peripheral regions, or the disparity in the focal points between the dominant and non-dominant eye, to create multifocality and improve the near vision.2,20–30 Mesopic pupil size was larger in our varifocal group. However, mesopic pupil size may not correlate with pupil size in normal/bright light or during reading due to different amplitudes of pupil constriction in different individuals. Ideally, we would have recorded actual pupil size during our various measurements. However, this is not feasible in a clinical setting and there were no restrictions regarding pupil size by the manufacturer.
It has also been shown previously using computer-assisted topographic analysis of corneas after refractive surgery that a minority of corneas achieve a multifocal lens effect, such that they maintain reasonable acuity over a range of defocus, thereby reducing the symptoms of presbyopia.18
It is important to understand the contribution of different elements used in multifocal ablation profiles to near vision, and their detrimental effect on distance vision. In general, four important elements are induction of spherical aberration, myopic target, monovision component, and optical zone size. The induction of negative spherical aberration may improve near vision but may have a detrimental influence on distance vision.31,32 Similarly, a myopic refraction will improve near vision but reduce distance vision. The monovision component (ie, each eye having a different myopic target) may be beneficial to near vision but detrimental to stereovision.4,33 Larger optical zone sizes may on the one hand limit the gains in near vision and on the other hand reduce the compromises in distance vision. However, it is debatable which of these components is more influential than the others.34,35
In this study, we compared symmetric SupraCor LASIK (varifocal ablations) to TissueSaving LASIK (monofocal parabolic non-aspheric ablations). In contrast to expectations raised by theoretical considerations, both ablation patterns resulted in similar refractive and visual outcomes in near, intermediate, and distance vision. The varifocal ablations were planned to result in a clinical plano refraction with a central near zone (corresponding to an addition of approximately +2.00 D) and a surrounding intermediate and far zone of the ablation profile (Figure A, available in the online version of this article).
The varifocal ablations were planned to result in a clinical plano refraction with a central near zone of approximately 2-mm diameter (corresponding to an addition of approximately +2.00 D) and a surrounding intermediate and far zone of the ablation profile. Sagittal schematic drawing of the ablation profile (above) and cross-sectional view of the preoperative anterior corneal curvature (dotted line) and the intended postoperative anterior corneal curvature (below).
Varifocal ablations are intended to induce spherical aberrations to facilitate multifocality and benefit near and far vision simultaneously. In contrast, the monofocal ablation group received non-aspheric ablation profiles. Because these profiles do not incorporate the natural asphericity of the human cornea, it can be expected that the treatment induces a change in the spherical aberration of the cornea depending on the natural corneal shape, thus potentially also resulting in a multifocal cornea. That may be one reason why both ablation patterns yielded similar refractive and visual outcomes in near, intermediate, and distance vision.
A second reason for the similar outcomes of both ablation profiles may be that we did not aim for a myopic target refraction in the varifocal ablations as is commonly done in presbyopic corrections (and in contrast to the recommendations of the manufacturer). We rather opted to avoid the influence of a myopic target and a monovision component on our comparison of the two ablation profiles in this study. However, the mean achieved postoperative refraction was more myopic in the varifocal than in the monofocal group, which theoretically has aided near vision at the expense of distance vision in the varifocal group.
Another reason for equivalent outcomes with both profiles may be that the intended steep central corneal zone in varifocal ablations (Figure A) theoretically acting as a near add may be masked by the epithelium. Figures B–C (available in the online version of this article) show examples of such epithelial masking after other conditions in optical coherence tomography scans. The epithelium smooths the anterior corneal surface, depending on the local change of stromal curvature.36
Examples of irregular corneal stromal surfaces due to trauma or inflammatory processes that are masked by localized epithelial hypoplasia or hyperplasia resulting in a smooth anterior (epithelial) surface.
Example of epithelial masking of the central near addition zone 4 years after varifocal laser in situ keratomileusis. Axial power map and anterior float with central steepening in Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) examination (top row). Corresponding total corneal thickness map and epithelial thickness map (anterior segment optical coherence tomography, Avanti; Optovue, Fremont, CA) revealing epithelial thinning over the central near addition zone of 2-mm diameter (bottom row). Minimum epithelial thickness is 39 µm (marked with *) and maximum epithelial thickness is 61 µm (marked with +).
The patient population in this study had hyperopic presbyopia. Therefore, we may assume that the nonaspheric monofocal ablations indirectly induced negative spherical aberrations that are beneficial for near vision because the preexisting corneal asphericity was not incorporated into the ablation profile. However, these assumptions cannot be extrapolated for myopic corrections where non-aspheric monofocal ablations may induce positive spherical aberrations. Moreover, results of our non-aspheric ablations cannot be extrapolated to aspheric monofocal ablations that may induce less negative spherical aberrations, reducing the multifocality effect.
It can be further argued that the extent of spherical aberration induction in monofocal ablations directly depends on the optical zone size and ablation depth/volume of the treatment. In our monofocal ablation cohort, the optical zone size was 6.5 mm, whereas the attempted SEQ in the treatments ranged from 1.13 to 4.00 D (mean: 2.28 D). We assume that, for this patient population, an optical zone size of 6.5 mm was able to induce sufficient negative spherical aberrations to improve near vision to a similar extent as the varifocal ablations. However, both ablation patterns may result in different outcomes for other optical zone sizes and ablation volumes. Results can therefore not be extrapolated to other optical zone sizes, whereas the diameter of the central addition zone is fixed by the algorithm.
A small patient cohort, statistically different baseline SEQs in both groups, and short follow-up times could be considered as limitations of our study. However, even if a statistically significant difference between varifocal and monofocal ablations could be shown in a larger sample size, it is reasonable to assume that this may be due to the reduced standard error in each group, yet the mean differences would remain approximately the same. Therefore, even in the event of reaching statistical significance, a clinically relevant difference is not to be expected.
Varifocal LASIK outcomes as presented here are comparable to outcomes reported with other modern presbyopic approaches such as symmetric PresbyMAX.37 However, comparing results of different studies evaluating presbyopia treatments may be difficult because a standardization for the measurement of near and intermediate vision has been missing until reporting methods were proposed recently.37
In our direct comparison in a hyperopic population, however, varifocal ablations were not superior to monofocal ablations. Varifocal LASIK (SupraCor) results (and PresbyMAX results37) have been improved in terms of safety and efficacy by adding some of the components discussed above such as induction of different levels of spherical aberrations and different myopic targets for either eye. Yet it is worth considering that monofocal approaches can also be similarly refined, using the same components.38,39 For example, a recent Cochrane library review found no difference of multifocal intraocular lenses and monovision with monofocal intraocular lenses after cataract extraction.40 Similarly, a large comparative study found no significant difference between monovision LASIK and refractive lens exchange with multifocal intraocular lenses.41
In this small cohort of patients with hyperopic presbyopia with emmetropia as target refraction, symmetric varifocal ablations resulted in no further advantage on near vision compared to monofocal parabolic ablations. This counterintuitive main outcome could only be observed by directly comparing both treatment modalities to each other under the same conditions (ie, no myopic target) rather than evaluating the absolute performance of each modality individually. This emphasizes the importance of having a control group when evaluating a presbyopia treatment.
It can be speculated that epithelial remodeling masks the clinical impact of varifocal ablation pattern and that spherical aberrations are also induced, with non-aspheric monofocal ablations contributing to similar results with both ablation patterns.
The improved near visual acuity reported with presbyopic laser ablations in the literature may be amplified by a myopic target refraction and partial monovision. Further comparison to hyperopic monovision treatments performed using monofocal parabolic ablations could be essential to render answers to whether the spherical aberration induction through multifocal ablation profiles is sufficient to reach better near vision without diminishing distance vision.
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Preoperative Demographic and Refractive Dataa
|Parameter||Varifocal LASIK||Monofocal LASIK||P|
|No. of eyes||16||14||–|
|No. of patients||8||7||–|
|Mesopic pupil diameter (mm)||6.24 ± 0.55 (2.32 to 7.87)||5.01 ± 0.83 (3.6 to 6.2)||< .005|
|Median age (y)||52 (49 to 60)||53 (48 to 59)||.40|
|Preoperative SEQ (D)||1.8 ± 0.59 (0.88 to 3.00)||2.28 ± 0.83 (1.13 to 4.00)||.05|
|Preoperative refractive astigmatism (D)||−0.45 ± 0.33 (−1.25 to 0.00)||−0.52 ± 0.27 (−1.00 to −0.25)||.30|
|Preoperative corneal thickness (µm)||584 ± 26 (543 to 624)||588 ± 23 (547 to 624)||.30|
|Preoperative average keratometry (D)||44.14 ± 1.37 (41.80 to 46.50)||43.58 ± 1.43 (41.20 to 45.50)||.377|
|Preoperative angle kappa (°)||5.09 ± 1.74 (2.32 to 7.87)||5.69 ± 0.71 (4.76 to 6.68)||.40|
|Preoperative higher order aberrations (µm)||0.33 ± 0.14 (0.18 to 0.65)||0.33 ± 0.07 (0.26 to 0.40)||.769|
|Preoperative spherical aberrations (µm)||0.29 ± 0.18 (0.08 to 0.67)||0.19 ± 0.11 (0.08 to 0.29)||.368|
Postoperative Refractive Data at 3 Monthsa
|Parameter||Varifocal LASIK||Monofocal LASIK||P|
|SEQ relative to intended target (emmetropia) (D)||−0.45 ± 0.38 (−1.25 to 0.13)||−0.12 ± 0.46 (−1.38 to 0.50)||.02|
|Refractive astigmatism (D)||−0.38 ± 0.41 (−1.25 to 0.00)||−0.52 ± 0.31 (−1.00 to 0.00)||.15|