Aspheric Wavefront-guided LASIK to Treat Hyperopic Presbyopia: 12-Month Results With the VISX Platform

Patients and Methods

Abbott Medical Optics (AMO) sponsored a prospective, nonrandomized, multicentered clinical trial conducted under an Investigational Treatment Authorization (ITA) by Health Canada. This trial had no association with the United States Food and Drug Administration nor was there a similar study performed in the United States. It was not intended to achieve regulatory approval. All procedures conformed to the Declaration of Helsinki requirements for research involving human patients, and the protocol was approved by the Ottawa Hospital Research Ethics Board. All patients signed an informed consent form. The results of this study reflect a cohort of patients enrolled and treated at the University of Ottawa Eye Institute.

Patients were recruited by the University of Ottawa Eye Institute. Inclusion criteria were hyperopia up to +4.00 diopters (D) sphere and astigmatism up to +1.50 D cylinder; age 45 to 70 years; and =+1.25 D add at 16 inches at the time of enrollment. All eyes were required to demonstrate refractive stability, defined as =0.50-D change in sphere or cylinder that could be confirmed by clinical records. Patients were instructed to discontinue soft contact lens wear for 2 weeks and rigid contact lens wear for 4 weeks prior to baseline measurements and surgery. All patients were required to have corrected distance visual acuity (CDVA) of at least 20/20 and corrected near visual acuity (CNVA) of at least 20/25. The planned treatments could not result in <250 µm of residual stromal bed. Wavefront refraction, manifest refraction, and cycloplegic refraction could not differ by more than ±0.75 D of sphere or cylinder or 15° of cylinder axis for astigmatism >0.50 D. All patients had a normal ocular surface on slit-lamp examination with no evidence of dry eye or lid or corneal abnormalities. Pupil size as measured by the aberrometer had to be =4.0 mm without pharmacologic agents, and the anticipated postoperative K-reading had to be <50.00 D. The remaining exclusion criteria followed the standard refractive surgery guidelines.

Sixty-six eyes of 33 hyperopic patients received aspheric presbyopic ablation treatment between August 2004 and August 2006. Sixty-six percent of the cohort were women. Mean age was 55.1±4.6 years. Mean refractive error was +1.77±0.56 D sphere (range: 0.75 to 3.50 D) and 0.41±0.34 D cylinder (range: 0.00 to 1.50 D) with spherical equivalent refraction (SE) of +1.97±0.59 D (range: 0.75 to 3.63 D). Mean CDVA was 20/15±3 letters and distance-corrected near visual acuity (DCNVA) was J5±1 line before surgery.

All patients underwent bilateral aspheric LASIK treatments using the VISX STAR S4 excimer laser system (AMO) and the Amadeus microkeratome (Surgical Instrument Systems [SIS] AG, Biel, Switzerland). The 9.5-mm ring was used whenever possible and target flap thickness was 140 µm. Twenty-three eyes of 13 patients were treated using the VISX STAR S4 IR system (AMO) with iris registration technology, which became available while the study was in progress.

The aspheric treatment, which consisted of a full-distance, wavefront-guided correction (CustomVue, AMO) procedure and a custom-designed aspheric ablation shape based on mesopic pupil size, was generated by WaveScan software (AMO). In general, the presbyopic correction occurs in addition to the CustomVue hyperopic correction, which is different for every eye (Fig ). The presbyopic correction is different for every eye because it is scaled by the mesopic pupil size to keep the ratio of the “near vision zone” and the “distance vision zone” roughly constant across patients. The area of the distance vision zone is four times larger than the central near vision zone, resulting in a ratio of 1:4. Scaling the treatment to the patient’s mesopic pupil size ensures a balance between near and distance vision. No patients received monovision or were intentionally left with residual myopia. After healing, this ablation pattern resulted in a steeper central cornea expanding the depth of focus and resulting in improved visual function over a wider range of distances with minimal degradation of distance visual quality.

Figure 1. A) Aspheric ablation for correction of hyperopic presbyopia consisting of an aspheric correction (approximately 6 mm, depending on mesopic pupil size) and a peripheral blend resulting in a 9-mm total ablation area. B) Compared to hyperopic ablation (blue line), the aspheric ablation (red line) results in a central add zone, increasing near vision. The difference between the blue and red lines represents the central near add of the aspheric ablation. The ablation is scaled to the patient’s mesopic pupil size so that the central near zone and the total correction are at a fixed 1:4 ratio. C) Six-month postoperative higher order aberration wavefront map (in diopters) shows central myopic and peripheral distance zones.

All patients were required to attend follow-up at 1 week and 1, 3, 6, 9, and 12 months. Visual performance evaluations and questionnaires were collected during pre- and postoperative visits. Monocular uncorrected distance visual acuity (UDVA), CDVA, and CNVA under photopic (85 cd/m ²) and mesopic (3 cd/m ²) illumination as well as high and low contrast visual acuities were measured (Vector Vision, Greenville, Ohio). Binocular uncorrected distance and near photopic high contrast visual acuities were also measured. Mesopic contrast sensitivity was measured at 3, 6, 12, and 18 cycles per degree (cpd) and tested with 15 levels of contrast (~0.12 to 0.15 logCS per step) at each spatial frequency. Baseline and postoperative evaluations included corneal topography (Humphrey Atlas; Carl Zeiss Meditec, Jena, Germany), pupil size (Procyon; Haag-Streit UK, Essex, England), wavefront measurement (WaveScan), anterior segment examinations, applanation tonometry, cycloplegic refractions, dilated fundus examinations, and administration of questionnaires.

Questionnaires were created for the study and were not validated independently. Patients were asked to respond to questions in four major areas: satisfaction with vision at different times of the day and under different lighting conditions and tasks (11 questions); frequency of visual symptoms (7 questions); consistency, sharpness, and comfort of vision postoperatively without correction versus preoperative with correction (6 questions); and frequency of spectacle use for common daily activities during day and night (7 questions). Reading performance using the MNRead chart (Precision Vision, LaSalle, Illinois) was collected at baseline and at 1 and 3 months postoperatively. Reading acuity (based on the number of words read correctly), maximum reading speed, and critical print size (smallest font at which maximum speed was still maintainable) were measured using the MNRead chart.

Near vision was measured at 40 cm using a logMAR letter chart (I. Bailey, University of California, Berkeley, California). The results were also converted into Jaeger notation. The conversion was based on the Rosenbaum Pocket Vision Screener (GF Health Products Inc, Atlanta, Georgia). Distance equivalent Snellen acuity printed on the Rosenbaum chart does not represent the actual angular size of the optotypes on the chart at a typical viewing distance.

Results

Discussion

Hyperopic patients tend to experience a slight reduction of postoperative CDVA and contrast sensitivity, which can be explained by the relative minimization of the retinal image size due to removal of preoperative corrective lenses. In addition, the design principle of aspheric ablation expands the useful depth of field in the presbyopic eye, thereby regaining near vision. In expanding depth of field, a certain amount of image clarity is unavoidably compromised. Nonetheless, our data analysis shows that this aspheric shape design preserves distance vision at a satisfactory level. Patients achieved an average result of 20/20 CDVA with no eye worse than 20/25 ^-3. The loss of lines of CNVA and DCNVA at 6 months was in part due to instability of the ocular tear film. Some patients experienced fluctuating vision and symptoms of dry eye with mild punctate keratitis. Frequent use of artificial tears and temporary punctal occlusion were helpful, and most eyes regained some or all of the lines lost at 12 months. Mesopic contrast sensitivity functions of these presbyopic patients were also preserved within the population range of normal.

Customized wavefront-guided refractive treatments were a component of the aspheric ablations performed with the VISX STAR S4 IR laser. Based on the history of CustomVue refractive treatment to improve contrast sensitivity function, ³⁷ we concluded that even with the slight reduction caused by the aspheric shape, contrast sensitivity function would remain within normal limits. Subjective questionnaire results showed no reduction in satisfaction with visual clarity or night vision with glare. No significant increase in symptoms of halo, ghosting, or double images after surgery was noted. In the opinion of the authors, preserving distance visual performance is the first step towards a successful presbyopic surgery.

Improved near vision following hyperopic excimer laser correction can be the result of a combination of an overcorrection resulting in a myopic shift, induced negative spherical aberrations following hyperopic ablation alone, or application of an additional treatment to intentionally create a more aspheric shape. In our study, we demonstrated an average improvement of three lines of DCNVA, improvement of =2 lines in 70% of eyes, and retention of maximum reading speed. These improvements are attributable to the ablation shape because all effects of residual refractive error were removed from DCNVA results. Residual myopia would improve near visual acuity and residual hyperopia could hinder near visual acuity.

Our study results showed minimal residual refractive error; nonetheless, DCNVA improved over baseline. To evaluate the effect of the new “central near” aspheric shape on near vision compared to that achieved by a hyperopic CustomVue treatment, a small study of 20 patients using similar enrollment criteria and ablation pattern to our study was performed with the nondominant eye treated with the aspheric shape and the dominant eye received a regular CustomVue hyperopic treatment. ³⁸ Compared to 90% and 95% of eyes in our study that achieved uncorrected near visual acuity (UNVA) and DCNVA, respectively, of J3 or better at 6 months, Kraff ³⁸ reported that only 21% and 16%, respectively, achieved J3 with hyperopic CustomVue ablation in the dominant eye. For eyes treated with aspheric ablation, Kraff noted similar results to our study with UNVA of J3 or better in 100% of eyes at 6 months compared to 90% in our study. Also, our finding that the magnitude of negative spherical aberration change correlated with better DCNVA adds further support to the efficacy of the new shape.

Based on the success criteria used by the authors—simultaneous distance vision of 20/25 or better and near vision of J3 or better—the study data showed good results. Ninety-three percent of patients met these criteria with binocular simultaneous uncorrected vision at 6 months and 100% met the criteria at 12 months after surgery. Although these criteria for success may not be acceptable for all patients in a typical clinical practice setting, there was an overall high patient satisfaction in the study cohort.

In the authors’ experience, which was confirmed by the analysis, patient selection is a critical component in maximizing postoperative satisfaction. A patient should have enough hyperopia to require spectacles for distance vision and be sufficient for them to demonstrate three or more lines of improvement at near (ie, 20/50 [J3] or worse). Patients should also understand that 3 to 6 months may be needed for the brain to adapt to the aspheric shape before benefits of the correction can be fully appreciated. ^17,33,39 The management of patient expectations is also essential for postoperative satisfaction. Among a population of well-selected patients, this treatment can improve functional vision for distance and intermediate distances (60 cm) and may provide some benefit for near (40 cm). It will not, however, meet the needs of someone with demanding near vision tasks.

Contact lenses can cause reversible corneal topographic abnormalities. These contact lens–associated topographic abnormalities include irregular astigmatism, loss of radial symmetry, and the absence of normal, progressive flattening from the center to the periphery of the cornea. If contact lens–related abnormalities are not permitted to resolve prior to the aspheric treatment, they will be permanently ablated onto the corneal surface. This is an important factor in patient selection and preoperative management. To optimize outcomes, contact lenses must be discontinued prior to the aspheric treatment. Soft contact lenses should be discontinued at least 2 weeks prior to examination and treatment. Hard polymethylmethacrylate (PMMA) or rigid gas permeable lenses should be discontinued at least 3 weeks prior to examination and treatment with stable topography (keratometry) and refraction.

Mean age of this cohort was 55.1±4.6 years (range: 45 to 65 years). This relatively older population is more likely to have dysfunctional tear syndrome as a result of age, hormonal changes associated with menopause, and the increased likelihood for the use of medications that can result in reduced tear function. Careful preoperative evaluation and optimization of the precorneal tear film is important to obtain the best refraction and wavefront measurements. ⁴⁰ Tear film dysfunction treatment options include lubricants, topical steroids, oral tetracycline, punctal plugs, and use of cyclosporine 0.05% (Restasis; Allergan, Irvine, California). ⁴¹ Because tear function is typically compromised for at least 3 months after ablation, aggressive management of the tear film and ocular surface is necessary to allow optimal visual function following surgery. Patients with severe dysfunctional tear syndrome that is unresponsive to treatment should not undergo this procedure.

An older population is also more likely to have early nuclear sclerotic lenticular changes. Patients with nuclear sclerotic lenticular changes are not ideal candidates for hyperopic aspheric ablation as they are likely to have progression of lenticular changes resulting in suboptimal postoperative results.

A “pushed plus technique” must be used for the manifest refraction. Cycloplegic refraction is a very important component of the preoperative evaluation. True cycloplegia eliminates accommodation and allows evaluation of the refractive error free from the influence of accommodation. This is particularly important in identifying the amount of latent hyperopia. The cycloplegic refraction should be performed 30 minutes after installation of cyclopentolate 1%. When performing the cycloplegic refraction, only sphere should be refined.

Manifest and cycloplegic sphere should be within 0.75 D. If the amount of latent hyperopia exceeds 0.75 D, manifest refraction after cycloplegia is necessary to bring the manifest and cycloplegic refractions to within 0.75 D. If the difference exceeds 0.75 D, the patient should not be treated until his/her accommodative tone decreases. Any untreated latent hyperopia will become manifest over time, resulting in reduced uncorrected near, intermediate, and distance visual function.

The AMO aspheric ablation profile for presbyopic hyperopes results in improved visual function by steepening the central cornea. There is a 1:1 correlation between the amount of hyperopic refractive change and central corneal steepening. The central cornea should not be steepened to >50.00 D as the risk of apical corneal scarring is increased. ⁴² Also, if the cornea is steepened too much, the relationship between the eyelid, precorneal tear film, and corneal epithelium may be altered, resulting in poor optical performance.

Ideally, there should be no residual refractive error following aspheric treatment. A well developed Custom-Vue hyperopia nomogram should be used to optimize outcomes for the aspheric treatment.

The aspheric ablation profile extends to 9 mm in diameter. A flap must be created that will expose at least 9 mm of stroma that is well centered over the pupil.

Environmental conditions must be carefully controlled. The temperature in the laser room should range from 68° to 72°F, and the relative humidity in the laser room should range from 40% to 45%. During ablation, a dry stromal bed provides the best results. ⁴³ The use of a LASIK drain is discouraged because of increased local humidity, resulting in an undercorrection.

Long-term follow-up of our results showed refractive stability. The depth-offield advantage also stabilized during the follow-up period. We believe the current aspheric refractive procedure is a good alternative for presbyopic patients with low to moderate hyperopia who are not ready for intraocular implant surgery. This treatment potentially could be applied following intraocular lens implantation to correct a residual hyperopic refractive error while enhancing near vision.

This study demonstrated negative spherical aberration correlated well with improved near performance, which was also reported by Alió et al. ³⁰ In addition, our results showed that vertical coma and other aberrations could hinder near visual performance and patient satisfaction. Decentered ablations on spherical aberration could reduce the effectiveness of the aspheric shape design and induce coma along with other higher order terms. Registration and centration during ablation should reduce unwanted aberrations and preserve the effect of aspheric ablation. This study used a wavefront-driven customized aspheric shape, which may explain the higher predictability and lower loss of contrast sensitivity relative to other similar shape designs that did not take patients’ individual wavefront data into consideration. ^15,17 Jung et al ²⁸ saw a tendency for mean SE to digress (0.33±0.45 D at 6 months), which accompanied a gradual decline in near vision outcomes. Alió et al ¹⁷ also saw poorer SE values (-0.55±0.40 D). The ability of wavefront technology to measure higher order aberrations of the eye and compensate for them during surgery likely accounts for the positive difference in our results.

Alió et al ¹⁷ were the first to report a prospective clinical trial on central presbyLASIK, which was aimed to correct hyperopia and restore up to +1.50 D of pseudoaccommodation. Mean preoperative SE of the 50 eyes was +1.60±0.63 D and the treatments were performed with proprietary software from Technovision using an H.Eye.Tech excimer laser (Technovision, Munich, Germany and Bausch & Lomb, Rochester, New York). Mean postoperative SE was -0.37±0.55 D. After 6 months, 64% of patients had 20/20 or better UDVA and 72% had UNVA of 20/40 or better. Twenty-eight percent lost a maximum of 2 lines CDVA. After 6 months, 12% of 50 eyes were retreated with standard LASIK for distance. Spectacle independence for all distances was achieved in 72% of patients.

Jung et al, ²⁸ using a similar program on the VISX STAR laser, treated 54 eyes of 27 patients with either LASIK or PRK central presbyLASIK. Mean SE of the 54 eyes was +1.16±0.82 D preoperatively and at 6 months in 28 eyes was +0.33±0.45 D. Sixty-four percent of patients achieved simultaneous binocular vision of 20/25 and J3 at near 6 months after surgery. Four percent of eyes lost a maximum of 2 lines of distance vision and no lines for near. The authors note a gradual decline in near visual outcomes associated with regression of mean SE. In comparison, the patients in our study had more hyperopia with a mean SE of +1.96 D with less than +0.12 D change from 1 to 12 months. As a result, at 6 months 93% of patients achieved binocular simultaneous uncorrected vision in our study compared with 64% in Jung et al’s study.

For patients wishing to avoid invasive intraocular surgery, an aspheric ablation can be a preferable option. It reduces the risk of retinal detachment by keeping a clear lens and retaining current accommodations, and it allows the option of correcting refractive error, astigmatism, and some higher order aberrations at the same time. With age, the crystalline lens may show more positive spherical aberrations and there may be a gradual hyperopic shift; both factors may reduce the long-term effectiveness of this procedure. At that point, cataract surgery with IOL implantation may restore both good distance and near vision. Although the additional corneal aspheric ablation is small, calculation of the correct IOL power may be more challenging. The use of a monofocal lens might be more advantageous than a multifocal lens, where the combination of ocular aberrations could degrade the visual quality. As new ablation profiles generated by optimized algorithms ³⁶ and better registration and centration techniques evolve, there is an even greater potential to deliver more precise and effective results, thus aspheric ablations will become an even stronger option for presbyopic patients. Treatment of hyperopic patients with this aspheric shape is being performed by a limited number of clinicians in Europe and South America. The clinical study on presbyLASIK was closed in 2008 and the procedure is not being used in Canada or the United States as approval was never sought in either country.