PRESBYOPIA COMBINED WITH any refractive error has been a significant treatment challenge for refractive surgeons. Traditionally, the principles used for monovision contact lenses have been applied to corneal refractive surgery.¹ However, this practice retains many of the limitations found with such contact lenses, including loss of fusion and stereoacuity.²

Multifocal corneal ablation profiles have also been suggested; however, although an overall improvement in visual acuity has been recorded for both near and distance vision, the efficacy has remained relatively low,³ and safety and quality of vision can be compromised.⁴ A better solution that offers improved visual results and greater tolerance is still required.

PRESBYOND Laser Blended Vision

It is helpful to consider presbyopia as the inability to accommodate, rather than a decrease in depth of field of the eye. This decrease can be overcome, at least in part, using an optimized ablation profile that controls postop spherical aberration, thus increasing the depth of field of each eye without significantly compromising visual quality, contrast sensitivity, or night vision. The optimization used for PRESBYOND is based on the patient’s age, refraction, preoperative spherical aberration, tolerance for anisometropia, and treatment centered on the corneal vertex.

We learned in the 1990s that spherical aberration increases in myopic ablations, leading to a decrease in visual quality and contrast sensitivity.⁵ My early work in wavefront-guided repair of night vision disturbances, using what was at the time the highest-resolution aberrometer (210µm) coupled with Gaussian small-spot (0.7mm) high-repetition rate excimer laser ablation, taught me that even a modest decrease (27%) in harmful levels of spherical aberration restored contrast sensitivity and night vision quality to normal.⁶

This led me to consider up to approximately 0.6µm of spherical aberration (Optical Society of America, 6mm) as tolerable—this level can be filtered by the brain. This led to the concept of using spherical aberration to increase the depth of field of the eye.⁶

Within a few years, several researchers were able to experimentally duplicate this concept using adaptive optics systems, and to demonstrate that extended depth of field increased linearly with the increase in spherical aberration, but only up to a certain point.⁵ Most important to note here is that adaptive optics studies proved that the depth of field increased with both positive and negative spherical aberration, showing that the effect was due to the spherical aberration itself, rather than a zonal change in refractive sphere power (eg, in positive spherical aberration, the larger the pupil, the more myopic the sphere of the refraction).

These laboratory experiments confirmed our surgical clinical research findings that a “therapeutic” range for spherical aberration producing extended depth of field existed, beyond which there were “toxic” effects of halos and reduced contrast sensitivity.

During my early work developing an algorithm for presbyopic correction, the initial aim was to be able to adjust depth of field enough to provide clear vision from distance through intermediate to near, creating an eye that could see 20/20 at distance and also see a computer screen and read J1. We discovered that, with photopic pupil diameters, the depth of field could be safely increased to 1.50D for any starting refractive error. Given a 1.50D depth of field, it would not be possible to obtain full distance and full near vision monocularly; therefore, based on the time-tested concept of introducing a degree of anisometropia between the eyes, the nondominant eye was set up to be slightly myopic so that the predominantly distance (dominant) eye was able to see at distance to intermediate, while the predominantly near (non-dominant) eye was able to see in the near range and up to intermediate.

Both eyes had similar acuity in the intermediate region, an optimal situation for stereopsis. Microanisometropia in this case draws on the inherent cortical processes of neuronal gating and blur suppression by “interocular rivalry” (the ability for conscious attention to be directed to the specific area with the best image quality within the entire visual field of both eyes). This contrasts with other attempts to treat presbyopia by inducing a cornea with 2 distinct focal points within the same eye: “intraocular rivalry.”

A further component contributing to the increase in depth of field, which persists even in eyes that have lost the ability to change crystalline lens power during the accommodative effort, is the increase in depth of field afforded by pupil constriction during accommodation. The combination of controlled induced corneal aberrations and pupil constriction significantly increases the depth of field on the retinal image. Intraretinal and cortical processing and edge detection are the final components of laser blended vision: the pure retinal image, which is modified by spherical aberration, is further enhanced by central processing to yield the perception of clear, well-defined edges.

In principle, as described above, the depth of field can be enhanced through the introduction of either positive corneal spherical aberration, in which case corneal power increases with zonal diameter, or negative aberration, in which power decreases with distance from the corneal vertex.^5,7

Most patients have some nascent positive spherical aberration before treatment, which is added to by the positive spherical aberration induced by standard myopic ablation. The important thing is to control the induction of spherical aberration to avoid increasing it above the tolerance threshold, which can cause loss of contrast sensitivity, and night vision disturbances, and can result in a topographic central island. To account for this possibility, the ablation profile includes a precompensation factor.

A standard large zone (7.00mm) hyperopic ablation induces negative spherical aberration that, in the case of hyperopic correction, is unlikely to increase above the tolerance threshold, even with up to +7.00D of correction, because most patients start with some positive spherical aberration, and the range of hyperopic treatments is smaller than the range of myopic treatments.⁸

In emmetropic patients, you cannot rely on the ablation inducing spherical aberration, so the spherical aberration component of the calculation is increased. This has an impact on the refractive accuracy. As emmetropic patients have high expectations and low tolerance to refractive inaccuracy, the best option is to increase the depth of field somewhat and ensure that the microanisometropia component is as accurate as possible.

The ablation profiles, taking age and preop spherical aberration into account, are referred to as nonlinear aspheric ablation profiles because the spherical aberration component is governed by a nonlinear function.

Results

The outcomes using PRESBYOND Laser Blended Vision with the MEL 80 excimer laser (Carl Zeiss Meditec) have been published for myopia up to -8.50D,⁹ hyperopia up to +5.75D,¹⁰ and emmetropia.¹¹ All treatments were performed as bilateral simultaneous LASIK. For inclusion, patients had to be medically suitable for LASIK, presbyopic with corrected distance visual acuity no worse than 20/25 in either eye, and have a tolerance of at least -0.75D of anisometropia. The standard microanisometropia protocol corrected the dominant eye to plano and the nondominant eye to -1.50D irrespective of age.

At 1-year follow up, binocular uncorrected distance visual acuity was 20/20 or better, and binocular uncorrected near visual acuity was J2 or better in 95% of myopes, 77% of hyperopes, and 95% of emmetropes. Retreatment rates were 19%, 22%, and 12%, respectively, although they would have been 5%, 6%, and 4% had the criterion for retreatment been 20/32. The safety in terms of corrected distance visual acuity and contrast sensitivity was the same as for standard LASIK, with no eyes losing more than 1 line.

Mean mesopic contrast sensitivity either remained the same or improved slightly at 3, 6, 12, and 18 cycles per degree for all 3 populations. Stereoacuity, although slightly reduced, has been shown to be maintained at a functional level of 100-400 seconds.¹² Similar results have been reported by other groups, also reporting very high patient satisfaction and no reduction in quality of vision.^12-16

The results of PRESBYOND in commercial airline pilots have also recently been published.¹⁷ The results demonstrated that this technique can achieve good binocular vision in the very challenging cockpit environment, which requires clear vision at a range of distances and viewing positions, including optimal distance vision for taxiing and approach, clear intermediate vision to accurately view radio and autopilot systems, and sharp focus at near to operate navigation systems and overhead panels. All pilots achieved the visual criteria for aeromedical recertification by 1 month after treatment and reported that their newly gained spectacle independence improved cockpit functionality when compared with their previous refractive correction method.

The principle of correcting refractive error while modulating spherical aberration to benefit the depth of field can be equally applied to cataract surgery with intraocular lens (IOL) placement. A previously pseudophakic patient can be treated by laser blended vision protocols to set a total final spherical aberration of the eye that provides extraordinary range of vision.

Performing cataract surgery on a patient with prior laser blended vision in the cornea enables the choice of a monofocal IOL of appropriate asphericity to leave the eyes with optimized spherical aberration, without resorting to diffractive optics and all of the quality of vision and adaptation issues that are introduced by intraocular rivalry, as well as reduced contrast and the selective quantization of the reading distance.

Conclusion

The combination of microanisometropia with increased depth of field through appropriate nonlinear aspheric ablation profiles improves visual outcomes substantially in comparison with the conventional monovision approach.

This goal can be achieved in the cornea and in conjunction with cataract surgery. Trials have shown that PRESBYOND Laser Blended Vision is effective in presbyopic patients with refractive errors between +5.75D and -9.00D, including emmetropic presbyopes. With the safety advantages of modern femtosecond LASIK, the rapid bilateral surgical procedure, and a recovery time of a few hours, patient satisfaction is extremely high. ■

References

1. Goldberg DB. Laser in situ keratomileusis monovision. J Cataract Refract Surg. 2001;27(9):1449-1455.
2. Fawcett SL, Herman WK, Alfieri CD, et al. Stereoacuity and foveal fusion in adults with long-standing surgical monovision. J AAPOS. 2001;5(6):342-347.
3. El Danasoury AM, Gamaly TO, Hantera M. Multizone LASIK with peripheral near zone for correction of presbyopia in myopic and hyperopic eyes: 1-year results. J Refract Surg. 2009;25(3):296-305.
4. Pinelli R, Ortiz D, Simonetto A, et al. Correction of presbyopia in hyperopia with a center-distance, paracentral-near technique using the Technolas 217z platform. J Refract Surg. 2008;24(5):494-500.
5. Rocha KM, Vabre L, Chateau N, Krueger RR. Expanding depth of focus by modifying higher-order aberrations induced by an adaptive optics visual simulator. J Cataract Refract Surg. 2009;35(11):1885-1892.
6. Reinstein DZ, Archer TJ, Couch D, et al. A new night vision disturbances parameter and contrast sensitivity as indicators of success in wavefront-guided enhancement. J Refract Surg. 2005;21(5):S535-S540.
7. Marcos S, Barbero S, Jimenez-Alfaro I. Optical quality and depth-of-field of eyes implanted with spherical and aspheric intraocular lenses. J Refract Surg. 2005;21(3):223-235.
8. Reinstein DZ, Carp GI, Archer TJ, et al. LASIK for the correction of high hyperopic astigmatism with epithelial thickness monitoring. J Refract Surg. 2017;33(5):314-321.
9. Reinstein DZ, Archer TJ, Gobbe M. LASIK for myopic astigmatism and presbyopia using non-linear aspheric micro-monovision with the Carl Zeiss Meditec MEL 80 platform. J Refract Surg. 2011;27(1):23-37.
10. Reinstein DZ, Couch DG, Archer TJ. LASIK for hyperopic astigmatism and presbyopia using micro-monovision with the Carl Zeiss Meditec MEL80. J Refract Surg. 2009;25(1):37-58.
11. Reinstein DZ, Carp GI, Archer TJ, Gobbe M. LASIK for the correction of presbyopia in emmetropic patients using aspheric ablation profiles and a micro-monovision protocol with the Carl Zeiss Meditec MEL80 and VisuMax. J Refract Surg. 2012;28(8):531-541.
12. Russo A, Reinstein DZ, Filini O, et al. Visual and Refractive Outcomes Following Laser Blended Vision With Non-linear Aspheric Micro-anisometropia (PRESBYOND) in Myopic and Hyperopic Patients. J Refract Surg. 2022;38(5):288-297.
13. Ganesh S, Brar S, Gautam M, Sriprakash K. Visual and refractive outcomes following laser blended vision using non-linear aspheric micro-monovision. J Refract Surg. 2020;36(5):300-307.
14. Falcon C, Norero Martinez M, Sancho Miralles Y. [Laser blended vision for presbyopia: Results after 3 years]. J Fr Ophtalmol. 2015;38(5):431-439.
15. Prasad KK, Smitha TS, Shetty SS, Poojary P. Laser-blended vision-LASIK for presbyopia and initial clinical experience in 100 Indian patients. J Vis Sci. 2015;1:37-39.
16. Zhang T, Sun Y, Weng S, et al. Aspheric micro-monovision LASIK in correction of presbyopia and myopic astigmatism: early clinical outcomes in a Chinese population. J Refract Surg. 2016;32(10):680-685.
17. Reinstein DZ, Ivory E, Chorley A, et al. PRESBYOND laser blended vision LASIK in commercial and military pilots requiring class 1 medical certification. J Refract Surg. 2023;39(1):6-14.

Dr. Reinstein founded the London Vision Clinic in 2002, and holds professorships at Columbia, Ulster, and Sorbonne Universities. He is a consultant for Carl Zeiss Meditec and CSO Italia, and has a financial interest in ArcScan Inc.