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PentaVision

Ophthalmology Management

Article

New approaches to laser vision correction

Recent advances in refractive surgery have expanded the tools available to ophthalmologists.

By: Vinicius S. De Stefano, MD, PhD, Ronald R. Krueger, MD, MSE
Ophthalmology Management January 1, 2020 Vol 24, Issue January 2020 Page(s): 46, 48, 76

Since the first description of LASIK in Greece in the early 1990s by Pallikaris et al,1 refractive surgery has evolved exponentially. From conventional broad-beam lasers and rudimentary screening techniques, the procedure has become safe and predictable,2 with ultra-thin and high-frequency lasers, real-time eye-tracking, customized treatments and enhanced preoperative screening.

Topography-guided excimer ablation is one of the most recent FDA-approved technologies to use laser vision correction.3 It utilizes high-resolution corneal topographic height maps to generate a customized ablation profile consisting of anterior corneal higher-order aberrations (HOAs) and an accurate measure of the anterior corneal astigmatism.4 Other methods of vision correction have also been introduced and are continually evolving, like the FDA-approved small-incision lenticule extraction (SMILE), which has recently had its indications expanded.5

TOPOGRAPHY-GUIDED ABLATION

Topography-guided treatments (TGTs) have been used outside the United States for many years to reshape irregular corneas (post-transplant, for example) in order to achieve a smooth surface and better visual acuity.6,7 With better imaging techniques and more familiarity with the procedure, the idea of TGT is now applied to regular corneas as well. The objective is to overcome possible side effects, including halos, glare and reduced contrast sensitivity. These side effects have been attributed to the increased HOAs, induction of positive spherical aberration and decreased corneal asphericity that is associated with the ablation profile of traditional LASIK refractive surgery.

In the United States, Alcon introduced Contoura Vision, which relies on a series of high-quality topographic images being uploaded to the system. A customized profile is then created based on the cornea shape and the patient’s target correction.

One of the major challenges with Contoura is the astigmatism correction. In some cases, the manifest cylinder is different from the topographic cylinder in magnitude, orientation or both. Many research papers have addressed this hurdle. A.J. Kanellopoulos, MD, introduced the term topography-modified refraction,8 in which the topographically measured astigmatism is used to determine the total cylinder correction, with only the spherical component being adjusted to maintain the same spherical equivalent.8 Many approaches have refined this technique. One example is an approach that includes analysis of wavefront maps and Scheimpflug-derived metrics in an individualized fashion.9 Other variations include vector analysis10 and the LYRA protocol.11

Moreover, studies from groups outside the United States have attested to the safety and efficacy of using TGT outside the FDA-approved guidelines. A study from Canada has enrolled 76 eyes from patients with more than 2.0 D of astigmatism and irregular corneas with excellent results.12 Chen X et al also presented data of a similar research cohort but using transepithelial PRK with the iVis suite (iVis Technologies) devices, the Precisio preoperative screening unit and the iRes excimer laser.13 Other laser platforms that apply similar concepts are the customized aspheric treatment zone ablation, or “CATz,” with the NAVEX Advanced Vision Excimer Laser platform (Nidek) and the iDesign suite with the Star S4 IR Laser suite (Johnson & Johnson Vision). The latter is considered wavefront-guided, given it utilizes a Hartmann-Shack wavefront aberrometer to customize the ablation profile.

One of the primary reasons why some surgeons have not adopted topography-guided systems is the amount of effort and time required to plan each surgery. To help with the crucial part of the procedure, some systems have been developed in order to offer a systematic approach to preoperative planning. Nidek uses its own software, FinalFit, to generate the ablation maps and compare pre- and postoperative results. Phorcides Analytic Engine (Phorcides), an independently developed and recently released software program, incorporates data from Scheimpflug-based tomography and vector analysis. Case reports have shown exciting results; however, more studies are needed to analyze its efficacy in a cohort of refractive patients.

In a yet-to-be published, multicenter, industry-supported study of topography-guided LASIK, analyzing eyes with significant disparity between preop manifest cylinder and topographic cylinder, the Phorcides analytical planning software had the best theoretical sphero-cylindrical outcomes, which was closely followed by the topographically measured astigmatism, with the manifest refractive astigmatism being worst. This preliminary study illustrates the comparative advantage of Phorcides vector analysis in the planning of topography-guided LASIK.14

SMILE

The advent of advanced femtosecond lasers has allowed the creation of other refractive procedures aside from excimer laser-based surgeries. Femtosecond lenticule extraction was first described in the last decade. The technique evolved to what is now called SMILE. The VisuMax femtosecond laser (Carl Zeiss Meditec) received FDA approval in 2016 for the treatment of myopia from -1.0 D to -8.0 D and astigmatism up to -0.5 D. In 2018, its indications expanded to -10.0 D of myopia, and myopic astigmatism up to 3.0 D.5

SMILE has already been proven to be a safe and efficient procedure,15 with refractive results comparable to LASIK and PRK.16 One of the major advantages of SMILE over LASIK is the decreased complaints of postoperative dry eyes, especially in patients with pre-existing disease.17 This difference is not significant when compared to PRK; however, SMILE has less postoperative discomfort and a quicker visual recovery compared to surface ablation.18

The theoretical biomechanical advantage of SMILE has been shown using air-puff devices and in more advanced simulation studies.19,20 Nevertheless, the same rigorous criteria should be used in preoperative screening, since case reports of post-SMILE have been published and, in some cases, it is possible to observe that the preoperative cornea was already showing signs of biomechanical instability.21

Studies have analyzed the feasibility of SMILE for the treatment of hyperopia, describing two different approaches. The first is to change the laser algorithm in order to create a “doughnut-shaped” lenticule — thicker in the periphery and thinner centrally.22 The other is to implant an allogenic SMILE-harvested lenticule to the recipient’s stroma and reshape it afterward using an excimer laser.23 The latter approach has not been widely described in humans yet, but there are studies describing the surgical technique in animal models.24

FINAL REMARKS

Adapting to a new procedure and its nuances is critical to achieving the desired results. Adequate patient selection, use of surgical simulation tools like dry and wet labs and constant learning with peer-reviewed literature are key components to a successful and smooth transition. OM

REFERENCES

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  2. Aristeidou A, Taniguchi EV, Tsatsos M, et al. The evolution of corneal and refractive surgery with the femtosecond laser. Eye Vis (Lond). 2015;2:12.
  3. U.S. Food and Drug Administration. Summary of Safety and Effectiveness Data (SSED). PMA P02005/S12. 2013.
  4. Pasquali T, Krueger R. Topography-guided laser refractive surgery. Curr Opin Ophthalmol. 2012;23:264-268.
  5. U.S. Food and Drug Administration. Summary of Safety and Effectiveness Data (SSED). PMA P150040/S003. 2018.
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  7. Laíns I, Rosa AM, Guerra M, et al. Irregular astigmatism after corneal transplantation—efficacy and safety of topography-guided treatment. Cornea. 2016;35:30-36.
  8. Kanellopoulos AJ. Topography-modified refraction (TMR): adjustment of treated cylinder amount and axis to the topography versus standard clinical refraction in myopic topography-guided LASIK. Clin Ophthalmol. 2016;10:2213-2221.
  9. De Stefano VS, Meister C, Ehlke GL, Krueger RR. Analysis of planning strategies in primary eyes gaining a line or more of visual acuity after topography-guided laser in situ keratomileusis. J Cataract Refract Surg. 2019;45:321-327.
  10. Alpins NA, Stamatelatos G. Clinical outcomes of laser in situ keratomileusis using combined topography and refractive wavefront treatments for myopic astigmatism. J Cataract Refract Surg. 2008;34:1250-1259.
  11. Ozulken K, Yuksel E, Tekin K, Kiziltoprak H, Aydogan S. Comparison of wavefront-optimized ablation and topography-guided contoura ablation with LYRA protocol in LASIK. J Refract Surg. 2019;35:222-229.
  12. Wallerstein A, Caron-Cantin M, Gauvin M, Adiguzel E, Cohen M. Primary topography-guided LASIK: Refractive, visual, and subjective quality of vision outcomes for astigmatism ≥2.00 diopters. J Refract Surg. 2019;35:78-86.
  13. Chen X, Stojanovic A, Simonsen D, Wang X, Liu Y, Utheim TP. Topography-guided transepithelial surface ablation in the treatment of moderate to high astigmatism. J Refract Surg. 2016;32:418-425.
  14. Stulting RD, Durrie DS, Potvin RJ, et al. ­­­Analysis of Astigmatic Programming for Optimal Results of Topography-Guided Treatment with an Excimer Laser. J Cataract Refract Surg. 2020 (in review).
  15. Ivarsen A, Asp S, Hjortdal J. Safety and complications of more than 1500 small-incision lenticule extraction procedures. Ophthalmology. 2014;121:822-828.
  16. Moshirfar M, Shah TJ, Skanchy DF, Linn SH, Durrie DS. Meta-analysis of the FDA Reports on patient-reported outcomes using the three latest platforms for LASIK. J Refract Surg. 2017;33:362-368.
  17. Sambhi R-DS, Sambhi GDS, Mather R, Malvankar-Mehta MS. Dry eye after refractive surgery: A meta-analysis. Can J Ophthalmol. August 2019.
  18. Moshirfar M, Somani AN, Motlagh MN, et al. Comparison of FDA-reported visual and refractive outcomes of the toric ICL lens, SMILE, and topography-guided LASIK for the correction of myopia and myopic astigmatism. J Refract Surg. 2019;35:699-706.
  19. Shetty R, Francis M, Shroff R, et al. Corneal Biomechanical Changes and Tissue Remodeling After SMILE and LASIK. Investig Opthalmology Vis Sci. 2017;58:5703-5712.
  20. Seven I, Vahdati A, Pedersen IB, et al. Contralateral eye comparison of SMILE and flap-based corneal refractive surgery: computational analysis of biomechanical impact. J Refract Surg. 2017;33:444-453.
  21. Randleman JB. Ectasia after corneal refractive surgery: Nothing to SMILE about. J Refract Surg. 2016;32:434-435.
  22. Reinstein DZ, Pradhan KR, Carp GI, et al. Small incision lenticule extraction for hyperopia: 3-month refractive and visual outcomes. J Refract Surg. 2019;35:24-30.
  23. Li M, Li M, Sun L, et al. In vivo confocal microscopic investigation of the cornea after autologous implantation of lenticules obtained through small incision lenticule extraction for treatment of hyperopia. Clin Exp Optom. 2018;101:38-45.
  24. Williams GP, Wu B, Liu YC, et al. Hyperopic refractive correction by LASIK, SMILE or lenticule reimplantation in a non-human primate model. PLoS One. 2018;13:e0194209.

About the Authors

Vinicius S. De Stefano, MD, PhD, is a first-year resident at the Truhlsen Eye Institute, University of Nebraska Medical Center. He completed an ophthalmology residency and a refractive surgery fellowship at the Federal University of São Paulo, Brazil. He defended his Ph.D. thesis in 2018 after completing a postdoctoral fellowship in corneal biomechanics at the Cleveland Clinic. He has also finished a year-long cornea fellowship at the Medical University of South Carolina in June 2019.

Vinicius S. De Stefano, MD, PhD, is a first-year resident at the Truhlsen Eye Institute, University of Nebraska Medical Center. He completed an ophthalmology residency and a refractive surgery fellowship at the Federal University of São Paulo, Brazil. He defended his Ph.D. thesis in 2018 after completing a postdoctoral fellowship in corneal biomechanics at the Cleveland Clinic. He has also finished a year-long cornea fellowship at the Medical University of South Carolina in June 2019.

Ronald R. Krueger, MD, MSE, is the newly appointed McGaw professor and chairman of the department of ophthalmology and visual science at the University of Nebraska Medical Center and director of the Stanley M. Truhlsen Eye Institute. He was previously a professor in the division of ophthalmology and medical director of the department of refractive surgery at the Cole Eye Institute of the Cleveland Clinic. Relevant disclosures: Dr. Krueger is a consultant for Alcon and Johnson & Johnson Vision.

Ronald R. Krueger, MD, MSE, is the newly appointed McGaw professor and chairman of the department of ophthalmology and visual science at the University of Nebraska Medical Center and director of the Stanley M. Truhlsen Eye Institute. He was previously a professor in the division of ophthalmology and medical director of the department of refractive surgery at the Cole Eye Institute of the Cleveland Clinic.
Relevant disclosures: Dr. Krueger is a consultant for Alcon and Johnson & Johnson Vision.

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