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Ocular Wavefront-Guided Treatment

  • Mohamed Shafik Shaheen
  • Ahmed Shalaby Bardan
  • Hani Ezzeldin
Chapter

Abstract

Efforts to correct refractive errors have led to the development of customized topography guided (or corneal wavefront-guided) (TG or CWF) and ocular (or whole-eye) wavefront guided (WFG) ablation. The possibility of achieving supernormal vision in terms of acuity and contrast has fuelled the imagination and creativity of vision researchers to pursue the goal of customized wavefront refractive surgery. This goal is achieved by generating an optimal ablation pattern based on individual anatomical and functional characteristics of the treated eye. The wavefront sensor allows the clinician not only to measure the defocus and astigmatism that are the most important determinants of refractive error, but also “higher order aberrations” (HOAs) as well. Defocus and astigmatism are referred to as lower order aberrations (LOAs). HOAs, such as coma and spherical aberration, refer to aberrations other than defocus and astigmatism.

The visual benefit in some eyes in the normal population is considerable. These eyes have substantial amounts of HOAs just as some normal eyes have a large amount of astigmatism. In these patients, wavefront sensing is a powerful tool in characterizing their optical abnormality, which was previously difficult to describe. It is noteworthy that visual acuity is a far less sensitive measure of the benefits of correcting HOAs than contrast sensitivity. This is because the contrast sensitivity function decreases quickly at the acuity limit and a significant increase in contrast sensitivity increases visual acuity only minimally. Thus, the greatest gains in correcting HOAs are noted in improved contrast particularly under low light conditions.

WFG Laser in Situ Keratomileusis (LASIK) is safe and effective for the correction of primary myopia or primary myopic astigmatism and that there is an increased level of patient satisfaction. The WFG procedure seems to have similar or better refractive accuracy and uncorrected visual acuity outcomes compared with conventional LASIK. Likewise, there is evidence of improved contrast sensitivity and fewer visual symptoms, such as glare and halos at night, compared with conventional LASIK. Even though the procedure is designed to measure and treat both LOAs and HOAs, the latter are generally increased after WFG LASIK. The reasons for the increase in HOAs are likely multifactorial, but the increase is typically less than that induced by conventional LASIK.

Wavefront sensors can also be used to diagnose and possibly treat a variety of conditions including corneas with “irregular astigmatism” from corneal transplantation, radial keratotomy (RK), decentred or irregular ablations, and central islands. It can give an objective measure to the patient’s own subjective symptoms of glare and haloes.

Currently, the use of WFG surface ablation is a breakthrough in the management of mild cases of keratoconus (KC). It’s used to manage the spherocylindrical error and the HOAs after halting the progression by corneal cross linking (CXL).

In the average, nonsurgical eye, the blurring caused by HOAs is not particularly large. It is equivalent to only about 0.3 diopter (D) of defocus.

There are many factors that limit how much we can optimize human vision.

These include: Pupil diameter, chromatic aberration, dependence of HOAs on accommodative state, accommodative lag, rapid changes in wave aberration over time, changes in wave aberrations with age, depth of field, photoreceptor sampling and neural factors, biomechanical effects in the cornea, accuracy of centration of correction.

When the pupil diameter is about 3 mm or smaller, HOAs are greatly reduced and the optical quality of the eye is determined mainly by blurring due to the diffraction of light at the pupil. Clearly, customized correction cannot undo the blur caused by diffraction. However, in young eyes, which tend to have large pupils, dim conditions such as night driving, and eyes with especially large amounts of HOAs, customized correction may be valuable.

The aberrometer measurement is one of the most critical elements of the WFG LASIK procedure. The precision of the laser ablation depends on obtaining an accurate assessment of the aberrations of the eye. A variety of aberrometers is currently available, but those most commonly used for WFG LASIK are based on a Hartmann-Shack sensor.

Many studies reported superior results of myopic WFG compared to wavefront-optimized (WFO) LASIK and standard non-wavefront treatments.

Although the UDVA and refractive outcomes were similar between conventional and WFG LASIK with the AMO-VISX Star 4 platform, it was shown that WFG treatment had significantly better outcomes than conventional LASIK in terms of contrast sensitivity, glare under mesopic conditions and subjective complaints. No correlation with pupil size was found.

Several studies have evaluated the safety and efficacy of WFG enhancements with LASIK or surface ablations in treating residual refractive errors, postoperative HOAs and refractory LASIK flap striae in symptomatic patients after previous keratorefractive procedures. Those studies found that WFG treatments were most beneficial in patients with highly aberrated corneas.

As the creation of a LASIK flap itself increases HOAs, some surgeons support the idea that customized ablation is best performed using surface ablation such as PRK or LASEK. Some studies have demonstrated that the degree of aberration increases with the level of attempted refractive correction. The largest increase occurred in spherical aberration, possibly due to the transitional zone from the treated to the untreated cornea, but subclinical decentrations and biomechanical effects may also have contributed.

Keywords

Wavefront Wavefront-guided Wavefront-optimised Aberrations Coma Spherical aberration Improved contrast sensitivity Wavefront sensing Aberrometers Aberrometry Customised 

References

  1. 1.
    Liang J, Williams D. Aberrations and retinal image quality of the normal human eye. J Opt Soc Am A. 1997;14:2873–83.CrossRefGoogle Scholar
  2. 2.
    Williams DR, Yoon G-Y, Porter J, et al. Visual benefit of correcting higher-order aberrations of the eye. J Refract Surg. 2000;16:S554–9.PubMedGoogle Scholar
  3. 3.
    Williams D, Yoon G, Guirao A, et al. How far can we extend the limits of human vision? In: MacRae S, Krueger R, Applegate R, editors. Customized corneal ablation. Thorofare, NJ: Slack; 2001.Google Scholar
  4. 4.
    Schallhorn SC, et al. Wavefront-guided LASIK for the correction of primary myopia and astigmatism a report by the American Academy of Ophthalmology. Ophthalmology. 2008;115:1249–61.CrossRefPubMedGoogle Scholar
  5. 5.
    Tuan KM, et al. Predicting patients’ night vision complaints with wavefront technology. Am J Ophthalmol. 2006;141:1–6.CrossRefPubMedGoogle Scholar
  6. 6.
    Applegate RA, Howland HC, Klyce SD. Corneal aberrations and refractive surgery. In: MacRae S, editor. Customized corneal ablation. Thorofare, NJ: Slack; 2001.Google Scholar
  7. 7.
    Shafik Shaheen M, El-Kateb M, Hafez TA, et al. Wavefront-guided laser treatment using a high-resolution aberrometer to measure irregular corneas: a pilot study. J Refract Surg. 2015;31:411–8.CrossRefGoogle Scholar
  8. 8.
    Shafik Shaheen M, Shalaby Bardan A, Pinero D, Ezzeldin H, El-Kateb M, Helaly H, Khalifa M. Wave front–guided photorefractive keratectomy using a high-resolution Aberrometer after corneal collagen cross-linking in Keratoconus. Cornea. 2016;35(7):946–53.CrossRefGoogle Scholar
  9. 9.
    Guirao A, Williams DR. Higher order aberrations in the eye and the best subjective refraction. Providence, RI: Optical Society of America Annual Meeting; 2000.Google Scholar
  10. 10.
    Charman N. Ocular aberration and supernormal vision. Optician. 2000;220:20–4.Google Scholar
  11. 11.
    Martinez C, Applegate R, Klyce S, et al. Effect of pupil dilation on corneal optical aberrations after photorefractive keratectomy. Arch Ophthalmol. 1998;115:1053–62.CrossRefGoogle Scholar
  12. 12.
    Amano S, Amano Y, Yamagami S, et al. Age-related changes in corneal and ocular higher-order wavefront aberrations. Am J Ophthalmol. 2004;137:988–92.CrossRefPubMedGoogle Scholar
  13. 13.
    Chernyak DA. From wavefront device to laser: an alignment method for complete registration of the ablation to the cornea. J Refract Surg. 2005;21:463–8.PubMedGoogle Scholar
  14. 14.
    Mihashi T. Higher-order wavefront aberrations induced by small ablation area and sub-clinical decentration in simulated corneal refractive surgery using a perturbed schematic eye model. Semin Ophthalmol. 2003;18:41–7.CrossRefPubMedGoogle Scholar
  15. 15.
    Fay AM, Trokel SL, Myers JA. Pupil diameter and the principal ray. J Cataract Refract Surg. 1992;18:348–51.CrossRefPubMedGoogle Scholar
  16. 16.
    Schallhorn S, Brown M, Venter J, Teenan D, Hettinger K, Yamamoto H. Early clinical outcomes of wavefront-guided myopic LASIK treatments using a new-generation hartmann-shack aberrometer. J Refract Surg. 2014;30(1):14–21.PubMedGoogle Scholar
  17. 17.
    Porter J, Guirao A, Cox IG, Williams DR. Monochromatic aberrations of the human eye in a large population. J Opt Soc Am A Opt Image Sci Vis. 2001;18:1793–803.CrossRefPubMedGoogle Scholar
  18. 18.
    Shafik Shaheen M, Massoud TH, Ezzeldin H, Khalifa MA. Four-year visual, refractive, and contrast sensitivity outcomes after wavefront- guided myopic LASIK using an advanced excimer laser platform. J Refract Surg. 2013;29(12):816–22.CrossRefGoogle Scholar
  19. 19.
    Khalifa MA, Allam WA, Shafik Shaheen M. Visual outcome after correcting the refractive error of large pupil patients with wavefront-guided ablation. Clin Ophthalmol. 2012;6:2001–11.CrossRefPubMedPubMedCentralGoogle Scholar
  20. 20.
    Bababeygy SR, Zoumalan CI, Manche EE. Visual outcomes of wavefrontguided laser in situ keratomileusis in eyes with moderate or high myopia and compound myopic astigmatism. J Cataract Refract Surg. 2008;34:21–7.CrossRefPubMedGoogle Scholar
  21. 21.
    Bahar I, Levinger S, Kremer I. Wavefront-guided LASIK for myopia with the Technolas 217z: results at 3 years. J Refract Surg. 2007;23:586–91.PubMedGoogle Scholar
  22. 22.
    Varley GA, Huang D, Rapuano CJ, Schallhorn S, Boxer Wachler BS, Sugar A, Ophthalmic Technology Assessment Committee Refractive Surgery Panel, American Academy of Ophthalmology. LASIK for hyperopia, hyperopic astigmatism, and mixed astigmatism: a report by the American Academy of Ophthalmology. Ophthalmology. 2004;111:1604–17.CrossRefPubMedGoogle Scholar
  23. 23.
    Sáles CS, Manche EE. One-year outcomes from a prospective, randomized, eye-to-eye comparison of wavefront-guided and wavefront-optimized LASIK in myopes. Ophthalmology. 2013;120(12):2396–402.CrossRefPubMedGoogle Scholar
  24. 24.
    Moussa S, et al. Comparison of short-term refractive surgery outcomes after wavefront-guided versus nonwavefront-guided LASIK. Eur J Ophthalmol. 2016;26(6):529–35.CrossRefPubMedGoogle Scholar
  25. 25.
    Reinstein DZ, Neal DR, Vogelsang H, et al. Optimized and wavefront guided corneal refractive surgery using the Carl Zeiss Meditec platform: the WASCA aberrometer, CRS-Master, and MEL80 excimer laser. Ophthalmol Clin North Am. 2004;17(2):191–210.CrossRefPubMedGoogle Scholar
  26. 26.
    Binder PS, Rosenshein J. Retrospective comparison of 3 laser platforms to correct myopic spheres and spherocylinders using conventional and wavefront-guided treatments. J Cataract Refract Surg. 2007;33(7):1158–76.CrossRefPubMedGoogle Scholar
  27. 27.
    Lee MJ, Lee SM, Lee HJ, et al. The changes of posterior corneal surface and high-order aberrations after refractive surgery in moderate myopia. Korean J Ophthalmol. 2007;21:131–6.CrossRefPubMedPubMedCentralGoogle Scholar
  28. 28.
    Lee HK, Choe CM, Ma KT, et al. Measurement of contrast sensitivity and glare under mesopic and photopic conditions following wavefront-guided and conventional LASIK surgery. J Refract Surg. 2006;22:647–55.PubMedGoogle Scholar
  29. 29.
    Montague AA, Manche EE. CustomVue laser in situ keratomileusis treatment after previous keratorefractive surgery. J Cataract Refract Surg. 2006;32:795–8.CrossRefPubMedGoogle Scholar
  30. 30.
    Kanellopoulos AJ, Pe LH. Wavefront-guided enhancements using the Wave- Light excimer laser in symptomatic eyes previously treated with LASIK. J Refract Surg. 2006;22:345–9.PubMedGoogle Scholar
  31. 31.
    Alio JL, Montes-Mico R. Wavefront-guided versus standard LASIK enhancement for residual refractive errors. Ophthalmology. 2006;113:191–7.CrossRefPubMedGoogle Scholar
  32. 32.
    Endl MJ, Martinez CE, Klyce SD, McDonald MB, Coorpender SJ, Applegate RA, et al. Irregular astigmatism after photorefractive keratectomy. J Refract Surg. 1999;15(Suppl 2):S249–51.PubMedGoogle Scholar
  33. 33.
    Seiler T, Kaemmerer M, Mierdel P, Krinke HE. Ocular optical aberrations after photorefractive keratectomy for myopia and myopic astigmatism. Arch Ophthalmol. 2000;118(1):17–21.CrossRefPubMedGoogle Scholar
  34. 34.
    Marcos S, Barbero S, Llorente L, Merayo-Lloves J. Optical response to LASIK surgery for myopia from total and corneal aberration measurements. Invest Ophthalmol Vis Sci. 2001;42(13):3349–56.PubMedGoogle Scholar
  35. 35.
    Moreno-Barriuso E, Lloves JM, Marcos S, Navarro R, Llorente L, Barbero S. Ocular aberrations before and after myopic corneal refractive surgery: LASIK-induced changes measured with laser ray tracing. Invest Ophthalmol Vis Sci. 2001;42(6):1396–403.PubMedGoogle Scholar
  36. 36.
    Pallikaris IG, Kymionis GD, Panagopoulou SI, Siganos CS, Theodorakis MA, Pallikaris AI. Induced optical aberrations following formation of a laser in situ keratomileusis flap. J Cataract Refract Surg. 2002;28(10):1737–41.CrossRefPubMedGoogle Scholar
  37. 37.
    Porter J, MacRae S, Yoon G, Roberts C, Cox IG, Williams DR. Separate effects of the microkeratome inci- sion and laser ablation on the eye’s wave aberration. Am J Ophthalmol. 2003;136(2):327–37.CrossRefPubMedGoogle Scholar
  38. 38.
    Schwiegerling J, Snyder RW. Corneal ablation patterns to correct for spherical aberration in photorefractive keratectomy. J Cataract Refract Surg. 2000;26(2):214–21.CrossRefPubMedGoogle Scholar
  39. 39.
    Gatinel D, Malet J, Hoang-Xuan T, Azar DT. Analysis of customized corneal ablations: theoretical limitations of increasing negative asphericity. Invest Ophthalmol Vis Sci. 2002;43(4):941–8.PubMedGoogle Scholar
  40. 40.
    Schwiegerling J, Snyder RW, Lee JH. Wavefront and topography: keratome-induced corneal changes demonstrate that both are needed for custom ablation. J Refract Surg. 2002;18(5):S584–8.PubMedGoogle Scholar

Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Mohamed Shafik Shaheen
    • 1
  • Ahmed Shalaby Bardan
    • 2
    • 3
  • Hani Ezzeldin
    • 4
  1. 1.University of AlexandriaAlexandriaEgypt
  2. 2.Department of OphthalmologyUniversity of AlexandriaAlexandriaEgypt
  3. 3.Sussex Eye HospitalBrightonUK
  4. 4.Department of Refractive SurgeryHorus Vision Correction CenterAlexandriaEgypt

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