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.
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References
Liang J, Williams D. Aberrations and retinal image quality of the normal human eye. J Opt Soc Am A. 1997;14:2873–83.
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.
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.
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.
Tuan KM, et al. Predicting patients’ night vision complaints with wavefront technology. Am J Ophthalmol. 2006;141:1–6.
Applegate RA, Howland HC, Klyce SD. Corneal aberrations and refractive surgery. In: MacRae S, editor. Customized corneal ablation. Thorofare, NJ: Slack; 2001.
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.
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.
Guirao A, Williams DR. Higher order aberrations in the eye and the best subjective refraction. Providence, RI: Optical Society of America Annual Meeting; 2000.
Charman N. Ocular aberration and supernormal vision. Optician. 2000;220:20–4.
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.
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.
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.
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.
Fay AM, Trokel SL, Myers JA. Pupil diameter and the principal ray. J Cataract Refract Surg. 1992;18:348–51.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Montague AA, Manche EE. CustomVue laser in situ keratomileusis treatment after previous keratorefractive surgery. J Cataract Refract Surg. 2006;32:795–8.
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.
Alio JL, Montes-Mico R. Wavefront-guided versus standard LASIK enhancement for residual refractive errors. Ophthalmology. 2006;113:191–7.
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.
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.
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.
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.
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.
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.
Schwiegerling J, Snyder RW. Corneal ablation patterns to correct for spherical aberration in photorefractive keratectomy. J Cataract Refract Surg. 2000;26(2):214–21.
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.
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.
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Shaheen, M.S., Bardan, A.S., Ezzeldin, H. (2018). Ocular Wavefront-Guided Treatment. In: Sinjab, M., Cummings, A. (eds) Customized Laser Vision Correction. Springer, Cham. https://doi.org/10.1007/978-3-319-72263-4_6
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