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For nearly two decades, LASIK has been considered a safe and effective option for the surgical correction of vision, helping millions of achieve excellent vision without glasses. However, no surgery is completely risk-free, and related and unrelated events have created an ongoing decline in the number of LASIK surgeries since 2008. Unrelated influencers included the economic downturn, leaving many individuals without the resources to pay for an elective surgery at that same time that generation X, a significantly smaller population than baby boomers, entered the age range that is most likely to benefit from LASIK.
In addition to the general economic climate, the Ophthalmic Devices Panel of the US Food and Drug Administration held a meeting in April of 2008 to discuss patient reported outcomes (PROs). Accusations of gross negligence, connections between LASIK patients and increased suicide rates, and high failure rates were all used to request that a moratorium be placed on LASIK devices. The result has been stagnant interest in LASIK among refractive surgeons, and the need to educate both surgeons and patients on the results of the PROWL studies, new developments in technology, and actualized LASIK outcomes.
Following the negative panel discussion in 2008, the Patient Reported Outcomes with LASIK (PROWL) questionnaire was developed to obtain measurable pre and post surgery data on patient reports of expectations, satisfaction, and visual outcomes. Following the completion of PROWL-1, which included military personnel at the US Naval Base in San Diego, CA and PROWL-2, which included civilian data, the preliminary findings confirm high patient satisfaction rates following LASIK. In addition, they increase understanding of visual symptoms reported such as halos, glare, starburst, ghosting, and dry eye.
The PROWL studies provided compelling data, showing that overall, less than 1% of subjects experience significant or debilitating difficulties doing usual activities due to vision symptoms, irrespective of correction. In fact, far more patients have the visual symptoms listed above prior to LASIK surgery than do 6 months post-LASIK. In addition, LASIK outcomes are only getting better. In a comparison of pre-op best corrected visual acuity vs. post-op binocular uncorrected visual acuity, 34% of patients had 20/12 BCVA pre-op compared to 76% achieving 20/12 or better UCVA at 6 months post-op. 100% of patients achieve 20/25 or better UCVA post-op with 99% achieving 20/16 or better UCVA.
Along with penetration of the LASIK market by the femtosecond laser, improvements in wavefront aberrometry have expanded the range of treatable patients as well as improved outcomes across all groups of patients. The same high-resolution wavefront aberrometry imaging used by NASA has been adapted to map large refractive ranges with full gradient topography, capturing images of the eye with a level of detail heretofore unavailable.
Placido disk topographers and Fourier reconstruction algorithms have been the industry standard. However, these devices are limited by their inability to directly capture skew rays and their sensitivity to the radial component of the gradient. Full gradient topography fills in these gaps, potentially increasing accuracy by providing central corneal coverage, capturing both x and y slopes for each spot, reconstructing the corneal elevation much like previous Hartmann-Shack sensor methods.
Wavefront-Guided vs Wavefront-Optimized
Conventional LASIK relies of refraction results and the preferences of the patient when asked to compare corrective lens options during an exam. Wavefront-optimized uses the sphere and cylinder prescription from the patient’s exam, and administers additional extra pulses in the periphery of the laser ablation area to manage the LASIK induced spherical aberration so that the patient is left with zero spherical aberration.[i] However, by applying the same number of pulses to every patient with the same prescription, wavefront optimized LASIK does not optimally treat patients with severe spherical aberration pre-operatively and can actually make their night vision worse. Two problems wavefront-optimized cannot address include asymmetrical higher order aberrations, such as coma or trefoil, and worsening the vision of a patient with negative spherical aberration.[ii]
Wavefront-guided, on the other hand, reduces all higher order aberrations. Relying on a very precise method of optic measurement, wavefront-guided technology shines an infrared laser light into the eye and measures how the eye’s optical system affects the distorted light wave produced on its way back out. The software then divides the surface of the eye into a grid of 1000 squares and calculates the number of laser pules to apply to each individual square to create a focused light ray that penetrates through each part of the cornea and pupil to focus perfectly on the fovea. The new high-definition Hartmann-Shack wavefront sensor provides five times higher spatial resolution, a higher dynamic range, and eight times higher local slope range that its predecessor system.[iii]
Initial published studies are demonstrating that the improved accuracy of the wavefront-guided profile is positively impacting LASIK outcomes. One published report of the new Hartmann-Shack aberrometer demonstrated a reduced mean manifest spherical equivalent from -3.28 + 1.79 D at baseline to -0.03 + 0.29 D 1 month after surgery, bringing it within 0.50 D of target in 93.0% of eyes.[iv] Uncorrected distance visual acuity of 20/16 or better was attained in 79% of eyes, 20/20 or better in 93.4% and 20/25 or better in 96.7%. Mean manifest astigmatism decreased from -0.72 D to -0.14 D.
The increase in sampling points and the application of Fourier algorithms that use all valid data within the pupil aperture, even for non-circular shaped pupils, allows this enhanced aberrometer to effectively measure irregular corneas[v] and induces a minimal amount of higher order aberrations, regardless of the level of myopic correction achieved or the preoperative magnitude of aberrations.[vi] In addition, the new aberrometer was found to be safe, effective and predictable in patients with simple or compound myopic astigmatism and refractive cylinder >2.00 D.[vii]
New educational materials are necessary to help refractive surgeons understand this new technology and how it differs from previous wavefront-guided aberrometers. This CME program will also help them appreciate the exceptional outcomes that can be generated with a much wider range of patients, and learn how to grow the market with the next generation of LASIK patients.
 Amano S, Amano Y, Yamagami S, Miyai T, Miyata K, Samejima T, Oshika T. Age-related changes in corneal and ocular higher-order wavefront aberrations. Am J Ophthalmol. 2004 Jun;137(6):988-92.
2 Yoon G, Macrae S, Williams DR, Cox IG. Causes of spherical aberration induced by laser refractive surgery.
J Cataract Refract Surg. 2005 Jan;31(1):127-35. Accessed February 17, 2015.
3 Neal D.R, Baer C.D., Copland J, et al. Combined wavefront aberrometer and new advanced corneal topographer. ASCRS 2008; MP392.
4 Schallhorn S, et al. Early Clinical outcomes of wavefront-guided myopic LASIK treatments using a new generation Hartmann-Shack aberrometer. J Refract Surg. 2014;30(1):14-21.
5 Shaheen MS, El-Kateb M, Hafez TA, Pinero DP, Khalifa MA. Wavefront-guided laser treatment using a high-resolution aberrometer to measure irregular corneas: A pilot study. Journal of Refractive Surgery 2015:31(6):411-418.
6 Smadja D, et al. WAvefront analyses after wavefront-guided myopic LASIK using a new generation aberrometer. J Refract Surg 2014;30(9):610-615.
7 Schallhorn S, Venter JA, Hannan SJ, Hettinger KA. Clinical outcomes of wavefront-guided laser in situ keratomileusis to treat moderate-to-high astigmatism. Clinical Ophthalmology 2015:9;1291-1298.
The views and opinions expressed in this educational activity are those of the faculty and do not necessarily represent the views of The Dulaney Foundation and Cataract and Refractive Surgery Today.