Eyeworld Daily News

2015 ASCRS San Diego Daily Monday

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Page 69 of 72

EW San Diego 2015 5 by Doyle Stulting, MD, PhD Topography-guided LASIK: A paradigm shift in refractive laser treatment R efractive surgery has advanced significantly in the past 2 decades. When it was first introduced, we were able to reduce or eliminate patients' dependence on glasses or contact lenses. In ex- change for spectacle independence, however, patients sometimes had to accept unwanted visual side effects. Today, topography-guided treatment LASIK with the WaveLight Allegret- to Wave Eye-Q Laser (Alcon, Fort Worth, Texas) can provide not only freedom from glasses and contact lenses, but also improved quality of vision. 1 There are several differences between topography-guided custom- ized LASIK and wavefront-guided customized LASIK. Wavefront-guid- ed customized LASIK has traditional- ly been based on wavefront mea- surements obtained by projecting multiple light beams into the eye and measuring the location of the corresponding light reflected from the retina. With topographers, we can measure many more points of curvature on the cornea over a wider area than is possible with wavefront measurement devices. For example, the Topolyzer (Alcon), used in conjunction with the WaveLight Laser, measures corneal curvature at approximate- ly 22,000 locations on the cornea, while the WaveLight wavefront analyzer (Alcon) measures only 168 sites, and the WaveScan (Abbott Medical Optics, Abbott Park, Ill.) measures only 240 points per WaveScan technology specifications. Another benefit of topography is that measurements are not limited by the pupil. Wavefront measure- ments require light to reach the reti- na through the pupil, so the size and location of the pupil limits the area that can be measured. In contrast, corneal topographic measurements can be applied to the entire cornea. Additionally, highly aberrat- ed eyes and those with corneal opacities can produce inaccurate aberrometer measurements because aberrometers cannot always identify the source of light leaving the eye and because light may be scattered by the corneal opacities. In contrast, topography-guided treatment can be used successfully to evaluate highly aberrated eyes. Aberrometer measurements are also affected by the state of accommodation (which can induce high-order aberrations in addition to spherical refractive changes), early cataract, and vitreous opacities. Surgical correction of lenticular high-order aberrations can be problematic because they tend to change with time. Additionally, wavefront-guided treatments do not necessarily compensate for off-axis rays of light passing through lenticu- lar opacities from different locations on the cornea. Because corneal topography does not provide information about low-order optical abnormalities of the eye—spherical error and regular astigmatism—topography-guided refractive treatments cannot be based on corneal topography alone. For topography-guided treatment, refractive measurements of the eye's optical system must be obtained independently of topographic measurements. Topography-guided treatment software combines both refractive and topographic informa- tion to generate the pattern of laser shots that will improve vision. Study summary The Topography-guided Treatment Study Group investigated the visual outcomes of topography-guided LASIK. This prospective, non- randomized study was performed at 9 clinical sites in the United States and included 249 eyes of 212 patients with myopia or myopic astigmatism treated with topogra- phy-guided treatment LASIK using the WaveLight Allegretto Wave Eye-Q Laser. Outcome measures included manifest refraction, UCVA, best spectacle-corrected visual acuity (BSCVA), visual complaints, adverse events, responses to questionnaires, and complete ophthalmologic examinations. Patients included in this study were between the ages of 18 and 65 years (mean: 34 years) and had up to –9.0 D of spherical equivalent myo- pia at the spectacle plane with up to 6.0 D of astigmatism, correctible to at least 20/25 in each eye. Forty-four percent were men, and 56% were women. Eyes with prior refractive surgery, significant lenticular astig- matism, abnormal topographies, a calculated residual stromal bed thickness less than 250 µm, or other ocular pathology that might affect the results of LASIK were excluded. Postoperative examinations were performed at day 1, week 1, and months 1, 3, 6, 9, and 12. Visual acuities and refractive errors were measured with the Early Treatment Diabetic Retinopathy (ETDRS) charts and protocol. The study found that topogra- phy-guided treatment resulted in a significant reduction in manifest re- fraction spherical equivalent (MRSE) and cylinder, reaching stability at 3 months after treatment. Mean MRSE was 0.06±0.33 D at 3 months and 0.00±0.27 D at 1 year. Mean cylinder was 0.19±0.32 D at 3 months and 0.19±0.30 D at 1 year. Three months postoperatively, 91.9% of eyes were within 0.50 D of plano, and at 1 year, 94.8% of eyes were within 0.50 D of plano. Figure 1: Cumulative postop UCVA (ETDRS) " Subjects who underwent topography-guided LASIK in the clinical trial experienced improvements in physical/ social functioning, driving, visual symptoms, optical problems, and problems with corrective lenses that were evident at 3 months and continued to improve through 12 months postoperatively, compared to their habitual refractive correction method (glasses or contact lenses) preoperatively 1 " Doyle Stulting, MD, PhD continued on page 6 Figure 2: Postop BSCVA compared to preop BSCVA (change in lines)

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