Correspondence
Manoj Motwani
Motwani LASIK Institute, 4520 Executive Dr., Suite 230, San Diego, CA 92121, USA
Tel +1 858 554-0008
Email drmmlj@gmail.com
Purpose: This study analyzes every eye that had an outcome greater than 0.25D of sphere or astigmatism from planned goal after treatment with WaveLight Contoura with LYRA Protocol.
Methods: The study included 266 consecutive eyes treated with LASIK Contoura using the LYRA Protocol. All LASIK procedures were performed on the WaveLight EX500 excimer laser. Flaps were created with either the Alcon WaveLight FS200 femtosecond laser or the Moria M2 microkeratome. Eyes that were off by > 0.25 diopters (D) sphere or cylinder from the targeted goal within 3 months after surgery were identified and analyzed for cause. Topographical, higher-order aberration, and epithelial maps were created.
Results: Causes for inaccurate outcomes were biomechanical corneal change from LASK flap creation (9.78% of total eyes), pre-operative epithelial compensation of corneal higher-order aberration (4.1% of total eyes), changes to lamellar corneal tension from laser ablation causing a hyperopic shift (1.9% of total eyes), epithelial thickening over the ablation area post-operatively causing a refractive change (1.5% of total eyes), and posterior astigmatism (0.75%).
Conclusion: The causes of the majority of inaccurate outcomes have not been properly defined and must be incorporated into further improving outcomes. Current and planned advances in technology do not address the majority of these causes.
Introduction
Although for some years now leading refractive surgeons have been discussing and encouraging the need for better refractive outcomes, there has been little published trying to discern the exact causes of inaccurate outcomes. The prevailing thought in the refractive research and device manufacturing community is to use the Gullstrand model, in other words to treat the eye as a fixed entity wherever more technology and refinement can lead to hyper-accurate outcomes. Nomogram analysis software systems such as IBRA and Surgivision Datalink attempt to refine the procedure with the underlying assumption that the vast majority, if not all, corneas will react essentially the same to a procedure. The admitted goal of Alcon clinical experts is a system that has under a 2% enhancement rate, and well-respected surgeons who are clinical consultants of Alcon quote enhancement rates of under 1% with Wavefront Optimized Ablation (WFO) on the WaveLight EX500 laser.
Enhancement decisions vary from center to center. Some are based on the vision, some based on the refraction and patient complaints, and the fact that patient populations/types of corrections (myopic vs hyperopic, etc.) performed vary from center to center. There is no set standard for reporting for enhancements, except perhaps achievement of a certain level of vision. This is highly inexact, as patients with significant refractive errors can still manage to get 20/20 or 20/25 on the chart but have poor quality of vision. Patients will still complain of blurred vision, doubled vision, night glare, halos, and other visual artifacts.
Furthermore, this issue is exacerbated by surgeons not performing topographies or refractions post-operatively, and only taking visions as a standard of success. Visions themselves are inaccurate, as many centers have uncalibrated chart projectors, and are subject to issues such as dry eyes, allergic inflammation, patient fatigue, etc. At our center, we have never achieved an enhancement rate anywhere as low as 1 or 2% with any system or procedure used, or even with any particular patient population studied. For example, at our center when we looked at a large population of patients treated with WFO (Wavefront Optimized) via LASIK performed on the WaveLight EX500 we had an enhancement rate of about 10%. This enhancement rate is far greater than the 2% or less reported by some surgeons, but we perform enhancements for small corrections based on patient complaints and measurable deviation from goal of 0.50D or more from target and not just achieved vision.
Historically, most attempts to improve refractive outcomes have mainly been through technology. Software systems such as the Phorcides Analytic Engine and new technologies such as Ray Tracing also assume a fixed model that simply does not change, ie, the eye at the time of scanning and analysis will remain the same fixed shape after a refractive procedure, and only affected by the procedure itself.1 Since there is no way to predict further changes over time due to aging processes, those factors are simply not included.
When we embarked on studying epithelial compensation for higher-order aberration utilizing the new OCT epithelial thickness mapping technology by Optovue, we were attempting to confirm changes we saw on post-operative topographies over the first few days to weeks after topographic guided ablation with the LYRA Protocol. This attempt to understand inaccurate outcomes led to further study of a large group of consecutive eyes that had such a treatment performed and fit within the FDA approved treatment range of Contoura. To remove the subjective nature to the refractive outcomes and enhancement rates, we created a different standard based on the fact that no patients reported visual complaints with refractions less than or equal to 0.25D of sphere or astigmatism. We noted that although Snellen vision was important, we had patients with refractive errors and 20/15 vision that would complain, while patients with 20/20 vision and no refractive error that were completely happy. Thus, we retrospectively analyzed every single eye of a large cohort that had LASIK performed with Contoura with LYRA Protocol, and an outcome that was off by greater than 0.25D of sphere or astigmatism, essentially greater than or equal to 0.5D, in an attempt to discern the reasons for the inaccurate refractive outcomes in an attempt to guide attempts to improve accuracy.
Stemming from the results of this analysis are two separate manuscripts, where the authors describe epithelial compensation for corneal higher-order aberrations, as well as a biomechanical change upon flap creation in certain types of corneas. These manuscripts have been submitted separately for publication to examine these topics in greater detail. This retrospective study reports on the overall analysis and different reasons for inaccurate outcomes at 3 or more months post-operatively in the overall cohort of 266 eyes.
Article Source
Analysis and Causation of All Inaccurate Outcomes After WaveLight Contoura Laser Treatment:
https://www.dovepress.com/analysis-and-causation-of-all-inaccurate-outcomes-after-wavelight-cont-peer-reviewed-fulltext-article-OPTH
