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 documents a biomechanical corneal change related to corneal flap creation in certain patients leading to an irregular ablation pattern and an inaccurate refractive outcome.
Methods: This retrospective study included consecutive eyes treated with primary 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 greater than or equal to 0.50 diopters (D) sphere or cylinder from the targeted goal within 3 months after surgery were identified. Topographical, higher order aberration, and epithelial maps were created. Of these eyes, approximately 10% of eyes were found to have undergone a biomechanical change upon flap creation that led to an inaccurate outcome.
Results: Six representative cases are presented that demonstrate the biomechanical change, outcomes, and treatment. All patients demonstrated an elliptical, irregular ablation pattern on post-operative topography, lateralized the thinnest point of the cornea relative to the corneal apex on Pentacam pachymetry maps, and irregular corneal epithelial thickening at the periphery of the elliptical ablation.
Conclusion: A biomechanical change during flap creation can occur in certain types of corneas during LASIK flap creation and subsequent treatment with topographic-guided ablation leading to an irregular ablation and suboptimal refractive outcomes.
Introduction
Dr. Cynthia Roberts theorized in manuscripts in 2002 and 2005 that the creation of a flap during LASIK could actually alter the cornea without causing corneal ectasia.1,2 She also theorized that laser ablation of corneal lamellae could also cause a shift in the cornea leading to unexpected refractive outcomes.3
Since early 2016, we have utilized WaveLight Contoura topographic-guided ablation (Alcon Surgical, Fort Worth, Texas) to make a more uniform cornea for myopic/myopic astigmatism patients.4–7 This process treats the anterior elevation of the cornea which is a combination of corneal higher order aberration and lower order astigmatism. Once this is treated, the spherical power of the cornea can be adjusted. Although very accurate, even with large disparities in between manifest and Contoura measured astigmatism, certain patients would have an inaccurate outcome notable within the first 2 weeks of correction, and this outcome simply would not change significantly over time.
We speculated that perhaps this was epithelial compensation of corneal aberration, and initially evaluated all cases through that lens, while also analyzing for other causes such as posterior ocular astigmatism, including lenticular astigmatism, or some other reason not yet theorized.
When post-operative topographies were further examined, it was noted that certain patients had an elliptical ablation that also showed some variation in depth in the bed of the ablation especially at the periphery. Initially, we were concerned this was a tracking issue with the laser, but as analysis continued a further pattern was noted to show that there were biomechanical changes occurring in the cornea.8 Alcon Clinical Support analyzed the intra-operative tracking scans to and reported no loss of tracking or rotation of the eye during laser ablation. Sissimos Lemonis of Alcon Clinical Support also brought to our attention Dr. Cynthia Roberts’ work, and the “Roberts Effect” during LASIK flap creation. This analysis determined that there was a one-time biomechanical effect occurring in certain patients upon LASIK flap creation that was causing inaccurate Contoura laser ablation leading to inaccurate outcomes.
Source
Biomechanical Changes to the Cornea from LASIK Flap Creation Resulting in Iatrogenic Irregular Astigmatism:
https://www.dovepress.com/biomechanical-changes-to-the-cornea-from-lasik-flap-creation-resulting-peer-reviewed-fulltext-article-OPTH