EyeWorld Korea March 2021 Issue

Tear Optics in SMILE Surgery any of the clinical risk factors such as corneal thickness or topography will alter methylation. Currently, this ques- tion is being researched. Dr. Sethu finally emphasized that “epigenetic biomarkers have a future because different people will have different epigenetic profiles and may respond differently. This is the future.” Dr. Sheetal Mahuvakar began her pre- sentation on tear optics by discussing the importance of a proper initial work-up of dry eye in any of her pa- tients due to the fact that dry eye sta- tus impacts the quality and outcome of refractive surgery. In understand- ing tear optics, two machines are important in Dr. Mahuvakar’s practice: LipiView and OQAS HD Analyzer. The LipiView provides reliable lipid layer thickness measurements in both nor- mal eyes and dry eyes. The OQAS HD Analyzer provides an objective view of vision quality by measuring the scat- and if the risk factors associated with tissue response, ultrastructural changes, cellular functions, and gene expression are understood well, then clinicians may be able to modulate wound healing and provide favorable clinical outcomes. The foundational question to ask first when researching tissue response is: how are these proteins regulated? It begins with messenger RNA (mRNA) taking information from the DNA to produce these proteins. However, there is also some sort of orchestra- tion occurring with the switching on and off of these genes. During refrac- tive surgery, what is the importance of a switch on or switch off of a certain gene? This is where epigenetics comes in. Epigenetics refers to a variety of processes which regulates gene expression programs without changes in DNA sequence. Dr. Sethu provided a nice analogy of epigenetics to an airplane on a runway. If the runway represents the DNA, the aeroplane represents chro- matin or co-factors, the passenger represents gene-specific transcription factors, and the runway lights rep- resents the epigenetic modifications, then the landing decision, either “go” or “no go,” guides whether epigenetic modifications are made, allowing the gene to switch on or off. Many factors can cause genes to switch on or off including development and aging, environmental toxins, diet, stress, pathogens, and even surgery. In terms of wound healing after refractive surgery, epigenetics plays a very critical factor. As Dr. Sethu explained, “Methylation is one of the critical chemical modifications of the DNA which happens and that is what we saw in the research.” From the research, after 3 days of surgery, either SMILE or LASIK, one can see a difference in site level methylation. At 14 days, however, much more is going on. There are more genes that are switched on after 14 days post-SMILE or post-LASIK with functions of immunomodulating, ECM regulating, and cellular signal- ing. The biggest question that comes from this epigenetic work is whether tering of light in the optical pathway. The clinician is able to view what the patient is able to perceive in terms of a clear image compared to a blurry image. Additionally, the OQAS HD Analyzer provides a modular transfer function, indicating whether the tear film is affecting vision. As for the impact of refractive sur- gery on tear optics, Dr. Mahuvakar precluded her surgery experience by stating that SMILE procedures result in a higher preservation of corneal nerves whereas LASIK damages more corneal nerves. In her experience, she saw, with LipiView, slightly better lipid layer thickness in an eye that had undergone SMILE at 3 months com- pared to a LASIK eye. Ocular surface index (OSI) and visual break-up time was also better in the SMILE eye than the LASIK eye. Better outcomes in SMILE compared to LASIK were also seen with ocular surface inflamma- tion, Meibomian gland drop-out, cor- neal nerve regeneration, and normal epithelial healing. Dr. Mahuvakar emphasized in her take home points that patients should be evaluated preoperatively using any evaluative machines that are avail- able for use in the clinic. Second, it is important to customize the surgery to the patient’s specific conditions and symptoms in order to improve dry eye outcomes. Postoperatively, patients should again be evaluated using the same available machines and treated for dry eye if necessary. Figure 4. Epigenetic markers can be identified through methylation after both SMILE and LASIK procedures, resulting in altered genes. 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