Eyeworld

FALL 2024 | EYEWORLD | 47 R References (continued) 11. Reinstein DZ, et al. Change in epithelial thickness profile 24 hours and longitudinally for 1 year after myopic LASIK: three-dimensional display with Artemis very high-frequency digital ultrasound. J Refract Surg. 2012;28:195–201. 12. Reinstein DZ, et al. LASIK for the correction of high hyperopic astigmatism with epithelial thickness monitoring. J Refract Surg. 2017;33:314–321. 13. Reinstein DZ, et al. Tran- sepithelial phototherapeutic keratectomy protocol for treating irregular astigmatism based on population epithelial thickness measurements by Artemis very high-frequency digital ultrasound. J Refract Surg. 2014;30:380–387. 14. Rohlf D, et al. Outcomes of LASIK vs PRK enhancement in eyes with prior cataract surgery. J Cataract Refract Surg. 2023;49:62–68. 15. Reinstein DZ, et al. Epithelial thickness mapping for corneal refractive surgery. Curr Opin Ophthalmol. 2022;33:258–268. Relevant disclosures Huang: Canon, Cylite, Genentech, Intalight, Visionix Reinstein: ArcScan, Carl Zeiss Meditec, CSO Waring: None Contact Huang: huangd@ohsu.edu Reinstein: dzr@londonvisionclinic.com Waring: georgewaringiv@gmail.com dry eye assessment, EBMD evaluation, identi- fication of contact lens warpage, and post-re- fractive surgery where the epithelial remodeling will alter the refractive measurements, which is especially important in hyperopic eyes. LASIK may have advantages over PRK in these patients, he said, as LASIK has been demonstrated to be more accurate, and the shorter recovery time results in a faster visu- al recovery. PRK should be reserved for cases where medically indicated, he added. Dr. Waring also addressed the question of if it would be more favorable to do a LASIK enhancement or a PRK enhancement. One thought is that if we perform LASIK, we are now accounting for the non-uniform epithelium and altering it potentially much less, he said, adding that this makes sense, and there is literature to support this. 14 "However, we also think that more often patients are better suited for PRK enhancement in a post-refractive state," Dr. Waring said. If they've already had LASIK, that's typically where you run into issues. Most of the time, patients do well with a PRK enhancement in these circumstances, he said, and there are additional potential benefits in form fruste or subclinical epithelial basement changes, micro striae, or with subtle or superficial flap irregu- larities. It can often be therapeutic in a surface ablation treatment, as well as to normalize the corneal surface and shape. "We think there can be an appropriate role for surface ablation in these circumstances. With that said, we also see an opportunity to refine outcomes and predic- tion factors if we can crack the code on pre- dictive modeling and adjustments for variable epithelial thickness in the post-refractive state." Dr. Huang said that he finds both LASIK and PRK effective when there is residual refractive error, and it depends on surgeon preference. Sometimes you may have a scar or previous re- fractive surgery that makes the cornea irregular, and transepithelial PTK/PRK can improve topo- graphic regularity. "The epithelium can serve as an excellent smoothing agent. I often use transepithelial ablation to improve the postop topography and reduce the postop aberrations, and that helps improve the best corrected visual acuity," he said. "However, the surgeon should look at the epithelial map to see if the epithe- lium is masking the irregularity or creating the irregularity. If you have primary epithelial deformation due to dry eye or eyelid effect, transepithelial ablation should be avoided—it would exacerbate the irregularity." Discussing epithelial mapping technology, Dr. Huang primarily uses the Visionix (formerly Optovue) Avanti or Solix technology. Both have epithelial mapping capability. "I mainly use it to distinguish between secondary epithelial modulation and primary epithelial deformation. In secondary epithelial modulation, the epithe- lium becomes thinner to compensate for areas where the anterior stromal surface is steeper or more elevated due to ectasia, scar, deposits, or dystrophies. In primary epithelial deformation, the underlying stroma is smooth, but the epithe- lial layer is irregular due to lid wiper effect, dry eye, or contact lens warpage. It is important to distinguish between these two disease process- es," Dr. Huang said. Dr. Huang, and his colleague, Yan Li, PhD, also mentioned several technologies that offer epithelial mapping: MS-39 (CSO), ANTERION (Heidelberg Engineering), and CIRRUS HD- OCT (Carl Zeiss Meditec). Dr. Reinstein noted a recently published paper 15 that found continued improvement and wider implementation of epithelial thick- ness mapping in OCT devices. He thinks that refractive surgeons should be using epithelial thickness mapping as a tool for all preoperative screening and postoperative assessment and added that it can be easily incorporated as part of the process. "Following refractive surgery, the same preoperative scans can be repeated postoperatively; this is especially useful, as difference maps can then be plotted to monitor progress," he said. For those just getting started in epithelial mapping, Dr. Reinstein said it's important that epithelial maps are used within a multimodal approach in conjunction with other imaging devices in order to build a full picture of the cornea, especially in keratoconus screening. "I would advise liaising with the device manufac- turer to ensure that the most optimal scales and color settings are used to be able to detect small irregularities in the cornea," he said. "Difference maps should also be regularly used and are es- pecially useful in detecting subclinical changes in the epithelium."

• Cover