EyeWorld Asia-Pacific June 2021 Issue

REFRACTIVE 36 EWAP JUNE 2021 Approaching Complex Cataract and Anterior Segment Reconstruction 30 –31 July 2021 Singapore Saturday, 31 July 2021, 13:00 – 13:55hrs (Singapore Time UTC+8) Not to beMissed! Register Today! The APACRS LIM Lecture is the highest honor conferred by the APACRS will deliver a lecture on Ike K. Ahmed . Log on apacrs-snec2021.org for registration and meeting information. Virtual Meeting i l i epithelium has the ability to mask corneal irregularities when they are sufficiently subtle.” Diagnosing keratoconus early can ensure patients are being monitored closely for progression. If progression is observed, crosslinking could be performed to stop it before there are significant visual impacts. Dr. Reinstein explained that “epithelial mapping can demonstrate continued changes in the cornea after crosslinking that may not be apparent by just looking at surface topography.” Dr. Carones also uses epithelial mapping in screening candidates for laser refractive surgery. For example, a patient might be seen as having ectasia after refractive surgery when, if epithelial mapping had been performed preop, it might have been identified as early keratoconus. While both VHF ultrasound and OCT can map the corneal epithelium, there are differences in accuracy and mapping coverage, Dr. Reinstein said. “Our studies have demonstrated that VHF ultrasound epithelial measurement produces an accuracy of approximately 1 μm while OCT achieves approximately 3 μm,” 5 Dr. Reinstein explained, adding, “the main reasons for the lower accuracy of OCT relate to the fact that OCT is measuring epithelium and tear film together, the tear film itself being a big variable, as well as the effects of unknown refractive index within the epithelium. In our practice every single patient undergoes OCT epithelial mapping screening. Approximately 15% of patients go on to require definitive epithelial mapping by VHF ultrasound, which also gives us the best posterior chamber measurements at the same time for improved ICL sizing if the cornea ends up being classified as keratoconic.” Dr. Reinstein pointed out that histopathologic analysis of keratoconic corneas has confirmed the clinical observations of epithelial breakdown over an excessively steepened cone. 6,7 He was the first to describe the epithelial profile in keratoconus, demonstrating how it was considerably different from that of normal corneas. 8 “The epithelium was thinnest at the apex of the cone, and this thin epithelial zone was surrounded by an annulus of thickened epithelium,” he said. “While all eyes exhibited the same epithelial donut pattern, characterized by a localized central zone of thinning surrounded by an annulus of thick epithelium, the thickness values of the thinnest point and the thickest point as well as the difference in thickness between the thinnest and thickest epithelium varied greatly between eyes. There was a statistically significant correlation between the thinnest epithelium and the steepest keratometry, indicating that as the cornea became steeper, the epithelial thickness minimum became thinner.” From there, Dr. Reinstein