Eyeworld

50 | EYEWORLD | FALL 2024 R EFRACTIVE STRIKE! by Liz Hillman Editorial Co-Director About the physicians Brian Armstrong, MD Associate Professor of Ophthalmology Director of Cornea and Refractive Surgery University of Nebraska Medical Center Truhlsen Eye Institute Omaha, Nebraska Damien Gatinel, MD, PhD Head of the Anterior and Refractive Surgery Department Rothschild Foundation Paris, France Karolinne Maia Rocha, MD, PhD Professor of Ophthalmology Medical University of South Carolina Storm Eye Institute Charleston, South Carolina W hether you're doing laser vision correction or refractive cataract surgery with an advanced-tech- nology IOL, among the many measurements that influence procedural decisions are higher order aberra- tions (HOAs). "Corneal HOAs should be assessed during the preoperative evaluation for all refractive and cataract surgeries as a standard practice to inform surgical planning," said Brian Arm- strong, MD. "Missing preoperative HOAs can lead to suboptimal outcomes, including residual refractive error, poor visual quality, and visually significant dysphotopsias. Postoperative man- agement of a dissatisfied patient may involve IOL exchange or laser vision enhancement to address these issues." While whole chapters have been written on the topic of HOAs, Dr. Armstrong, along with Karolinne Maia Rocha, MD, PhD, and Damien Gatinel, MD, PhD, discussed measuring and quantifying HOAs, their impact on IOL selection for cataract surgery, procedure and candidate selection for corneal refractive surgery, and some of their eccentricities. Dr. Rocha said that HOAs and light scatter can be induced by various sources: dry eye, age-related cataract, posterior capsular opacifi- cation, vitreous floaters, keratoconus, and too small of an optical zone or decentered ablations post-corneal refractive surgery. No eye is per- fect, she said, though patients are more likely to tolerate/compensate for HOAs that they're "born with" compared to those that are induced. How to measure and quantify There are several technologies to identify and quantify HOAs. Dr. Rocha spoke about devices that use Shack-Hartmann wavefront sensors, ray tracing, double-pass sciascopy, OCTs, and Scheimpflug tomography. She said some devices measure the entire eye's aberration profile, the corneal HOAs, while others measure the cornea and the whole eye's aberrations. Dr. Rocha also talked about adaptive optics technology, which is not commercially available, that simulates the patient's vision when correct- ing and adding aberrations, and how much they can tolerate. Dr. Rocha shared two studies with an adaptive optics visual simulator showing that the patients' HOAs could be measured and cor- rected by the simulator. 1,2 One of these studies suggested that "adaptive optics technology may be of clinical benefit when counseling patients with highly aberrated eyes regarding their maxi- mum subjective potential for vision correction." 2 Dr. Armstrong said corneal HOAs are clini- cally assessed with advanced tomography devic- es like the Pentacam (Oculus), Galilei (Ziemer), and MS-39 anterior segment OCT (CSO). "These devices provide a detailed analysis of corneal HOAs by evaluating both anteri- or and posterior corneal surfaces, as well as pachymetry and densitometry data," he said. "They provide a quantification and stratifica- tion of HOAs. Placido disc-based topography is a more affordable method to quantify HOAs, though it does not provide data on posterior or total corneal HOAs. For the most cost-effective approach, one can infer increased HOAs from the reflection of irregular mires on a keratome- ter and keratoscope or scissor reflex seen with a retinoscope. While these tools offer insights into corneal irregularities, they lack the ability to quantify HOAs." Patient perspective Putting a number on HOAs is one thing, but understanding the patient's perception of them is important as well. "HOAs can diminish best spectacle correct- ed visual acuity and cause symptoms like glare and halos around lights, particularly in low light conditions. The impact is often more pro- nounced in patients with larger pupil sizes. You can determine the impact on vision of corneal HOAs by doing a diagnostic hard contact lens over refraction," Dr. Armstrong said. "Usually, the difference in best spectacle corrected vision with and without a hard contact lens can be attributed to HOAs. Clinically, we may perform contrast sensitivity testing to gauge the sub- jective impact of HOAs, which can be reduced in patients with increased HOAs. Wavefront aberrometry is another tool that provides a The impact of HOAs on refractive options and outcomes continued on page 52

• Cover