36 EyeWorld Asia-Pacific | December 2024 REFRACTIVE SURGERY How to measure and quantify There are several technologies to identify and quantify HOAs. Dr. Rocha spoke about devices that use ShackHartmann 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, while not commercially available, can simulate the patient’s vision when correcting 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 corrected 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 maximum subjective potential for vision correction.”2 Dr. Armstrong said corneal HOAs are clinically assessed with advanced tomography devices 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 anterior and posterior corneal surfaces, as well as pachymetry and densitometry data,” he said. “They provide a quantification and stratification 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 costeffective approach, one can infer increased HOAs from the reflection of irregular mires on a keratometer 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 just as important. “HOAs can diminish best spectacle corrected visual acuity and cause symptoms like glare and halos around lights, particularly in low light conditions. The impact is often more pronounced in patients with larger pupil sizes. You can determine the impact on vision of corneal HOAs by performing 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 subjective impact of HOAs, which can be reduced in patients with increased HOAs. Wavefront aberrometry is another tool that provides a comprehensive evaluation of total eye HOAs, offering both quantitative data and visual simulations for patient education. In our practice, we use a newer aberrometry device called the Osiris [CSO], which integrates with tomographic data from the MS-39 anterior segment OCT to provide a more comprehensive assessment of an eye.” Dr. Armstrong said that while there is no data-driven link between a person’s personality and their subjective perception of HOAs, the stereotypical “type A” personality is generally more likely to be bothered by visual quality issues that are related to HOAs.
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