Tissue-Saving Zernike Terms Selection in Customized Treatments for Refractive Surgery

Abstract

PURPOSE:To study the possibility of performing customized refractive surgery minimising the amount of ablated tissue without compromising visual quality. METHODS: A new algorithm for the selection of an optimized set of Zernike terms in customized treatments for laser corneal refractive surgery was developed. Its tissue saving attributes have been simulated on 100 different wave aberrations at 6mm diameter. Outcomes were evaluated in terms of how much depth and volume was saved for each condition (in micrometers and in percentage), whether the proposed correction consists of either a full wavefront correction or an aberration-free treatment, and whether the proposed depth or volume was less than the one required for the equivalent aberrationfree treatment. RESULTS: Simulated outcomes showed an average saved depth of 5μm (0-16μm), and an average saved volume of 95μl (0-127μl) or 11% saved tissue (0-66% saved tissue). Proposed corrections were always less deep than full wavefront corrections and in 59% of the cases were less deep than equivalent aberration-free treatments. CONCLUSIONS: Even though Zernike modes decomposition is a mathematical description of the aberration, it is not the aberration itself. Not all Zernike modes affect the optical quality in the same way. The eye does not see through Zernike decomposition but with its own aberration pattern. However, it seems feasible to efficiently perform laser corneal refractive surgery in a customized form minimising the amount of ablated tissue without compromising the visual quality. Further clinical evaluations on human eyes are needed to confirm the preliminary simulated results presented herein. KEY WORDS: refractive surgery; visual quality; Zernike; tissue saving; wavefront; aberrations; depth; volume; time; aberration-free; free of aberrations; diffraction limited. RESUMEN OBJETIVO: Estudiar la posibilidad de realizar tratamientos personalizados de cirugía refractiva donde se minimice la cantidad de tejido ablacionado sin que por ello se vea afectada la calidad visual. MÉTODOS: Se ha desarrollado un nuevo algoritmo para seleccionar un conjunto optimizado de términos de Zernike para su aplicación en tratamientos personalizados de cirugía refractiva corneal. Para 100 mapas de aberración de onda corneal (para un tamaño de pupila de 6 mm de diámetro), se ha simulado la capacidad de dicho algoritmo para preservar tejido corneal. El resultado de dicha simulación se ha analizado en función de cuanto espesor (en micras) o de cuanto volumen (en %) se preserva en cada situación (respecto a otra situación de referencia): si la corrección propuesta logra corregir todo el frente de onda o sólo las aberraciones de segundo orden, y si el espesor o el volumen que hay que ablacionar con esta configuración es menor que para un tratamiento estándar equivalente, donde se traten de corregir únicamente las aberraciones de segundo orden. RESULTADOS: Las simulaciones arrojaron un "ahorro" promedio de tejido ablacionado igual a 5 μm en términos de espesor máximo que se h...

Six-Month Clinical Outcomes of Customized Treatments Minimized for Depth and Time in Laser Corneal Refractive Surgery

“…Different approaches for minimizing the tissue consumption in refractive surgery were proposed and have been extensively discussed. 22 When to use customized strategies in refractive surgery has been discussed previously, as well. [18][19][20][21] Our experience suggests that wavefront-customized treatments can only be successful if preexisting aberrations are greater than repeatability (eg, repeatability of diagnostic 50 and treatment devices) and biological noise (eg, day-to-day variabilities in visual acuity, refraction, or aberration in the same subject).…”

“…22 With this basis, we have proposed a different metric for dioptric equivalence. Our proposed metric is identical to the power vector notation for the low orders and allows to define a general optical blur as a general expression for the one proposed by Thibos et al…”

“…The idea to optimize the customized treatment to reduce the ablated thickness while retaining the positive aspects is therefore pertinent. 22 The development of new algorithms or ablation strategies for performing laser corneal refractive surgery in a customized form, minimizing the amount of ablated tissue without compromising the visual quality, and potentially maximizing visual performance without increasing the factors of risk would be of great value for the refractive surgery community and ultimately for the health and safety of the patients. Therefore, the topic ''customized treatments minimized for depth and time in laser corneal refractive surgery'' is worth analyzing because its clinical implications are not yet deeply explored.…”

“…which represents the proposed objective determination of the actual clinical relevance of the single terms in a Zernike expansion of the wavefront aberration 22. Objective Minimization of the Maximum Depth of a Customized Ablation Based on the Zernike Expansion of the Wavefront Aberration…”

Corneal-Wavefront guided transepithelial photorefractive keratectomy after corneal collagen cross linking in keratoconus

“…Furthermore, the calculation of corneal asphericity as a 3-D fit renders more accurate results when it is based on the corneal wavefront aberrations rather than on the corneal topography of the principal meridians 27 . The wavefront guided profiles also allow customization of the ablation profiles to minimize the tissue ablation specially critical in keratoconus cases 28, 29, 30. The use of corneal wavefront based ablation on irregular corneal surface for these keratoconic patients could be argued, however, we favoured corneal wavefront based profiles mainly due to their theoretical advantages over topography based profiles, namely customizability, tissue saving, same optical origin (as corneal topography), best attainable CDVA and the best attainable topographic regularization.…”