Optimisation of the ablation profiles in customised treatments for laser corneal refractive surgery

El propósito de este trabajo es estudiar la posibilidad de realizar cirugía refractiva personalizada reduciendo al mínimo la cantidad de tejido extirpada sin comprometer la calidad visual, así como evaluar la aplicación de estos métodos para reducir al mínimo el tejido ablación a la minimización objetivo de profundidad y el tiempo de ablaciones personalizadas. Se desarrolló un nuevo algoritmo para la selección de un conjunto de términos de Zernike optimizado en los tratamientos personalizados para cirugía láser refractiva corneal. Sus atributos de ahorro de tejido se han simulado en 100 aberraciones de onda diferentes en 6 mm de diámetro. Los resultados de la simulación se evaluaron en términos de cuánta profundidad y volumen se redujo para cada condición (en micras y en porcentaje), si la corrección propuesta consiste en una corrección completa de frente de onda o de un tratamiento libre de aberración, y si la profundidad o el volumen propuesto fue menor que la requerida para el tratamiento equivalente libre de aberración. Los resultados clínicos y los atributos de ahorro de tejido fueron evaluados en dos grupos (minimizar la profundidad: MD, y minimizar el volumen: MV; 30 ojos cada uno), más un grupo control (frente de onda corneal: CW, 30 ojos). Los resultados clínicos fueron evaluados en términos de previsibilidad, seguridad y sensibilidad al contraste. Los resultados de la simulación mostró una profundidad media ahorrada de 5μm (0-16μm), y un volumen medio salvado de 95nl (0-127nl) o una reducción de 11% en tejido (0-66% ahorro de tejido). La correcciones propuestas siempre fueron menos profundas que las correcciones de frente de onda completo y en el 59% de los casos fueron menos profundos que los tratamientos equivalentes libres de aberraciones. En un primer caso, la ablación se redujo significativamente en un 15% en comparación con la corrección personalizada completa. La refracción se corrigió a niveles subclínicos, la agudeza visual sin corrección mejoró a 20/20, la agudeza visual mejor corregida aumentó en 2 líneas, las aberraciones se redujeron aproximadamente un 40% en comparación con los niveles basales preoperatorios, y la zona óptica funcional de la córnea se amplió en aproximadamente un 40% en comparación con los niveles basales preoperatorios. Se redujeron trébol, coma, aberración esférica, y RMS de las aberraciones de orden superior. En la evaluación clínica, el 93% de los tratamientos CW, el 93% en el grupo MD y 100% en el grupo MV se encontraron dentro de 0,50 D de la SEq después de la operación. El 40% de los tratamientos CW, el 34% en el grupo MD y 47% en el grupo MV mejoró por lo menos una línea de AVMC después de la operación. El ahorro de tejido arrojó una reducción media de 8μm (1-20μm) y un ahorro de tiempo de 6s (1-15s) en el grupo de MD, y 6μm (0-20μm) y el 8 (2-26s) en el grupo MV

Corneal functional optical zone under monocular and binocular assessment

Background: In this retrospective randomized case series, we compared bilateral symmetry between OD and OS eyes, intercorneal differences and Functional Optical Zone (FOZ) of the corneal aberrations. Methods: Sixty-seven normal subjects (with no ocular pathology) who never had any ocular surgery were bilaterally evaluated at Augenzentrum Recklinghausen (Germany). In all cases, standard examinations and corneal wavefront topography (OPTIKON Scout) were performed. The OD/OS bilateral symmetry was evaluated for corneal wavefront aberrations, and FOZ-values were evaluated from the Root-Mean-Square (RMS) of High-Order Wavefront-Aberration (HOWAb). Moreover, correlations of FOZ, spherical equivalent (SE), astigmatism power, and cardinal and oblique astigmatism for binocular vs. monocular, and binocular vs. intercorneal differences were analyzed. Results: Mean FOZ was 6.56 ± 1.13 mm monocularly, 6.97 ± 1.34 mm binocularly, and 7.64 ± 1.30 mm intercorneal difference, with all strongly positively correlated, showing that the diameter of glare-free vision is larger in binocular than monocular conditions. Mean SE was 0.78 ± 1.30 D, and the mean astigmatism power (magnitude) was 0.46 ± 0.52 D binocularly. The corresponding monocular values for these metrics were 0.78 ± 1.30 D and 0.53 ± 0.53 D respectively. SE, astigmatism magnitude, cardinal astigmatism component, and FOZ showed a strong correlation and even symmetry; and oblique astigmatism component showed odd symmetry indicating Enantiomorphism between the left and right eye. Conclusions: These results confirm OD-vs.-OS bilateral symmetry (which influences binocular summation) of HOWAb, FOZ, defocus, astigmatism power, and cardinal and oblique astigmatism. Binocular Functional Optical Zone calculated from corneal wavefront aberrations can be used to optimize refractive surgery design

Long-term Outcomes After LASIK Using a Hybrid Bi-aspheric Micro-monovision Ablation Profile for Presbyopia Correction

PURPOSE: To evaluate visual outcomes 6 years after hybrid bi-aspheric multifocal central laser in situ keratomileusis for presbyopia correction (PresbyLASIK) treatments. METHODS: Thirty-eight eyes of 19 patients consecutively treated with central PresbyLASIK were assessed. The mean age of the patients was 51 ± 3 years at the time of treatment with a mean spherical equivalent refraction of −0.57 ± 1.98 diopters (D) and mean astigmatism of 0.58 ± 0.57 D. Monocular corrected distance visual acuity (CDVA), corrected near visual acuity (CNVA), and distance-corrected near visual acuity (DCNVA), uncorrected distance visual acuity (UDVA), uncorrected intermediate visual acuity (UIVA), distance-corrected intermediate visual acuity (DCIVA), and uncorrected near visual acuity (UNVA) were assessed preoperatively and postoperatively for the dominant eye, non-dominant eye, and binocularly. Subjective quality of vision and near vision were assessed using the 10-item, Rasch-scaled, Quality of Vision (QoV) Questionnaire and Near Activity Visual Questionnaire (NAVQ), respectively. RESULTS: At 6 years postoperatively, mean binocular UDVA was 20/18 ± 4 and mean binocular UNVA and UIVA were 0.11 ± 0.13 and −0.08 ± 0.08 logRAD, respectively. Spherical equivalent showed a slow hyperopic drift of +0.10 D per year with refractive astigmatism stable from 6 weeks postoperatively. Defocus curves showed an improvement of 0.4 Snellen lines at best focus from 1 to 6 years of follow-up, reaching preoperative levels. Compared to the preoperative status, the corneal and ocular spherical aberrations (at a 6-mm diameter) decreased and were stable from 3 months of follow-up. Questionnaires revealed a postoperative unaided QoV score comparable to preoperative scores and with an improved postoperative unaided NAVQ score compared to preoperative scores with best correction. CONCLUSIONS: Presbyopic treatment using a hybrid bi-aspheric micro-monovision ablation profile is safe and efficacious even after 6 years postoperatively. The postoperative outcomes indicate improvements in binocular vision at far, intermediate, and near distances. An 8% re-treatment rate should be considered to increase satisfaction levels, including a 3% reversal rate

Aspheric Optical Zones in hyperopia with the SCHWIND AMARIS

Purpose: To evaluate the corneal Functional Optical Zone (FOZ) and the Effective Optical Zone (EOZ) of the ablation, among eyes that underwent LASEK/Epi-LASEK treatments for hyperopic astigmatism. Methods: Twenty LASEK/Epi-LASEK treatments with mean defocus +2.21 ± 1.28 D performed using the SCHWIND AMARIS were retrospectively evaluated at 6-month follow-up. In all cases pre-/post-operative Corneal-Wavefront analyses using the Keratron-Scout (OPTIKON2000) were performed. FOZ-values were evaluated from the Root-Mean-Square of High-Order Wave-Aberration (RMSho), whereas EOZ-values were evaluated from the changes of Root-Mean-Square of High-Order Wave-Aberration (ΔRMSho) and Root-Mean-Square of the change of High-Order Wave-Aberration (RMS(ΔHOAb)). Correlations of FOZ and EOZ with Planned Optical Zone (POZ) and Defocus correction (SEq) were analyzed using a bilinear function. Results: At six-month, defocus was −0.04 ± 0.44 D, ninety percent eyes were within ± 0.50 D from emmetropia. Mean RMSho increased 0.18 ± 0.22 μm, SphAb −0.30 ± 0.18 μm, and Coma 0.07 ± 0.18 μm 6-month after treatment (6-mm diameter). Mean FOZPre was 7.40 ± 1.48 mm, mean POZ was 6.76 ± 0.22 mm, whereas mean FOZPost was 5.53 ± 1.18 mm (significantly smaller, p < 0.0001; bilinear correlation p < 0.005), mean EOZΔRMSho 6.47 ± 1.17 mm (bilinear correlation p < 0.005), EOZRMS(ΔHOAb) 5.67 ± 1.23 mm (significantly smaller, p < 0.0005; bilinear correlation p < 0.05). EOZ positively correlates with POZ and declines steadily with SEq. A treatment of +3 D in 6.50-mm POZ results in 5.75-mm EOZ (7.75-mm NPOZ), treatments in 7.00-mm POZ result in about 6.25-mm EOZ (8.25-mm nomogrammed POZ). Conclusions: FOZPost was significantly smaller than FOZPre. EOZΔRMSho was similar to POZ, whereas EOZRMS(ΔHOAb) was significantly smaller. Differences were larger for smaller POZ or larger Defocus. SEq up to +2 D result in EOZ, at least, as large as POZ. For SEq higher than +2 D, a nomogram for OZ can be applied

Optimization of the Spot Spacings for Reducing Roughness in Laser-Induced Optical Breakdown Processes for Corneal Laser Vision Correction

The aim of this work is to implement an algorithm that simulates a simplified cutting surface based on laser-induced optical breakdown (LIOB). The algorithm includes the definition of a possible positioning of the laser pulses and calculation of the roughness for different parameter settings (including LIOB threshold, pulse energies, and spot spacings) as the difference between simulated and ideal target cut (local differences within the cut, i.e., the waviness of the simulated cut vs. the homogeneity of the ideal target cut). Furthermore, optimizations of specific variables, such as spot distance (along the pathway), track distance (between lines/tracks), and pulse energy, are performed. The simulations suggest that lower pulse energies (well above the LIOB threshold) combined with asymmetric spacings (spot-to-track distance ratio >> 1) may be effective to lower the roughness of laser cuts generated by LIOB processes. The importance of lowering pulse energies (well above the threshold) emphasizes the need for the LIOB threshold to remain low (as low as possible). Reducing roughness by decreasing spacings (thus, increasing dose for same pulse energies) may have negative implications in visual recovery (risk for overdose). In all cases, the roughness is multiple times larger (rougher) than equivalent simulations for ablative procedures