Causes of spherical aberration induced by laser refractive surgery

Yoon, Geunyoung; MacRae, Scott; Williams, David R.; Cox, Ian

doi:10.1016/j.jcrs.2004.10.046

Cited by 149 publications

(100 citation statements)

References 20 publications

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“…After myopic procedures, induced spherical aberrations tend to be positive and correlated with the magnitude of intended correction. [5][6][7][8] The increase in spherical aberration influences the visual function of the patient, 4,9 as measured by contrast-sensitivity function (CSF) and low luminance visual acuity. Further, if significant spherical aberration is induced by refractive surgery, the correction of defocus could also be affected.…”

Section: Introductionmentioning

confidence: 99%

“…Jiménez et al 13 showed that pre-and postsurgery asphericity values scale with the cube of pre-to postcorneal radii. For an aspherical surface, spherical aberration is proportional to asphericity (Q ¼ pÀ1), 8 which accounts for the increase in spherical aberration. However, when the exact Munnerlyn formula is used, without ablation efficiency reduction, Gatinel et al 14 reported that the postsurgery corneal asphericity does not increase.…”

Section: Introductionmentioning

confidence: 99%

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Postsurgery corneal asphericity and spherical aberration due to ablation efficiency reduction and corneal remodelling in refractive surgeries

Kwon

Bott

2008

Eye

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Purpose To explain the origin of changes in corneal asphericity and induced spherical aberration after laser refractive surgery. Methods A rigorous model, CASIM (corneal ablation simulator), has been developed to model the ablation profile design, the shotby-shot ablation process and the corneal remodelling that occurs through healing. The dependence of corneal asphericity, induced spherical aberration, and achieved refractive correction on corneal remodelling, and the ablation efficiency reduction caused by the angle of incidence of the excimer beam on the curved cornea are compared to the clinical outcomes reported in the literature. Results When the exact Munnerlyn formula is used, the CASIM modelling and the clinical data exhibit a high degree of correlation. The modelling predicts that the postoperative cornea will be oblate, with substantial induced spherical aberration. A 6-month postsurgery asphericity is predicted by CASIM with a correlation of R 2 ¼ 0.94. The corneal remodelling included in CASIM accounts, on the average, for 45 and 69% of the increase in asphericity and spherical aberration, respectively, with the remainder due to the ablation efficiency. Conclusions The modelling shows that clinically observed increases in corneal asphericity and induction of spherical aberration can be explained by the effects of corneal remodelling due to healing and by the ablation efficiency reduction due to laser angle of incidence. The model is capable of predicting clinical outcomes for procedures performed with flying spot laser systems and could be used to design compensated ablation profiles to improve the clinical outcomes for custom as well as conventional laser refractive procedures.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Postsurgery corneal asphericity and spherical aberration due to ablation efficiency reduction and corneal remodelling in refractive surgeries

Kwon

Bott

2008

Eye

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“…All ablations were non-wavefront-guided but were based on aspheric 25 aberration-neutral (Aberration-Free TM ) profiles (and not on the profiles proposed by Munnerlyn 26 ) to balance the induction of spherical aberration 27,28 (prolateness optimization 29,30 ). This approach included a multidynamic aspherical transition zone, aberration and focus shift compensation due to tissue removal, pseudo-matrix-based spot positioning, enhanced compensation for the loss of efficiency; 31 all based on theoretical equations validated with ablation models and clinical evaluations.…”

Section: Methodsmentioning

confidence: 99%

Bilateral Symmetry before and Six Months after Aberration-Free™ Correction with the SCHWIND AMARIS TotalTech Laser: Clinical Outcomes

Arbelaez

Vidal

Arba-Mosquera

2010

Journal of Optometry

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PURPOSE:To compare the preoperative and postoperative bilateral symmetry between OD and OS eyes that have undergone femto-LASIK using the Ziemer LDV femtosecond laser system, the SCHWIND AMARIS Excimer Laser and the Aberrationfree TM profiles implemented in the SCHWIND Custom Ablation Manager software. METHODS: A total of 25 LASIK patients were bilaterally evaluated at the six-month follow-up visit. In all cases standard examinations, pre-and postoperative analysis with corneal wavefront topography (OPTIKON Scout) were performed. Aberration-free TM aspheric treatments were devised using the Custom Ablation Manager software and ablations were performed by means of the SCHWIND AMARIS flying-spot excimer laser system (both SCHWIND eyetech-solutions). In all cases LASIK flaps were created using an LDV femtosecond laser (Ziemer Group). The OD/OS bilateral symmetry was evaluated in terms of corneal wavefront aberration. RESULTS: Preoperatively, 11 Zernike terms showed significant bilateral (OS-vs.-OD) symmetry, and only 6 Zernike terms were significantly different. Overall, 23 out of the 25 patients showed significant bilateral symmetry, and only 2 out of 25 patients showed significant differences. None of the aberration metrics changed from pre-to postoperative values by a clinically relevant amount. At the 6-month postoperative visit, 12 Zernike terms showed significant symmetry, and 8 terms were significantly different. Overall, 22 out of 25 patients showed significant bilateral symmetry (OS vs. OD), and only 3 out of 25 patients showed significant differences. Also, this postoperative examination revealed that 6 Zernike terms lost significant OS-vs.-OD symmetry, but 4 Zernike terms gained significant symmetry. Finally, 4 patients lost significant bilaterality, and 2 patients gained significant bilaterality: bilateral symmetry between eyes was better maintained in those patients with a clear preoperative bilateral symmetry. CONCLUSIONS: Aberration-Free Treatments with the SCHWIND AMARIS did not induce clinically significant aberrations, maintained the global OD-vs.-OS bilateral symmetry, as well as the bilateral symmetry between corresponding Zernike terms (which influences binocular summation). RESUMEN OBJETIVO:Comparar la simetría bilateral (OD-OS) preoperativa y postoperativa, en ojos sometidos a una operación de femto-LASIK donde se empleó el sistema láser de femtosegundos Ziemer LDV, el láser de excímero SCHWIND AMARIS y donde se implementaron perfiles de ablación Aberration-free TM (sin aberraciones) en el software de control del láser (SCHWIND Custom Ablation Manager). MÉTODOS: Se evaluaron bilateralmente un total de 25 pacientes de LASIK transcurridos 6 meses de la operación. En todos los casos se llevó a cabo una revisión estándar, y se realizaron medidas pre-y postoperativas de topografía corneal (OPTIKON Scout). Se diseñaron tratamientos asféricos de tipo Aberration-free TM utilizando el software de control del láser, denominado Custom Ablation Manager. La ablación se realizó mediante el sistem...

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“…Several studies have demonstrated that this causes the increase in spherical aberration after LASIK surgery. [25][26][27] . Our multizone analysis reveals that the actual increase in the Q values in the optical zone is even greater ͑about +1͒.…”

Section: One Examplementioning

confidence: 99%

Multizone model for postsurgical corneas: analysis of standard and custom LASIK outcomes

González¹,

Hernández-Matamoros²,

Navarro

2008

J. Biomed. Opt.

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Abstract. A multizone model for postsurgical corneal topography is presented and applied to a comparative analysis of the outcome of standard and customized myopic LASIK. The different zones are segmented automatically by a clustering algorithm. The algorithm uses a set of three local descriptors, which correspond to normalized physical magnitudes computed for each point of the corneal topography map: Gauss curvature, root-mean-square ͑RMS͒ fit error to an ellipsoid surface model, and distance to the center of the topographic map. Both presurgical and post-LASIK corneal topographies of 31 eyes were analyzed using monozone and multizone models. The patients were classified into three groups according to the different LASIK treatments applied: Allegretto, Zyoptix, and PlanoScan. For post-LASIK corneas, the multizone model provided a lower fit error, an average of 1.2± 0.4 m versus 2.4± 0.7 m ͑monozone͒. The comparative analysis of the three different LASIK treatments showed no improvement of custom over standard treatments. The outcomes of Zyoptix and PlanoScan were basically equivalent and consistent with previous findings: The higher-order aberration ͑HOA͒ increased by a factor of two. The increase in HOA was higher, by a factor of three, after the Allegretto treatment. The mutizone model shows a higherfidelity representation and permits a deeper understanding of the postsurgical cornea.

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Causes of spherical aberration induced by laser refractive surgery

Cited by 149 publications

References 20 publications

Postsurgery corneal asphericity and spherical aberration due to ablation efficiency reduction and corneal remodelling in refractive surgeries

Postsurgery corneal asphericity and spherical aberration due to ablation efficiency reduction and corneal remodelling in refractive surgeries

Bilateral Symmetry before and Six Months after Aberration-Free™ Correction with the SCHWIND AMARIS TotalTech Laser: Clinical Outcomes

Multizone model for postsurgical corneas: analysis of standard and custom LASIK outcomes

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