Objective Evaluation of Planned Versus Achieved Stromal Thickness Reduction in Myopic Femtosecond Laser-assisted LASIK

Kanellopoulos, Anastasios John; Georgiadou, Stella; Asimellis, George

doi:10.3928/1081597x-20150820-09

Cited by 13 publications

(15 citation statements)

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“…Contrary to our findings, Kanellopoulos et al 24 reported a lower central ablation efficiency of 97.2% with a similar laser (Wavelight EX500) in myopic LASIK. The difference may be explained by the following: First, Kanellopoulos et al measured the difference between the preoperative and postoperative stromal thicknesses.…”

Section: Discussioncontrasting

confidence: 99%

“…This could artifactually decrease the measured ablation depth in the study. 24 Second, the ablation efficiency tends to be higher for a deeper ablation (nonlinear effect) due to stromal dehydration. The tissue ablation depth used in our study was deeper than the LASIK stromal ablation depth in the study by Kanellopoulos et al In addition, there was a time interval between the myopic ablation and hyperopic ablation (approximately 50 seconds) in our study.…”

Section: Discussionmentioning

confidence: 99%

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Guiding flying-spot laser transepithelial phototherapeutic keratectomy with optical coherence tomography

Yokogawa

Tang

et al. 2017

Journal of Cataract and Refractive Surgery

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PURPOSE To analyze transepithelial phototherapeutic keratectomy (PTK) results using optical coherence tomography (OCT) and develop a model to guide the laser dioptric and depth settings. SETTING Casey Eye Institute, Portland, Oregon, USA. DESIGN Prospective nonrandomized case series. METHODS Patients with superficial corneal opacities and irregularities had transepithelial PTK with a flying-spot excimer laser by combining wide-zone myopic and hyperopic astigmatic ablations. Optical coherence tomography was used to calculate corneal epithelial lenticular masking effects, guide refractive laser settings, and measure opacity removal. The laser ablation efficiency and the refractive outcome were investigated using multivariate linear regression models. RESULTS Twenty-six eyes of 20 patients received PTK to remove opacities and irregular astigmatism due to scar, dystrophy, radial keratotomy, or previous corneal surgeries. The uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) were significantly improved (P < .01) by 3.7 Snellen lines and 2.0 Snellen lines, respectively, to a mean of 20/41.2 and 20/22.0, respectively. Achieved laser ablation depths were 31.3% (myopic ablation) and 63.0% (hyperopic ablation) deeper than the manufacturer’s nomogram. The spherical equivalent of the corneal epithelial lenticular masking effect was 0.73 diopter ± 0.61 (SD). The refractive outcome highly correlated to the laser settings and epithelial lenticular masking effect (Pearson R = 0.96, P < .01). The ablation rate of granular dystrophy opacities appeared to be slower. Smoothing ablation under masking fluid was needed to prevent focal steep islands in these cases. CONCLUSIONS The OCT-measured ablation depth efficiency could guide opacity removal. The corneal epithelial lenticular masking effect could refine the spherical refractive nomogram to achieve a better refractive outcome after transepithelial ablation.

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Section: Discussioncontrasting

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Guiding flying-spot laser transepithelial phototherapeutic keratectomy with optical coherence tomography

Yokogawa

Tang

et al. 2017

Journal of Cataract and Refractive Surgery

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“… 35 The variability in the maximum ablated tissue by the excimer laser also constitutes an independent factor. 36 …”

Section: Discussionmentioning

confidence: 99%

Comparison of corneal biomechanics after myopic small-incision lenticule extraction compared to LASIK: an ex vivo study

Kanellopoulos¹

2018

OPTH

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PurposeTo investigate ex vivo potentially different corneal biomechanical properties after small-incision lenticule extraction (SMILE) versus LASIK for myopic correction.MethodsThirty human donor corneas were subjected to either myopic SMILE or femtosecond laser-assisted LASIK. Donor corneas were assigned to six investigative groups: Group A, −3.00 D (diopters) SMILE; Group B, −8.00 D SMILE; Group C, −3.00 D LASIK; and Group D, −8.00 D LASIK. Additionally, two control groups were formed: Group E, SMILE and Group F, LASIK. All groups consisted of five corneas, randomly allocated. The corneas in the control groups were subjected to the corresponding femtosecond-laser lamellar cuts but not to tissue removal. Evaluation of biomechanical tensile strength was conducted by biaxial force application. Primary outcome measures were stress at 10% and 15% strain, and Young’s modulus at 10% and 15% strain.ResultsIn SMILE, the average relative difference (Δ) of the four outcome measures was −34.46% for −3.00 D correction versus control Group E and −49.34% for −8.00 D correction versus control Group E. In LASIK, average Δ was −24.88% for −3.00 D correction versus control, and −52.73% for −8.00 D correction versus control. All these differences were statistically significant; SMILE compared to LASIK for the same myopic correction appears to result in more biomechanical reduction for −3.00 D corrections by −26%, while a nonstatistically significant difference was noted in −8.00 D corrections.ConclusionBoth SMILE and LASIK procedures do substantially alter corneal biomechanical properties, and the degree of tensile strength reduction is statistically significantly correlated to the extent of myopic correction. Additionally, SMILE procedure seems to result in more tensile strength reduction in lower myopic corrections compared to LASIK, and similar tensile strength reduction to LASIK in higher myopic corrections when compared to LASIK.

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“…Nowadays, more complex ablation profiles, such as wavefront, wavefront optimized, or topography guided, complicate the calculation of ablation depth. Consequently, the refractive surgeon relies on the estimated ablation depth provided by the laser machine's software [11] .…”

Section: Discussionmentioning

confidence: 99%

Actual Depth Ablation in LASIK and FEMTOLASIK Surgeries for Correction of Myopia and Myopic Astigmatism

Khalil

Hassan²

2022

International Journal of Medical Arts

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Article informationBackground: Proper calculation of ablation depth associated with LASIK and FEMTOLASIK surgeries is mandatory to estimate the post-refractive surgery remaining stroma to avoid the possibility of post-operative ectasia and to correct the maximum error to meet the patient's needs and safety. Purpose: The current work aimed to assess the actual depths of ablation after the LASIK versus the FEMTO-LASIK surgeries. Patients and Methods: Forty eyes of 20 patients were included in this prospective nonrandomized interventional study. They had myopia or myopic astigmatism, and scheduled for LASIK or FEMTOLASIK surgery. Pentacam was used to check the thickness of the thinnest corneal location and to exclude the possibility of keratoconus. They were divided into two groups according to the technique used to correct the error. Group I for LASIK and Group II for FEMTOLASIK surgery. Ablation was performed in all cases using the Allegretto excimer laser machine.After surgery, all patients received a combination of topical tobramycin 0.3% and dexamethasone 0.1% eye drops four times daily for 10 days, and topical Sodium Hyaluronate eye drops [2 mg/ml] four times daily for one month. All patients were examined at one day and one week postoperatively for evidence of flap malposition, striae, epithelial defects, or diffuse lamellar keratitis. Pentacam was used for follow up at 3 months after surgery to re-evaluate the thinnest central location. Results: In group I, the mean actual tissue ablation per one diopter was 13.3 microns for 6.5 mm treatment zone, and 11.9 microns for 6.0 mm treatment zone, while in group II, it was 13.4 microns for 6.5 treatment zone, and 11.8 microns for 6.0 treatment zone. There was insignificant difference between actual tissue ablation following the LASIK versus the FEMTOLASIK surgeries. Conclusion:The actual ablation depth should be considered to calculate the remaining stromal depth after LASIK or FEMTOLASIK surgeries for treatment of myopia or myopic astigmatism to avoid the possibility of post-LASIK or FEMTOLASIK ectasia and to correct the maximum error that meets the patient's needs.

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Objective Evaluation of Planned Versus Achieved Stromal Thickness Reduction in Myopic Femtosecond Laser-assisted LASIK

Abstract: Actual objective stromal thickness reduction following myopic LASIK correlates well with the attempted versus achieved refractive change.

Cited by 13 publications

References 15 publications

Guiding flying-spot laser transepithelial phototherapeutic keratectomy with optical coherence tomography

Guiding flying-spot laser transepithelial phototherapeutic keratectomy with optical coherence tomography

Comparison of corneal biomechanics after myopic small-incision lenticule extraction compared to LASIK: an ex vivo study

Actual Depth Ablation in LASIK and FEMTOLASIK Surgeries for Correction of Myopia and Myopic Astigmatism

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