Comparison of Corneal Deformation Parameters After SMILE, LASEK, and Femtosecond Laser-Assisted LASIK

Shen, Yang; Chen, Zhi; Knorz, Michael C.; Li, Meiyan; Zhao, Jing; Zhou, Xingtao

doi:10.3928/1081597x-20140422-01

Cited by 93 publications

(76 citation statements)

References 27 publications

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“…[13][14][15] The Corvis ST (Oculus Optikgeräte GmbH; Wetzlar, Germany) was later introduced as a noncontact tonometer, which monitors the response of the cornea to an air pressure pulse using an ultra-highspeed Scheimpflug camera, and uses the captured image sequence to produce estimates of IOP and deformation response parameters. 16 Several articles have recently been published on the possible applications of the Corvis ST, particularly evaluating possible biomechanical differences in the cornea after undergoing refractive surgery procedures, [17][18][19][20][21][22] between normal and keratoconic patients, [23][24][25][26] after cross-linking, 27 and in patients with glaucoma. [28][29][30][31] However, it has been demonstrated that IOP and pachymetry have important influences on most corneal biomechanical metrics provided by both the Corvis ST and ORA.…”

Section: Resultsmentioning

confidence: 99%

Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients

et al. 2016

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n 1619, Scheiner provided the first precise description of the corneal shape using glass balls of known curvatures.1 From that first description, many other diagnostic tools have been developed to describe corneal shape, from keratometry to corneal topography (front surface curvature maps), 2 then into three-dimensional corneal tomography systems.3 More recently, it has been shown that corneal biomechanical behavior plays an important role in maintaining corneal shape, which is necessary for light refraction and clear vision, 4 and should therefore be considered in understanding the development of ectatic diseases 5,6 and the results of surgery. 4,7 Until recently, the evaluation of corneal biomechanical properties had been restricted to ex vivo laboratory studies 5,8 and mathematical corneal models. METHODS: Seven hundred five healthy patients were included in this multicenter retrospective study. The biomechanical response data were analyzed to obtain normative values with their dependence on corrected and clinically validated intraocular pressure estimates developed using the finite element method (bIOP), central corneal thickness (CCT), and age, and to evaluate the influence of bIOP, CCT, and age. RESULTS:The results showed that all DCRs were correlated with bIOP except deflection amplitude (DefA) ratio, highest concavity (HC) radius, and inverse concave radius. The analysis of the relationship of DCRs with CCT indicated that HC radius, inverse concave radius, deformation amplitude (DA) ratio, and DefA ratio were correlated with CCT (rho values of 0.343, -0.407, -0.444, and -0.406, respectively). The age group subanalysis revealed that primarily whole eye movement followed by DA ratio and inverse concave radius were the parameters that were most influenced by age. Finally, custom software was created to compare normative values to imported examinations.CONCLUSIONS: HC radius, inverse concave radius, DA ratio, and DefA ratio were shown to be suitable parameters to evaluate in vivo corneal biomechanics due to their independence from IOP and their correlation with pachymetry and age. The creation of normative values allows the interpretation of an abnormal examination without the need to match every case with another normal patient matched for CCT and IOP.[J Refract Surg. 2016;32(8):550-561.]

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Section: Resultsmentioning

confidence: 99%

Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients

et al. 2016

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“…There were no significant differences between the results in small-incision lenticule extraction and those in the other procedures. 71 It is conceivable but currently inconclusive that smallincision lenticule extraction may offer increased postoperative corneal biomechanical stability compared with LASIK.…”

Section: Corneal Biomechanical Strengthmentioning

confidence: 99%

Small-incision lenticule extraction

Moshirfar¹,

McCaughey²,

Reinstein³

et al. 2015

Journal of Cataract and Refractive Surgery

177

116

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“…In this case no mechanical difference can be expected. Also, in vivo measurements of corneal biomechanics after SmILE and LASIK surgery using air-puff deformation systems are inconclusive [11][12][13]17,33 potentially because they do not measure long-term deformation, which is essential for maintaining the corneal shape over time. In our experimental setting we applied the load gradually from the posterior surface and then measured its relaxation behavior under constant load.…”

Section: Discussionmentioning

confidence: 99%

Biomechanical Differences Between Femtosecond Lenticule Extraction (FLEx) and Small Incision Lenticule Extraction (SmILE) Tested by 2D-Extensometry in Ex Vivo Porcine Eyes

Spiru

Kling

Hafezi

et al. 2017

Invest. Ophthalmol. Vis. Sci.

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Citation: Spiru B, Kling S, Hafezi F, Sekundo W. Biomechanical differences between femtosecond lenticule extraction (FLEx) and small incision lenticule extraction (SmILE) refractive procedures tested by 2D-extensometry in ex vivo porcine eyes. Invest Ophthalmol Vis Sci. 2017;58:259158: -259558: . DOI:10.1167 PURPOSE. To evaluate the biomechanical stability of ex vivo porcine corneas after femtosecond lenticule extraction (FLEx) and small incision lenticule extraction (SmILE) refractive surgeries.METHODS. Forty-five porcine eyes were equally divided into three groups: Groups 1 and 2 were treated with FLEx and SmILE procedure, respectively. Group 3 served as control. A refractive correction of À14 diopters (D) with a 7-mm zone using either a 160-lm flap (FLEx) or a 160-lm cap (SmILE) was performed. For two-dimensional (2D) elastic and viscoelastic biomechanical characterization, two testing cycles (preconditioning stress-strain curve from 1.27 to 12.5 N, stress-relaxation at 12.5 N during 120 seconds) were conducted. Young's modulus and Prony constants were calculated.RESULTS. At 0.8% of strain, FLEx (370 6 36 kPa) could resist a significantly lower stress than SmILE (392 6 19 kPa, P ¼ 0.046) and the control group (402 6 30 kPa, P ¼ 0.013). Also, FLEx (46.1 6 4.5 MPa) had a significantly lower Young's modulus than the control group (50.2 6 3.4 MPa, P ¼ 0.008). The Young's modulus of SmILE (48.6 6 2.5 MPa) had values situated between untreated corneas and FLEx-treated corneas. When compared to untreated controls, the stress resistance decreased by 8.0% with FLEx and 2.5% with SmILE; Young's modulus decreased by 5.1% with FLEx and 1.04% with SmILE. With a cap-based procedure, both anterior cap and stromal bed carry the intraocular pressure, while in a flap-based procedure, only the stromal bed does.CONCLUSIONS. Compared to flap-based procedures like FLEx, the cap-based technique SmILE can be considered superior in terms of biomechanical stability, when measured experimentally in ex vivo porcine corneas.

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Comparison of Corneal Deformation Parameters After SMILE, LASEK, and Femtosecond Laser-Assisted LASIK

Abstract: Applanation time (applanation 1) and deformation amplitude (as measured with the CorVis ST tonometer) may be helpful in assessing corneal biomechanical changes after corneal refractive surgery. The relations between these parameters should be discussed in further studies.

Cited by 93 publications

References 27 publications

Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients

Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients

Small-incision lenticule extraction

Biomechanical Differences Between Femtosecond Lenticule Extraction (FLEx) and Small Incision Lenticule Extraction (SmILE) Tested by 2D-Extensometry in Ex Vivo Porcine Eyes

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