Comparison of Two Cap Thickness in Small Incision Lenticule Extraction: 100μm versus 160μm

Miao He, Wei Wang, Hui Ding, Xingwu Zhong, Miao He, Wei Wang, Hui Ding, Xingwu Zhong

Abstract

Purpose: To compare the changes of biomechanical properties, endothelial cell density (ECD), and posterior corneal elevation (PCE) after femtosecond small incision lenticule extractions (SMILEs) with 100μm versus 160μm cap thicknesses.

Methods: A total of 12 rabbits were randomly assigned into two groups of 6 each. SMILE was performed at a depth of either 160μm (160-cap group) or 100μm (100-cap group). Corneal biomechanics, PCE, ECD were evaluated pre-operatively, 1week, 1 month, 2 months, 3 months, and 4 months post-operatively by Pentacam, Corvis ST, in vivo confocal microscopy (IVCM) respectively. The Young's modulus was obtained by strip-extensometry test 4 months after surgery.

Results: At each time point, the second applanation time (A2T) was similar between the groups with the exception of 4 months after surgery (22.66±0.16 ms in the 160-cap group versus 21.75±0.29 ms in the 100-cap group, p = 0.004). Neither deformation amplitude (DA) nor the first applanationtime (A1T) were significantly different between the two groups. The postoperative posterior surface did not shift forward, the changes of PCE and ECD were not significantly different between the two groups at any observation time. Young's modulus was higher in the 160-cap group than that in the 100-cap group with no statistical significance (P>0.05). Regression analyses showed that the PCE changes and Young's modulus were not affected by cap thickness (CT) or residual stromal bed thickness (RBT) (All P>0.05).

Conclusions: The differences of corneal biomechanics, posterior surface elevation, or ECD changes were quite small when using 100μm or 160μm cap thicknesses in SMILE.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Corvis ST output parameters.
Fig 1. Corvis ST output parameters.
IOP, intraocular pressure; CCT, central corneal thickness.
Fig 2. Changes of posterior surface elevation…
Fig 2. Changes of posterior surface elevation in the comparative map measured by Pentacam.
Twenty-one points (red points) in the map were selected, including the corneal apex, eight points in the 4mm diameter annulus (0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°semimeridians) and twelve points in the 6 mm diameter annulus (0°, 30°,60°,90°, 120°,150°,180°, 210°, 240°, 270°, 300°, 330°semimeridians).

References

    1. Mastropasqua L, Calienno R, Lanzini M, Colasante M, Mastropasqua A, Mattei PA, et al. evaluation of corneal biomechanical properties modification after small incision lenticule extraction using Scheimpflug-based noncontact tonometer. Biomed Res Int.2014; 2014: 290619 10.1155/2014/290619
    1. Wang D, Liu M, Chen Y, Zhang X, Xu Y, Wang J, et al. differences in the corneal biomechanical changes after SMILE and LASIK. J Refract Surg.2014; 30: 702–707. 10.3928/1081597X-20140903-09
    1. Wu D, Wang Y, Zhang L, Wei S, Tang X. corneal biomechanical effects: small-incision lenticule extraction versus femtosecond laser-assisted laser in situ keratomileusis. J Cataract Refract Surg.2014; 40: 954–962. 10.1016/j.jcrs.2013.07.056
    1. Schmack I, Dawson DG, McCarey BE, Waring GR, Grossniklaus HE, Edelhauser HF. cohesive tensile strength of human LASIK wounds with histologic, ultrastructural, and clinical correlations. J Refract Surg.2005; 21: 433–445.
    1. Reinstein DZ, Archer TJ, Randleman JB. mathematical model to compare the relative tensile strength of the cornea after PRK, LASIK, and small incision lenticule extraction. J Refract Surg.2013; 29: 454–460. 10.3928/1081597X-20130617-03
    1. El-Massry AA, Goweida MB, Shama A, Elkhawaga MH, Abdalla MF. contralateral eye comparison between femtosecond small incision intrastromal lenticule extraction at depths of 100 and 160 mum. Cornea.2015; 34: 1272–1275. 10.1097/ICO.0000000000000571
    1. Randleman JB, Russell B, Ward MA, Thompson KP, Stulting RD. risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology.2003; 110: 267–275.
    1. Bak-Nielsen S, Pedersen IB, Ivarsen A, Hjortdal J. repeatability, reproducibility, and age dependency of dynamic scheimpflug-based pneumotonometer and its correlation with a dynamic bidirectional pneumotonometry device. Cornea.2015; 34: 71–77. 10.1097/ICO.0000000000000293
    1. Hon Y, Lam AK. corneal deformation measurement using scheimpflug noncontact tonometry. Optom Vis Sci.2013; 90: e1–e8. 10.1097/OPX.0b013e318279eb87
    1. Chen X, Stojanovic A, Hua Y, Eidet JR, Hu D, Wang J, et al. reliability of corneal dynamic scheimpflug analyser measurements in virgin and post-PRK eyes. PLoS One.2014; 9: e109577 10.1371/journal.pone.0109577
    1. Salvetat ML, Zeppieri M, Tosoni C, Felletti M, Grasso L, Brusini P. corneal deformation parameters provided by the corvis-st pachy-tonometer in healthy subjects and glaucoma patients. J Glaucoma.2015; 24: 568–574. 10.1097/IJG.0000000000000133
    1. Nemeth G, Hassan Z, Csutak A, Szalai E, Berta A, Modis LJ. repeatability of ocular biomechanical data measurements with a Scheimpflug-based noncontact device on normal corneas. J Refract Surg.2013; 29: 558–563. 10.3928/1081597X-20130719-06
    1. Leung CK, Ye C, Weinreb RN. an ultra-high-speed Scheimpflug camera for evaluation of corneal deformation response and its impact on IOP measurement. Invest Ophthalmol Vis Sci.2013; 54: 2885–2892. 10.1167/iovs.12-11563
    1. Buzard KA. introduction to biomechanics of the cornea. Refract Corneal Surg.1992; 8: 127–138.
    1. Tejwani S, Shetty R, Kurien M, Dinakaran S, Ghosh A, Roy AS. biomechanics of the cornea evaluated by spectral analysis of waveforms from ocular response analyzer and corvis-st. PLoS One.2014;9: e97591 10.1371/journal.pone.0097591
    1. Kling S, Marcos S. contributing factors to corneal deformation in air puff measurements. Invest Ophthalmol Vis Sci.2013; 54: 5078–5085. 10.1167/iovs.13-12509
    1. Tian L, Wang D, Wu Y, Meng X, Chen B, Ge M, et al. corneal biomechanical characteristics measured by the corvis scheimpflug technology in eyes with primary open-angle glaucoma and normal eyes. Acta Ophthalmol.2016; 94: e317–e324 10.1111/aos.12672
    1. McPhee TJ, Bourne WM, Brubaker RF. location of the stress-bearing layers of the cornea. Invest Ophthalmol Vis Sci.1985; 26: 869–872.
    1. Guell JL, Verdaguer P, Mateu-Figueras G, Elies D, Gris O, El HM, et al. smile procedures with four different cap thicknesses for the correction of myopia and myopic astigmatism. J Refract Surg.2015; 31: 580–585. 10.3928/1081597X-20150820-02
    1. Ganesh S, Patel U, Brar S. posterior corneal curvature changes following refractive small incision lenticule extraction. Clin Ophthalmol.2015; 9: 1359–1364. 10.2147/OPTH.S84354
    1. Ciolino JB, Belin MW. changes in the posterior cornea after laser in situ keratomileusis and photorefractive keratectomy. J Cataract Refract Surg.2006; 32: 1426–1431.
    1. Wang Z, Chen J, Yang B. posterior corneal surface topographic changes after laser in situ keratomileusis are related to residual corneal bed thickness. Ophthalmology.1999; 106: 406–410.
    1. Zhang H, Wang Y, Xie S, Wu D, Wu W, Xu L. short-term and long-term effects of small incision lenticule extraction (SMILE) on corneal endothelial cells. Cont Lens Anterior Eye.2015; 38: 334–338. 10.1016/j.clae.2015.03.011
    1. Hatami-Marbini H. hydration dependent viscoelastic tensile behavior of cornea. Ann Biomed Eng.2014; 42: 1740–1748. 10.1007/s10439-014-0996-6
    1. Hatami-Marbini H, Etebu E. hydration dependent biomechanical properties of the corneal stroma. Exp Eye Res.2013; 116: 47–54. 10.1016/j.exer.2013.07.016
    1. Seiler T, Matallana M, Sendler S, Bende T. does Bowman's layer determine the biomechanical properties of the cornea? Refract Corneal Surg.1992; 8: 139–142.
    1. Wilson SE, Hong JW. Bowman's layer structure and function: critical or dispensable to corneal function? a hypothesis. Cornea.2000; 19: 417–420.

Source: PubMed

Sponsorzy i współpracownicy

Warunki medyczne

Interwencje lekowe

3
Subskrybuj