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Comparing corneal biomechanical properties after flap-based ReLEx FLEX and flap-free ReLEx SMILE by Scheimpflug-based imaging (Corvis ST®): a randomized, paired-eye study

Poster Details

First Author: I.Pedersen DENMARK

Co Author(s):    A. Vestergaard   A. Ivarsen   J. Hjortdal        

Abstract Details


Small Incision Lenticule Extraction (ReLEx smile) is an intrastromal flap-free refractive technique, which may preserve corneal integrity better than flap-based techniques such as femtosecond lamellar extraction (ReLEx flex). With the Corvis ST (Oculus Inc., Germany), it is possible to obtain high-speed Scheimpflug pictures of corneal deformation during a metered collimated air-pulse. By looking at defined lengths and time lapses during deformation, highest concavity, and rebounce, it may be possible to assess corneal biomechanical properties in vivo. The purpose of this study was to compare corneal biomechanical properties after ReLEx flex and ReLEx smile, by analysing parameters available with the Corvis ST.


Department of Ophthalmology, Aarhus University Hospital, Denmark.


The retrospective study included 25 patients treated for moderate to high myopia (-6 to -10 diopters). The patients were randomly selected from a prospective paired-eye study, in which they were randomly treated with ReLEx smile in one eye and ReLEx flex in the other. All eyes were measured with Corvis ST more than 6 months after operation. Only Corvis ST parameters with repeatability coefficients of variation <10% were analyzed. Parameters describing applanation during inward deformation and rebound were: Deflection length at first applanation (A1 deflection length), Time until first applanation (A1 time) and Time until second applanation (A2 Time). Parameters describing highest concavity were: Radius at highest concavity (HC radius), Amplitude at maximum deformation (HC deformation amp.), Deflection length at highest concavity (HC deflection length), and Time until highest concavity (HC time). The intraocular pressure (IOP) and central corneal thickness (CCT) were also obtained with Corvis ST.


Average IOP and CCT were 9.9±2.4 mmHg and 463±64 μm in ReLEx Smile treated eyes, and 9.9±2.3 mmHg and 464±62 μm in ReLEx flex treated eyes. No statistical differences were found in IOP and CCT. Paired t-test revealed no statistically significant differences in A1 Time, A2 Time, A1 deflection length, HC time, HC radius, HC deformation amp, and HC deflection length between eyes treated with ReLEx smile and ReLEx flex (p>0.05).


The minimally invasive ReLEx smile preserves the collagen fibers better than the flap-based ReLEx flex. However, the present paired-eye study showed no significant differences in the corneal biomechanical properties between the flap-free ReLEx smile and the flap-based ReLEx flex as determined with Corvis ST. Thus, the intact anterior stromal cap in ReLEX smile may not contribute to the corneal rigidity as expected. This may be explained by a longer arch length in the superficial cap than in the profound stromal pocket after ReLEx smile. Due to the difference in the arch lengths, the collagen fibrils may have a corrugated arrangement, when the cap is positioned against the stromal bed, and may not contribute to the biomechanical strength of the cornea. FINANCIAL INTEREST: NONE

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