Purchase this article with an account.
Iben Bach Pedersen, Sashia Bak-Nielsen, Anders Ivarsen, Jesper Hjortdal; Comparing the Corneal Biomechanical Stability after LASIK, ReLEx FLEx and ReLEx SMILE with Ultra High Speed Camera (Corvis® ST). Invest. Ophthalmol. Vis. Sci. 2013;54(15):3136.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Laser refractive surgery involves removal of corneal tissue. Modern flap-free laser treatments of the cornea (SMILE) may weaken the cornea to a lesser extent than flap based treatments (FLEx and LASIK). With the new device, Corvis ST from Oculus, it is possible to measure high-speed pictures of the corneal deformation during an air-pulse. With the deformation amplitude (DA) and the deformation radius (DR) at highest concavity, changes in the corneal rigidity after laser refractive surgery may be compared.
Patients treated for high myopia (-9,5 to -4,5 D) more than one year ago were invited for a follow up examination. Eighty-seven patients operated on both eyes participated, and were divided into 3 refractive groups: Laser-Assisted In Situ Keratomileusis, LASIK (30 patients) Femtosecond Lenticule Extraction, ReLEx-FLEx (30 patients) Small Incision Lenticule Extraction, ReLEx-SMILE (27 patients) The average uncorrected visual acuity, best corrected visual acuity and IOP was similar in all refractive groups. With Corvis ST, the central corneal thickness (CCT), DA and DR was measured, and corneal corrected IOP (IOPcc) was measured with the Ocular Response Analyser. Furthermore 30 healthy persons between 20-30 years were measured as a control group.
There were no significant differences in IOPcc between the 4 groups. As DA and DR correlated linearly with CCT, DA and DR were adjusted to a corneal thickness of 476 µm in all groups. DR in all refractive groups was significantly lower than the control group, but no significant differences were found between the refractive groups (Table 1). LASIK had a significantly lower DA, when compared with SMILE and the control group. There was no significant difference in DA between SMILE and the control group (Table 2).
The low DR in all refractive groups indicates that laser refractive surgery results in higher corneal elasticity despite adjusting for differences in CCT. The significantly lower DA in LASIK could be a result of stress-stiffening appearing in untouched collagens. As more collagens are left untouched after flap-free laser treatments (SMILE), the stress on each collagen fiber becomes less. A DA more similar to the control group may support, that SMILE is a more biomechanically neutral corneal laser refractive procedure.
This PDF is available to Subscribers Only