الفهرس 
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Abstract
Corneal refractive surgery is the most performed ophthalmic
procedure in the world. Despite the huge leaps in advancing this
technology to reduce the risks of intraoperative and postoperative
complications, there is still a very small risk to develop sight
threatening complication such as cornea ectasia.
Corneas at risk of ectasia are usually thinner with abnormal
topographies, but some normal thin corneal with normal topographies
have developed ectasia, a distinction sometimes hard to make between
myopia with such corneas and subclinical cases of keratoconus or
forme frust keratoconus.
The Oculus Corvis ST (Oculus Optikgeräte, OCULUS, Wetzlar,
Germany) is a noncontact High-Speed (UHS ST) tonometer,
supported by Scheimpflug Technology, designed to obtain in vivo measurements of corneal biomechanical properties; this device allows
monitoring corneal deformation response to a symmetrically metered
air pulse.
This biomechanical study should not be used as the sole test to
detect the suitability of the eyes for refractive surgery but as an
adjunct to the clinical and topographical test.
This is a small prospective clinical interventional series study
carried out from March 2016 to April 2017 on 50 eyes of 28 patients
were equally divided in to two groups; group I underwent wavefront
optimized LASIK procedure and group II underwent femto SMILE
procedure. We studied corneal biomechanics before and three month
after refractive surgery.
In our study the average of age is 25.31±3.56 ranging (20-38)
years in group I and26.84±3.72 ranging (21-36) years in group II . The
average of treated MRSE was -5.47±1.16 ranging (from -4.0 to -7.75)
diopter in group I, and The average of treated MRSE was -5.52±1.14
ranging (from -4.0 to -8.5) diopter in group II. The average of the preoperative
central cornea thickness was 524.97±16.35 ranging (506-
567) μm in group I,and The average of the pre-operative central
cornea thickness was 531.62±16.22 ranging (513-603) μm in group II
.The average of tissue ablated is 68.5±22.1 ranging (41-89) μm in
group I ,and The average of lenticule thickness is 70.3±19.8 ranging
(52-98) μm in group II. The preoperative values of deformation
amplitude was within normal ranges in all patients.