Review On Corneal Hysteresis Ande Its Changes Following Lasik Surgery:

Ayman Hagag Abd-elbaky Elnajar

Corneal hysteresis is an importanrt indication of the biomechanical properties of the cornea it is an indicator of viscous damping in the cornea during inward and outward applanation pressure events that is determind by the visco-elastic properties of the corneo-scleral shell corneal hysteresis is the difference between the inward and outward applanation pressure.The ora is anew device which is a non-contact tonometer that measures iop as well as new metrics ;hysteresis and corneal resistance factor crf in which apatented dynamic bi-directional applanation process enables measurement of corneal biomechanical properties using an traditional air puff tonometers generates force/pressure on the cornea it also provides apressure measurement that is significantly less affected by the cornea thn other methods of tonometry.Some factors also play arole in ch value ch in normal eyes was higher than in patients with ocular disease such as keratoconus and fuchs corneal dystrophy also ch values related to the severity of the disease as it is decreasing with ocular disease such as keratoconus and fuchs corneal dystrophy also ch value related to the severity of the fuchs as it is decreasing with the severity of the disease aging process lowers ch it higher the ch in glaucoma patients ch is significantly lower than average with amuch wider range when compared to normal subjects with the ever increasing popularity of refractive surgery the knowledge of the factors that determine the biomechanical properties of the eye and their importance in the management of disease process has gained importance better understanding of corneal biomechanics might allow for improved predictability of refractive surgery outcomes anmd may also improve the preoperative identification of eyes at risk of developing ectasia after refractive surgery.