الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Serious corneal conditions including ulcers or perforations commonly result in challenging clinical scenarios with rapid subsequent vision loss and ocular globe disintegration. It is still possible for severe corneal infections, traumas, or systemic disorders to result in corneal perforations, which frequently need surgical repair despite current improvements in pharmaceutical and surgical treatment. In a procedure known as penetrating keratoplasty (PKP), which is also known as a corneal transplant or corneal graft, a damaged or diseased area of the cornea is surgically removed, and healthy tissue from a donated human cornea typically obtained from an eye bank is then implanted in its place. The cornea is viscoelastic, that means it achieves both viscous and elastic properties while being deformed. Two devices available to measure the biomechanical propotions of the cornea in vivo, and both machines use non contact air pulse- based tonometry; the Ocular Response Analyzern (ORA; Reichert Ophthalmic Instruments, Depew, NY, USA, 2004) and the Oculus Corvis ST; (CST; Oculus Optik-gerate, Inc., Wetzlar, Germany, 2010). Here, corneal biomechanical properties are assessed by a rapid air pulse which deforms the cornea in and outwards, while corneal deformation is registered by an electro – optical system (ORA) and also with Scheimpflug imaging (CST). The ORA estimates several parameters among which corneal hysteresis (CH) and a corneal resistant factor (CRF) are the most prevelant parameters reported when describing corneal viscoelastic properties. CORVIS ST Scheimpflug analyzer obtains parameters in 3 stages during the air puff step , first the air puff starts , and the cornea is flattened in the center This corresponds to the first applanation during the inward stage of the air puff . Then the pressure continues up to the peak pressure at which the highest concavity is achieved . Finally , the air-puff pressure decreases , and the cornea returns to the baseline state, achieving the second applanation just before the cornea’s recovery to its original shape. The latest dynamic corneal response parameters, available in the updated version of the Corvis ST tonometer software are: 1. Biomechanichally corrected intra ocular pressure (IOPb) value is aparameter independent of CCT and age. 2. The Corvis biomechanichal index is available in the Vincigurra Screening Report as an indicator of analyzed dynamic corneal response parameter (deformation amplitude ratio, stiffness parameters A1, integrated inverse radius and ARTH). Our study included 30 eyes of patients had penetrating keratoplasty (PKP), Patients were evaluated preoperatively; this included history taking, slit lamp examination, fundus examination and intraocular pressure, uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), cycloplegic refraction. The Corvis ST (CST) was done to assess the corneal biomechanics. Patients were evaluated before removal of the corneal suture after PKP operation at least after 6 months of the operation and after 3 months of removal of the corneal sutures. Patients were evaluated using CORVIS-ST. Our study included 30 patients 19 males (63.6%) and 11 females (36.7%) with average age 32.07 ± 10.6 years. Difference from before removal of the corneal sutures (at least after 6 months of PKP operation) and after 3 months of removal of the corneal sutures was: Significant reduction of CCT (p<0.001*), peak distance (p<0.001*), deformation amplitude (p<0.001*), deformation amplitude ratio (p<0.001*) , integrated concave radius (integ. Radius) (p<0.001*), ARTH (p<0.001*) Insignificant reduction of A1 applanation (P=0.872), A1velocity (p=0.463), A2 applanation (P=0.710), A2 velocity (P=0.602). Significant increase of the radius of curvature (p<0.001*), stiffness parameters at A1 (SPA1) (p<0.001*), Corvis biomechanical index (CBI) (p=0.007*). Insignificant increase in IOPb (P=0.650).