UPDATES IN CORNEAL BIOMECHANICAL PROPERTIES
Mohamed Hamdy Mohamed Fathy Silem;
Abstract
SUMMARY
T
he cornea is the transparent membrane covering the front of the eye.It is a powerful refracting surface, providing 2/3 of the eye's focusing power. The adult cornea is only about 1/2 millimeter thick and is comprised of 5 layers:epithelium, Bowman's membrane, stroma, Descemet's membrane and the endothelium.
The individual variation in the corneal rigidity has been suggested to be related to the physical dimensions of the tissue especially its thickness. Thus, central corneal thickness could be regarded as an indirect measurement of corneal rigidity. Other biomechanical parameters such as elasticity or viscoelastic properties may also influencethe corneal resistance.
Corneal hysteresis is considered an indicator of the visco-elastic properties of the cornea, i.e. the ability of the tissue to absorb and dissipate energy. It is suggested that subjects whose corneas exhibit low corneal hysteresis (soft cornea), are probable candidates for a variety of ocular diseases and complications. Corneal resistant factor is a measurement of the cumulative effects of both the viscous and elastic resistance encountered by the air jet while deforming the corneal surface. The recently developed Ocular Response Analyzer proposes to measure corneal biomechanical properties in vivo.
Potential clinical applications of the corneal hysteresis and corneal resistant factor measurements in the area of refractive surgery are obvious.central corneal thickness is a primary factor used for screening candidates for refractive surgery. Patients with thinner corneas are considered to be at higher risk of developing post-LASIK corneal ectasia.
The easily identifiable differences in corneal hysteresis and corneal resistant factor between normal and compromised corneas suggest how these metrics provide a more complete characterization of the biomechanical state of the cornea than central corneal thickness. This observation, coupled with the fact that corneal hysteresis and corneal resistant factor areonly weakly correlated with central corneal thickness, leads us to believe that the corneal hysteresis measurement will be a useful tool for laminating potential LASIK patients who are at risk of developing post-LASIK ectasia. They also have potential uses in post-LASIK follow up.
Clinical data from several studies show a universal reduction in post-LASIK corneal hystersis and corneal resistant factor. Some experts hypothesize that reduced post-LASIK corneal hysteresis/corneal resistant factor is not primarily a function of corneal thinning, but rather a result of weakening of the structure related to the creation of the flap and laser ablation, which change the visco-elastic characteristics of the cornea.
T
he cornea is the transparent membrane covering the front of the eye.It is a powerful refracting surface, providing 2/3 of the eye's focusing power. The adult cornea is only about 1/2 millimeter thick and is comprised of 5 layers:epithelium, Bowman's membrane, stroma, Descemet's membrane and the endothelium.
The individual variation in the corneal rigidity has been suggested to be related to the physical dimensions of the tissue especially its thickness. Thus, central corneal thickness could be regarded as an indirect measurement of corneal rigidity. Other biomechanical parameters such as elasticity or viscoelastic properties may also influencethe corneal resistance.
Corneal hysteresis is considered an indicator of the visco-elastic properties of the cornea, i.e. the ability of the tissue to absorb and dissipate energy. It is suggested that subjects whose corneas exhibit low corneal hysteresis (soft cornea), are probable candidates for a variety of ocular diseases and complications. Corneal resistant factor is a measurement of the cumulative effects of both the viscous and elastic resistance encountered by the air jet while deforming the corneal surface. The recently developed Ocular Response Analyzer proposes to measure corneal biomechanical properties in vivo.
Potential clinical applications of the corneal hysteresis and corneal resistant factor measurements in the area of refractive surgery are obvious.central corneal thickness is a primary factor used for screening candidates for refractive surgery. Patients with thinner corneas are considered to be at higher risk of developing post-LASIK corneal ectasia.
The easily identifiable differences in corneal hysteresis and corneal resistant factor between normal and compromised corneas suggest how these metrics provide a more complete characterization of the biomechanical state of the cornea than central corneal thickness. This observation, coupled with the fact that corneal hysteresis and corneal resistant factor areonly weakly correlated with central corneal thickness, leads us to believe that the corneal hysteresis measurement will be a useful tool for laminating potential LASIK patients who are at risk of developing post-LASIK ectasia. They also have potential uses in post-LASIK follow up.
Clinical data from several studies show a universal reduction in post-LASIK corneal hystersis and corneal resistant factor. Some experts hypothesize that reduced post-LASIK corneal hysteresis/corneal resistant factor is not primarily a function of corneal thinning, but rather a result of weakening of the structure related to the creation of the flap and laser ablation, which change the visco-elastic characteristics of the cornea.
Other data
| Title | UPDATES IN CORNEAL BIOMECHANICAL PROPERTIES | Other Titles | الجديد فى الخصائص البيوميكانيكية للقرنية | Authors | Mohamed Hamdy Mohamed Fathy Silem | Issue Date | 2017 |
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