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Slide 2 1 In the name of god In the name of god Slide 3 2 Viscoelastics It is better to term them Ophthalmic Viscosurgical Device OVDS Dr.sayyed ezatollah memarzadeh 1388/11/29 Dr.sayyed ezatollah memarzadeh 1388/11/29 Slide 4 3 TERMINOLOGY viscosity? viscosity? It is a measure of resistance of a fluid which is being deformed by either shear stress or tensional stress which depends on concentration, molecular weight, size of molecules It is a measure of resistance of a fluid which is being deformed by either shear stress or tensional stress which depends on concentration, molecular weight, size of molecules Compare honey versus water Compare honey versus water Elasticity? Elasticity? Continuum mechanisms of bodies which deform reversibly under stress Continuum mechanisms of bodies which deform reversibly under stress Slide 5 4 What are viscoelastics? Substances having dual properties Substances having dual properties viscosity of fluid viscosity of fluid elasticity of gel or solid elasticity of gel or solid Slide 6 5 PHYSICAL PROPERTIES Viscoelasticity Viscoelasticity Viscosity Viscosity Pseudoplasticity Pseudoplasticity Surface tension Surface tension Cohesiveness Cohesiveness Dispersivness Dispersivness Slide 7 6 PHYSICAL PROPERTIES Pseudoplasticity? Pseudoplasticity? The ability of a solution to transform under pressure from a gel to a liquid like substance The ability of a solution to transform under pressure from a gel to a liquid like substance Slide 8 7 Slide 9 8 PHYSICAL PROPERTIES Surface tension? Surface tension? It is the coating ability of viscoelastic material. It is the coating ability of viscoelastic material. Lower surface tension provides better coating and low contact angle. Lower surface tension provides better coating and low contact angle. Slide 10 9 Slide 11 10 Slide 12 11 Slide 13 12 PHYSICAL PROPERTIES Cohesiveness? Cohesiveness? It is the ability of viscoelastics to adhere to themselves tightly It is the ability of viscoelastics to adhere to themselves tightly Cohesive viscoelastics generally have high- molecular weights, high surface tension (bad coating ability) and high pseudoplasticity. Cohesive viscoelastics generally have high- molecular weights, high surface tension (bad coating ability) and high pseudoplasticity. Slide 14 13 PHYSICAL PROPERTIES Dispersivness? Dispersivness? It is the ability of a viscoelastics with little ability to adherence It is the ability of a viscoelastics with little ability to adherence Dispersive viscoelastics generally have low molecular weight, low surface tension (good coating ability) Dispersive viscoelastics generally have low molecular weight, low surface tension (good coating ability) Slide 15 14 Slide 16 15 PHYSICAL PROPERTIES Viscosity: makes a material protective and lubricating. makes a material protective and lubricating.Elasticity: provides protection from vibrating instruments and other mechanical impacts. provides protection from vibrating instruments and other mechanical impacts.Pseudoplasticity: allows the material to deform and to safely manipulate tissues. allows the material to deform and to safely manipulate tissues. Optical properties: Transparency (primary prerequisite) Color slightly different from aqueous which helps to distinction. Surface tension: To determine whether it can be use to elevate or to depress the surrounding tissue. Slide 17 16 Ideal chemical properties Easy to inject Easy to inject Non inflammatory Non inflammatory Non pyrogenic Non pyrogenic Non toxic Non toxic Inert Inert Hydrophilic Hydrophilic Cause less raise IOP Cause less raise IOP No particle or clumps No particle or clumps Able to be diluted and not to prevent the movement of metabolites and waste products Able to be diluted and not to prevent the movement of metabolites and waste products Slide 18 17 ROLE OF OVDS To maintain an anatomic space created by surgeon and maintenance of AC To maintain an anatomic space created by surgeon and maintenance of AC Protection of cornea endothelium from mechanical trauma Protection of cornea endothelium from mechanical trauma To enable easy manipulation of tissues in the eye To enable easy manipulation of tissues in the eye To provide coating ability to implant instrument To provide coating ability to implant instrument To prevent the formation of undesirable fibrin coagulum To prevent the formation of undesirable fibrin coagulum Slide 19 18 Slide 20 19 CLASFICATION OF OVDS According to: According to: Zero shear viscosity which is directly proportional to the molecular wt. of substance. Zero shear viscosity which is directly proportional to the molecular wt. of substance. Cohesive strength. Cohesive strength. Slide 21 20 HIGH VISCOSITY-COHESSIVE OVDS 1_ super viscous- cohesive OVDS (zero shear viscosity more than 10,00,000mps) e.g. healon GV I-Visc plus 2_ viscous cohesive OVDS( zero shear viscosity between 100.1000-10,00,000 mps) healon e.g. I-Visc I-Visc amvisc amvisc amvisc plus amvisc plus provisc provisc Slide 22 21 CARACTRISTICS All these products contain Na- hyaluronate All these products contain Na- hyaluronate Used as space tactical tools Used as space tactical tools High cohesiveness results in easy removal as a single mass at the end surgical procedure,thus preventing increase of IOP post op. High cohesiveness results in easy removal as a single mass at the end surgical procedure,thus preventing increase of IOP post op. Slide 23 22 LOWER VISCOSITY DISPERSIVE OVD s 1-medium viscosity dispersive OVDs (zero shear viscosity between 100,00-100,000 mps ) e.g. viscoat e.g. viscoat vitrax vitrax cellugel cellugel ocucoat ocucoat 2- very low viscosity dispersive OVDs e.g. unmodified HPMC agent e.g. unmodified HPMC agent Slide 24 23 Slide 25 24 CARACTRISTICS Most of them are derived from wood pulp Most of them are derived from wood pulp Thy are helpful in compromised endothelial conditions as they are capable of dividing the AC into OVD occupied space and surgical zone in which irrigation and aspiration can be continued as surgical compartilization . Thy are helpful in compromised endothelial conditions as they are capable of dividing the AC into OVD occupied space and surgical zone in which irrigation and aspiration can be continued as surgical compartilization . They are difficult to remove at the end of surgeries because of low cohesion. They are difficult to remove at the end of surgeries because of low cohesion. Slide 26 25 THE VISCOADAPTIVE DEVICE (HEALON-5) The high viscosity cohesive and low viscosity dispersive OVDS all have their own drawbacks. The high viscosity cohesive and low viscosity dispersive OVDS all have their own drawbacks. high viscous cohesive OVDS is a superior spice tactical agent but has poor coatability and,low viscosity dispersive OVDS have good coatability but disperses to small droplet during aspiration so difficult to remove at the end of surgery,traps air bubbles and reduce visibility. They cannot maintain space effectively high viscous cohesive OVDS is a superior spice tactical agent but has poor coatability and,low viscosity dispersive OVDS have good coatability but disperses to small droplet during aspiration so difficult to remove at the end of surgery,traps air bubbles and reduce visibility. They cannot maintain space effectively Slide 27 26 Slide 28 LECTUER 03114476010 392