In the name of god

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In the name of god

2ViscoelasticsIt is better to term them Ophthalmic Viscosurgical Device OVDS

Dr.sayyed ezatollah memarzadeh 1388/11/29

3TERMINOLOGY 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 Compare honey versus water Elasticity?Continuum mechanisms of bodies which deform reversibly under stress

4What are viscoelastics? Substances having dual properties

viscosity of fluid

elasticity of gel or solid

5PHYSICAL PROPERTIESViscoelasticityViscosity PseudoplasticitySurface tensionCohesivenessDispersivness

6PHYSICAL PROPERTIESPseudoplasticity?

The ability of a solution to transform under pressure from a gel to a liquid like substance

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8PHYSICAL PROPERTIESSurface tension? It is the coating ability of viscoelastic material. Lower surface tension provides better coating and low contact angle.

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12PHYSICAL PROPERTIESCohesiveness?It is the ability of viscoelastics to adhere to themselves tightlyCohesive viscoelastics generally have high-molecular weights, high surface tension (bad coating ability) and high pseudoplasticity.

13PHYSICAL PROPERTIESDispersivness? 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)

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15PHYSICAL PROPERTIESViscosity: makes a material protective and lubricating.

Elasticity: provides protection from vibrating instruments and other mechanical impacts.

Pseudoplasticity: 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.

16Ideal chemical propertiesEasy to injectNon inflammatoryNon pyrogenicNon toxicInertHydrophilicCause less raise IOPNo particle or clumpsAble to be diluted and not to prevent the movement of metabolites and waste products

17ROLE OF OVDSTo maintain an anatomic space created by surgeon and maintenance of ACProtection of cornea endothelium from mechanical traumaTo enable easy manipulation of tissues in the eyeTo provide coating ability to implant instrument To prevent the formation of undesirable fibrin coagulum

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19CLASFICATION OF OVDSAccording to:Zero shear viscosity which is directly proportional to the molecular wt. of substance. Cohesive strength.

20HIGH VISCOSITY-COHESSIVE OVDS1_ 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 amvisc amvisc plus provisc

21CARACTRISTICSAll these products contain Na- hyaluronateUsed as space tactical toolsHigh cohesiveness results in easy removal as a single mass at the end surgical procedure ,thus preventing increase of IOP post op .

22LOWER VISCOSITY DISPERSIVE OVD s 1-medium viscosity dispersive OVDs (zero shear viscosity between 100,00-100,000 mps ) e.g. viscoat vitrax cellugel ocucoat2- very low viscosity dispersive OVDs e.g. unmodified HPMC agent

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24CARACTRISTICSMost of them are derived from wood pulpThy 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.

25THE VISCOADAPTIVE DEVICE (HEALON-5)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

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