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In the name of god

In the name of god. Viscoelastics. It is better to term them Ophthalmic Viscosurgical Device OVDS Dr.sayyed ezatollah memarzadeh 1388/11/29 . TERMINOLOGY. viscosity?

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In the name of god

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  1. In the name of god

  2. Viscoelastics It is better to term them Ophthalmic Viscosurgical Device OVDS Dr.sayyed ezatollah memarzadeh 1388/11/29

  3. TERMINOLOGY 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

  4. What are viscoelastics? Substances having dual properties • viscosity of fluid • elasticity of gel or solid

  5. PHYSICAL PROPERTIES • Viscoelasticity • Viscosity • Pseudoplasticity • Surface tension • Cohesiveness • Dispersivness

  6. PHYSICAL PROPERTIES • Pseudoplasticity? The ability of a solution to transform under pressure from a gel to a liquid like substance

  7. PHYSICAL PROPERTIES • Surface tension? It is the coating ability of viscoelastic material. Lower surface tension provides better coating and low contact angle.

  8. PHYSICAL PROPERTIES • Cohesiveness? • 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.

  9. PHYSICAL PROPERTIES • Dispersivness? 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)

  10. PHYSICAL PROPERTIES Viscosity: 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.

  11. Ideal chemical properties • Easy to inject • Non inflammatory • Non pyrogenic • Non toxic • Inert • Hydrophilic • Cause less raise IOP • No particle or clumps • Able to be diluted and not to prevent the movement of metabolites and waste products

  12. ROLE OF OVDS • To maintain an anatomic space created by surgeon and maintenance of AC • Protection of cornea endothelium from mechanical trauma • To enable easy manipulation of tissues in the eye • To provide coating ability to implant instrument • To prevent the formation of undesirable fibrin coagulum

  13. CLASFICATION OF OVDS • According to: • Zero shear viscosity which is directly proportional to the molecular wt. of substance. • Cohesive strength.

  14. 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 amvisc amvisc plus provisc

  15. CARACTRISTICS • All these products contain Na- hyaluronate • 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 .

  16. LOWER VISCOSITY – DISPERSIVE OVD s 1-medium viscosity dispersive OVDs (zero shear viscosity between 100,00-100,000 mps ) e.g. viscoat vitrax cellugel ocucoat 2- very low viscosity dispersive OVDs e.g. unmodified HPMC agent

  17. CARACTRISTICS • 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’. • They are difficult to remove at the end of surgeries because of low cohesion.

  18. THE 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…

  19. ضمن عرض پوزش بدلیل حجم بالای LECTUER ادامه اسلایدها امکان پذیر نمیباشد در صورت نیاز به ادامه لطفا به واحد سمعی و بصری مرکز آموزشی درمانی فیض مراجعه و یا با شماره تلفن 03114476010 داخلی 392تماس حاصل نمائید با تشکر

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