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VISCOELASTIC MATERIALS IN OPHTHALMOLOGYDR OLORUNDARE O.K.25/05/2011OUTLINEIntroductionRheologic characteristicsDesired Properties of an Ideal VEMClassification of VEMViscoelastic components of VEMCommercial VEM preparations Uses of VEMComplicationsConclusion

INTRODUCTIONA group of agents with varying degrees of viscosity and elasticity used during ophthalmic surgery.

Dual PropertiesViscosity of a fluidElasticity of a gel or solid

ViscosurgeryUse of substances with viscous, elastic and pseudoplastic ppties during & after ocular surgery.

INTRODUCTIONConcept for developmentprecision tissue specific action

Also referred to as OVDsOphthalmic Viscosurgical Device

RHEOLOGIC CHARACTERISTICSRelevant rheologic characteristics of OVDsViscosityElasticitySurface tensionPseudoplasticity

RHEOLOGIC CHARACTERISTICSViscosityIs the measure of resistance to flow, (a function of the molecular weight of the substance.)

Also dependent on the rate of flow, which is also known as the shear rate, varies inversely with temperature.

The viscosity of a solution can be increased by increasing either the concentration or the molecular weight of the solution.

RHEOLOGIC CHARACTERISTICSElasticity

the ability of a solution to return to its original shape after being stressed.

The amount of elasticity increases with increasing M.W. and greater chain length of the molecules

RHEOLOGIC CHARACTERISTICSPseudoplasticity ability to transform when under pressure, from a gel-like substance to a more liquid substance.

The more pseudoplastic a material is, the more rapidly it changes from being highly viscous at rest to a thin, watery solution at high shear rates.

RHEOLOGIC CHARACTERISTICSSurface Tension Determines the coating ability of the VEM

can be estimated by measuring the angle formed by a drop of the VEM on a flat surface

Lower surface tension and lower contact angle indicate a better ability to coat.

Desired Properties of an Ideal VEMSterileNon inflammatoryElectrolyte balancedWater solubleNon toxicNon immunogenicPH bufferedHighly purifiedNon pyrogenicOptically clearCoats tissues and instruments

Easy to instillEasy to removeInertLong shelf lifeParticle freeDoes not obstruct aqueous outflow Retention under positive pressure in the eye Does not interfere with instruments or IOL placement

10Classification of VEMsAccording toZero shear viscosity, directly proportional to the m.w.Cohesive strength

Viscocohesive VEMsViscodispersive VEMsViscoadaptive VEMs

11Classification of VEMsCohesive VEMs have high viscosity, high molecular weight, high pseudoplasticity, and high surface tension. are better for manipulation of tissue and space maintenanceare easily removedhave poor coating ability

12Classification of VEMsViscodispersive VEMs have lower viscosity, lower molecular weight, lower surface tension, and lower pseudoplasticityare better for coating surfaceshave poor space maintenance abilityare not easy to remove

13Classification of VEMsViscodispersive VEMs Have both cohesive and dispersive properties depending on the degree of turbulence present

At low shear rates, are extremely viscous and cohesive, but at midrange flow rates they fracture, manifesting dispersive behavior

14Viscoelastic components of VEMsSodium Hyaluronate: high molecular weight biopolymer occurring in many connective tissues throughout the bodyManufactured from rooster combs, bovine vitreous, umbilical cordMost elastic, viscous,& pseudoplasticT1/2 1 day in aqueous, 3 days in vitreousDisadvantages- High cost, requires refrigeration, not autoclavable, poor coating ability

15Viscoelastic components of VEMsChondroitin Sulfate: medium molecular weight biopolymer, mainly found in extracellular matrix of connective tissue e.g corneaManufactured from Shark fin cartilageHas good coating ability, little/ no IOP elevation post operativelyPoor space maintenance

16Viscoelastic components of VEMsHydroxypropyl Methylcellulose (HPMC): cellulose polymer composed of D-glucose molecules linked together by -glycosidic bonds, occurs in plants not animalsMade from cotton and wood pulpLow cost, autoclavable, Easy storage at room temperature, good coating abilityNot metabolized intraocularly, easily irrigatedPoor space maintenance

17Viscoelastic components of VEMsPolyacrylamideSynthetically produced polymer similar to hyaluronateIt is a linear long chain molecule, non toxic, requires no refrigeration and is inert inside the eyeRapidly cleared from the AC and because of its stability does not degrade

18COMMERCIAL VEM PREPARATIONS Healon, Healon GV, Healon 5Amvisc, Amvisc PlusAMOVitraxProViscViscoatOcucoatCellugel

Hymecel Adatocel Visilon Ocuvis MicroViscOphthalin, Ophthalin Plus

USES OF VEMsCataract SurgeryProtection of corneal endotheliumControl of capillary oozingIn maintenance of ACIn capsulorrhexisIn viscoexpression of lens nucleus CCCIn capsular bag filling and IOL implantationProtect tissues from vibration & turbulenceSeal small PC rent

USES OF VEMsGlaucoma SurgeryIn Viscocanalostomy

KeratoplastyProtect corneal endothelium when removing corneal button in donor eyeProvides an even and circular trephinationViscodelamination of cornea in lamellar keratoplasty

USES OF VEMsRetinal detachment SurgeryAs vitreous substitutes (help in pushing retina towards the choroid)In dissection of epiretinal membrane (releasing tractional bands)Achieving hemostasisRepositioning detached retina

USES OF VEMsIn Traumatic casesTo separate salvageable tissue from damaged tissuesTo restore collapsed globe in posterior segment traumaMiscellaneousIn refractory dry eye syndromeViscoanaesthesia

COMPLICATIONS Iris prolapse if injected in retroirideal areaBlockage of orifices preventing rapid wound closureHampered movement of drugsIOP elevation post operatively 6 24hrs post-op resolves in 72hrCrystallization on lens surfacePseudoanterior uveitisCalcific band keratopathy as occurred as a complication to Chondroitin sulphate.

CONCLUSION No single VEM is ideal under all circumstances

The Choice of a viscoelastic substance depends largely on the intended surgical use.

The physicochemical ppties, desirable & undesirable clinical effects must be considered when choosing.

Ophthalmologic surgeons should keep up with recent developments of OVDs and relevant surgical techniques for better patient care.

SUTURE MATERIALS IN OPHTHALMOLOGY OUTLINEDEFINITIONCRITERIA FOR AN IDEAL SUTURECLASSIFICATION OF SUTURESSUTURE NEEDLES CONCLUSION

DefinitionSuture is a strand of material that is used to

approximate and maintain separated tissue until the natural healing process occurs or

ligate blood vessels to secure haemostasis

Criteria for an ideal sutureeasy to handle and knot minimal tissue reaction does not support bacterial growth high tensile strengthno allergic reactionno carcinogenic action absorbed after serving its functioneasy sterilization inexpensive

CLASSIFICATION OF SUTURESSutures are classified according to their degradation propertiesABSORBABLE undergo rapid degradation in tissues, losing their tensile strength within 60 days.

NON ABSORBABLEthat generally maintain their tensile strength for longer than 60 daysCLASSIFICATION OF SUTURESABSORBABLE

Natural absorbable sutures are digested by body enzymes which attack and break down the suture strand

Synthetic absorbable sutures are hydrolyzed

hydrolyzation results in a lesser degree of tissue reaction following implantation.

CLASSIFICATION OF SUTURESNON ABSORBABLEnot digested by body enzymes or hydrolyzed in body tissue.

Made from a variety of non biodegradable materials

encapsulated or walled off by the bodys fibroblasts.

Remain where they are buried within the tissues.

When used for skin closure, they must be removed postoperatively.

ABSORBABLE NATURAL SUTURES CATGUT

Serosal layer of intestine of cattle or submucosa of sheep. Tanned with chromic salt to delay absorption - brown gamma radiation or ethylene oxide proteolytic enzymatic digestion.Plain catgut retains its tensile strength for about a week. absorption rate is about 10-15 days. Chromic 17-21days , 30days. handling of the material is excellent, doesnt snag, Laying of knots is accurate .Marked tissue reaction

USES Conjunctival closure

ABSORBABLE NATURAL SUTURES COLLAGEN SUTURES From Achilles tendons of cattle. more consistent in smoothness and strength than catgut, Easy to tie,Less tissue reaction than catgut Loses strength like catgut

USESConjunctival closure

ABSORBABLE SYNTHETIC SUTURES POLY GLACTIN 910 (VICRYL)copolymer of glycolic and lactic acid in the ratio 90/10.

Coated-vicryl is a multifilament polyglactin 910 coated with polyglactin 370 and calcium stearate

Makes the surface smoother and reduces tissue drag, improves knotting and handling characteristic.

High tensile strength, Secure knotting, Soft and pliable, Easy to handle, mild tissue reaction. Retains tensile strength for 2-3wks and total absorption in 60-90days.

ABSORBABLE SYNTHETIC SUTURES POLY GLACTIN 910 (VICRYL)Monocryl (Polyglecapone 25) which is monofilament vicryl is absorbed in 20 days.

USESstrabismus surgery (6/0)Oculoplastic surgery (6/0)Trabeculectomy (8/0)Conjunctival closure (8/0)Sclerotomy closure (7/0)

ABSORBABLE SYNTHETIC SUTURES POLYGLYCOLIC ACID (PGA) SUTURES (DEXON)A synthetic absorbable suture produced by the polymerization of glycolide to polyglycolic acid.

Dexon S - braided PGA without coatingDexon plus treated with surface lubricant Poloxamer 188

Absorption is by hydrolysis .Total absorption occur at 60-90 days post op.

Minimal tissue reaction (no protein),to knot securely requires 3 throws.

ABSORBABLE SYNTHETIC SUTURES Has high tensile strengthKnot slippage is rarechronic suture infections.Tissue drag Sterilization with Ethylene oxide

uses strabismus surgery Eyelid surgeries (6/0)

NON-ABSORBABLE NATURAL SUTURESBRAIDED SILK/MERSILKraw silk thread spun by larva of the silk wormIt behaves as a very slow absorbable suture.Knots welldyed black for easy visibility in tissues Sterilization is by gamma radiation.

USES Superior rectus bridle during cataract surgeryTraction sutures/eyelid retractionTemporary traction purposes on Extraocular muscles (8/0)

NON-ABSORBABLE NATURAL SUTURESTWISTED VIRGIN SILK (ETHICON)Excellent handling property, Knot security and knots well.Moderate tissue reaction, tensile strength lasts 3-6mths, inelastic, suture ends are soft and well tolerated.

USESFor limbal wound closure as in cataract surgery (8/0)Trabeculectomy (9-0 or 8-0)Conjunctival closureSkin incisions (7/0)

NON-ABSORBABLE NATURAL SUTURESCOTTONNatural origin, manufactured by twisting the seed hairs of long fibre cotton.

Properties are similar to that of silk though ranked as a weak suture, gains strength when wet.

NON-ABSORBABLE SYNTHETIC SUTURESPOLYAMIDES/NYLON (ETHILON)Nylons are polyamide polymer derived by chemical synthesis.monofilament and multifilament formsMultifilament nylon (Nurolon) More tissue reaction, Good knot security, black. Absorption: Its degraded and absorbed in about 2 years.Characteristic:- (monofilament)

NON-ABSORBABLE SYNTHETIC SUTURESPOLYAMIDES/NYLON (ETHILON)Poor knot security due to a low coefficient of friction, stiff suture ends which must be buried to avoid irritation.Sterilization of nylon sutures is by gamma irradiation.

USES Corneal wound closure (suture of choice in cataract surgery)Corneal graftingOculoplastic surgeryNON-ABSORBABLE SYNTHETIC SUTURESPOLYESTER (DACRON)Are polymer of terephthalic acid and glycolethylene. Have superior strength and durability.Very little inflammatory reaction, Elastic and unaffected by tissue fluids. Colour in Blue or undyed

USESCataract surgerycorneal graftingintraocular suturingRetinal surgery

NON-ABSORBABLE SYNTHETIC SUTURESPOLYPROPYLENE (PROLENE) Provide smooth passage through tissue with minimal tissue reaction, Very high tensile strength Inert suture and infected wound could heal in its presence, Handles comfortably. Soft and pliable, The elastic nature of the material locks knot securityNON-ABSORBABLE SYNTHETIC SUTURESPOLYPROPYLENE (PROLENE) Colour code: Blue or clearSterilization: - By ethylene oxide/autoclaving

USES Cataract surgeryCorneal graftingIris repairIntraocular lens fixationOculoplastic surgery

NON-ABSORBABLE SYNTHETIC SUTURESMETALLIC SUTURES:Its an alloy of steel with molybdenum, chromium and nickel. usually monofilament, They are used with sophisticated applicators and stapling guns.Characteristics:-Monofilament steel is extremely strong, Inert, high knot security Limitation:-Metal fatigue may occasionally occur fracture.Sterilization is by autoclaving

Ideal ophthalmic suture needlesenough rigidity to prevent easy bending sufficient length sufficient diameter to create a tract for the suture knot to be buried as atraumatic as possible

Suture needles All needles are made of stainless steelthe suture is swedged or glued onto the needle

A suture needle has 5 geometries Length - distance of the circumference from the swage to the pointChord length - distance of the straight line from the swage to the point (which determines the width of the bite) Radius- length of the line from the center of the circle Needle diameter - measured in mils (1/1000 of an inch) and 1 mil is about 25 um ,a smaller diameter needle required less force and cause less trauma during passage through the tissue Bicurve - two radii on a needle, the radius near the point is usually shorter than the radius of the body near the swage

SELECTION OF SUTURE MATERIALS/NEEDLESDepends on: composition and properties of the Suture material, task ahead, surgeons choice, Diameter of the suture material, Effect of inserting the suture into the tissue

Surgical needles are composed of 3 anatomic parts;The Swage the thickest portion of the needle and the portion to which the suture material is attachedBodythe mid portion of the needle.Point: cutting or reverse cuttingthe sharpest portion and is used to penetrate the tissueTypes of needlesGrouped into four main types according to the point configuration (i.e.. the shape of the point): cutting reverse cutting taper point spatulaTypes of needlesCUTTING triangularcuts at tips and edgesof the needlemay pull out tissue during needle passage

Types of needlesREVERSE CUTTINGtriangular with cutting edge at the bottom cuts at tips and edges of needle ideal for oculoplasticsurgery as the needle allows easy passage through epidermis accidental perforationmay occur with partialthickness suture suchas rectus scleral fixation

Types of needlesTAPER POINTround and taper toa point, cuts at the tip only atraumatic, produces the smallest hole of all needles, useful in iris repair

Types of needlesSPATULA4 or 6 sided with cutting edges on theside cuts at tip and sides parallel to the tissue plane allows needle to splitthe tissue plane andavoid accidental perforation most commonly usedneedle for anterior segment surgery.

CONCLUSION