OPHTHALMIC VISCOSURGICAL DEVICES

SIVATEJA CHALLA

INTRODUCTIONSubstances having dual properties

1.Viscocity of fluid

2.Elasticity of gel or solid

HISTORY• Viscosurgery was a term coined by Balazs

• Sodium Hyaluronate was 1st used in ophthalmic surgery as viscoelastic in 1972 as a replacement for vitreous & aqueous humor

IDEAL VISCOELASTIC• Ease of infusion

• Retention under +ve pressure in eye

• Retention during phaco

• Easy removal/no removal needed

• Doesnt interfere with instruments/IOL placement

• Protects endothelium

• Nontoxic

• Does not obstruct aq.outflow

PROPERTIES

viscoelasticity

viscosityPseudo

plasticitysurface tension

RHEOLOGICAL PROPERTIES

VISCOELASTICITY

• Elasticity refers to the ability of a solution to return to its original shape after being stressed

• Elasticity allows the anterior chamber to reform after deformation by depression on the cornea when external forces are released.

VISCOSITY

• Viscosity  reflects a solution's resistance to flow,

• A function of the molecular weight of the substance.

• Viscosity of OVDs is measured in centipoise (cPs) or centistokes (cSt), which are measures of the resistance to flow relative to a given shear force.

• The higher the solution's molecular weight, the more it resists flow

PSEUDOPLASTICITY

• Pseudoplasticity refers to a solution's ability to transform when under pressure, from a gel-like substance to a more liquid substance

• 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.

SURFACE TENSION

- The coating ability of an OVD is determined not only by the surface tension of material itself but also by the surface tension of the contact tissue, surgical instrument or IOL.

- By measuring the angle formed by a drop of OVD on a flat surface (contact angle),the coating ability is estimated.

- At lower surface tension & lower contact angle, better ability to coat.

COMPOSITION

Viscoelastics

Sodium Hyaluron

ateChondroitin Sulfate HPMC

SODIUM HYALURONATE• Biopolymer, disaccharide

• occurring in many connective tissues throughout the body, including both the aqueous and vitreous humors

•  Hyaluronate has a half-life of approximately 1 day in aqueous and 3 days in vitreous.

• Mainly present in visco cohesives

CHONDROITIN SULFATE

• Chondroitin sulfate (CDS) is another viscoelastic biopolymer that is found as one of the three major mucopolysaccharides in the cornea.

• Obtained from shark fin cartilage

• Eliminated from the anterior chamber in approximately 24 to 30 hours

• Coats tissues but poor space maintainer

HYDROXYPROPYL METHYL CELLULOSE

• Does not occur naturally in animals but is distributed widely in plant fibers

• Easy availability• Ease of preparation• Storage at room temperature• Ability to with stand autoclaving• Main component in dispersives

HYALURONATE PRODUCTS

Healon, Healon5, Healon GV, Healon D

Amvisc, Amvisc plus, Provisc

HA+CS PRODUCTS

Viscoat, Discovisc

HPMC PRODUCTS

Occucoat, Cellugel

CLASSIFICATION OF OVDS

High viscosity-cohesive OVDs

Lower viscosity-dispersive OVDs

Viscoadaptive OVDs

1

2

3

COHESIVES VS DISPERSIVES COHESIVES DISPERSIVES

High viscocity Low viscocity

Low mol wt High mol wt

Long chain molecules Short chain molecules

Adhere to themselves through intramolecular bonds, resists breaking apart.

They adhere well to external surfaces, e.g., tissues and instruments.These materials tend to break apart easily

High degree of pseudoplasticity and high surface tension

Lower surface tension and lower pseudoplasticity

COHESIVE DISPERSIVE

HIGH VISCOSITY--COHESIVES

SUPER VISCOUS VISCOUS1.Healon GV(1.4%)2.Ivisc plus 1.Ivisc

2.Provisc3.Healon(1%)4.Amvisc

• All products contain Na.hyaluronate

• Indications of highviscous cohesive OVD-

-To deepen the AC

-To enlarge small pupils

-to dissect adhesions

-during IOL implantation

ADVANTAGES

1.Maintain space at low shear rates

2.Easily displaced at high shear rates

3.Sticks together,aspirated out easily

4.Low risk of post op IOP rise even if retained

DISADVANTAGES

1.Minimal coating,so less endothelial protection

LOWER VISCOSITY-- DISPERSIVES

MEDIUM VISCOCITY VERY LOW VISCOCITY

1.Viscoat2.Vitrax3.Cellugel4.Biovisc

1.Occucoat2.Ocuvis3.I-cell4.Hymecel5.Viscilon

Most of them are Hydroxypropyl methyl cellulose

ADVANTAGES

1.Excellent coating and gives superior endothelial protecton

DISADVANTAGES

1. Complete removal of dispersive OVDs is difficult because the molecules do not tend to join together and do not aspirate as a unit,

2. Do not maintain or stabilise spaces

3. Can form microbubbles and obscure view

4. High risk of post op IOP rise

VISCOADAPTIVES• Behaviour changes at different flow rates

• Acts as a viscous cohesive agent at lower flow rate & as a pseudo-dispersive agent at higher flow rates

• Adapts its behaviour to surgeon’s needs during surgery

• Highly purified non inflammatory high mol.wt. Na Hyaluronate at a 2.3% conc. dissolved in a physiological buffer

• Example HEALON 5

ADVANTAGES

• 1. Crystal clear & has higher refractive index than aq.humor, so increases clarity within surgical field.

• Ability to bind to & to protect delicate corneal endoth. cells from debris & turbulence during phaco

• Helpful in small pupil as it causes viscomydriasis

• Neutralises the +ve vitreous pressure & prevents the capsulorrhexis extension

DISADVANTAGES

1.Risk of post op IOP rise if retained

CLINICAL USES

Cataract surgery

• Protection of endothelium

• Maintaining of AC

• CAPSULAR RHEXXIS

• Cleavage of lens structure

• Visco ecpression of lens

• Phacoemulsification of nucleus

• IOL implantation

• dilate the pupil & maintain a good intraoperative mydriasis

SOFT SHELL TECHNIQUE• Developed by Arshinoff

• Use of both lower viscosity dispersive & high viscosity cohesive OVDs together to minimise their drawbacks & to get best properties of both

SOFT SHELL TECHNIQUE

ULTIMATE SOFT SHELL TECHNIQUE

USES• Floppy iris syndrome,the soft-shell technique can

hold the iris in place throughout the surgery.

• cases of broken zonules, the dispersive OVD can compartmentalize the eye and keep vitreous pushed posteriorly, while the cohesive OVD keeps the anterior chamber formed and pressurized.

• highly myopic eyes, dispersive OVDs protect the cornea, while re-application of cohesive OVDs to pressurize the anterior segment can minimize traction on the vitreous base and decrease retinal risk

GLAUCOMA SURGERY

Visco-canalostomy

• Means opening of schlemm’s canal by OVD

• A Nonpenetrating procedure ,independent of external filtration

• Advantages-decrease risk of infection,

-decrease incidence of cataract

-hypotony

-flat AC

-Excludes risk of late infection & conjunctival & episcleral scarring

• Healon GV and healon5 are used

KERATOPLASTY

• Used to fill the AC before removing corneal button from donor eyes as it helps to protect corneal endothelium and provides an even and circular trephination

• In recipients eyes helps to have even and circular trephination,protects other intraocular structures maintains IOP and prevents sudden collapse of AC during trephination

• In lamellar keratoplasty helps in the dissection of deep stroma during dissection of recipients stroma,called viscodelamination of cornea

POSTERIOR SEGMENT SURGERIES

• In strabismus sx Force required to bring the muscle to its insertion is significantly less with the use of subconjunctival viscoelastic

• In plastic surgery during DCR helps in identifying lacrimal sac

• Viscoelastics have a role in canalicular repair where the uninjured canaliculus is irrigated with fluorescein dye tinted viscoelastic , that spills from the other end ; helping to locate the proximal end of the injured canaliculus

• In AS trauma helps to separate salvageable tissues from damaged tissues during sx

RECENT USES

VISCOSTAINING OF CAPSULE

• Techniques-staining from above under an air bubble & intracameral subcapsular inj.of Fl.Na ( staining from below)with blue-light enhancement.

• Any instrument entering eye will cause some air to escape with rise of lens-iris plane

• A small amount of high density viscoelastic placed near incision prevents air escape & minimizes risk of sudden collapse.

• Alternatively-dye mixed with OVD called as viscostaining of ant.lens capsule covers ant capsule without coming in contact with corneal endoth.

VISCO ANASTHESIA

• Mixture of OVD with an anesthetic soln (known as VISTHESIA) had advantages of viscosurgery, maintainence of ACD, capsular bag expansion, protection of corneal endothelium.

• Prolongs anesthesia

• No extra surgical step for intracameral inj. Of lidocaine

• Contains topical component -0.3% hyaluronic acid with 2% lidocaine in a single dose unit

• Intracameral component-1.5%hyaluronic acid with 1% lidocaine

REMOVAL OF OVD’S -Rock & Roll method

-Two compartment technique

-Bimanual irrigation & aspiration technique

COMPLICATIONS OF OVD USE

• Post-op. increase in IOP

- Occurs in 1st 6-24 hrs & resolves spontaneously within 72 hrs

- Due to mechanical resistance at TM

• Crystallization of IOL surfaces

- Due to precipitation or deposition of viscoelastic soln.

- Fern like or amorphous appearance

- IOL should be explanted & exchanged

Capsular block syndrome or Capsular bag distension syndrome (CBS)

Characterised by accumulation of liquefied substance within a closed chamber inside the capsular bag, formed because the lens nucleus or the PCIOL optic occludes the ant. capsule opening created by capsulorhexis

• Classified as :

1.Intra-op – time of nucleus luxation following hydro-dissection

2.Early post-op

3.Late post op. – with liquefied after cataract

• eg.Use of high density viscoelastic agent like Healon GV causes late CBS

• Reduced distance visual acuity and improved near acuity due to induced myopia :forward shift of IOL.

• IOP is normal, despite shallow anterior chamber.

• Treatment is done by yag laser application to anterior capsule to allow OVD to escape anteriorly or posterior capsule may be lasered with escape of OVD posteriorly.

Pre treatment - Accumulation of turbid fluid in the space between IOL and posterior capsule

Pre treatment UBM - UBM showing in the bag IOL and posterior bowing of posterior capsule

Post treatment UBM - UBM confirming disappearance of retro IOL space following YAG laser

Post treatment - Following YAG laser capsulotomy disappearance of turbid fluid

• Calcific band keratopathy

- Occurs with chondroitin sulphate containing OVDs

• Pseudo Anterior uveitis

- Due to OVDs viscous nature & the electrostatic charge of it

- RBCs & inflammatory cells remain in AC giving it appearance of uveitis

- Spontaneously resolves within 3 days

- Intra ocular hemorrhage may be trapped between vitreous space & OVD in AC mimicking VH

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