OPHTHALMIC VISCOSURGICAL DEVICES

DR.PRATIK MOHOD

INTRODUCTION

Substances having dual properties

1.Viscocity of fluid2.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

The viscoelastic substances must be Non toxic Nonpyrogenic Non inflammatory Nonimmunogenic Sterile for ude in human eye

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 PRODUCTSHealon, Healon5, Healon GV, Healon DAmvisc, Amvisc plus, Provisc

HA+CS PRODUCTSViscoat, Discovisc

HPMC PRODUCTSOccucoat, Cellugel

Classification of OVDs

High viscosity-cohesive OVDs

Lower viscosity-dispersive OVDs

Viscoadaptive OVDs

12

3

Classification High Viscosity cohesive A)super viscous

cohesive(>1000000mPs) B)Viscous Cohesive; OVD(bet

N100000and 10000 Lower viscosity dispersive Viscoadaptive(Healon-5)

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

ADVANTAGES1.Maintain space at low shear rates2.Easily displaced at high shear rates3.Sticks together,aspirated out easily4.Low risk of post op IOP rise even if retainedDISADVANTAGES1.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

ADVANTAGES1.Excellent coating and gives superior endothelial protectonDISADVANTAGES1. 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 spaces3. Can form microbubbles and obscure view4. 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

DISADVANTAGES1.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 surgeryVisco-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 usesVISCOSTAINING 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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