OCULAR VISCOSURGICAL

DEVICESDr. Nikhil R P

Junior Resident Dept. of Ophthalmology

Narayana medical college

History ■ In 1970’s first ACIOL and PCIOL’s were invented and the move

from ICCE to ECCE resulted in Increased number of Post OP Corneal Decompression that resulted in full thickness corneal grafts

■ Dr Endre A Balazs introduced Viscoelastics■ He worked on structure and biological activity of hyaluronan, a

viscoelastic substance present in all tissues■ Swedish pharmacia patented it and introduced HEALON . 1980

Characteristics of ideal viscoelastic■ Inert and iso- osmotic ■ Non inflammatory and non toxic ■ Optically clear ■ Contaminant free , particle free ■ Should have a pH similar to AC ■ Cost effective ■ Should not interfere with wound healing ■ It should have high viscosity to prevent damage to tissues

Commonly used families of OVDs

■ Sodium hyaluronate ■ Chondroitin sulphate ■ Hydroxypropyl methylcellulose

Sodium hyaluronate

■ Its a biopolymer found in connective tissues including trabecular meswork, aqueous and vitreous humour

■ Hyaluronate refers to conjugate base of hyaluronic acid

■ It is used as a single combination or in combination with chondritin sulpahte

Chondritin Sulphate

■ Its a biopolymer found in Extra cellular matrix

■ It is used for coating but h as less viscosity

■ High concentration causes endothelial dehydration and endothelial cell toxicity

■ 3% Na Ha + 4% CS – good coating ability + good cell protection

Hydroxypropyl methylcellulose

■ It is a disaccharide with side chains ■ Hydrophillic ■ It is synthesized from methylcellulose , a component

of plant fibres■ Used as a lubricant because of its wetting and coating

capacity ■ Once injected , it shows inflammatory reactions and

difficult to metabolise ■ It is difficult to remove from AC

Physical properties of OVD

■ Viscosity ■ Pseudoplasticity ■ Elasticity ■ Coatability ■ Cohesiveness ■ Dispersiveness

Viscosity ■ Internal friction caused by molecular attraction that leads

to a solution’s resistance to flow

■ Determined by molecular weight

■ It denotes the protective and lubricating property of a viscoelastic

■ High molecular weight and high concentration have highest viscosity

■ High viscosity solutions tend to stay within the AC and separate the tissues well

■ Shear force/rate- stress that is applied parallel to the material

Pseudoplasticity

■ Aka Rheofluidity■ It refers to changes in viscosity with different shear

rates

■ It is the ability of the solution to transform from gel like state into liquid like state(viscosity reduces) under pressure ( shear force )

Low shear Medium shear High shear

Substance at rest Eg: Instruments movement in eyes

Substance under force

Viscosity increases Viscosity decreases

Gel form Liquid form

This property enables easy injection and removal of an agent

Elasticity ■ It refers to ability of a substance or material to return to

it original shape after being deformed ( stretched or compressed )

■ Elastic substances are good for maintaining space

■ High molecular weight highly elastic

Coatability /Lubricating power ■ It measures the adhesion capacity of OVD

■ It is inversely proportional to surface tension and the contact angle b/w OVD and a solid material

■ Low surface tension, low contact angles, more negatively charged OVDs better coat the endothelium

■ HPMC, Chondritn sulphate > Na Hya

Cohesiveness ■ It is the degree to which the material adheres to itself

■ It depends on molecular weight, strength of molecular binding and elasticity

■ The more cohesive an OVD, the lower the flow rate and hence they are good for space maintaining and are easily removed

Dispersiveness

■ It is the tendency of a material to disperse when injected into AC

Cohesive / dispersive index

■ Its is defined as percentage of viscoelastic agent aspirated/100mmhg

■ The higher the CDI , the quicker the substance can be aspirated when a certain amount of aspiration is reached

Classification of OVDs

■ Dispersive ■ Cohesive ■ Combination ■ Viscoadaptive

Dispersive

■ Low viscosity ■ Ability to coat intraocular structures ■ The molecules behave separately and build up a

solution ( honey Like ) ■ They tend to stay in fluidic movements of phaco surgery

■ Eg: HPMC, Dispersive Na Ha

Cohesive

■High viscosity ■Able to give pressure to the eye and create space

and maintain space ■They act like a gel

■Eg: Cohesive Na-Ha, Super Cohesive Na Ha

Combination

■ New generation ■ Highly viscous dispersive OVDs ■ Advantages of both cohesives and dispersive

Viscoadaptive OVD■ Changes its behaviour at different flow rates

■ Eg: Healon 5 ( Abbott Medical optics ) ■ :Low flow rate – it is very viscous and cohesive

High flow rate – it becomes pseudo dispersive and effectively protects endothelial cells

Cohesive OVDs Dispersive OVDs

High molecular weight Low molecular weight

High viscosity Low viscosity

Molecules Adhere to themselves Adhere to external surfaces

Resist breaking apart Tend to break apart

High pseudoplasticity Low pseudoplasticity

Easy to remove from the eye using Irrigation and Aspiration

More difficult to remove from the eye

Advantages of Cohesive OVDs Disadvantages of cohesive OVDsCreate , deepen and maintain space in AC

They can come out of the eye easily as a whole during surgery under intense vitreous pressure

Clear vision , transparency They do not stay attached to corneal endothelium

Ideal for flattening of AC for Rhexis Some of the substances have high risk post OP raised IOP if not completely removed ( Healon 5 )

Ideal to open capsular bag for IOL insertion

They are unwillingly removed due to fluidic movements during phaco surgery

They eenlarge and stabilize the size of the pupil

Easy to remove at the end of the procedure

Eg: Healon , Healon GV , Provisc , Amvisc

Advantages of dispersive OVDs Disadvantages Ability to coat the intraocular structures

Low viscosity dispersives do not maintain spaces well

They separate the spaces. They hold vitreous back in case of weak zonules or in case of PC rent

May have air bubbles inside or form microbubbles during surgery

Ability to lubricate IOL and injector Difficulty to remove at the end of procedure They fragment into small pieces during irrigation and aspiration and this may obscure the visualisation of PC during surgery

Eg: Vitrax, Viscat , OcuCoat

HYALURONATE PRODUCTSHealon, Healon5, Healon GV, Healon D, I-Visc,Amvisc, Amvisc plus, Provisc

HA+CS PRODUCTSViscoat, Discovisc

HPMC PRODUCTSOccucoat, Cellugel

COHESIVE DISPERSIVE

CLINICAL APPLICATIONS Cataract surgery■ Protection of endothelium■ Maintaining of AC■ CAPSULAR RHEXXIS■ Cleavage of lens structure■ Visco -expression of lens■ Phacoemulsification of nucleus■ IOL implantation■ dilate the pupil & maintain a good intraoperative mydriasis■ Iris herniation or prolapse■ Posterior capsule tear ■ Pediatric cataract Sx – while performing capsulorrhexis

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

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

Floppy iris syndrome ■ Because of use of systemic TAMSULOSIN, a selective

alpha 1 blocker

■ During cataract surgery, it presents as an undulating iris. The iris has a tendency to prolapse and progressive miosis is observed

Glaucoma surgeryVisco-canalostomy■ Means opening of schlemm’s canal by OVD■ A Non penetrating 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

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 endothelium

VISCO ANASTHESIA■ Mixture of OVD with an anesthetic soln (known as VISTHESIA)

had advantages of viscosurgery, maintainence of AC depth, capsular bag expansion, protection of corneal endothelium.

■ Prolongs anesthesia

■ 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• 0.3mm I/A tip, flow rate – 25 to 30 ml/min, vacuum 350

to 500 mm Hg• -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 capsulorrhexis

■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.

■ 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 haemorrhage may be trapped between vitreous

space & OVD in AC mimicking VH

Thank you