Ophthalmic Viscoelastic devices

Ophthalmic Viscoelastic devices

1. OPHTHALMIC VISCOSURGICAL DEVICES Dr Binesh Tyagi Fellow - Phaco Refractive Dept NDSSEH

2. Recent DNB Q s Dec 2013 Broadly classify viscoelastic substances. What is soft shell technique? Important precautions in phaco with low endothelial counts? (2+4+4) June 2012 What are viscoelastics ? Classification? Indications of each? Side effects? (1+3+4+2)

3. history In 1970s the move from ICCE to ECCE resulted in increased number of post operative corneal decompensations that needed full thickness corneal grafts. Dr Endre A Balazs introduced viscoelastics and coined term Viscosurgery He worked on structure and biological activity of hyaluronan , a viscoelastic substance present in all tissues. Sodium hyaluronate was 1st used in ophthalmic surgery as viscoelastic in 1972 as a replacement for vitreous & aqueous humor . Swedish Pharmacia AB patented it and introduced HEALON in 1979

4. INTRODUCTION Substances having dual properties 1.Viscocity of fluid 2.Elasticity of gel or solid

5. Ideal viscoelastic Ease of infusion Retention under + ve pressure in eye Retention during phaco Easy removal Doesn't interfere with instruments/IOL placement Protects endothelium Does not obstruct Aqueous Outflow

6. Ideal viscoelastic properties Non toxic Nonpyrogenic Non inflammatory Nonimmunogenic Sterile Inert and iso -osmotic Optically clear Contaminant free , particle free Should have a pH similar to AC Cost effective Should not interfere with wound healing

7. Rheological properties Viscosity Pseudoplasticity Elasticity Coatability Cohesiveness Dispersiveness

8. viscosity Viscosity  reflects a solution's resistance to flow Internal friction caused by molecular attraction - leads to solution’s resistance to flow The higher the solution's molecular weight, the more it resists flow 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. High viscosity solutions tend to stay in the AC and separate the tissues well Shear force/rate- stress that is applied parallel to the material

9. Elasticity It refers to ability of a substance or material to return to its original shape after being deformed (stretched or compressed)

10. 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.

11. 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, Chondroitin Sulphate > Na Hya .

12. pseudoplasticity Pseudoplasticity  AKA rheofluidity refers to a solution's ability of the solution to transform from gel like state into liquid like state(viscosity reduces) under pressure ( shear force ) 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. This property enables easy injection and removal of an agent 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

13. 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.

14. Dispersiveness It is the tendency of a material to disperse when injected into AC Its is defined as percentage of viscoelastic agent aspirated/100mm Hg The higher the CDI , the quicker the substance can be aspirated when a certain amount of aspiration is reached Cohesive dispersive index

15. COMPOSITION

16. Sodium hyaluronate It is a glycosaminoglycan and long-chain polymer of disaccharide units of Na-glucuronate-n-acetylglucosamine Occur in many connective tissues throughout the body, including both the aqueous and vitreous humors  Hyaluronate has a half-life of approx1 day in aqueous, 3 days in vitreous. Mainly present in visco cohesives

17. Chondroitin Sulfate Sulfated glycosaminoglycan (GAG) A chain of alternating sugars (n- acetylgalactosamine  and glucuronic acid) Found as one of the three major mucopolysaccharides in the cornea. Obtained from shark fin cartilage Eliminated from the anterior chamber in approx 24 to 30 hours Coats tissues but poor space maintainer

18. 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

19. others Ocugel Combination of HPMC and chondroitin sulfate Offers better viscosity and coating. As the viscoelasticity is much less it requires a large bore cannula for insertion and aspiration ability. Collagen Derived from Human placental collagen (type IV) 2 percent solution is obtained as supernatant after centrifugation for removal of fibrillar material. a protein whereas the other viscoelastic substances are polysaccharides. Cellugel synthetic polymer of modified carbohydrate Advantages it can be autoclaved, does not require refrigeration, and may be stored at room temperature for two years. It can be injected with a 25 gauge cannula. Newer viscoelastics poly TEGMA 40 percent ( triethylenglycol monomethacrylate ) poly GLYMA (glycerol monomethacrylate ).

20. Classification High Viscosity cohesive super viscous cohesive(>1,000,000mPs) 1.Healon GV(1.4%), 2.Ivisc plus Viscous Cohesive; OVD(bet 1,000,000and 10,000) 1.Ivisc, 2.Provisc, 3.Healon(1%), 4.Amvisc Lower viscosity dispersive Medium viscosity 1.Viscoat, 2.Vitrax, 3.Cellugel, 4.Biovisc Very low viscosity 1.Occucoat, 2.Ocuvis, 3.I-cell, 4.Hymecel, 5.Viscilon Viscoadaptive (Healon-5)

21. Cohesive High viscosity Able to give pressure to the eye Create and maintain space They act like a gel High mol wt Long chain molecules Adhere to themselves through intramolecular bonds, resists breaking apart. High degree of pseudoplasticity and high surface tension

22. Advantages of Cohesive OVDs Disadvantages Create , deepen and maintain space in AC Come out of the eye easily as a whole during surgery under intense vitreous pressure Clear vision , transparency 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 Unwillingly removed due to fluidic movements during phaco surgery They enlarge and stabilize the size of the pupil Easy to remove at the end of the procedure Eg : Healon , Healon GV , Provisc , Amvisc

23. Dispersive Low viscosity Ability to coat intraocular structures The molecules behave separately and build up a solution. They tend to stay in fluidic movements of phaco surgery Low viscosity Low mol wt Short chain molecules They adhere well to external surfaces, e.g., tissues and instruments. These bonds tend to break apart easily Lower surface tension and lower pseudoplasticity Eg : HPMC, Dispersive Na Hyaluronate

24. 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

25. COHESIVE DISPERSIVE

26. viscoadaptives Behaviour changes at different flow rates viscous cohesive agent at lower flow rate 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

27. uses

28. cataract surgeries Protection of epithelium Protection of endothelium Control of capillary oozing Maintaining AC Capsular rhexis 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 Pediatric cataract Sx – while performing capsulorhexis

29. 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

30. Soft shell technique

31. Ultimate Soft Shell Technique ( USST ) Uses viscoadaptive and BSS (instead of dispersive). Makes all cases much easier, and more stable.

32. SST-USST combinations ( T ri- S oft S hell T echniques) Use layers of dispersive against the cornea, Cohesive centrally to establish stability, BSS (Or XYLO-PHE) on the lenticular surface (for a Low-viscosity surgical space). Optimizes pupil dilation.

33. tri soft shell technique

34. Uses- soft shell technique Floppy iris syndrome - 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

35. Glaucoma surgery

36. Visco-canalostomy Means opening of schlemm’s canal by OVD A non penetrating procedure ,independent of external filtration Advantages- -Decrease incidence of cataract -Hypotony and flat AC -Excludes risk of late infection & conjunctival & episcleral scarring Cyclodialysis To achieve a small cyclodialysis , OVD can be injected between sclera and ciliary body around the edge of the cleft. The abandoned cyclodialysis operation could be reintroduced in aphakic and pseudophakic eyes, using the tissue separating and space maintaining properties of viscoelastic substance.

37. 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.

38. Posterior segment surgeries Replace diseased vitreous Reattach & provide temporary tamponade in retinal holes and detachments Reattach giant retinal tears Restore IOP after release of subretinal fluid Maintain IOP after vitrectomy Achieve surgical dissection of membranes Protect corneal endothelium during gas injection in Aphakic eyes Separate membranes from lens or retina To protect against possible inflammation, use of steroid therapy, sub-tenon injection at the End of surgery, or administration of systemic Steroid is indicated.

39. trauma Anterior segment in primary trauma sorting out of the traumatized tissues and their separation from each other hopelessly crushed tissues are removed and the salvageable ones are reposited and sutured. Thus a deliberate and orderly reconstruction is possible, making secondary procedures less frequent and simple. In posterior segment injury the collapsed globe can be restored to a near normal shape intraocular pressure can be raised to a level where a careful evaluation of the situation and restoration of the wall of the eye is possible.

40. In strabismus sx Significantly less force required to bring the muscle to its insertion with the use of subconjunctival viscoelastic coating of extraocular muscles lead to during surgery with viscoelastic cushion indicate a significant decrease of scarring of the epimuscular tissue. During repeated probing and irrigation of the lacrimal drainage system in elderly, if the passage is filled with viscoelastic substance the patency can be expected to be maintained from one month to six months 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 EXTRA OCULAR PROCEDURES

41. 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 .

42. VISCO ANASTHESIA Mixture of OVD with an anaesthetic (known as VISTHESIA®) had advantages of viscosurgery( maintenance of ACD, capsular bag expansion, protection of corneal endothelium) Prolongs anaesthesia 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

43. Removal of ovd’s -Two compartment technique -Rock & Roll method -Bimanual Irrigation & Aspiration technique

44. COMPLICATIONS OF OVD USE Post-op. Increase in IOP - Occurs in 1 st 6-24 hrs & resolves spontaneously within 72 hrs - Due to mechanical resistance at Trabecular Meshwork. Crystallization of IOL surfaces - Due to precipitation or deposition of viscoelastic soln. - Fern like or amorphous appearance - IOL should be explanted & exchanged

45. 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

46. 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.

47. 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

48. 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 Vit h’ge .

49. PG Corner