2. Outline
1. Definition: Viscoelastics
2. The Five Main Characteristics of Viscoelastic Substances
1) Cohesiveness
2) Viscosity
3) Elasticity
4) Adhesiveness
5) Pseudo-plasticity.
3. Types of Viscoelastics
1) Cohesive viscoelastic substances
2) Dispersive viscoelastic substances
4. Viscoadaptive: the twin properties
5. The Uses of Viscoelastic Material
6. Removal of Viscoadaptive
3. Definition: Viscoelastics
Substances that are highly used in cataract surgery.
Provides better control over an operation.
Relies on five main characteristics: viscosity,
elasticity, adhesiveness, cohesiveness, and pseudo-
plasticity.
4.
5. 1- Cohesiveness:
Cohesiveness is the extent according to which a
material can adhere to itself.
Viscoelastics substances with high molecular weight
tend to have high cohesiveness and those with low
molecular weight have low cohesiveness.(ie: mercury)
6. 2- Viscosity:
The viscosity of a fluid is a measure of its resistance to
gradual deformation by shear stress or tensile stress.
(ie:honey)
7. 3- Elasticity:
Elasticity is the ability of a viscoelastic to regain its
original shape after being compressed, deformed, or
elongated.
Allows the absorption of energy and thus deflecting
any impact that could damage the tissue.
8. 4- Adhesiveness:
the ability of various viscoelastics to adhere to the
surface of the tissues, instruments and IOLs
(Intraocular lens) (ie:glue)
9. 5- Pseudoplasticity:
It is the capacity to pass from a high to a low state of
elasticity, or Viscosity reduction of non-Newtonian
fluids under conditions of shear stress.(ie: ketchup)
11. 1- Cohesive viscoelastics
Viscoelastics that are very cohesive and have high
viscosity are mostly useful to create surgical space and
in stabilizing tissues.
12. 2-Dispersive viscoelastic
Viscoelastics that are very dispersive and have low
viscosity will break very easily when injected into the
eye and will disperse in fragments. They have a
tendency to form a layer that will adhere to and coat
different structures of the eye.
13. Viscoadaptive:
Healon5 is an example of an ophthalmic viscosurgical
device (OVD) that has been called a viscoadaptive,
meaning that it can act as both a dispersive and
cohesive material.
14. The twin properties:
During high-flow-rate phacoemulsification,
turbulence in the anterior chamber breaks Healon5
apart, and it behaves like a dispersive OVD, which is
important for safely removing the cataract.
When movement in the anterior chamber is less
turbulent, the Healon5 behaves cohesively, allowing it
to be used to move tissue and maintain space.
15. The Uses of Viscoelastic Material
Anterior chamber-filling and maintenance
It is important that the viscoadaptive maintain a good, deep AC so
the surgeon can perform all surgical maneuvers safely and
comfortably.
Capsulorhexis
Viscoelastics flattens the capsule to ease the capsulorhexis
dissection.
16. The Uses of Viscoelastic Material
Hydrodissection/ hydrodeliniation
The viscoelastic product should protect these ocular structures from the
turbulence of the fluids and the surgeon’s maneuvers.
Phacoemulsification
The viscoadaptives are super cohesive, with a high degree of elasticity to
absorb the mechanical vibrations. They are also pseudoplastic and could be
easily removed.
17. The Uses of Viscoelastic Material
Irrigation and aspiration:
It should allow removal of the remaining cortex while maintaining the AC.
This should be completed while providing protection to the ocular
structures.
Capsular bag filling/IOL implantation
Viscoadaptives should be easily injected in the bag, re-inflate the capsular
bag, have good transparency, and allow for safe implantation of the IOL
18. Removal of viscoadaptive
Rock and Roll technique:
the irrigation and aspiration hand piece is placed on the optic of the IOL as
it is rocked back and forth, allowing the viscoadaptive to flow from behind
the bag to the AC where it can be removed.
Two Compartment Technique:
By going behind the IOL with the irrigation and aspiration tip into the
capsular bag immediately after IOL implantation without starting the flow
of irrigation fluid one can ensure the complete removal of t he
viscoadaptive substance.
