2. Properties of silicon oil
Polymer of siloxane (R2-SiO2)
PDMS (most common)
Hydrophobic, liquid and clear
Silicone fluids, silicone rubber, depending on R2
It is not an oil
3. Specific gravity
0.97 (PDMS)
Depends on R2
Higher SG, better contact with retina
Remains constant irrespective of viscosity
4. buoyancy
Upward exerting force of fluid/gas
Depends on difference of SG to aqueous
Gas (SG 0.001) exerts far greater upward force than silicon oil (SG 0.97)
5. Surface tension
It keeps an agent as a single bubble
high interfacial tension has fewer tendencies to deform or disperse into
small bubbles
less likely to pass through small openings, such as a retinal hole
Gas or air 80
Silicone oil 35
Perfluorocarbon liquids 40–45
6. viscosity
Resistance of fluid to deformity
Shear stress
Tensile stress
A higher energy is needed to disperse a large and highly viscous fluid
bubble into small droplets (emulsification)
Viscosity is expressed in centistokes
Not affected by SG or surface tension
Depends on length of polymer and MW
7. Removal of silicone oil
Theoretically, chorioretinal adhesion would have formed certainly by 1 month
6 weeks to 6 months
However, in some eyes with very poor ultimate anatomical/visual prognosis, it may be
left in the eye
Heavy oil no longer than 3 months
The type of SO and its viscosity, lens status and whether or not additional procedures
are to be carried out, will influence the method used
8. procedure
two port system : one for infusion and the other for SO aspiration
Passive
Active aspiration
Manual
keep the tip of the cannula within the oil globule as it reduces in size till
the end
Unwated movements at the end leads to loss of hold over the small oil
bubble which becomes difficult to regain due to fluid turbulence
Gentle depression of the ciliary body area will push any sequestered oil
bubbles into the vitreous cavity
9.
10. procedure
Maximum suction applied is limited
the pressure driving the flow of oil out of the eye would be the atmospheric
pressure plus the infusion pressure
Therefore, if passive aspiration were used, the aspirating pressure would be
the height of the infusion bottle
If active aspiration was used, the vacuum driving the flow would be much
higher (760 mmHg + bottle height)
Another important consideration is the length of the aspirating cannula
11. procedure
Poiseuille’s Law
flow is inversely and proportion to the length of the tubing
To minimize this length, no tubing should be used
The suction needs to be generated in a syringe connected directly to the
aspirating cannula
12. procedure
In combined phacoemulsification and uncomplicated SOR, a primary
posterior capsulotomy is made
Infusion is provided via an anterior chamber maintainer
In aphakic eyes with SO in the anterior chamber, a corneal wound can be
used to allow passive drainage of oil
fundus should be evaluated at the end of the procedure
13. Implications of SOR
potential risk of retinal redetachment
higher in eyes with PVR or in with high-risk of developing PVR
Most redetachments occur within 6 months after SO removal
previous unsuccessful surgeries and longer axial lengths are associated
with higher failure rates
Prophylactic 360° laser or the use of encircling band may reduce the rate
of redetachment
14. Implications of SOR
Difficult to ensure the eye is free of emulsified oil at the end
Patients may complain of floaters due to residual oil droplets
air-fluid exchange at the end of oil removal to remove residual droplets can be
tried
Where fluid-air exchange is done, multiple repetitions are preferable
The flute needle is kept at the air-fluid meniscus where oil comes to float and can
be seen and removed
Anterior chamber emulsified oil should be washed thoroughly, with attention to
the angles
