Presented by:
C.Sundarraj

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Intravitreal injection of vitrectomised eye:computer modeling
Diseases
• AMD-1.75 million people affected
• Diabetic retinopathy
• Glaucoma, and
• Retinitis pigmentosa
• Difficulty in treatment
• Delivering effective doses of the drugs to target tissues in the vitreous chamber of the eye- challenging
Intravitreal Injection
• Most direct approach to delivering drugs to the tissues
• Drugs injected directly into the vitreous are rapidly eliminated.
• Repeated injections are needed since the half-life of drugs in the vitreous is relatively short. This cause patient discomfort and may further lead to complications such as vitreous hemorrhage, infection, and lens or retinal injury.
Intravitreal Injection
• Predicting concentration distribution
• Narrow concentration window of drug
• Concentration distribution depends on the properties of the vitreous substitute, the diffusion coefficient of the drug and the permeability of the retinal surface.
• In order to assess the effectiveness of the injected drug, it is critical to know the drug distribution within the eye following the injection
Vitrectomy
A surgery to remove some or all of the vitreous humour from the eye to repair very large tears in retina,reduce vision loss caused by bleeding in vitreous.
• Modeling
• Governing eqns
Boundary conditions
• Pressure at the hyaloid membrane to be same as that of aqueous humor
• The concentration is set to zero i.e., C = 0 at the hyaloid membrane
• At the surface of the lens a no-flux boundary condition is applied
• At the outer surface of the retina the drug concentration is set to zero i.e., C = 0
• vitreous substitutes is silicone oil.
• In the present study we have assumed that the drug is released at the center of the vitreous chamber and that the injected drug initially has a homogenous distribution within a cylindrical region after injection.
Simulation
• VH- porous medium –normal eye
• VH- liquid -victrectomised eye
• Vitreous substitute- silicone oil and water
Results
• Pressure contour
• Velocity profile
• At centre of retina
Important conclusions
• The concentration distribution depends on the vitreous fluids,permeability of retina and the diffusion coefficient of the drug.
• Water as vitreous fluids exhibit higher drug transport rates than silicone oil
• Convection effects are smaller due to the higher viscosity, and diffusion is more important
• In the case of direct injection, for water as vitreous fluid, the retinal drug concentration levels reach high values, even for low diffusivity drugs, and such situations can lead to retinal toxicity.
• For drugs with high diffusion coefficient (and retinal permeability),a more uniform distribution of the drug is obtained along the surface of the retina whereas for the low diffusion coefficient drugs the concentration of drug is localized along the posterior surface of the retina.
Further scope
• Convection effects due to thermal gradient in vitreous may be considered.
• Location optimization of subsequent injection may be developed using the initial concentration distribution.
• Vitrectomised eye –simulation is the best way for predicting drug concentrations.