fundamentals of a retinal prosthesis: a surgical perspective of
TRANSCRIPT
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Fundamentals of a retinal prosthesis: a surgical
perspective of suprachoroidal / epiretinal
prostheses
P.J.Allen
Bionic Vision Australia
Medical Bionics Conference 2011
prostheses
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Surgical Aims
• Safe
– For the eye
– Overall patient health
• Easily reproducible procedure• Easily reproducible procedure
– Able to teach surgeons worldwide
• Stable for the lifetime of the patient
– Device stable in position
– Minimal risk longterm surgical complications
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Our approach
• Cadaver trial surgery
• Animal model
• Human surgery
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Human anatomy
• Axial length 24mm (21 – 26mm)
• Coats of the eye
– Cornea and sclera
– Uveal tract
– Retina
• Need to develop a surgical approach which
satisfies the surgical aims
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Anatomy of the eye
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Surgical approaches
• Suprachoroidal space
– Potential space between the sclera and the
choroid
– Traversed by the vortex veins and posterior ciliary
nerves / blood vesselsnerves / blood vessels
• Subretinal space is beneath the retina
• Epiretinal approach on the surface of the retina
• Within the sclera
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Vitreous cavity
Within the sclera
Suprachoroidal space
Subretinal space
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Cat model
• Axial length 22mm
• Coats of the eye
– Band of anterior thick sclera approx 7mm
wide
– Thin sclera posterior to this
• Under developed extraocular mucles
• Large anterior chamber
• Greater lens volume
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Cat model
• Third eyelid
• Tapetum
– Reflective layer within the choroid
• Area centralis
• Vortex veins and posterior ciliary blood
vessels
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Feline surgical model
Human eye Feline eye
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External view of cat eye
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Cat cadaver eye
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Suprachoroidal surgery - cadavers
• Extensive use of cadaver eyes
• Initially anatomical dissections to familiarise
the surgeons with the cat eye
• Surgery performed in cadavers as much as
possible prior to live animals
• Any form / major changes surgery returned to
cadavers prior to proceeding on with live
animals
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Surgical approach development
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Suprachoroidal surgery
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Implant Body Evolution
pat. pend.
Allen, Villalobos & Williams
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Suprachoroidal surgery
• The surgical plan initially worked up in the
cadaver
• Then used in the acute studies
• Modified for chronic passive studies
• Modified for chronic active studies
• Preparation for humans
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Suprachoroidal surgery
Design retuned to cadaver for further lead modification Allowing final design iteration
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Suprachoroidal surgery
• Advantages– Ease of surgery
– Anatomical stability
– Choroid may act as a heat sink
• Disadvantages– Proximity to neural elements
• Unknowns– Spatial resolution
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Epiretinal surgery
• Requires vitrectomy to be performed
– Posterior vitreous detached
– Core and peripheral vitreous removed
• Feline model• Feline model
– Large lens so lensectomy also performed
– Able to detach gel compared to rabbit
• Device tacked to retina
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Vitrectomy surgery
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Cadaver “open sky” approach
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Demonstration of tacking
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Evolution of device
Assessment in acute surgery guides
changes to form
With these changes being evaluated
in cadavers prior to further live animal
work
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Epiretinal surgery
• Advantages
– Proximity to neural elements
– Vitreous cavity fluid can be utilised as a heat sink
– Prosthesis may be visualised through a dilated
pupilpupil
• Disadvantages
– Adhesion, possible difficulties in chronic
attachment
• Unknowns
– Lack of stability may cause variable proximity to
neural elements long-term
– Lack of stability may cause variable thresholds
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Conclusions
• The development of a retinal prosthesis requires a
combination of cadaver and animal work
• Surgical team needs to work closely with the
engineering team to determine device specificationsengineering team to determine device specifications
• Feedback with iteration important
• Device evolution occurs in parallel with evolution of
surgical techniques