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Alternatives words to Enucleation
(removal of the globe from the orbit)
• Evisceration
– Removal of the contents of the eye, while maintaining an
intact scleral shell attached to the extraocular muscles
• Exenteration
– Removal of the globe along with all the soft tissues of the
orbit, eyeball, fat, muscles
• Enucleation
– Removal of the eyeball, but the adjacent structures of the
eye socket and eyelids remain
Classification of orbital implants
• Integrated (Hydroxyapatite)
– Integration of fibrovascular tissues into the porous
structure of the implant
• Nonintegrated (glass, rubber, silicone, steel, gold, silver,
acrylic, PMMA)
– No unique apparatus for attachments to the extraocular
muscles
– Do not allow ingrowth of organic tissue into their inorganic
substance
Pegging of Hydroxyapatite Implants
• Rough surface: wrapped
(covered) with donor
sclera or other material
• Anchor the extraocular
muscles to the implant
• Pegging after 6 month:
adequate vascularization
Integrated Implant
costs, wrapping material
• Porous Hydroxyapatite: FDA approved
• Porous Polyethylene: FDA approved
• Fibrovascular ingrowths to the central core of the implant
• Advantages:
– does not require donor sclera or other type of wrapping
material
– Costs lower in comparison to hydroxyapatite
– Extraocular muscles sutured directly to the implant
SURVEY OF OPHTHALMOLOGY 44 (2000) 277
Wrapping Material
• Volume augmentation
• Improved motility (moving)
• Decreased rates of extrusion
• Extra barrier to the environment
• Donor Sclera
– The sclera is trimmed to fit the implant, with the use of 4-0 or 5-0
nonabsorbable suture
– available, expensive, risk of disease exists
• Autologous Tissue
– fascia, dermis, pericardium,
– not elicit a foreign body response, and vascularize rapidly
– additional surgical time
• Synthetic Meshes
– eliminates the possibility of disease transmission
– Gore-Tex and Vicryl
Retinal detachment
• The retina is made up of two layers: the sensory retina
and the retinal pigment epithelium, or RPE. The sensory
retina contains light-sensitive nerve cells. The RPE is a
layer of support cells behind the sensory retina.
• In retinal detachment, the sensory retina pulls away from
the RPE, and fluid builds up between the two layers. Or a
retinal tear can cause fluid to collect under the retina and
may cause the retina to detach
Scleral buckles
• Using for repair of natural age-related posterior
vitreous detachment
• Introduced first in 1930s
• Autogenous tendon or fascia
– Elimination of rejection
– Extra surgery
• Dura mater or sclera of cadavers
– Host rejection
– Pathogen transmission
• Biostable and bioabsorbable materials
Scleral buckles
• Pushes in, or “buckles,” the sclera toward the middle of the eye
• Effect on the sclera relieves the traction on the retina
– Allowing the retinal tear to settle against the wall of the eye
• May cover only the area behind the detachment
• Or
• It may encircle the eyeball like a ring
• Effectively holds the retina against the sclera until scarring
seals the tear and prevents fluid leakage which could cause further retinal
detachment
• Scleral buckles come in many shapes and sizes. The encircling band is usually
a thin silicone band sewn around the circumference of the sclera of the eye.
In rare instances, a metallic clip (tantalum clips) may be used
Glaucoma
• Glaucoma is a disease that puts increased pressure on the optic nerve, which
transmits visual information from the eye to your brain for interpretation. As
the optic nerve becomes damaged, peripheral vision deteriorates.
Ability to drive, walk, and do many other everyday activities.
Reduces central vision, finally resulting in permanent blindness.
It is often a process which occurs so gradually that most do not notice until
their vision has been severely limited.
http://www.staar.com/html/glaucoma-products.html
GFI
• 1969: Molteno
– large surface area needed to disperse the aqueous, acrylic tube,
acrylic plate
• 1973: Molteno
– draining the fluid away from the source, silicon tube
• 1976: Krupin
– pressure-sensitive, unidirectional valve that provides resistance
to the flow of aqueous and prevents hypotony from 11 mmHg to
9 mmHg
• 1993: Ahmed
– Pressure sensitive, unidirectional valve that is designed to open
when the IOP is 8 mm Hg
Valve tube shunt
The short tube is inserted into the anterior chamber.
The valve is totally enclosed in silicone rubber and is
attached to the sclera.
The long tube is drawn temporally through the
conjunctiva, shortened and left at the bottom of the
lower fornix. Aqueous is then delivered
continuously and distributed over the surface of
the eye.
Chemical injuries
• Pemphigoid ( ‫)تاول‬
• Stevens-Johnson syndrome
– cell death causes to separate layer in the body
• Repeated failed surgeries
• Trachoma ( ‫)زخم‬
• Traumatic injuries
• Certain forms of keratitis
• Mooren's ulcer
– rapidly progressive, painful, ulcerative keratitis
Some Ocular Disease
• Anisometropia : the two eyes have unequal
refractive power
• Myopia: nearsightedness
• Hyperopia: farsightedness
• Antimetropia: wherein one eye is myopic and
the other is hyperopic
• Diplopia: double vision
Contact Lenses
• Severe ametropia: defective refraction of light in the
eye )‫)نقص انکساری بینایی‬
• Severe anisometropia: defect causing one eye to
refract light differently than the other ( ‫)ناهمسانی‬
• Aphakia: absence of the natural lens of the eye
• Regular post operativea astigmatism like that which
occurs following corneal transplantation
• Irregular astigmatism in which the patient’ s vision is
distorted by irregularities in the corneal surface
possibly caused by corneal scarring
History
• 1508: Leonardo de Vinci plan
• 1880s: Glass shell covered eye
• 1940s: Discovery of PMMA
• 1948: Kevin Tuohey, HCL from PMMA rods
– Good optical properties
– light in weight
– acceptable surface wettability
– Durability
– Limitation: the low oxygen permeability
• 1970s: Polycon Laboratories, Rigid Gas Permeable contact lens,
– copolymerising methyl methacrylate (MMA) with methacrylatefunctionalised
siloxanes such as methacryloxypropyltris (trimethyl
siloxy silane) (TRIS).
– The oxygen permeability, modulus of elasticity, hardness and
wettability of these materials are modulated by the MMA/
TRIS/crosslinker ratio.
History
• 1950: PDMS
– excellent optical properties, tear resistance and high oxygen permeability
– Limitations: poor tear wetting, binding tear lipids and contact lens
adhesion to the cornea
• 1961: Otto Wichterle, first Soft Contact Lens, PHEMA
– contained 38% water
– excellent wettability
– Comfort in wearing
– Limitations: low tear resistance and a tendency to bind tear proteins
• Recently:
– Plasma surface modification of PDMS
– PDMS – Hydrogels combination
– NVP: N- vinyl pirrolidone
– GMA: glyceryl methacrylate
– Hexafluoro isopropyl methacrylate (HFIM) withTRIS,MMA
• Improved mechanical properties and oxygen permeability
• poor wettability
Ref: Biomaterials 22 (2001) 769-785
Effect of water content on oxygen
permeability
To date: much of the
work in this field has
been directed towards
developing materials
with improved oxygen
permeability with less
concern for the
contribution of the
material surface to the
inflammatory response
to long-term wear.
Inflammation
• Surface characteristics:
– Affect the adhesion and activation of neutrophils
influence
the inflammatory response to the lens.
• Bacterial adhesion to contact lens materials:
– Pseudomonas aeruginosa
– Staphylococcus aureus
– Staphylococcus epidermidis
• Microbial keratitis
• Corneal ulceration
Cataract
• The most common treatable form of blindness
• The most frequent form of ophthalmic surgical
procedure
• 1.6 million operations being performed per annum in
the USA
• Insertion of an intraocular lens (IOL) to compensate
for the loss of the natural crystalline lens
• During cataract extraction the anterior lens capsule is
opened and the contents of the capsular bag removed
IOL
• Anterior chamber IOL
– Sits in front of the iris but behind the cornea
• Iris clip lens
– Sits in the pupil
• Posterior chamber IOL
– Sits behind the iris within or on the capsular bag
– Use for the correction of aphakia (absence of the
natural lens of the eye)
IOL
• 1949: Harold Ridley, using PMMA
• Low weight and biocompatibility
• low surface energy:
– corneal endothelial damage on insertion
– adhesion of inflammatory cells to the IOL
• Other problems
– iris adhesion
– uveitis
Uvea: the part of the eye that contains the iris and ciliary body and choroid
Attempts to improve the
biocompatibility of IOLs
• Produce a highly polished surface
• Generation of both soft, high-energy surfaces using
NVP and HEMA and hard low-energy surfaces using
perfluoropropane
• Binding of heparin and hyaluronic acid to the outer
surface
• Use of phosphorylcholine-based polymeric coatings
to reduce protein adsorption, cellular adhesion and
neutrophil activation
Examples of intraocular lens
materials
IOL Requirements
• Handling
• Foldability
• Acrylic lens against silicons
– unfolds more slowly and in a more controlled way
– higher refractive index made thinner IOL
• hydrophilic materials less damaging to the corneal
endothelium
– Lower levels of inflammatory response in terms of cellular adhesion
and foreign body response
• Recent studies:
– phosphorylcholine-based acrylate polymers
– Using Benzotriazole:
– viscoelastic IOL: