Alternatives words to Enucleation (removal of the globe from the orbit) Evisceration – Removal of...

Alternatives words to Enucleation(removal of the globe from the orbit)

• Evisceration– Removal of the contents of the eye, while maintaining anintact scleral shell attached to the extraocular muscles• Exenteration– Removal of the globe along with all the soft tissues of theorbit, eyeball, fat, muscles• Enucleation– Removal of the eyeball, but the adjacent structures of theeye 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 extraocularmuscles– Do not allow ingrowth of organic tissue into their inorganicsubstance

Pegging of Hydroxyapatite Implants

• Rough surface: wrapped(covered) with donorsclera or other material• Anchor the extraocularmuscles to the implant• Pegging after 6 month:adequate vascularization

Integrated Implantcosts, 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 5-0nonabsorbable 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 posteriorvitreous 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 scarringseals 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, whichtransmits 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.

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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 resistanceto the flow of aqueous and prevents hypotony from 11 mmHg to9 mmHg• 1993: Ahmed– Pressure sensitive, unidirectional valve that is designed to openwhen the IOP is 8 mm Hg

Valve tube shuntThe 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 unequalrefractive 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 theeye نقص انکساری بینایی))• Severe anisometropia: defect causing one eye torefract light differently than the other ( ناهمسانی)• Aphakia: absence of the natural lens of the eye• Regular post operativea astigmatism like that whichoccurs following corneal transplantation• Irregular astigmatism in which the patient’ s vision isdistorted by irregularities in the corneal surfacepossibly 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 methacrylatefunctionalisedsiloxanes such as methacryloxypropyltris (trimethylsiloxy silane) (TRIS).– The oxygen permeability, modulus of elasticity, hardness andwettability 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 lensadhesion 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 wettabilityRef: Biomaterials 22 (2001) 769-785

Effect of water content on oxygen permeability

To date: much of thework in this field hasbeen directed towardsdeveloping materialswith improved oxygenpermeability with lessconcern for thecontribution of thematerial surface to theinflammatory responseto long-term wear.

Inflammation

• Surface characteristics:– Affect the adhesion and activation of neutrophils

influencethe 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 surgicalprocedure• 1.6 million operations being performed per annum inthe USA• Insertion of an intraocular lens (IOL) to compensatefor the loss of the natural crystalline lens• During cataract extraction the anterior lens capsule isopened 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 thenatural 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 usingNVP and HEMA and hard low-energy surfaces usingperfluoropropane• Binding of heparin and hyaluronic acid to the outersurface• Use of phosphorylcholine-based polymeric coatingsto reduce protein adsorption, cellular adhesion andneutrophil activation

Examples of intraocular lensmaterials

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 cornealendothelium– Lower levels of inflammatory response in terms of cellular adhesionand foreign body response• Recent studies:– phosphorylcholine-based acrylate polymers– Using Benzotriazole:– viscoelastic IOL: