Cornea transplant

Another widespread application of cold storage of tissue for transplantation is that of preservation of the cornea. Inj uries leading to corneal scarring, various kinds of diseases, and the production of comeal opacity are leading causes of blindness. Cornea transplantation is a commonly used and highly successful procedure. It... 

This discovery soon led to the use of PMMA in cornea transplants and in the replacement of damaged skull bones. 

The life story of Canadian Lieutenant Eddie Baker demonstrates a heartwarming example of progress. Baker was blinded in WWI by sniper fire. After the war, he devoted himself to improving the fives of blinded veterans. He raised the funds used to start the Canadian National Institute for the Blind (CNIB) and, later, was involved in the development of eye banks. The downstream effect of his efforts was the first cornea transplant in Canada, performed in 1956 on a WWI veteran, 40 years after he was blinded by gas (Wilton, 1996). While this is wonderfijl medical progress, it cannot undo the fact that there is still no antidote against SM. 

Wilton, P. (1996). First cornea transplants meant blind WWI veterans saw first sights in 40 years. Can. Med. Assoc. J. 155 1325-6. Wulf, H.C., Aasted, A., Darre, E. Niebuhr, E. (1985). Sister chromatid exchanges in fishermen exposed to leaking mustard gas shells. Lancet i 690-1. 

The development of polymeric drug delivery devices for sustained ophthalmic CsA release is an active area of research for uveitis, vitreous inflammation, dry eye, and prevention of cornea transplant rejection. The use of these specialized CsA-delivering ophthalmic systems (e.g., implants nanoparticle and microsphere injections) cannot be completely reviewed in this chapter and readers are referred to an alternative text. A sample of applicable polymers for delivery of CsA for uveitis and vitreous inflammation is offered in the accompanying table (Table 15.4). The treatment of posterior uveitis and vitreous inflammation usually involves chronic therapy (often years) of topical agents and frequent intravitreal injections for disease control. These therapies are often impractical and subject to medical non-adherence [33]. Polymeric implants or injectable polymer sustained release systems can potentially improve patient outcomes through optimized intraocular drug concentrations. 

These drugp possess anti-inflammatory activity and are used for inflammatory conditions, such as allergic conjunctivitis, keratitis, herpes zoster keratitis, and inflammation of the iris. Corticosteroids also may be used after injury to the cornea or after corneal transplants to prevent rejection. 

The five layers of the cornea contain no blood vessels but are nourished by tears, oxygen, and aqueous humor. Minor corneal abrasions heal quickly. Moderate abrasions take 24 to 72 hours to heal. Deep scratches may scar the cornea and require corneal transplant if vision is impaired. Do not use eye patches to treat corneal abrasion, as they decrease oxygen delivery, increase pain, and increase the chance of infection.3... 

Eyes are especially susceptible to vesicants. In addition to the immediate corrosive effects, the cornea of the eye can become inflamed (keratitis) after a latency of 6-10 years. This condition can progress to blindness. Corneal lesions may reoccur even after receiving a corneal transplantation. 

Griffith M, Hakim M, Shimmura S, Watsky MA, Li F, Carlsson D, Doillon CJ, Nakamura M, Suuronen E, Shinozaki N, Nakata K, Sheardown H. Artificial human corneas Scaffolds for transplantation and host regeneration. Cornea 21 S54-S61 (2002). 

The topical ophthalmic antiviral preparations appear to interfere with viral reproduction by altering DNA synthesis. Trifluridine is effective treatment for herpes simplex infections of the conjunctiva and cornea. Ganciclovir is indicated for use in immunocompromised patients with cytomegalovirus (CMV) retinitis and for prevention of CMV retinitis in transplant patients. Foscarnet is indicated for use only in AIDS patients with CMV retinitis. 

The transplantation of amniotic membrane does not suffice for the treatment of a severe LSC deficiency due to a bum [37]. In such a case, it needs to be associated with an LSC transplantation. The amniotic membrane is first sutured to the deepithelialized cornea and the limbal graft is set astride the edge of the amniotic membrane [38]. The cicatrization of the comeal epithelium is completed for 75-100% cases within 3 weeks when the LSC deficit is incomplete and for 70% cases when the deficit is complete [39, 40]. 

Holland, J.H., Schwartz, G.S. The evolution of epithelial transplantation for severe ocular surface disease and a proposed classification system. Cornea 15, 549-556 (1996)... 

Tsai, R.J., Tseng, S.C. Human allograft limbal transplantation for comeal surface reconstmction. Cornea 13, 389-400 (1994)... 

Ucakhan, 0.0., Koklu, G., Firat, E. Nonpreserved human amniotic membrane transplantation in acute and chronic chemical eye injuries. Cornea 21, 169-172 (2002)... 

Hanada, K., Shimazaki, J., Shimurra, S., et ah Multilayered amniotic membrane transplantation for severe ulceration of the cornea and sclera. Am J Ophthalmol 131, 324-3311 (2001)... 

Stoiber, J., Muss, W.H., Pohla-Gubo, G., Ruckhofer, J., Grabner, G. Histopathology of human corneas after amniotic membrane and limbal stem cell transplantation for severe chemical burn. Cornea 21, 482-489 (2002)... 

Fogla, R., Padmanabhan, R Deep anterior lamellar keratoplasty combined with autologous limbal stem cell transplantation in unilateral severe chemical injury. Cornea 24, 421-425 (2005)... 

Once it is possible to expand a clinically defined and safe cell lineage for transplant, it is also necessary to be able to store the viable cells for subsequent attempts or procedures. This can avoid further surgery on the same patient. This demands the development of crypreservation methods for cells and tissues, involving a tissue bank (blood, skin, bones, cornea, bone marrow, umbilical cord blood, etc.). Cryopreservation must be efficient for long periods of storage, since the frozen cells may be required years after the initial deposit. 

Other examples of tissues exhibiting active and passive tension include cornea, cardiovascular tissue, and cartilage. When a corneal transplant is trephined out from a cadaver eye, the corneal material to be transplanted shrinks from about 8.5 mm to about 8.0 mm as a result of unloading of the passive and active tensions that exist. In the cardiovascular system, passive and active stresses along the longitudinal and transverse directions of the vessel wall provide in situ strains that are as high as 50% in the carotid artery. 

Compared to the amount of research that has been invested in the study of SM skin injury, the eye has received relatively little attention during the last 20-30 years. The eye is, however, a target tissue that has a high potential for successful intervention against SM. There has been some use of comeal transplantation after mustard gas injury however, there is a high risk for transplant rejection due to inflammation and vascularization of the cornea. Despite this, keratoplasty has been used successfully in some blinded Iraq-Iran conflict veterans (Richter et al., 2006). It is likely to be one of the more successful techniques to restore vision to severely exposed individuals, especially if the limbus is also transplanted. This is needed to provide an additional supply of comeal epithelial stem cells, which become depleted over the years of trying to heal the SM latent wounds. 

Tsai RJ, Li LM, Chen JK. Reconstruction of damaged corneas by transplantation of autologous limbal epitheUal cells. N Engl J Med 2000 343 86-93. 

Recent research has demonstrated that adult human corneal endothelial cells can be grown in culture and transplanted into recipient corneas. Because human endothelial cells retain the capacity to proliferate, growth factors and inhibitors are under study as a potential method for regenerating damaged endothelial cells and increasing cell density to restore endothelial layer function. 

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