Cornea Krachmer Pdf Free 18: Discover the Latest Techniques and Advances in Corneal Imaging and Ther

Shield ulcers can occur in the superior sectors of the cornea; these are noninfectious, oval-shaped circumscribed epithelial ulcer with underlying stromal opacification. After the ulcer heals, an anterior stromal opacity can persist.

Cornea Krachmer Pdf Free 18

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Despite the relative immune privilege of the cornea as a transplanted tissue (both the recipient corneal bed and the anterior chamber are immune-privileged sites), the most common cause of corneal graft failure in all reports is allogeneic rejection. In first-time graft recipients with no vascularisation of the recipient's corneal bed, 2-year survival rates exceed 90%; this decreases to 35% to 70% in recipients with high-risk factors for rejection. In one-third of all corneal grafts fail, signs of a destructive attack by the immune system have been observed. A rejection episode results in a loss of donor endothelial cells, which are critical for the maintenance of corneal transparency. This activity highlights the role of the interprofessional team in caring for patients with the challenge of corneal graft rejection.

Objectives:Review the preoperative characteristics that may lead to graft failure.Describe the features of corneal graft rejection.Summarize the treatment of corneal graft rejection.Outline the role of the interprofessional team in caring for patients with the challenge of corneal graft rejection.Access free multiple choice questions on this topic.

The corneal bed and the anterior chamber are immune-privileged sites, but despite the relative immune privilege of the cornea as a transplanted tissue, the most common cause of corneal graft failure in all reports is allogeneic rejection. In first-time graft recipients with no vascularisation of the recipient's corneal bed, 2-year survival rates exceed 90%; this decreases to 35% to 70% in recipients with high-risk factors for rejection. In one-third of all corneal grafts fail, signs of a destructive attack by the immune system have been observed. A rejection episode results in a loss of donor endothelial cells, which are critical for the maintenance of corneal transparency.[1] As human endothelial cells do not repair by mitosis, the consequence is that donor corneal transparency is lost if cell density falls below the threshold necessary for the prevention of stromal swelling.

Endothelial decompensation results either from an irreversible episode of acute graft rejection or at an interval following one or more episodes of rejection, which have been reversed by therapy. Endothelial cells are thus the critical target in the allogeneic response.[2] While the reversal of acute graft rejection episodes does not present such challenges in the cornea as in other transplanted tissues, effective prophylaxis in corneal graft recipients identified at high risk of rejection is much less evidence-based.[2] Thus, the impact of graft rejection continues to justify a high priority in corneal research.[3]

Preoperative characteristics of the graft-recipient eye can be identified in many patients to indicate a significantly high risk of graft failure. Proposed graft-recipient corneas with two or more quadrants of deep vascularisation or one bearing a previously rejected graft that is inflamed at the time of transplantation are at a significantly higher risk of rejection.[7] There is less robust evidence in the published literature that grafts in children, large-diameter donor corneas, and the proximity of the donor cornea to the recipient limbus cause a higher risk.

More than one of these factors may exist in a patient. Furthermore, one or more of the above factors may predispose the patient to rejection due to additional clinical features that confer a significant risk of graft failure.[8] These additional complications include glaucoma or ocular surface disease. Clinicians must evaluate these preoperative clinical features carefully to decide whether to proceed with corneal transplantation.[9] Once transplantation is successfully completed, care must be taken to prevent postoperative events that lead to rejection, for example, vascularization of recipient cornea or graft wound, suture loosening, or graft infection.[10]

In reports from large cohorts of corneal graft recipients, the proportion experiencing rejection at some stage post-transplant ranges from 18% to 21%. In those graft recipients in whom rejection occurs, reported rates of successful reversal of the rejection episode range from 50% to 90%.[11] Allograft rejection occurs most commonly in the second 6 months post-grafting, and it has been reported that more than 10% of the observed reactions can occur as late as four years after surgery. This data indicates that all corneal grafts need long-term surveillance and are at risk indefinitely. Epithelial rejection comprises approximately 2% of graft rejections.

The high success rate in corneal transplantation is possible because the cornea is an immune-privileged organ in the human body. The other factors contributing to success are avascularity and lack of lymphatics. The avascularity prevents infiltration by inflammatory cells and immune-responsive cells. In the absence of lymphatics, the foreign antigen presentation is also limited. Moreover, the number of MHC antigens expressed on the other tissues is comparatively less, thus further enhancing immune privilege.[13]

The specific immunological response of the host cornea to the donor corneal button/tissue is defined as corneal graft rejection. The diagnosis of graft rejection is made only when the graft has remained clear for at least 2 weeks after the corneal transplant. The challenge is to differentiate it from primary graft failure and the other caused by non-immunological graft failures. As per a detailed literature review, the incidence of graft rejection is maximum within the first 18 months and then reduces, although graft rejection has been reported even more than 20 years after the primary transplantation.[14]

It is the presence of corneal edema on the first postoperative day after corneal transplantation. The probable reasons are iatrogenic or surgical trauma, deficiency in storage, transport, or improperly stored tissue, and inherent deficiency in the tissue. As per the recommendations by American Eye Bank Association, the minimal endothelial count for the donor tissue should be 2000 cells/and the storage time should be less than 7 days.[15]

Descriptions of pathological features of corneal transplant rejection result from the examination of replaced grafts following irreversible failure.[16] These specimens illustrate late changes in end-stage corneal opacification, usually months following rejection treatment.[17] Characteristic findings in the stroma are vascularisation with mononuclear cell infiltration and keratocyte loss, few if any endothelial cells remain. Several studies have shown increased numbers of HLA class II positive cells infiltrating stroma in sections of rejected grafts.[18]

On detailed slit lamp examination, the typical clinical signs of corneal graft rejection are rejection lines in the epithelium, subepithelial focal infiltrates, corneal edema, patchy stromal infiltrate, Khodadoust endothelial line, presence of keratic precipitates, neovascularization. A corneal graft is labeled immunological failed if the rejection episode doesn't clear even after 2 months of intensive treatment.[20]

Secondary glaucoma is a vital complication post corneal transplantation. On every visit, intraocular pressure must be recorded. The preferred method would be a non-contact tonometer to avoid contact with the transplanted tissue and prevent any incidence of graft rejection or dehiscence.[40]

The objective of treatment is to reverse the rejection episode at the earliest possible time, minimize donor endothelial cell loss, and preserve graft function. With the anatomical advantage that corneal transplants are superficial, intensive administration of a topical corticosteroid, such as dexamethasone 0.1%, successfully reverses most endothelial rejection episodes. In most cases in which topical steroid fails to reverse rejection, it is likely to be due to delay in recognition and initiation of treatment resulting in significant donor endothelial cell loss. In others, failure to reverse rejection may be due to the failure of topical steroids to reverse effector components of the allogeneic response.[11]

The best treatment for cornea graft rejection is treating and preventing an episode of immune-mediated graft rejection. The prevention can be divided into preoperative, intraoperative, and postoperative risk factors for graft rejection.

The postoperative factors important in managing corneal graft rejection are timely and regular follow-up and reducing the host immune response to the donor graft. Timely steroid administration and suture management in decreasing suture-related vascularization and rejection.

The management of corneal graft rejection rests on prompt detection and aggressive steroid therapy. It is important to counsel the patient to present immediately if any symptoms of graft rejection like pain, redness, and decreased vision are noticed. It is highly important to know the varied drug options available to manage corneal graft rejection.[49]

This is again implicated for high-risk patients of corneal graft rejection. The recommended dose is 15 mg/kg/day for 2 days later, half dosage for 2 days, and then adjusted to reduce blood levels of 100-200 mg/l for 6 months to prevent or reverse the acute graft rejection episode. The patients should be monitored with liver and renal function tests.[55]

The prognosis in corneal grafts depends on several factors such as meticulous preoperative case selection, preoperative timing, storage and transport of donor graft, intraoperative surgical technique, meticulous postoperative examination, early detection, classification of rejection, and prompt, timely intervention with corticosteroids. The visual prognosis is governed by graft host junction opposition, centration, clarity, and graft survival postoperatively. Approximately 75% of endothelial rejections can be reversed with an excellent visual outcome. Fine and Stain, in their analysis, documented that about 50% of vascularized grafts and 66% of grafts without vascularization resulting in rejection can be reversed.[67] 2ff7e9595c