FEATURES:
(Always examine the cornea under high magnification)
Once it has been noted that the patient has undergone a corneal transplant, the patient needs to be examined in detail as follows.
Cornea:
Sutures –
Pattern – continuous or interrupted or mixed.
Number of sutures
The integrity of sutures – tight, loose, broken, cheese wiring through donor or recipient cornea, focal vascularization towards a specific suture, mucus strands/suture abscess, burial of knots
Graft Host junction:
Apposition
Interface Haze / opacification
Wound dehiscence/ectasia
Graft
the graft Is Full thickness or lamellar by looking at the edges of the graft.
Check the graft for:
Corneal integrity,
signs of rejection
Epithelial Rejection – Epithelial rejection may be seen in two morphologically different variants.
a line located near engorged limbal vessels, with migration across the graft-recipient interface. The line consists of lymphocytes, plasma cells, and neutrophils. These lines can precede endothelial rejection by days to weeks.
a ring concentric with the limbus, which begins peripherally at the graft-host junction and progresses by shrinking centrally to a point. The rejection line represents a region of the destruction of donor epithelium; the resulting epithelial defect is covered by host epithelium that grows inward from the remaining host cornea and limbus to cover the graft.
Subepithelial Rejection: The second type of epithelial rejection is characterized by the presence of subepithelial infiltrates. These infiltrates consist of leukocytes and frequently have an appearance similar to the subepithelial infiltrates seen in adenoviral keratoconjunctivitis. These lesions may change location and shape over time, and they generally disappear without intervention after several weeks.
Endothelial Rejection
the most common form cause for about 50% of graft rejections - However, if graft rejection is diagnosed early and treated with corticosteroids aggressively, irreversible graft failure can often be avoided by minimizing the loss of endothelial cells
Classic endothelial rejection presents with an endothelial rejection line (Khodadoust line) that usually begins at a vascularized portion of the peripheral graft-host junction and progresses, if untreated, across the endothelial surface over several days. The rejection line consists of mononuclear white cells that damage endothelial cells as the line sweeps across the endothelium. Generally, a mild-to-moderate anterior chamber reaction is present. The damaged endothelium is unable to properly dehydrate the corneal graft; as a result, the donor cornea is clear ahead of the rejection line and is cloudy and edematous behind it.
A second variant of endothelial rejection is more diffuse in character, with scattered keratic precipitates and an anterior chamber reaction indicative of endothelial rejection and damage. In this type of endothelial rejection, stromal edema typically is not localized, but rather generalized throughout the graft, consistent with the generalized endothelial damage. The combination of keratic precipitates, an anterior chamber reaction, circumcorneal injection, and regions of corneal edema should be diagnosed as corneal graft rejection. In some cases, it may be difficult to distinguish graft edema from rejection and graft edema from endothelial insufficiency. Because rejection may be reversible, treating patients as if they have graft rejection is best.
• Look at the recipient’s Cornea for Signs of Dystrophy
• Look at the cornea of the other eye for signs of Keratoconus or Dystrophy
• Look for Epithelial ingrowth / down growth.
• Keratometry
(Usually, with such conditions, the examiner would want to assess your clinical skills in using the slit lamp.)
LENS
• Lens: Intraocular lens implant, especially anterior chamber IOL, suggests Pseudophakic Bullous keratopathy as the cause of transplant.
ANTERIOR CHAMBER:
• Reaction
• ACIOL
• Tube Implant
IRIS AND PUPIL:
• Nonreactive dilated pupil – Urrets Zavalia Syndrome
CONJUNCTIVA, EPISCLERA & SCLERA
• Blue Sclera – associated with collagen vascular disease, may be associated with Keratoconus.
• Signs of Scleral tear repair
Intraocular Pressure:
Systemic Features for Corneal Transplantation:
Questions:
What are the post-operative complications of corneal grafts?
Problems related to surgery:
Wound leak, re-suturing, patching, or contact lenses are useful
Flat chamber/iris incarceration in the wound: poor integrity of the wound or high IOP. Early surgical intervention important
Glaucoma: aggressive treatment is important
Endophthalmitis
Suture-related problems:
tightening, loosening, infectious abscesses, and vascularization along suture tracks, etc.
Non-immune corneal problems
Primary endothelial failure: from deficiency of donor endothelium and the graft is oedematous from the first postoperative day and remains so without inflammatory signs
Persistent epithelial defect: usually heal in 14 days. Exclude ocular surface disease, e.g., dry eye, exposure, trichiasis, etc
Recurrence of primary disease: e.g., viral/amoebic keratitis
Infectious keratitis: increased by decreased corneal sensation and topical steroid used. Late non-immune endothelial failure: oedematous graft months or years later without inflammatory signs
Postoperative corneal astigmatism:
treated by removing sutures, use of contact lenses, and sometimes refractive surgery.
Graft rejection
rare within the first 2 weeks, early recognition gives good results. Endothelial rejection is the most serious. Inflammatory precipitates are seen on the endothelial surface in linear form (Khodoudoust line). Untreated, it causes corneal edema.
Subepithelial infiltrates may resemble adenoviral infection, may be directed at the donor epithelium or keratocytes, may predate more serious rejection donor epithelium may be directed, give a rejection line. As the host cells replace lost donor epithelium, this rejection is important in that it may herald endothelial rejection.
Continuous topical steroids are the treatment of choice, and ointment does not possess good bioavailability. Can be given by periocular injection. Systemic steroids and sometimes topical cyclosporin are useful in reversing the rejection.
What is the difference between graft rejection and failure?
The term graft rejection refers to a specific immunologic response of the host to the donor corneal tissue. It should be distinguished from other non-immune mediated graft failures, such as primary donor failure. Primary donor graft failure is defined as cornea edema that never clears from the immediate postoperative period secondary to inherent deficiencies in the donor graft, surgical trauma, or improperly stored tissue.[4] It is advised by the Eye Bank Association of America that ideal donor corneas should have at least 2000 cells/mm2 and be stored for less than 7 days.[5] Diagnosis of rejection should only be made in grafts that have remained clear for at least 2 weeks following surgery. The incidence of rejection is greatest in the first year and a half following the transplant but can occur up to 20 years or more after surgery. Guilbert et al. reported an average keratoplasty-to-rejection time of 19.8 ± 20.4 months (among 299 patients who experienced a rejection episode). The progression from rejection to failure was 49% [6].
What is the fate of PKP grafts?
In uncomplicated or "low risk” penetrating keratoplasty (PKP) primary grafts, the survival rate with local immune suppression has been reported to be as high as 95% at 5 years(1)
In contrast, in “high-risk” recipients, such as those with vascularization of the cornea, the failure rate can easily exceed 35% in three years(2)
Stromal immune rejection can occur in DALK between 1-24%. [9] Clinically, stromal rejection can present with stromal infiltrates and neovascularization within the graft-host interface.[8]
DSEK has a mean endothelial rejection rate of 10% (range 0% to 45%) and an average primary graft failure of 5% (range 0% to 29%), according to a review by the American Academy of Ophthalmology (AAO).[10]
DMEK has a very low rejection rate (mean of 1.9%, range 0% to 5.9%).[11] According to a 2017 report by the AAO, DMEK has a primary graft failure rate of 1.7% (range 0% to 12.5%) and a secondary graft failure rate of 2.2% (range 0% to 6.3%).[11]
What are the factors contributing to the immune privilege of the cornea?
Absence of vascularity that hinders delivery of immune elements
Absence of corneal lymphatics that prevents delivery of antigens to T cells in lymph nodes
Expression of FAS ligand that can induce apoptosis of stimulated Fas+T cells
An unusually low expression of MHC antigens
A unique spectrum of immunomodulatory factors that inhibit T cell and complement activation (3)
Despite being an “immunologically privileged” site, the most common cause of graft failure is irreversible, immunologic allograft rejection.
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