Corneal graft
 

A penetrating corneal graft performed for advanced keratoconus. The sutures are interrupted. A tetonic graft performed for peripheral corneal perforation  resulting from rheumatoid arthritis-related corneal melt

The patient has a R/L or bilateral corneal graft(s). This may be penetrating or lamellar (look at the edge of the graft for the  thickness ). The sutures are interrupted / continuous or a combination of both. If the graft is eccentric as in the picture  above, it is likely to be tetonic (for descemetocele or perforating cornea). Check the graft for: signs of rejection which may be epithelial, stromal or endothelium. Rejection lines on the endothelium is called  Khodahoust's line. Do not forget to look for keratic precipitates as well as cells or flare in the anterior chamber. security of the suture and any pannus around the suture(s) Look for the cause for corneal grafts: presence of intraocular lens especially anterior chamber lens suggest pseudophakic bullous keratopathy look at the recipient cornea for signs for corneal dystrophy (this is especially obvious with macular dystrophy  which extend to the peripheral cornea) examine the other eye for signs of dystrophies or keratoconus. in tetonic graft observe the patient's hands for rheumatoid arthritis which may be the cause of peripheral  corneal melt

Questions:

1. How are donor cornea being stored in the eye bank?

Answer                              The two main methods of storing corneas are by refrigeration at 4°C
                             or in organ culture at 31 to 37°C . The former method is used
                             predominantly in the USA, whereas organ culture is now used by
                             most of the major European eye banks.

                             Virtually all eyes coming into an eye bank are likely to carry surface

                             microbial contaminants. Eyes are therefore first washed in several
                             changes of sterile saline, immersed in a dilute iodine solution, which is
                             neutralized with sodium thiosulphate, and then given a final wash in
                             saline to reduce as far as possible any contamination on the ocular
                             surface. The cornea with a 3-4mm rim of selera is then carefully
                             excised taking care to avoid damage to the endothelium. A suture is
                             placed through the scleral rim and the cornea is suspended in about
                             80-ml of tissue culture medium. All of these procedures are carried
                             out in a Class II biological safety cabinet both to create a sterile area
                             for dissection of the cornea and to protect the technician from
                             potentially hazardous human tissue. The corneas are then stored in an
                             incubator at 34°C. After a week, a sample of medium is withdrawn
                             to check for bacterial and fungal infection - up to 4% of corneas are
                             discarded for this reason. Apart from the longer storage time
                             afforded by organ culture, there is a much greater opportunity to
                             detect bacterial fungal infection in the tissue than with hypothermic
                             storage and, consequently, there is a reduced risk of post-operative
                             endophthalmitis: it is estimated that the incidence of endophthalmitis is
                             perhaps up to 20-fold lower with organ-cultured corneal grafts.

2. How is the cornea assessed before being used for graft?

Answer
 The quality of the tissue is assessed, primarily by examination of the
              endothelium by light microscopy, three days before the scheduled
              date of grafting to allow estimation of endothelial cell density and to
              detect endothelial damage or other abnormalities. A minimum cell
              density of 2200 cells/mm2 with no central stromal opacity is
               considered acceptable for penetrating grafts: corneas that do not
                meet these criteria are made available for lamellar grafts or
               epikeratoplasty. This quality assessment means that no age limits to
               corneal donation need be set. While it is true that with increasing age
               there is a greater likelihood that the corneas will not be suitable for
               full-thickness grafts, simply because of the decline in endothelial cell
               density with age, half of the corneas from donors over 80 years old
               do in fact turn out to be suitable for transplantation.

                Because corneas become oedematous and thickened during organ

                culture, they are transferred to tissue culture medium containing 5%
                dextran after assessment of the endothelium. The osmotic effect of
                 the dextran thins the cornea and returns it towards normal thickness
                 prior to surgery. It is not feasible to include dextran in the long-term
                 organ culture medium because it does slowly permeate the stroma
                 and is even taken up into endothelial cells by endocytosis. The
                 corneas can remain in this medium for four days by which time they
                 would have been transported to a recipient hospital and grafted.

3. What are the post-operative complications of corneal graft and how would you manage them?

Answer
Problems related to surgery and sutures
wound leak: resuturing, patching or contact lenses
flat chamber/iris incarceration in the wound: poor integrity of the wound or high intraocular pressure. Early surgical intervention is important
endophthalmitis: parecentesis and vitreous tap for culture and sensitivity followed by intravitreous antibiotic with amikacin and vancomycin
suture-related problems: tightening, loosening, infectious abscesses and vascularization along suture tracks etc. The sutures are removed and appropriate treatment given

Non-immune corneal problems:

primary endothelial failure: from deficiency of donor endothelium or the cornea is sutured with the endothelium side up by mistake. Regraft is the only option
Persistent epithelial defect: this usually heal by 14 days. Treat any dry eyes, exposure keratitis or trichiasis.
recurrence of primary disease: treat the conditions such as herpes keratitis as appropriate
infectious keratitis: intensive topical antibiotics are needed
late non-immune endothelial failure: regraft is needed
post-operative corneal astigmatism: removed the offending sutures and consider the use of contact lens. Refractive surgery may be needed

Graft rejection
usually occurs after the first two weeks and early recognition is important for good outcome
endothelial rejection is the most serious. Keratic precipitates and Khoudahoust's lines may be seen. Patient should be admitted for intensive topical steroid
subepithelial infiltrates may resemble adenoviral infection, may be directed at the donor epithelium or keratocytes and may precede more serious rejection. Topical steroid is the treatment of choice
donor epithelium may be rejected giving to a rejection line. As the host cells replace lost donor epithelium, this rejection is less serious than endothelium rejection but it may precede endothelium rejection.

Return to the main page