Keratoplasty
Introduction
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Classification : (a) partial (anterior or posterior lamellar), (b) full-thickness (penetrating).
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Indications : (a) optical, (b) tectonic, (c) therapeutic, (d) cosmetic.
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Donor tissue : should be removed within 12–24 hr of death and stored under special conditions. Contraindications to donation include certain infections (e.g. HIV) and some forms of ocular disease.
Penetrating keratoplasty
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Technique : (a) determination of graft size, (b) trephination of donor tissue ( Fig. 8.1A ), (c) excision of host tissue ( Fig. 8.1B ), (d) fixation of donor button ( Fig. 8.1C ); postoperative topical steroids and cycloplegics.
Fig. 8.1
Penetrating keratoplasty: (A) trephination, (B) excision of host tissue, (C) fixation of donor button.
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
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Early postoperative complications : (a) persistent epithelial defect, (b) wound dehiscence, (c) uveitis, (d) elevation of intraocular pressure, (e) endophthalmitis, (f) fixed dilated pupil (Urrets–Zavalia syndrome).
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Late complications : (a) astigmatism, (b) recurrence of disease in graft ( Fig. 8.2A ), (c) wound separation, (d) retrocorneal membrane formation, (e) glaucoma, (f) cystoid macular oedema.
Fig. 8.2
Complications: (A) recurrence of microbial keratitis, (B) allograft rejection showing Khodadoust line, (C) epithelial rejection line, (D) Krachmer spots.
( Figure 8.2C,D courtesy of S. Tuft.)
Corneal graft rejection
Can be endothelial, stromal, epithelial (rare), or combined.
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Presentation : may be asymptomatic (particularly in early stages). Later with blurred vision, redness, photophobia and pain.
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Signs : (a) ciliary injection, (b) anterior uveitis, (c) linear endothelial precipitates (Khodadoust line) ( Fig. 8.2B ), (d) elevated epithelial line ( Fig. 8.2C ), (e) focal subepithelial (Krachmer) infiltrates ( Fig. 8.2D ), (f) stromal oedema (increase in central corneal thickness).
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Treatment : (a) topical steroid (dexamethasone 0.1% or prednisolone 1%) hourly for 24 hours tapered over months, (b) topical cycloplegics, (c) systemic and/or subconjunctival steroids, (d) topical ciclosporin, (e) systemic immunosuppressives may be used in some cases.
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Differential diagnosis : (a) graft failure (no inflammation), (b) infective keratitis, (c) sterile suture reaction, (d) epithelial ingrowth.
Superficial lamellar keratoplasty
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Technique : partial-thickness excision of the stroma.
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Indications : (a) opacification of the superficial one-third of the stroma, (b) marginal corneal thinning or infiltration, (c) Terrien marginal degeneration, (d) limbal tumours.
Deep anterior lamellar keratoplasty
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Technique : opaque corneal tissue removed almost to the level of Descemet membrane.
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Indications : (a) disease of the anterior 95% of corneal thickness with normal endothelium and intact Descemet membrane (e.g. no history of acute hydrops), (b) chronic inflammatory disease with a higher risk of rejection (e.g. atopic keratoconjunctivitis).
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Advantages : (a) no endothelial rejection, (b) less astigmatism, (c) structurally stronger globe, (d) increased availability of graft material because endothelial quality is irrelevant.
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Disadvantages : technically difficult and time-consuming; interface haze may limit visual outcome.
Descemet stripping endothelial keratoplasty
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Technique : (a) endothelium and Descemet membrane are removed (descemetorhexis), (b) folded donor tissue is introduced through a small limbal incision, (c) anterior chamber air.
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Indications : endothelial disease (e.g. pseudophakic bullous keratopathy).
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Advantages : (a) little refractive change, (b) structurally stronger globe, (c) no sutures.
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Disadvantages : (a) significant learning curve, (b) expensive equipment required for automated method, (c) posterior graft dislocation rate of 15%, (d) endothelial rejection can occur.
Limbal stem cell grafting
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Technique : (a) transplantation of a limbal area of limited size from a healthy fellow eye, (b) transplantation of a donor annulus and ex vivo expansion by tissue culture of either host or donor stem cells.
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Indications : (a) congenital, e.g. aniridia, (b) traumatic, e.g. chemical and thermal burns, (c) chronic inflammatory disease, e.g. Stevens–Johnson syndrome, ocular cicatricial pemphigoid, (d) ocular surface malignancy, (e) contact lens-related pathology.
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Complications : (a) infection, (b) rejection, (c) scarring of donor eye, (d) filamentary conjunctivitis, (e) conjunctivalization.
Keratoprosthesis
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Technique : insertion of an artificial corneal implant such as an osteoodontokeratoprosthesis ( Fig. 8.3A ), in which the patient’s tooth root and alveolar bone support an optical cylinder.
