Keratoplasty
Introduction
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Classification: (a) partial (anterior or posterior lamellar) or (b) full-thickness (penetrating [PKP]).
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Indications: (a) optical, (b) tectonic, (c) therapeutic, and (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, (c) excision of host tissue, and (d) fixation of donor button ( Fig. 7.1 ); postoperative topical steroids and cycloplegics.
Fig 7.1
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Early postoperative complications: (a) persistent epithelial defect, (b) wound dehiscence, (c) uveitis, (d) elevation of intraocular pressure, (e) endophthalmitis, and (f) fixed dilated pupil (Urrets–Zavalia syndrome).
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Late complications: (a) astigmatism, (b) recurrence of disease in graft, (c) wound separation, (d) retrocorneal membrane formation, (e) glaucoma, and (f) cystoid macular oedema.
Corneal graft rejection
Can be endothelial, stromal, epithelial (rare), or combined.
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Presentation: may be asymptomatic (particularly in early stages) or 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. 7.2 ), (d) elevated epithelial line ( Fig. 7.3 ), (e) focal subepithelial (Krachmer) infiltrates ( Fig. 7.4 ), and (f) stromal oedema.
Fig 7.2
Fig 7.3
Fig 7.4
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Treatment: (a) topical steroid (dexamethasone 0.1% or prednisolone 1%) hourly for 24 h, tapered over months; (b) topical cycloplegics; and (c) systemic and/or subconjunctival steroids, topical ciclosporin, and 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, and (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, and (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, and (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), and (b) folded donor tissue is introduced through a small limbal incision.
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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, and (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 still occur, and (e) visual outcome may not be as good as with PKP.
Keratoprosthesis
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Technique: insertion of an artificial corneal implant such as an osteoodontokeratoprosthesis ( Fig. 7.5 ) in which the patient’s tooth root and alveolar bone support an optical cylinder.
