Penetrating Keratoplasty in Keratitis: Indications and Contraindications
Primary Indications
Penetrating keratoplasty (PK) is indicated for keratitis when medical therapy fails to control the infection, when corneal perforation occurs or is imminent, or when deep stromal involvement makes other surgical approaches unsafe. 1
Therapeutic Indications
Visual improvement is the most common reason for full-thickness corneal transplant, particularly when edema with opacification involves all corneal layers 1
Tectonic restoration is required when the cornea is thin, perforated, or when perforation is imminent 1
Therapeutic transplant for unresponsive microbial infection that cannot be controlled with antimicrobial medication alone 1, 2
Early surgical intervention before disease becomes advanced is recommended for fungal keratitis that does not respond to antifungal medication 2
Specific Clinical Scenarios
Deep stromal scarring where perforation is more likely to occur during deep anterior lamellar keratoplasty (DALK), making PK the preferred approach 1
Peripheral corneal involvement extending beyond the central 7.5 to 9.0 mm, requiring oversized or tectonic grafts 1
Persistent corneal edema following hydrops 1
Combined anterior segment pathology requiring additional procedures such as iris reconstruction, cataract removal, IOL exchange, or vitrectomy 1
Contraindications
PK may be contraindicated if multiple prior full-thickness corneal transplants have failed or if extensive anterior segment scarring is present. 1
Absolute and Relative Contraindications
Multiple failed previous full-thickness transplants indicate poor prognosis for subsequent grafts 1
Extensive anterior segment scarring compromises surgical outcomes 1
Corneal thinning extending near the limbus makes PK more challenging and carries greater risk of failure 1
Deep stromal vascularization may be better managed with alternative approaches 1
Critical Surgical Principles
Complete Excision Requirement
It is critical that the surgical procedure remove the infected tissue in its entirety to effect a cure. 2 Incomplete excision of infected tissue is associated with recurrence, particularly in fungal keratitis where most recurrences appear within six weeks after surgery 3
Timing Considerations
Therapeutic keratoplasty should be performed before the disease becomes advanced 2
For bacterial keratitis, therapeutic success rates of 76.6% at one year have been reported 3
For fungal keratitis, therapeutic success rates of 72.4% at one year are achievable, though infection recurrence remains a significant problem 3
Complications and Outcomes
Major Complications
Infection recurrence occurs in 7.4% of cases, with fungal keratitis having higher recurrence rates than bacterial keratitis 2, 3
Graft rejection occurs in approximately 29.6% of cases 2
Secondary glaucoma (1.9%), cataract formation (4.6%), and poor refractive outcomes including anisometropia or high corneal astigmatism 1, 2
Endophthalmitis and graft failure are additional serious complications 1
Expected Outcomes
Anatomical integrity is achieved in approximately 91.3% of perforated eyes 4
Clear grafts are maintained in 60.9% of perforated eyes and 57.1% of eyes where perforation was imminent 4
Visual acuity of 20/100 or better is achieved in approximately 40.5% of therapeutic PK cases 4
Graft survival rates of 79.6% with clear grafts during follow-up have been reported for fungal keratitis 2
Common Pitfalls
Delaying surgical intervention until the infection is too advanced reduces therapeutic success rates 2, 3
Inadequate excision of infected tissue leads to recurrence, particularly in fungal cases 2
Inappropriate corticosteroid use during active infection, especially with Nocardia or fungal keratitis, leads to poor outcomes 1, 5
Failure to continue antifungal therapy postoperatively for 1-2 months with gradual tapering increases recurrence risk 2
Premature use of topical steroids before infection control is achieved (should wait at least 2 weeks post-PK for fungal cases) 2