Corneal surgery

Introduction

Corneal surgery in children is challenging and there is reluctance to perform these procedures due to poor outcomes. However, modern imaging modalities and surgical techniques allow for better patient selection and outcomes. Previously, almost all transplants were full-thickness penetrating keratoplasty (PKP). Now lamellar surgery allows for selective replacement of only the diseased part of the cornea ( Table 33.1 ) resulting in reduced rejection rate, need for steroid use, and susceptibility to trauma.

General Considerations and Preoperative Assessment

The choice of the most appropriate procedure depends on detailed ocular examination including anterior segment imaging (ultrasound biomicroscopy (UBM), B-scan ultrasound, and/or optical coherence tomography (OCT)). This may require examination under anesthesia (EUA) or sedation. Relevant factors include partial- or full-thickness involvement of the cornea (see Table 33.1 ), presence of glaucoma, and status of the crystalline lens and iris. The visual potential of the eye may also be limited by retinal and optic nerve disease.

Systemic abnormalities, including cardiopulmonary, central nervous, and genitourinary system abnormalities, are also common and impact safety of anesthesia. Finally, the tremendous importance of the family on the outcome of surgery must be emphasized. Parental commitment to long-term care beyond surgery, which includes compliance with eye drops, spectacle correction, amblyopia treatment, and frequent postoperative visits heavily influences the success of any intervention.

The main indications for surgery in infants are congenital corneal opacities (CCOs), the commonest of which is Peters anomaly (PA). Figure 33.1 shows a treatment algorithm for Peters anomaly that takes into account the phenotypic spectrum of the disease. If the opacity does not involve the central 3 mm of visual axis, management can be limited to the treatment of amblyopia and refractive correction. Opacities partially involving the visual axis with clear corneal periphery may be treated with optical iridectomy, a less invasive and viable long-term alternative to keratoplasty (see Fig. 33.1 ).

Penetrating Keratoplasty (PKP)

The timing of surgery for CCOs is a balance between obtaining best visual outcome whilst minimizing risk of complications. In general, a delayed surgery is technically easier, has less risk of glaucoma and graft rejection leading to better graft survival. However, the visual potential may be reduced if surgery is performed after the critical period of visual development. In dense opacities, keratoplasty by 3 months of age allows for preoperative assessments, counseling for parents, and systemic work up while offering adequate visual rehabilitation. Regular preoperative follow-up (every 2–3 weeks) is required to screen for glaucoma, which requires prompt diagnosis and intervention before keratoplasty. The second eye in bilateral cases can be performed a week after the first to simplify the drop regimen, follow-up, and suture removal planning for the family whilst reducing the risk of amblyopia.

Corneoscleral tissue in infants has low rigidity and high elasticity, and easily collapses during surgery. This in concert with elevated posterior vitreous pressure increases the risk of intraocular content expulsion. An experienced pediatric anesthetist delivering deep anesthesia with muscle relaxant, hyperventilation, and intravenous 20% mannitol (0.5 g/kg body weight) can help reduce posterior pressure. Mannitol is best given when the Flieringa ring is secured to the eye (see below). CCOs can be associated with an abnormally anterior conjunctival insertion onto the cornea, hence conjunctival recession helps preserve limbal stem cells. A suitably-sized Flieringa ring is secured to the globe for support. Iridocorneal or keratolenticular adhesions are divided with gentle injection of viscoelastic and blunt division of adhesions. Care should be taken to avoid damage to the lens. Donor and trephination sizing should account for the reduced size of the host cornea whilst ensuring that adequate numbers of corneal endothelial cells are transplanted. Oversizing the donor by 0.5 mm facilitates wound closure and vaulting of the cornea to increase anterior chamber (AC) depth. However, oversizing >0.5 mm may cause excessive corneal steepening, high myopia, and corneal exposure postoperatively. Furthermore, large donor diameter (>8.0 mm) is associated with reduced graft survival in children with PA.

A “sandwich technique” involves suturing the donor to the host tissue prior to complete removal of the host button to minimize open globe time during the surgery ( Video 33.1 ). Non-absorbable interrupted sutures are used in pediatric keratoplasty due to the risks of early suture loosening and infection.

Postoperatively, follow-up is frequent initially and aimed at identifying any signs of glaucoma, suture loosening, infection or rejection, any of which should trigger appropriate intervention. Antibiotic drops are required until sutures are removed. Topical steroids are frequently used initially and tapered over the ensuing months to once daily or alternate daily dose, then maintained in the long term to prevent rejection.