Pediatric Keratoplasty
Pediatric penetrating keratoplasty is technically more challenging than adult keratoplasty because of a smaller anatomical configuration, reduced rigidity and increased elasticity of the cornea and sclera, and alarming posterior pressure with forward movement of the lens-iris diaphragm. The cornea is often thinner and more pliable. Lens expulsion also appears imminent, particularly in infants. Therefore, every measure to reduce vitreous pressure should be employed. Working with an experienced pediatric anesthesiologist is desirable. Paralysis induced by a nondepolarizing muscle relaxant monitored with a peripheral nerve stimulator eliminates the risk of movement and contraction of the extraocular muscles. Hyperventilation and positioning the patient's head slightly higher than their feet can also reduce posterior pressure. Manual ocular massage or Honan balloon, applied at 30 mmHg for 5 min or more, is another effective maneuver. Preoperative intravenous mannitol (0.5-1.5 g/kg/dose) can be given to decrease vitreous volume. Peak action occurs approximately 45 min after administration. However, it must be used carefully because mannitol can cause hemodynamic instability and electrolyte imbalance. A lateral canthotomy can also be helpful in improving surgical exposure in some infants with small palpebral fissures and may reduce posterior pressure.
Corneal diameters should be measured to enable decisions about the size of the host bed and graft. A Flieringa or scleral support ring should be used in every pediatric keratoplasty to help prevent scleral collapse during surgery (Figure 1). The ring diameter should be 2-3 mm greater than the corneal diameter. It should be secured to the episclera over the pars plana with four interrupted 6-0 Vicryl® sutures, taking care to avoid perforating the thin sclera. Additional sutures can be placed to stabilize the ring if needed. Two 4-0 silk stay sutures tied to the ring can then be clamped to the drape to improve positioning of the eye. Care should be taken to ensure that the speculum, surgeon and assistant do not apply any pressure to the eye. Despite taking all precautions, one should be aware of and prepared for the possibility that the iris and lens can move forward as soon as the eye is opened.
(Enlarge Image)
Photograph of a child with iatrogenic acquired dense central corneal opacification, secondary to trauma from a tube shunt, undergoing penetrating keratoplasty. Note the scleral support ring is sized so that it is 2 mm away from the limbus in all directions. It is secured with four 6-0 Vicryl® sutures and two silk stay sutures to position the eye.
The geographic center of the cornea is identified and marked. The donor cornea is then punched and the recipient cornea is trephined. Most pediatric grafts vary in size between 6 and 7.5 mm. A small graft may be optically suboptimal because of larger pupil size in children. The lower number of viable endothelial cells transplanted in a small graft is another disadvantage. The donor graft should be oversized by 0.5-1 mm to provide adequate anterior-chamber depth, minimize the formation of goniosynechiae, lower the incidence of glaucoma and increase the morphological success of corneal grafting. Furthermore, oversized grafts can facilitate secure closure of the eye, but some surgeons feel that oversizing the graft by more than 0.75 mm increases the risk of drying and the steepness of the cornea.
An increase in fibrin formation in infants and children can produce iris adhesions to the wound. To avoid the synechiae, a viscoelastic agent should be placed in the anterior chamber as soon as the anterior chamber is entered. Viscoelastic agents can also help to lyse pre-existing iridocorneal adhesion. The viscoelastic agent placed on the lens-iris diaphragm before bringing the graft to the wound can protect the corneal endothelium from surgical trauma. Anterior chamber irrigation with a 100 U/ml heparin solution immediately after trephination of the recipient cornea has also been suggested to prevent fibrin formation, subsequent synechiae and secondary glaucoma. Wound closure is accomplished with 90% depth, 16 10-0 nylon sutures, as in adult corneal transplantation (Figure 2). As the sutures cannot be removed selectively in children, particular attention should be paid to equal distribution of the donor tissue in the recipient bed to minimize graft astigmatism. Interrupted sutures are preferable because they reduce the chance of wound dehiscence from a broken suture and allow for staged removal if they begin to erode before the wound is sufficiently healed. All suture knots should be buried to reduce the risk of infection and discomfort.
(Enlarge Image)
Same eye as in Figure 1 with a dense, membranous cataract with iris adhesions that was seen after removal of the host cornea.
The decision to perform peripheral iridectomy should be made judiciously. An iridectomy might deepen the anterior chamber, reducing the risk of anterior synechiae formation; however, it can also cause bleeding and crystalline lens trauma. Therefore, it should only be performed as prophylaxis against a sequestered pupil if the eye is inflamed prior to the transplantation, already has significant posterior synechiae or has had or is having a lensectomy with anterior vitrectomy. Furthermore, a concomitant pupilloplasty, lensectomy (Figure 3) and anterior vitrectomy should be conducted wherever necessary. After wound closure, the eye should be carefully inspected to ensure that there is no iridocorneal adhesion. Occasionally, while the child is still under anesthesia, the clear media may allow the surgeon to obtain an initial view of the retina and optic disc with an indirect ophthalmoscope. Subconjunctival injections of an antibiotic and a corticosteroid are given at the conclusion of the surgery.
(Enlarge Image)
The same eye as in Figure 1 & 2 with the graft sewn into place with 16 interrupted 10-0 nylon sutures.
Pediatric penetrating keratoplasty is technically more challenging than adult keratoplasty because of a smaller anatomical configuration, reduced rigidity and increased elasticity of the cornea and sclera, and alarming posterior pressure with forward movement of the lens-iris diaphragm. The cornea is often thinner and more pliable. Lens expulsion also appears imminent, particularly in infants. Therefore, every measure to reduce vitreous pressure should be employed. Working with an experienced pediatric anesthesiologist is desirable. Paralysis induced by a nondepolarizing muscle relaxant monitored with a peripheral nerve stimulator eliminates the risk of movement and contraction of the extraocular muscles. Hyperventilation and positioning the patient's head slightly higher than their feet can also reduce posterior pressure. Manual ocular massage or Honan balloon, applied at 30 mmHg for 5 min or more, is another effective maneuver. Preoperative intravenous mannitol (0.5-1.5 g/kg/dose) can be given to decrease vitreous volume. Peak action occurs approximately 45 min after administration. However, it must be used carefully because mannitol can cause hemodynamic instability and electrolyte imbalance. A lateral canthotomy can also be helpful in improving surgical exposure in some infants with small palpebral fissures and may reduce posterior pressure.
Corneal diameters should be measured to enable decisions about the size of the host bed and graft. A Flieringa or scleral support ring should be used in every pediatric keratoplasty to help prevent scleral collapse during surgery (Figure 1). The ring diameter should be 2-3 mm greater than the corneal diameter. It should be secured to the episclera over the pars plana with four interrupted 6-0 Vicryl® sutures, taking care to avoid perforating the thin sclera. Additional sutures can be placed to stabilize the ring if needed. Two 4-0 silk stay sutures tied to the ring can then be clamped to the drape to improve positioning of the eye. Care should be taken to ensure that the speculum, surgeon and assistant do not apply any pressure to the eye. Despite taking all precautions, one should be aware of and prepared for the possibility that the iris and lens can move forward as soon as the eye is opened.
(Enlarge Image)
Photograph of a child with iatrogenic acquired dense central corneal opacification, secondary to trauma from a tube shunt, undergoing penetrating keratoplasty. Note the scleral support ring is sized so that it is 2 mm away from the limbus in all directions. It is secured with four 6-0 Vicryl® sutures and two silk stay sutures to position the eye.
The geographic center of the cornea is identified and marked. The donor cornea is then punched and the recipient cornea is trephined. Most pediatric grafts vary in size between 6 and 7.5 mm. A small graft may be optically suboptimal because of larger pupil size in children. The lower number of viable endothelial cells transplanted in a small graft is another disadvantage. The donor graft should be oversized by 0.5-1 mm to provide adequate anterior-chamber depth, minimize the formation of goniosynechiae, lower the incidence of glaucoma and increase the morphological success of corneal grafting. Furthermore, oversized grafts can facilitate secure closure of the eye, but some surgeons feel that oversizing the graft by more than 0.75 mm increases the risk of drying and the steepness of the cornea.
An increase in fibrin formation in infants and children can produce iris adhesions to the wound. To avoid the synechiae, a viscoelastic agent should be placed in the anterior chamber as soon as the anterior chamber is entered. Viscoelastic agents can also help to lyse pre-existing iridocorneal adhesion. The viscoelastic agent placed on the lens-iris diaphragm before bringing the graft to the wound can protect the corneal endothelium from surgical trauma. Anterior chamber irrigation with a 100 U/ml heparin solution immediately after trephination of the recipient cornea has also been suggested to prevent fibrin formation, subsequent synechiae and secondary glaucoma. Wound closure is accomplished with 90% depth, 16 10-0 nylon sutures, as in adult corneal transplantation (Figure 2). As the sutures cannot be removed selectively in children, particular attention should be paid to equal distribution of the donor tissue in the recipient bed to minimize graft astigmatism. Interrupted sutures are preferable because they reduce the chance of wound dehiscence from a broken suture and allow for staged removal if they begin to erode before the wound is sufficiently healed. All suture knots should be buried to reduce the risk of infection and discomfort.
(Enlarge Image)
Same eye as in Figure 1 with a dense, membranous cataract with iris adhesions that was seen after removal of the host cornea.
The decision to perform peripheral iridectomy should be made judiciously. An iridectomy might deepen the anterior chamber, reducing the risk of anterior synechiae formation; however, it can also cause bleeding and crystalline lens trauma. Therefore, it should only be performed as prophylaxis against a sequestered pupil if the eye is inflamed prior to the transplantation, already has significant posterior synechiae or has had or is having a lensectomy with anterior vitrectomy. Furthermore, a concomitant pupilloplasty, lensectomy (Figure 3) and anterior vitrectomy should be conducted wherever necessary. After wound closure, the eye should be carefully inspected to ensure that there is no iridocorneal adhesion. Occasionally, while the child is still under anesthesia, the clear media may allow the surgeon to obtain an initial view of the retina and optic disc with an indirect ophthalmoscope. Subconjunctival injections of an antibiotic and a corticosteroid are given at the conclusion of the surgery.
(Enlarge Image)
The same eye as in Figure 1 & 2 with the graft sewn into place with 16 interrupted 10-0 nylon sutures.