Postoperative photograph of a child following suture removal. Fine neovascularization is visible along the superior suture tracks, showing the importance of early suture removal in children
Once sutures are removed, refraction should be performed and correction given as soon as possible. Many children can tolerate a contact lens, and depending on the difference in refraction between the two eyes, this maybe preferable to glasses. One challenge specific to pediatric patients is the concurrent management of amblyopia. Especially in cases of unilateral pathology, dense amblyopia can develop, leading to poor vision even in the presence of a clear graft.
Prognosis: The prognosis for graft survival as well as graft clarity is significantly worse for pediatric keratoplasty compared to adult keratoplasty. Among children, younger patients have worse outcomes, but it is not clear if this is due to patient age or indication, since younger patients are more likely to have surgery for congenital problems, which are more likely to be associated with other ocular pathology, including congenital glaucoma or anterior segment dysgenesis. In 2009, Yang et al. published a series of 144 surgeries in 72 eyes of children (under age 12 years) with Peters anomaly and only 56% of graft were clear at 6 months (Yang et al. 2009). Comparatively, in 2011 Ganekal published a series of pediatric (5–15 years of age) keratoplasties performed for acquired corneal pathology and 79% of grafts were clear at last follow up (6–18 months) (Ganekal et al. 2011). Other series which include a range of indications for transplantation report graft failure rates from 21 to 65% (Al-Torbak 2004; Lowe et al. 2011; Patel et al. 2005; Low et al. 2014; McClellan et al. 2003; Aasuri et al. 2000).
In 2016 Karadag et al. published a series of 35 children, age 2 months to 12 years, who had primary grafts for a variety of indications showed a mean graft survival time of 45.2 ± 5.8 months (Karadag et al. 2016). In their study, the presence of glaucoma was the most significant risk factor for graft failure. Particular attention must be paid to intraocular pressure, especially given the higher requirement for steroids in pediatric keratoplasty. We find the Icare tonometer (Icare USA, Raleigh, North Carolina) is relatively well tolerated by older children and easier to perform than applanation tonometry in transplant patients.
Deep Anterior Lamellar Keratoplasty (DALK)
Indications: For children with corneal pathology that spares the endothelium, DALK is the preferred surgical technique. The benefit of maintaining the host endothelium is even greater in children, due to their increased risk of graft rejection and their high endothelial cell count (Ashar et al. 2013a; Harding et al. 2010). Additionally, the surgery itself is safer, since there is less risk of expulsive hemorrhage (Reinhardt et al. 2011). Unfortunately, congenital corneal pathology rarely spares the endothelium, so this is mostly an option for older children with acquired pathology (secondary to injury or infection) or ectasia.
Graft preparation: A potential benefit of DALK is the ability to use one donor tissue for 2 grafts: one DALK and one DMEK. Alternatively, irradiated donor tissue could theoretically be used for DALK, since an intact endothelium is not needed. This would be especially beneficial in areas where there is a corneal tissue shortage. However, since there is a risk of perforation of Descemet’s membrane necessitating conversion to a penetrating keratoplasty, we recommend having a full thickness donor graft available when performing DALK.
As for penetrating keratoplasty, the desired graft size should be determined based on corneal measurements and after detailed examination of the child. Since the lifetime risk of graft rejection is significantly less for DALK than for penetrating keratoplasty, we recommend a larger graft size, typically 8 mm in diameter. Unlike in penetrating keratoplasty, the donor cornea button should be no more than 0.5 mm greater than the host trephination.
Donor tissue should be examined under a microscope on a separate sterile field prior to partial trephination of the host cornea. The graft is then cut as for penetrating keratoplasty, placed in corneal preservation medium, and kept covered in a sterile container until needed. After successful lamellar dissection of the host cornea, the endothelium can be removed using either a forceps to peel off the Descemet’s membrane or a dry cellulose sponge to rub off Descemet’s membrane and the endothelium. Trypan blue dye can be used to stain the membrane prior to removal to improve visualization.
Surgery: Multiple techniques have been described in the literature for DALK, including use of the femtosecond laser. Here we describe our preferred technique, a version of the big bubble technique described by Dr. Anwar. Multiple techniques have been described and controversy exists regarding the need to bare Descemet membrane (dDALK) versus achieving a predescemetic plane (pdDALK) (Sarnicola et al. 2010).
The cornea is marked as for penetrating keratoplasty with a center dot and an 8-ray corneal maker. Partial trephination can be performed with either a manual trephine or a vacuum trephine with a set depth of around 400 μm (or 100 μm less than the thinnest measured preoperative corneal thickness). We then remove the anterior stroma using a crescent blade to improve visualization (though some surgeons prefer to leave the entire stroma intact until after placement of the big bubble).
An angled 15 blade is used to cut a small slit into the posterior stroma, with the blade against the trephine edge. A tunnel is created using a flat spatula and then lengthened using a flat cannula attached to a 3 cc air-filled syringe. Once the tunnel is sufficient in length, the canula tip should be angled slightly down, and air smoothly injected until a big bubble forms. When a white ring reaches the edge of the trephination and the eye feels firm, the bubble is complete. Slowly remove the canula.
The eye is now quite firm, so release some aqueous fluid by making a posterior paracentesis. Inject a small air bubble into the anterior chamber to confirm displacement of the Descemet’s membrane. The remaining posterior stroma can now be removed. Using a 15 blade, carefully but quickly nick the posterior stroma to collapse the big bubble. The anterior chamber small bubble will move to the center when the big bubble collapses. Prior to proceeding, viscoelastic should be injected through the nick to push the Descemet’s membrane back, and the anterior chamber bubble should return to the periphery.
The remaining posterior stroma is removed in sections. Using blunt Vannas or DALK scissors, make radial cuts to form pie-shaped wedges and remove them. Once all sections are removed, rinse the bed with balanced salt solution to remove all viscoelastic. The graft, as described above, is then sutured to the bed using 16-interupted 10-0 nylon sutures, taking care not to perforate the Descemet’s membrane. As for penetrating keratoplasty, suture tension is checked and all knots are buried. Using a portable slit lamp, check for a Descemet’s detachment, visible as a double anterior chamber, at the conclusion of the case. If there is an area of detachment, the anterior chamber maybe filled with air and the patient left supine for 10 min or more prior to reversal of anesthesia. Since most children will not be able to follow postoperative positioning instructions, we do not recommend leaving an air bubble in the anterior chamber at the conclusion of surgery.
As with penetrating keratoplasty, if the patient did not receive a retrobulbar or subtenon’s block prior to surgery, one can be placed at the conclusion of the case to help with postoperative pain control. Ceftazidime (100 mg in 0.5 ml) and triamcinolone (20 mg in 0.5 ml) are injected subconjunctivally. Antibiotic or antibiotic/steroid ointment is applied, and the eye is patched and shielded. General anesthesia is then reversed. Most children tolerate the procedure well.
Postoperative care: Initial postoperative care is similar to care after penetrating keratoplasty, but one of the benefits of DALK is that the steroids can be tapered much more quickly. On the first postoperative day, we typically begin topical prednisolone acetate 1% every 2 h (or 8 times daily), a topical fluoroquinolone administered four times daily, and an antibiotic/steroid ointment at bedtime. The steroids should be tapered over 1–3 months, depending on the age of the child, as well as the pathology. Suture removal will also vary with the age of the child, but all sutures are typically removed by 3–4 months, even in older children.
Refractive correction should be given as soon as possible once all sutures are removed. Since DALK is typically perfumed for corneal scarring or ectasia, which are usually unilateral or asymmetric, there is often significant amblyopia present. This should be treated aggressively and as soon as possible to optimize lifelong visual potential.
Indications: Selective endothelial keratoplasty is the procedure of choice in adults with isolated endothelial dysfunction due to multiple advantages over penetrating keratoplasty including faster visual recovery, smaller incisions with fewer sutures, and preservation of the anterior host cornea. These advantages maybe confer even greater benefits in children. Faster visual recovery, weeks rather than months, is especially beneficial in children, since it decreases the risk of amblyopia. Smaller incisions confer less risk of subsequent postoperative would rupture, which is especially important in active children. Since sutures tend to loosen and vascularize more quickly in children, fewer sutures (and use of dissolvable sutures) lessens suture-related complications and may allow the surgeon to schedule fewer exams under anesthesia in the early postoperative period, since sutures may not need to be removed.
The primary reason that selective endothelial keratoplasty is not more commonly performed in children, despite its significant advantages, is that most pediatric corneal pathology is not limited to the endothelium. The most common indications for endothelial keratoplasty in adults are Fuchs’ endothelial dystrophy and pseudophakic bullous keratopathy, neither of which is common in children. Of the most common indications for corneal surgery in children, only CHED and PPCD are localized to the endothelium. The first reported cases of DSAEK in children were published in 2008, and both were performed in aphakic children with endothelial decompensation following complicated ocular surgeries (Jeng et al. 2008; Fernandez et al. 2008). Subsequently, several reports have shown good outcomes of DSAEK in patients with CHED, PPCD, congenital glaucoma, and Peters anomaly, and this is likely to become the standard of care over time as benefits are demonstrated and techniques refined (Ashar et al. 2012; Ashar et al. 2013b; Madi et al. 2012; Hashemi et al. 2012; Kymionis et al. 2012; Ramappa et al. 2012). There is a single case report of DMEK performed in a 12-year-old with Kearns–Sayre syndrome (Gonnermann et al. 2014).
The pros and cons of DMEK versus DSAEK for endothelial keratoplasty are topics of debate in the adult literature; however, in children, DSAEK is the preferred technique for several reasons. DMEK has a higher rate of rebubbling and primary graft failure, even in the most experienced hands (Hamzaoglu et al. 2015). Also, most pediatric indications for endothelial keratoplasty are associated with poor views into the anterior chamber, making unscrolling and placement of the thinner DMEK graft very difficult. The primary proven benefit of DMEK versus DSAEK is better vision, most notably higher rates of 20/20 and 20/25 Snellen visual acuity. Most children with corneal pathology do not have visual potential in the 20/20 range, so this benefit of DMEK versus DSAEK may not apply. There is some evidence that DMEK may have lower rejection rates than DSAEK. This would be of great benefit to children, so if modifications can be made to decrease the rate of rebubbling and primary graft failure, DMEK maybe worth considering in select children.
Prior to surgery, the decision must be made regarding management of the crystalline lens. Depending on the age of the patient and other ocular pathology, implantation of an intraocular lens may be beneficial to decrease the risk of posterior dislocation of the endothelial graft and allow retention of an air bubble.
Graft preparation: Endothelial grafts can be prepared either by the eye bank or by the surgeon. Most surgeons use tissue prepared by the eye bank. The eye bank can mark the graft with a letter, such as “S”, to confirm orientation. The size of the graft varies with indication for surgery and surgeon preference, but is typically 6.5–8.5 mm. When using precut tissue, it is critical to ensure that the donor button is attached to the host stroma and aligned properly before placing it on the corneal donor trephine. The graft is then cut as per full thickness keratoplasty. Once the graft is cut to size, a cohesive viscoelastic is placed on the endothelium to protect it prior to placement into an inserter or onto the eye.
Surgery: If the patient is aphakic or phakic, and the lens is not going to be removed during the surgery, topical 2% pilocarpine (3 doses 5 min apart) should be given to constrict the pupil and reduce risk of trauma to the natural lens during surgery.
We first make 3 paracentesis incisions: one superior, one inferior, and one nasal. One of the incisions will be used for the secondary instrument, one will be used to pull the graft through (depending on insertion technique), and one will be for placement of an anterior chamber maintainer. Due to the shallow anterior chamber in most pediatric patients, we routinely use an anterior chamber maintainer. A 2.75 mm main incision is placed temporally, and is widened to 4.5–5 mm just prior to graft insertion. Though some surgeons use a clear corneal incision for DSAEK, we recommend a scleral tunnel incision due to less astigmatism and better wound healing.
Use a sterile marker to mark the center of the cornea and a circular trephine the same size as the donor button to mark the area to be scored. The unhealthy Descemet’s membrane/endothelium is stripped off, following the mark, using a reverse Sinskey hook and then an endothelial stripper. Unlike in adult patients, the Descemet’s membrane rarely comes off as one smooth membrane, so extra care must be taken to ensure that the stromal bed is bare, especially centrally. The Descemet’s membrane, or fragments of Descemet’s membrane, is then sent to pathology. The peripheral stromal bed is then scraped to help with adherence.
Peripheral iridotomies are not always performed in adult DSAEK, but should be performed in all pediatric cases due to the higher risk of angle closure. This can be performed through the sideport incision using multiple techniques. One technique is using the port of a vitrector through the adjacent incision.
There are multiple methods of tissue insertion: forceps insertion, suture pull-through, various glides, and inserters. Surgeons should use the technique they are most comfortable with, with modifications as necessary. In children who are phakic, it is critical to avoid contact with the lens, so if a pull through technique is used, nasal and temporal incisions should be shifted 1 mm superiorly.
Once the graft is in place, and correct orientation is confirmed, the primary incision is sutured with three 9-0 vicryl or 8-0 nylon sutures. Since pediatric eyes tend to be softer than adult eyes, it is best to leave the anterior chamber maintainer in place until the main incision is closed. Once the eye is closed, the anterior chamber maintainer is removed, and a full air bubble is inserted through one of the side incisions.
Since many of these young patients are aphakic, precautions must be taken to ensure that the graft does not dislocate into the posterior segment. One option is to place one or more “safety sutures” into the graft. We typically use two 10-0 nylon sutures, which we pass full thickness through the donor button. It is important to pass the suture from the periphery to the center so as not to dislocate the graft. Sutures are not typically placed in adult DSAEK grafts, since they can lead to wrinkling or the graft, damage to the endothelium along the suture track, and will need to be removed. However, in children who may not be able to position postoperatively, especially in aphakic children, the benefits of suture placement may outweigh the risks.
One reason that endothelial keratoplasty is not as widely performed in children as in adults is that most children are not capable of the postoperative positioning that is usually required. At the conclusion of endothelial keratoplasty, a partial gas bubble (either air or a longer acting gas, such as SF6) is usually left in the anterior chamber. The patient is asked to remain in the supine position for as long as the gas bubble is present to promote graft adherence (24–48 h). In children who are not able to position, the risks of a gas bubble in the anterior chamber postoperatively outweigh the benefits, so the bubble should be removed once the safety sutures are placed if the child will be unable to position. In older children who are able to position, a small air bubble maybe left in place. If an air bubble is going to be left in place, a topical cycloplegic is given at the conclusion of surgery.
Postoperative care: Initial postoperative care is similar to care after penetrating keratoplasty, but one of the benefits of DSAEK is that the steroids can be tapered and sutures removed much more quickly. On the first postoperative day, we typically begin topical prednisolone acetate 1% every 2 h (or 8 times daily), a topical fluoroquinolone administered four times daily, and an antibiotic/steroid ointment at bedtime. If an air bubble was left in place, a topical cycloplegic is used until the air bubble resolves. The steroids should be tapered over 1–3 months, depending on the age of the child, as well as the pathology. Suture removal can be performed at 1–4 weeks, typically during the first postoperative EUA.
Patients need careful monitoring, especially in the immediate postoperative period, to ensure that the graft adheres to the host. Slit lamp exams are necessary to detect interface fluid and determine the need for possible rebubbling or repositioning.
Indications: Keratoprosthesis offers a number of benefits compared to standard penetrating keratoplasty, including no risk of rejection and rapid visual recovery leading to decreased risk of amblyopia (Aquavella et al. 2007; Traish and Chodosh 2010; Kang et al. 2012). Since the synthetic optic remains clear even if the donor cornea is rejected, rejection is not an issue (although extrusion is and currently limits the longevity of keratoprosthesis in children). Other benefits include absence of astigmatism, due to the synthetic optical center of the keratoprosthesis, which leads to improved vision and easy correction of any residual refractive error with a bandage contact lens, the power of which can be easily determined by retinoscopy. Examinations are easier, since the posterior pole can be visualized through the keratoprosthesis.