Pediatric penetrating keratoplasty
Pediatric penetrating keratoplasty (or full thickness cornea transplant) is defined as penetrating keratoplasty in a patient younger than 18 years old. It is often convenient, in order to look more accurately at preoperative, intraoperative, and postoperative issues, to divide these children into more narrowly defined age groups.
Indications for Pediatric Penetrating Keratoplasty
- Congenital causes of corneal opacities: Peters', glaucoma with corneal edema, Posterior Polymorphous Corneal Dystrophy (PPMD), Sclerocornea, Congenital hereditary endothelial dystrophy (CHED), etc
- Acquired traumatic causes of corneal opacities: laceration, scarring, cornea blood staining
- Acquired, non-traumatic causes of corneal opacities: infectious keratitis (HSV, bacterial, fungal), exposure keratitis, neurotrophic keratitis, interstitial keratitis, keratoconus, Stevens Johnson Syndrome (SJS), etc
Unique challenges associated with pediatric penetrating keratoplasty
Of course the most important preoperative consideration is whether the possible benefits of the surgery outweigh the possible risks and whether all alternatives to penetrating keratoplasty have been considered. For example, DSEK (Descemet's Stripping Endothelial Keratoplasty) and DALK (Deep Anterior Lamellar Keratoplasty) have been successfully performed for certain condiions in the pediatric population in recent years. Sectoral iridectomy can be considered if the peripheral cornea is clear. Finally, in cases of unilateral corneal opacities, it might be preferable to not doing any surgery in order to not risk making the patient even worse than they already are. In fact, because of the arduous postoperative care that is required and the low rates of success, some surgeons recommend never operating on unilateral cornea disease. Others believe that it is still worth the risks in order to give the patient a chance at binocular vision and to provide a "spare" in case something happens to the good eye.
Other considerations include the significant support network that is necessary to make this a successful surgery for an infant or child. Parents must realize that their child will need very frequent (possibly every hour in the early postoperative period) administration of topical steroids. They will need frequent postoperative visits. They will need coordination of care among cornea specialists, pediatric ophthalmologists, and possibly optometrists. They will require a commitment to amblyopia therapy in the postoperative period. There is significant time and cost involved in caring for these patients.
The anatomy of a young eye can present unique challenges.
- Low scleral rigidity can cause collapse of the globe during surgery and a scleral fixation ring such as a Flieringa ring (or a double Flieringa ring) or the McNeill-Goldman scleral fixation ring and blepharostat should be used to stabilize the globe. The blepharostat also helps provide better exposure which can be a problem in infants with small interpalpebral spaces.
- The younger the patient, the more pliable the tissue and more pliable or less rigid tissue is more difficult to handle and suture. Additional suturing challenges arise from the smaller size donor tissue that is used and the more shallow anterior chamber depth.
- Higher posterior pressure can cause forward displacement of the lens and iris and there is an increased risk for iris prolapse, lens extrusion, and even suprachoroidal hemorrhage when the cornea is removed and the globe is open. Positioning of the patient with the head higher than the rest of the body can help to reduce this intraocular pressure. Preoperative ocular massage or use of the Honan balloon can reduce the risk of high posterior pressure. Many surgeons use IV mannitol as well. Retrobulbar blocks should be avoided. Anesthesiologists can help by not using succinylcholine and also by hyperventilating the patient if needed.
Other surgical differences between penetrating keratoplasty in adults vs children include the use of smaller donor grafts (usually between 5.5 and 7mm in diameter) in younger children. Donor grafts should be oversized by .5 - 1mm. Interrupted or running sutures (or combinations) can be employed according to surgeon preference.
- Young children generate stronger inflammatory responses to surgery than adults do. Increased fibrin release inside of the eye can cause iris - cornea adhesions. The much quicker healing time in infants can cause contraction of the tissue at the 360 degree interface between host and donor tissue. This contraction of tissue can then lead to loosening of the sutures which is a risk factor for suture abscesses and neovascularization of the corneal tissue, both of which can lead to rejection and failure of the new cornea. For this reason, frequent postoperative exams are essential. Parents should be taught how to look at their children's corneas with a pen light every day and call if they notice signs of loose sutures or new infiltrates. Children should be brought in to see their surgeons frequently - maybe even 2-3 times per week for the first few weeks and then once per week for the next couple of months. In young infants, suture removal may begin as soon as 2 weeks after surgery and is often completed in about 3 months.
- Eye drops: Frequent application of topical steroids is essential to reduce the high risk of rejection. Some authors advocate steroid drops every hour for the first few days followed by a very slow taper. Others advocate drops 10 times per day for the entire first month.
- Risk of infection is high in these children. Loose sutures, epithelial defects, wound dehiscence, and high doses of topical steroids are all risk factors for infection. One study found a 27% risk of infection for infants in the early postoperative period. For this reason, topical antibiotic drops are often used for a longer period compared with adult postoperative regimens.
- Infants and young children are unable to cooperate with postoperative exams, instructions, or care. They can not be trusted to not rub their eyes during the healing period and this can lead to broken sutures and wound dehiscence. They may not tolerate the administration of necessary antibiotic and steroid drops and this can be a challenge for parents and other caregivers. Frequent exams under anesthesia are required during the postoperative period.
- Adult patients who undergo penetrating keratoplasty are told to expect a sometimes lengthy visual recovery. Especially if they have good vision in the other eye, it can take many many months before sutures are removed and they are refracted and fit for rigid gas permeable contact lenses that might provide them with the best corrected visual acuity. In infants and young children, amblyopia can cause rapid and permanent vision loss and it is imperative that their visual rehabilitation begin as soon as possible with proper correction for the postoperative eye and amblyopia therapy, often including patching of the "good" eye. Collaboration with pediatric ophthalmologists and possibly optometrists is essential.
The prognosis for pediatric penetrating keratoplasty is guarded and is definitely not as good as for adults. The main reasons for this are the high rate of graft failure (most commonly due to rejection and infection) and also the high rate of vision loss from amblyopia despite maintaining a clear graft. A review of the published data reveals varied success with pediatric penetrating keratoplasty.
In 1977, Waring and Laibson reported 87% success for acquired corneal opacities but only 1/11 clear grafts among congenitally cloudy corneas. 4 out of 11 of their eyes were NLP (no light perception vision) and were either enucleated or phthisical. Because of their poor results, they recommended not performing surgery on patients with unilateral corneal disease.
In 1984, Stulting published data on 91 patients all aged 14 or younger. Although he reported clear grafts at one year in 60% of patients with congenital opacities and 70-73% of patients with acquired causes of corneal opacities, only 29% of patients with congenital causes of opacities and only 45-67% of patients with acquired causes of opacities had vision better than 20/400. Only 3% of patients with congenital causes of opacities had vision better than 20/40; however, 17% of trauma patients had vision of 20/40 or better and so did 47% of patients with non-traumatic acquired opacities.
In 1990, Cowden published data from 66 surgeries in 57 eyes of 50 children aged 2 months to 14 years old. After a 1-10 years of follow-up, he reported 32 clear grafts, 30 failed grafts, and 4 eyes that were lost (one to endophthalmitis, 2 to phthisis, and one to a choroidal hemorrhage). Only about one third of the grafts performed for Peters', sclerocornea, or intrauterine infection were clear at one year. Among his patients, those who were oldest at surgery tended to do best. In infants less than one year old, only 25% of grafts were clear at one year. In children between 1 and 4 years old, about one half were clear at one year. And in children older than 4 years old, about two thirds were clear at one year.
- American Academy of Ophthalmology. Penetrating keratoplasty Practicing Ophthalmologists Learning System, 2017 - 2019 San Francisco: American Academy of Ophthalmology, 2017.
- Krachmer et al, CORNEA: Surgery of the Cornea and Conjunctiva, 3rd ed, Mosby, 2011. pp 1455-1472.