Talk:Boston Keratoprosthesis (KPro)

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Discussion of Edits made by user Brad.H.Feldman.DEC on article submission by user Klufas

Edit #1: “Currently, the Boston KPro is considered by some to be a primary treatment option in cases of repeat graft failure [17] and aniridia [18] , and, by a smaller percentage of surgeons, to be a primary option in cases of herpetic keratitis [19] and pediatric corneal opacities [20]. Pediatric KPro use in particular is still a controversial topic that is widely debated among corneal specialists because of the high level of care needed postoperatively and the possibly devastating complications of the procedure.”

Klufas Response:

The Boston Keratoprosthesis appears to be a good treatment option in pediatric corneal opacities given the rapid establishment of a clear visual access, excellent retention and minimal postoperative complications. In patients otherwise destined to develop dense amblyopia, this procedure provides the potential for visual improvement. A pediatric keratoprosthesis clinical series by Aquavella and colleagues showed 100% retention of all Boston KPros (median follow-up 9.7 months) and no instances of infectious endophthalmitis [1, 2]. In 7 instances (when the child was 4 or more years old) 86% had visual acuity 20/400 or better, with one patient achieving 20/30 vision. Close coordination between pediatric, cornea, vitreoretinal and glaucoma services are necessary to coordinate surgery and life-long postoperative care. Future long term studies are needed to further evaluate the outcomes of KPro placement in children, but early results appear promising. For comparison, in a series of eyes with Peters anomaly, the most common pediatric corneal opacity, treated with traditional corneal transplant, only 22-29% achieved 20/400 or better visual acuity outcomes with long-term follow-up (median 11.1 years) [3]. To add, with traditional penetrating keratoplasty for Peters anomaly, the question in studies is not if, but when the graft will fail. In these series the mean survival of traditional corneal grafts is only 20.1 months and graft failure rate is estimated at 61-65% [4, 5]. In addition, in post-PKP patients, due to significant astigmatism, best corrected vision often requires a RGP contact lens which many children can’t wear. The KPro is astigmatically neutral and often does not require glasses or contact lenses for good vision. Also, steroids can be stopped after KPro in pediatric patients whereas a traditional corneal transplant would require long-term steroids and the virtual certainty of cataracts and possibly glaucoma. Because of this data most corneal specialists believe KPro is a better primary option for children with corneal opacities than PKP.

Edit # 2. “Due to incomplete biointegration of hardware in the eye there is a significant risk of infectious endophthalmitis [23]”

Klufas response:

The authors recommend that this link be removed – the complication is infectious endophthalmitis after a specific surgical procedure and not ‘post-traumatic endophthalmitis’.

Edit #3. “The downside to BCL use is the increased risk of infection associated with contact lens use, especially when used on a chronic, extended wear basis.”

Klufas response:

Given the daily topical antibiotic prophylaxis for life, this complication has not been reported in clinical series. The same contact lenses have been retained for greater than 1 year without difficultly after KPro surgery [6]. However, it is important to note, that fungal keratitis and colonization has proven to be an issue in the certain climates – particularly in the southwestern United States and some international sites [7, 8].

Edit #4. “Despite best efforts at RPM monitoring and treatment with YAG laser, some patients will ultimately still progress and require more invasive surgical intervention.”

Klufas response:

This statement may be true but is not the typical outcome - the vast majority of RPMs, even recurrent RPMs, are amenable to YAG and only a minority are treated with surgical membranectomy. In the multicenter study, RPM affected 25% of eyes in the postoperative period, nevertheless, 65% were successfully treated with a single YAG membranectomy, 25% were not visually limiting and therefore did not require treatment, and only a small minority (11%) necessitated surgical membranectomy [9, 10].

Edit #5. “Infectious endophthalmitis is a catastrophic complication often resulting in loss of vision. The most comprehensive series reports the overall incidence of IE as 2.7% per patient year [24]--in effect one of the highest endophthalmitis rates of any ophthalmic surgical procedure currently performed. For perspective, this is 67.5x's higher than the rate for cataract surgery, and 13.5x's higher than the rate for glacuoma filtering surgery.”

Klufas response:

Studies have shown the incidence endophthalmitis after cataract extraction is 0.35% when only povidone iodine intraoperatively and postoperative topical antibiotics are used, and the incidence is reduced to 0.08% with intracameral cefuroxime [11, 12]. For glaucoma drainage implants, the rate of endophthalmitis from a literature review is reported from 0.8% to 6.3% with a mean rate of 2.0% [13]. It is inequitable to compare cataract/glaucoma surgery, a routine procedure, and keratoprosthesis surgery, an intervention performed in eyes often afflicted with multiple complicating issues. Additionally, the occurrence of infectious endophthalmitis is not a direct result of the surgical procedure – it usually occurs months to years later in the postoperative period and is a result of the incomplete biointegration of the device [14]. The rate reported in the wiki article must also be viewed in light of the fact that the series included eyes with autoimmune conditions (SJS, OCP) which are plagued by much higher rates of infection. Furthermore, since 1999, with topical daily antibiotic prophylaxis with vancomycin the infection rate was only 0.35% per patient year [15]. In eyes with preoperative diagnoses of burn, OCP, or graft failure/other (in essence excluding SJS eyes), the incidence of infectious endophthalmitis in eyes treated with vancomycin was zero. In terms of providing an accurate assessment of the KPro, while infectious endophthalmitis is a constant risk, it has been dramatically reduced with daily topical antibiotic application and typically only occurs in patients who are noncompliant with their daily antibiotics. Currently, the postoperative complication that is the biggest threat to KPro eyes, and the most difficult to treat, is glaucoma.

Klufas References

1. Aquavella, J.V., Pediatric keratoprosthesis: a new surgical approach. Ann Ophthalmol (Skokie), 2008. 40(2): p. 64-7.

2. Aquavella, J.V., et al., Pediatric keratoprosthesis. Ophthalmology, 2007. 114(5): p. 989-94.

3. Yang, L.L., et al., Long-term results of corneal graft survival in infants and children with peters anomaly. Ophthalmology, 1999. 106(4): p. 833-48.

4. Dana, M.R., et al., Corneal transplantation in children with Peters anomaly and mesenchymal dysgenesis. Multicenter Pediatric Keratoplasty Study. Ophthalmology, 1997. 104(10): p. 1580-6.

5. Rao, K.V., et al., Outcome of penetrating keratoplasty for Peters anomaly. Cornea, 2008. 27(7): p. 749-53.

6. Dohlman, C.H., et al., Protection of the ocular surface after keratoprosthesis surgery: the role of soft contact lenses. Clao J, 2002. 28(2): p. 72-4.

7. Barnes, S.D., C.H. Dohlman, and M.L. Durand, Fungal colonization and infection in Boston keratoprosthesis. Cornea, 2007. 26(1): p. 9-15.

8. Ament, J.D., et al., Global corneal blindness and the Boston keratoprosthesis type I. Am J Ophthalmol, 2010. 149(4): p. 537-9.

9. Klufas, M.A. and C.E. Starr, The Boston Keratoprosthesis : An update on recent advances. Cataract and Refractive Surgery Today September 2009. 9(9).

10. Zerbe, B.L., M.W. Belin, and J.B. Ciolino, Results from the multicenter Boston Type 1 Keratoprosthesis Study. Ophthalmology, 2006. 113(10): p. 1779 e1-7.

11. Prophylaxis of postoperative endophthalmitis following cataract surgery: results of the ESCRS multicenter study and identification of risk factors. J Cataract Refract Surg, 2007. 33(6): p. 978-88.

12. Anijeet, D., Endophthalmitis after cataract surgery. Ophthalmology. 117(4): p. 853-853 e1; author reply 853-5.

13. Wentzloff, J.N., et al., Endophthalmitis after glaucoma drainage implant surgery. Int Ophthalmol Clin, 2007. 47(2): p. 109-15.

14. Fintelmann, R.E., et al., Characteristics of endophthalmitis in patients with the Boston keratoprosthesis. Cornea, 2009. 28(8): p. 877-8.

15. Durand, M.L. and C.H. Dohlman, Successful prevention of bacterial endophthalmitis in eyes with the Boston keratoprosthesis. Cornea, 2009. 28(8): p. 896-901.

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