Boston keratoprosthesis

Boston keratoprosthesis (Boston KPro) is a collar button design keratoprosthesis or artificial cornea.[1] It is composed of a front plate with a stem, which houses the optical portion of the device, a back plate and a titanium locking c-ring.[2] It is available in type I and type II formats. The type I design is used much more frequently than the type II which is reserved for severe end stage dry eye conditions and is similar to the type I except it has a 2 mm anterior nub designed to penetrate through a tarsorrhaphy. The type I format will be discussed here as it is more commonly used.

Boston keratoprosthesis
Boston Kpro type 1 titanium posterior plate
Specialtyophthalmology

The type I Kpro is available in single standard pseudophakic power or customized aphakic optic with an 8.5 mm diameter adult size or 7.0 mm diameter pediatric size back plate. The device is currently machined from medical grade polymethylmethacrylate (PMMA) in Wilmington, Massachusetts in the United States.[3] During implantation of the device, the device is assembled with a donor corneal graft positioned between the front and back plate which is then sutured into place in a similar fashion to penetrating keratoplasty (corneal transplantation).[4]

Indications

The Boston KPro is a treatment option for corneal disorders not amenable to standard penetrating keratoplasty (corneal transplantation) or corneal transplant. The Boston KPro is a proven primary treatment option for repeat graft failure,[5] herpetic keratitis,[6] aniridia[7] and many pediatric congenital corneal opacities including Peter's anomaly.[8] The device is also used to treat cicatrizing conditions including Stevens–Johnson syndrome[9] and ocular cicatricial pemphigoid, and also ocular burns.[10][11]

Complications

Most common postoperative complications in order of decreasing prevalence include retroprosthetic membrane (RPM), elevated intraocular pressure/glaucoma, infectious endophthalmitis, sterile vitritis, retina detachment (rare) and vitreous hemorrhage (rare).[12][13][14][15]

Postoperative management
  1. Indefinite placement of a bandage contact lens is needed to maintain adequate ocular surface hydration and prevent stromal melt, dellen formation, tissue melt and necrosis.[16]
  2. Indefinite daily topical antibiotic prophylaxis.[17]
  3. Lifelong topical steroids.[18]
  4. Close follow-up with an ophthalmologist to monitor for complications associated with the device. Although the surgical procedure is relatively straightforward for surgeons trained to perform corneal transplants, the follow-up required after KPro placement is lifelong.[18]

Outcomes

Four major studies have been completed to date showing outcomes with the type I Boston KPro:

  1. Multicenter Boston KPro Study is the largest published to date with 141 Boston type I keratoprosthesis procedures from 17 surgical sites by 39 different surgeons.[14] At an average follow-up of 8.5 months, retention rate of the device was 95%, 57% had BCVA ≥ 20/200. Postoperative complications included RPM in 25%, high IOP in 15%, sterile vitritis complicated the postoperative course of 5% of eyes. Importantly, no cases of infectious endophthalmitis were reported in this large series.
  2. A large single surgeon series with 57 modern type I Boston KPro procedures from UCLA medical center.[12] At an average follow-up of 17 months, retention rate of the device was 84%, 75% had BCVA ≥ 20/200. Postoperative complications included RPM in 25%, high IOP in 15%, sterile vitritis complicated the postoperative course of 5% of eyes. Postoperative complications included RPM in 44%, high IOP in 18%, sterile vitritis complicated the postoperative course of 10% of eyes. No cases of infectious enophthalmitis were reported in this series.
  3. A single center study from UC Davis of 30 Boston type I KPro procedures.[13] At an average follow-up of 19 months, retention rate of the device was 83%, 77% had BCVA ≥ 20/200. Postoperative complications included RPM in 43%, high IOP in 27%, sterile vitritis complicated the postoperative course of 3% of eyes. The rate of infectious endophthalmitis in this study was 10%.
  4. A retrospective study of 36 Boston Type I KPro procedures from a single institution.[15] At an average follow-up of 16 months, retention rate of the device was 100%, 83% had BCVA ≥ 20/200. Postoperative complications included RPM in 65% and high IOP in 38%. Infectious endophthalmitis complicated 11% of eyes during the postoperative period.

History

Boston ophthalmologist Claes Dohlman began developing the Boston keratoprosthesis in 1965,[19] and refined it over the next decades.[20] It was approved by the U.S. Food and Drug Administration in 1992.[20] Fewer than 50 of the devices had been implanted before 2002, when popularity began increasing.[21] 1,161 had been placed by 2009,[21] 8,000 by 2012,[22] and 9,000 by 2014.[21]

The design of the device has evolved over its history. In 1996, eight holes were added in the back plate.[21] The holes allow the aqueous humour fluids of the eye to provide nutrients to the donor graft stroma and keratocytes.[23] The device is now available with either eight or 16 holes.[21] In 2004, a titanium locking c-ring was added to prevent intraocular unscrewing of the device.[2] In 2007, a threadless design replaced the previous screw-type one, simplifying assembly and reducing damage to the donor graft when the device is assembled during the surgical procedure.[23] The back plate was changed to titanium in 2012, due to titanium's biocompatibility.[21]

References
  1. Klufas MA, Starr CE (September 2009). "The Boston Keratoprosthesis: An update on recent advances". Cataract and Refractive Surgery Today. 9 (9).
  2. Dohlman C, Harissi-Dagher M (2007). "The Boston Keratoprosthesis: A New Threadless Design". Digital Journal of Ophthalmology. 13 (3).
  3. Khan B, Dudenhoefer EJ, Dohlman CH. Keratoprosthesis: an update. Curr Opin Ophthalmol. Aug 2001;12(4):282-287
  4. Todani A, Gupta P, Colby K (January 2009). "Type I Boston keratoprosthesis with cataract extraction and intraocular lens placement for visual rehabilitation of herpes zoster ophthalmicus: the "KPro Triple"". The British Journal of Ophthalmology. 93 (1): 119. doi:10.1136/bjo.2008.146415. PMID 19098045.
  5. Ma JJ, Graney JM, Dohlman CH (2005). "Repeat penetrating keratoplasty versus the Boston keratoprosthesis in graft failure". International Ophthalmology Clinics. 45 (4): 49–59. doi:10.1097/01.iio.0000176365.71016.28. PMID 16199966.
  6. Khan BF, Harissi-Dagher M, Pavan-Langston D, Aquavella JV, Dohlman CH (June 2007). "The Boston keratoprosthesis in herpetic keratitis". Archives of Ophthalmology. 125 (6): 745–9. doi:10.1001/archopht.125.6.745. PMID 17562983.
  7. Akpek EK, Harissi-Dagher M, Petrarca R, Butrus SI, Pineda R, Aquavella JV, Dohlman CH (August 2007). "Outcomes of Boston keratoprosthesis in aniridia: a retrospective multicenter study". American Journal of Ophthalmology. 144 (2): 227–231. doi:10.1016/j.ajo.2007.04.036. PMID 17543875.
  8. Aquavella JV, Gearinger MD, Akpek EK, McCormick GJ (May 2007). "Pediatric keratoprosthesis". Ophthalmology. 114 (5): 989–94. doi:10.1016/j.ophtha.2007.01.027. PMID 17467531.
  9. Sayegh RR, Ang LP, Foster CS, Dohlman CH (March 2008). "The Boston keratoprosthesis in Stevens-Johnson syndrome". American Journal of Ophthalmology. 145 (3): 438–44. doi:10.1016/j.ajo.2007.11.002. PMID 18207122.
  10. Tuft SJ, Shortt AJ (October 2009). "Surgical rehabilitation following severe ocular burns". Eye. 23 (10): 1966–71. doi:10.1038/eye.2008.414. PMID 19169226.
  11. Harissi-Dagher M, Dohlman CH (April 2008). "The Boston Keratoprosthesis in severe ocular trauma". Canadian Journal of Ophthalmology. 43 (2): 165–9. doi:10.3129/i08-009. PMID 18347618.
  12. Aldave AJ, Kamal KM, Vo RC, Yu F (April 2009). "The Boston type I keratoprosthesis: improving outcomes and expanding indications". Ophthalmology. 116 (4): 640–65. doi:10.1016/j.ophtha.2008.12.058. PMID 19243830.1
  13. Bradley JC, Hernandez EG, Schwab IR, Mannis MJ. Boston type 1 keratoprosthesis: the university of california davis experience. Cornea. Apr 2009;28(3):321-327
  14. Zerbe BL, Belin MW, Ciolino JB. Results from the multicenter Boston Type 1 Keratoprosthesis Study. Ophthalmology. Oct 2006;113(10):1779
  15. Chew HF, Ayres BD, Hammersmith KM, et al. (October 2009). "Boston Keratoprosthesis Outcomes and Complications". Cornea.
  16. Dohlman CH, Dudenhoefer EJ, Khan BF, Morneault S. Protection of the ocular surface after keratoprosthesis surgery: the role of soft contact lenses. Clao J. Apr 2002;28(2):72-74
  17. Durand ML, Dohlman CH. Successful prevention of bacterial endophthalmitis in eyes with the Boston keratoprosthesis. Cornea. Sep 2009;28(8):896-901
  18. Dohlman CH, Harissi-Dagher M, Khan BF, Sippel K, Aquavella JV, Graney JM. Introduction to the use of the Boston keratoprosthesis. Expert Review of Ophthalmology. 2006;1(1):41-48
  19. Prescott CR, Chodosh J (2013). "Boston Keratoprosthesis Surgical Technique". Ocular Surface Disease: Cornea, Conjunctiva and Tear Film. Elsevier Health Sciences. p. 407. ISBN 978-1455756230.
  20. Prescott CR, Chodosh J (2013). "Boston Keratoprosthesis in the Management of Limbal Stem Cell Failure". Copeland and Afshari's Principles and Practice of Cornea. JP Medical Ltd. p. 1194. ISBN 978-9350901724.
  21. Lee WB, Shtein RM, Kaufman SC, Deng SX, Rosenblatt MI (July 2015). "Boston Keratoprosthesis: Outcomes and Complications: A Report by the American Academy of Ophthalmology". Ophthalmology. 122 (7): 1504–11. doi:10.1016/j.ophtha.2015.03.025. PMID 25934510.
  22. Colby K (2014). "Future Directions for the Boston Keratoprosthesis". Keratoprostheses and Artificial Corneas. p. 181. doi:10.1007/978-3-642-55179-6_20. ISBN 978-3-642-55178-9.
  23. Harissi-Dagher M, Khan BF, Schaumberg DA, Dohlman CH (June 2007). "Importance of nutrition to corneal grafts when used as a carrier of the Boston Keratoprosthesis". Cornea. 26 (5): 564–8. doi:10.1097/ICO.0b013e318041f0a6. PMID 17525653.
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