Surgery Section - Keratoprosthesis

IMPORTANT REMINDER

This Medical Policy has been developed through consideration of medical necessity, generally accepted standards of medical practice, and review of medical literature and government approval status.

Benefit determinations should be based in all cases on the applicable contract language. To the extent there are any conflicts between these guidelines and the contract language, the contract language will control.

The purpose of medical policy is to provide a guide to coverage. Medical Policy is not intended to dictate to providers how to practice medicine. Providers are expected to exercise their medical judgment in providing the most appropriate care.

Description

A keratoprosthesis is a device intended to restore vision to patients with severe bilateral corneal disease for which a corneal transplant is not an option, such as in cases involving chemical injuries, pemphigoid, Stevens-Johnson syndrome, repeated failed surgeries, rosacea, trachoma, traumatic injuries, certain forms of keratitis, anterior cleavage syndrome, and Mooren's ulcer. A donor cornea would be unsuccessful because the disease state of the anterior segment would lead to rejection or opacification.

Keratoprosthetic devices differ in design but consist of a special tube that acts as a periscope that is anchored to the front surface of the cornea. The keratoprosthesis extends to the interior of the eye and may pass out of the eye, either through the eyelids or between fused eyelids. Implantation techniques differ, and success rates are variable and highly dependent upon the skill of the surgeon.

There are four permanent keratoprostheses that received 510(k) marketing approval by the U.S. Food and Drug Administration (FDA). The Boston Keratoprosthesis (Boston Kpro) by the Massachusetts Eye and Ear Infirmary and the Dohlman-Doane keratoprosthesis, by Mackeen Consultants, LTD received FDA approval in 1992.  The AlphaCOR™ (formerly Chirila KPro) by Argus Biomedical PTY, LTD was approved in 2002 and the Oculaid® by Ophtec B.V. USA, Inc. was approved in 2004.  A temporary keratoprosthesis is a Class II FDA approved device.

The Boston Scleral lens is a fluid ventilated gas permeable contact lens that rests entirely on the sclera. The lens creates a smooth liquid overlay on an irregular corneal surface that optically neutralizes corneal surface irregularities.  It is used to mask abnormal corneal astigmatism when traditional gas permeable contact lenses fail or it is used to manage severe ocular surface disease.  The Boston Scleral lens received FDA in 1994.  (2)

Note:  This policy is related to keratoprosthesis devices only and is not intended to address the Boston Scleral lens.

Policy/Criteria

Temporary and permanent keratoprostheses are considered investigational.

Scientific Background

This policy is based on a 1988 BlueCross BlueShield Association Technology Evaluation Center (TEC) Assessment. (3) The TEC assessment identified the following key questions in evaluating whether there is sufficient evidence to permit conclusions about the health outcome effects of keratoprostheses (KP):

1. What are the visual results of KP implantation? This can be assessed in terms of immediate visual acuity (VA), best attained VA, VA at final follow-up, and length of maintained visual improvement.
2. What are the complications of the procedure?
3. Is there a consensus of opinion or evidence on optimal devices and implantation techniques?

With regard to the first question, no clear conclusions can be reached about keratoprostheses. Flaws in many of the published studies and small subject samples do not allow comparisons on the key results related to visual acuity.

Regarding the second question, it can be concluded that complications are common, although good estimates of the rates of specific problems are not available. Regular postoperative care to monitor complications is necessary in all KP patients for the remainder of their lives or until the KP is removed. Serious complications include extrusion, retroprosthetic membrane, retinal detachment, tissue erosion around the KP, aqueous leaks, and glaucoma. The evidence suggests that nearly every patient experiences some postoperative problems with KP implantation.

There is currently no consensus in the literature on optimal devices or implantation techniques. There is insufficient evidence to prove the safety and efficacy of any one KP design. Similarly, an optimal surgical method has not been demonstrated.

Specifically, the published literature consists primarily of small case series with limited follow-up, in part due to the rarity of the procedure.  (4-11)  An exception is a 2005 report by Falcinielli and colleagues, describing a case series of 181 patients who received an osteo-odonto-keratoprosthesis (OOKP).  (12)Insertion of the OOKP device requires a complex staged procedure, in which the cornea is first covered with buccal mucosa. The prosthesis itself consists of a polymethyl methacrylate (PMMA) optical cylinder which replaces the cornea, held in place by a biological support made from a tooth extracted from the recipient. A hole is drilled through the dental root and alveolar bone, and the PMMA prosthesis placed within. This entire unit is placed into a subcutaneous pocket, then retrieved 6 to 12 months later for final insertion.  In Falcinielli’s report the median follow-up was 12 years. Survival analysis estimated that 18 years after surgery the probability of retaining an intact OOKP was 85% with reasonable visual acuity. Disadvantages of the OOKP device include limited visual field and the inability to measure intraocular pressure.

Aquavella and colleagues reported on a case series of 25 patients who received a Dohlman-Doane device. (13) This device consists of a PMMA button and stem, which is anchored in place using a corneal graft. With a follow-up time ranging from 2 to 12 months, 20 of the 25 patients had a visual acuity of 20/400 or better, with 12 patients achieving better than 20/40 vision. There were no dislocations or extrusions, and no reoperations were required.

The AlphaCor prosthesis consists of a PMMA device with a central optic region fused with a surrounding sponge skirt that allows biointegration into a donor cornea. The device is inserted in a two-stage surgical procedure. Studies have suggested that the AlphaCor device is safe, although thinning or “melting” of the anterior corneal surface can lead to loss of biointegration. (6,9) This complication seems most prevalent in patients with ocular herpes, therefore the AlphaCor device is contraindicated in these patients.

The BIOKOP device is similar in concept to the AlphaCor device in that a microporous polymer is used to promote host tissue integration. However, the results with this device have been disappointing.  In one case series of 11 patients with 5-year follow-up, the authors concluded that the BIOKOP keratoprosthesis was only able to restore vision for a short postoperative period. (11)  Limited success was due to instability of the device and postoperative complications.

In 2006, Zerbe and colleagues conducted a larger, multicenter, prospective case series in 136 eyes of 133 patients using the Boston Type 1 Keratoprosthesis. (14)  At an average follow-up of 8.5 months,  results showed improved vision to ≥ 20/200 in 57% of the eyes and a graft retention of 95%.  At one year follow-up, 62 of 136  eyes (56%) reported ≥ 20/200 vision. Participation in this ongoing study is voluntary on the part of surgeons, which could lead to reporting bias, with poor outcomes not being reported.  Over half the population was lost to follow-up at one year. The authors state that follow-up is still short.  Further studies with a larger sample size and longer follow-up are needed to verify improved health outcomes for this device.

In summary, successful development of a keratoprosthesis requires durable clarity, retention and bioincorporation. These features remain elusive, and the published literature reveals ongoing modifications of the design of the keratoprosthesis, both in terms of the optics and the techniques used for anchoring the optic in place, the surgical technique and the postoperative management. Randomized trials are likely not necessary, as patients can serve as their own controls, with comparison of pre- and postoperative visual acuity.  However, case series will likely remain small, due to the low volume of the procedure.  It should be noted that patients with severe corneal damage have few treatment options to prevent blindness. The American Academy of Ophthalmology has not established guidelines (15) for either a temporary or permanent keratoprosthesis, and considers this procedure to be a rare, last resort for treatment to prevent loss of the eye. (1)

The United Kingdom’s National Institute for Clinical Excellence (NICE) concludes that, “Current evidence on the safety and efficacy of insertion of hydrogel keratoprostheses does not appear adequate for this procedure to be used without special arrangements for consent and for audit or research.” (16)

An updated search of the MEDLINE database through June 30, 2008 found no new published studies that alter the conclusions reached above.

References

1. BlueCross BlueShield Association Medical Policy Reference Manual, Policy No. 9.03.01
2. The Boston Foundation for Sight.  www.bostonsight.org/aboutlens.htm, Updated 2002 (Verified 6/30/08)
3. TEC Assessment: Keratoprosthesis, 1988; BlueCross BlueShield Association Technology Evaluation Center, p.198
4. Kim MK, Lee JL, Wee WR, Lee JH. Seoul-type keratoprosthesis: preliminary results of the first 7 human cases. Arch Opthalmol 2002;120(6):761-6
5. Ray S, Khan BF, Dohlman CH, D'Amico DJ. Management of vitreoretinal complications in eyes with permanent keratoprosthesis. Arch Opthalmol 2002;120(5):559-66
6. Crawford GJ, Hicks CR, Lou X, et al. The Chirila Keratoprosthesis: phase I human clinical trial. Ophthalmology 2002;109(5):883-9
7. Nouri M, Terada H, Alfonso EC, et al. Endophthalmitis after keratoprosthesis: incidence, bacterial causes, and risk factors. Arch Ophthalmol 2001;119(4):484-9
8. Yaghouti F, Nouri M, Abad JC, et al. Keratoprosthesis: Preoperative prognostic categories. Cornea 2001;20(1):19-23
9. Hicks CR, Crawford GJ, Lou X et al. Corneal replacement using a synthetic hydrogel cornea, AlphaCor: device, preliminary outcomes and complications. Eye 2003;17(3):385-92
10. Hicks CR, Crawford GJ, Tan DT et al. AlphaCor cases: comparative outcomes. Cornea 2003;22(7):583-90
11. Alio JL, Mulet ME, Haroun H et al. Five year follow up of biocolonisable microporous fluorocarbon haptic (BIOKOP) keratoprosthesis implantation in patients with high risk of corneal graft failure. Br J Ophthalmol 2004;88(12):1585-9
12. Falcinelli G, Falsini B, Taloni M et al.  Modified osteo-odonto-keratoprosthesis for treatment of corneal blindness: long-term anatomical and functional outcomes in 181 cases.  Arch Ophthalmol 2005;123(10):1319-29
13. Aquavella JV, Qian Y, McCormick GJ, Palakuru JR.  Keratoprosthesis: the Dohlman-Doane device.  Am J Ophthalmol 2005;140(6):1032-1038
14. Zerbe BL, Belin MW, Ciolino JB Results from the multicenter Boston type 1 keratoprosthesis study.  Ophthalmology 2006;113(10):1779-1784
15. American Academy of Ophthalmology. http://one.aao.org/CE/PracticeGuidelines/ClinicalStatements.aspx (Verified 6/30/087)
16. National Institute for Clinical Excellence: Insertion of hydrogel keratoprosthesis. Accessible at http://www.nice.org.uk/nicemedia/pdf/ip/IPG069guidance.pdf (verified 6/30/08)

Cross References

None

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