 |
 |
The Boston Keratoprosthesis is an “artificial cornea” that can be used in severe corneal opacity. Many people with corneal disease can be helped by regular corneal transplantation involving tissue transplanted from human donors. This is the most common treatment for severe corneal opacity; however, in some cases such transplantation rapidly fails.
The Boston Keratoprothesis can be used after standard corneal transplant has failed or when such a transplant would be unlikely to succeed. Thus keratoprosthesis implantation is a procedure designed to help patients whose conditions are the most difficult to treat.
The Boston Keratoprosthesis has been under development since the 1960s, and has been gradually improved. It received FDA clearance in 1992. Over 1200 implantations have been performed (Spring 2007). It is the most commonly used artificial cornea in the United States and in the world.
The keratoprosthesis is made of clear plastic with excellent tissue tolerance and optical properties. It consists of three parts but when fully assembled, it has the shape of a collar-button. (See Figure 1) The device is inserted into a corneal graft, which is then sutured into the patient’s cornea like in standard transplantation. If the natural lens is in place, it is also removed. Finally, a soft contact lens is applied to the surface.
Successful implantation of Boston Keratoprosthesis in a traumatized eye following three failed standard corneal transplants.
The same patient with a colored contact lens.
A specialty firm can perfectly match the iris color of the normal left eye. Cosmetic appearance is close to ideal,
and visual acuity is 20/50.
Generally, indications for the Boston Keratoprothesis include:
Prior to surgery, a detailed history will be taken which helps to assess the corneal condition and determine if the patient is a good candidate for the surgery.
This one-step surgery is simpler and faster than procedures used in other keratoprosthesis models. Although general anesthesia is recommended, the recent trend is for performing the surgery under local anesthesia with intravenous sedation. Visual improvement is usually already seen the following day or week(s).
Because of possible complications that can result after many surgical procedures, patients with keratoprosthesis require relatively frequent ophthalmologic examination in the beginning. The patient should be seen the day following surgery, as well as during the first and second weeks after surgery. It is customary to return bimonthly for a check-up during the first year. After this time, examination by the surgeon every three to four months is also recommended.
For long-term postoperative safety it is recommended that the patient continuously wear a therapeutic soft contact lens (not felt by patient) and use prophylactic antibiotic drops once or twice daily. Thus, a life-long regimen of daily drops of antibiotics is prescribed to prevent infection. In addition, medications to control inflammation and/or glaucoma are used when necessary.
The Boston Keratoprosthesis is known for excellent long-term (many years) stability and safety. Its optical system can provide normal vision if the rest of the eye is undamaged.
The surgery is reversible at any time.
Corneal graft failure (in non-autoimmune diseases) is the main indication for this procedure.
The Boston Keratoprosthesis consists of two PMMA parts that clamp a corneal graft. The assembly is locked with a titanium ring. The graft is then sutured into the
patient's cornea like a standard graft. (The titanium locking ring does not prevent MRI imaging).
Patient evaluation often includes the following components. In some patients it may not be necessary to perform all the following tests; in others, additional tests may be
needed.
Other considerations include:
Keratoprosthesis surgery has an excellent outcome with non-autoimmune disease, patients with previous graft failures and no other ocular problems.
If the eye is pseudophakic, plan to keep the intraocular lens in place to prevent vitreous prolapse. The more involved care of children and individuals who cannot easily be followed frequently and regularly should be anticipated and the potential unknown long-term side effects should be discussed with the parents and/or caretakers. Patients with autoimmune disease (Stevens Johnson, ocular cicatricial pemphigoid, uveitis) have a more guarded prognosis.
Boston Keratoprosthesis for aniridia
Severe Herpetic keratitis
Same eye 1 month following Boston Keratoprosthesis with 20/30 vision
Severe chemical burn
Same eye 1 year following Boston KPro with 20/25 vision
The Boston Keratoprosthesis after healing into a cornea severely
damaged from fungal keratitis. Vision is 20/25 after four years.
The patient should be seen the following day, after one week, two weeks, one month, and every two months for the first year, and then every three to four months. Modify the schedule if problems arise.
Postoperative medication may include a fluoroquinolone. Prednisolone acetate 1% as needed. If pressure problems appear, steroids may be eliminated but the antibiotics should be used for life on a daily basis. Impress upon the patient the importance of compliance. Compounded vancomycin drops (14mg/ml) once daily may be added for safety in autoimmune disease, chemical burns or in monocular patients.
Soft contact lens should be worn around the clock on a long-term basis. The lens is very protective of the corneal tissue hydration. If lost, it should be replaced. Colored contact lenses can also be used to enhance the esthetic appearance. Your contact lens department may provide assistance.
The problems of melt and extrusion that were common previously have now been virtually eliminated. (See graph.)
Inflammmation can be an issue for eyes that have undergone many surgical procedures. In addition to topical steroids, occasional peribulbar injections of 40 mg of triamcinolone may be necessary.
Any retroprosthesis membrane can be opened with a YAG laser as long as no blood vessels have entered. Vascularized membranes are rare but may require surgery by a vitreo-retinal surgeon.
A sudden vitritis can form rarely with drastic reduction of vision. If there is no accompanying redness or pain, the vitritis is most likely sterile and can be treated with peribulbar triamcinolone and prophylactic antibiotics only. They always clear up.
Bacterial endophthalmitis is fortunately very rare in the graft failure group as long as the prophylactic antibiotics regimen is followed. No acute bacterial endophthalmitis has occurred as long as vancomycin has been given.
Glaucoma is common in patients needing the Boston Keratoprothesis and may get worse postoperatively. Standard drops are usually effective since they readily diffuse into the eye. Systemic carbonic anhydrase inhibitors have the expected effect. Finally, a glaucoma shunt may be resorted to in severe cases.
If necessary, the procedure is reversible back to a standard corneal graft or can be repeated.
The Boston Keratoprosthesis has excellent long-term stability and safety. It is also known for having excellent optics.
The following graph illustrates the retention rate of patients who receive the Boston Keratoprosthesis.
Keratoprosthesis still carries a somewhat greater burden post-operatively than standard keratoplasty. Successful outcome requires patient compliance, regular follow-up, and standard demands on physician time. However, in cases where further keratoplasty appears futile, keratoprosthesis can be most rewarding.
The device is manufactured under the auspices of Massachusetts Eye and Ear Infirmary, a hospital affiliated with Harvard Medical School. For further information, please consult the closest ophthalmologist with special expertise in corneal diseases, or contact us at 617-573-4463 or fax 617-573-4369, or email kpro@meei.harvard.edu
Click here to view Boston Keratoprothesis bibliography.
 | We comply with the HONcode standard for
health trustworthy information: Verify here. |
|
|
|