Artificial Cornea – The Boston Keratoprosthesis

When the cornea becomes severely diseased, it can be necessary to consider replacing it with a transplant from a donor or with a specially designed substitute. 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 Keratoprosthesis is an “artificial cornea” that can be used in patients with severe corneal opacity.  It was developed by one of our leading physician-scientists, the world-renown cornea specialist, Dr. Claes H. Dohlman.

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.

Development

The Boston Keratoprosthesis has been under development since the 1960s and has been gradually improved. It received FDA clearance in 1992. More than 3,000 implantations have been performed (January 2009). 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 and when fully assembled, has the shape of a collar-button.

Surgery

Generally, indications for the Boston Keratoprothesis include:

• Failed corneal graft, with poor prognosis for further grafting
• Vision less than 20/400 in the affected eye and additionally with lower than optimal vision in the opposite eye
• No end-stage glaucoma or retinal detachment.

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.

The device is inserted into a corneal graft, which is then sutured into the patient’s cornea as in standard transplantation. If the natural lens is in place, it is also removed. Finally, a soft contact lens is applied to the surface; it must be worn around the clock, everyday.  This does not cause any discomfort.

Our one-step surgery is simpler and faster than procedures used in other keratoprosthesis models; it generally requires about one and one half hours to complete. While general anesthesia is recommended, the recent trend is for performing the surgery under local anesthesia with intravenous sedation. Visual improvement is usually seen the following day or week(s).  Although the prosthesis is clear, use of a colored contact lens can perfectly match the iris color of the opposite eye.

Postoperative Care
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 the 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.

Stability and Safety
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.

Referring physicians and ophthalmologists trained in Boston Keratoprosthesis surgery may find more information on our Physician Resources webpages.