For many patients, corneal transplants offer a way to restore vision following injury or other disease-related and congenital forms of blindness. The traditional method for this procedure is to suture natural human corneal tissue from a donor eye into a recipient eye. In some cases, however, traditional corneal transplants fail, or a patient may not be a good candidate for natural tissue transplant due to special circumstances. When natural cornea transplant is not an option, more and more physicians are recommending artificial corneas, or keratoprosthesis, to restore precious vision.
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. Thus, the Boston Keratoprothesis can be used after standard corneal transplant has failed or when such a transplant would be unlikely to succeed. The 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. 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.
Generally, indicators of patients who require 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 by the performing surgeon. This helps to assess the corneal condition and determine if the patient is a good candidate for the surgery.
The surgical procedure is performed on an ambulatory basis with the patient returning home – or to a hotel if the patient is coming from a distance – the same day. Most surgeries are performed with the use of local anesthesia, with the exception of infants and young children where general anesthesia may be indicated. Patients can expect to be in the operating room area for at least three hours for this procedure, including one hour and 20 minutes for surgery as well as pre-operative and recovery time.
Because of possible complications that can result after many surgical procedures, patients with keratoprosthesis require relatively frequent ophthalmologic examination in the beginning. In all cases, patients return to the Boston Eye Group the day following surgery for reevaluation, necessary prescriptions, and post-operative care instructions. Additional follow-up exams are usually 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.
With keratoprosthesis, best possible vision is restored quickly and patients often achieve optimum visual levels within a few weeks after the surgery. Because the prosthesis is made of synthetic materials that never totally become incorporated into the body, prophylactic antibiotic drops must be used indefinitely. 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. Also, during the early months following surgery, a protective shield is worn while patients sleep at night. For long-term postoperative safety it is recommended that the patient continuously wear a therapeutic soft contact lens (not felt by patient).
Risks and Discomforts
For patients with severe dryness or inflamation, keratoprosthesis can give excellent results but is more risky. In some instances a membrane can develop behind the keratoprosthesis and interfere with vision. This membrane can be opened using a tiny laser beam without requiring additional surgery. Rarely, tissue around the stem of the prosthetic device dissolves which can lead to the leakage of fluid from the eye leading to infection or even vision loss. In such instances the surgery may have to be repeated.
In most cases, the cost of Keratoprosthesis is covered by major U.S. medical insurance plans. You should contact them prior to scheduling surgery to check. For patients who do not have insurance coverage, including foreign patients, please consult your surgical coordinator at the Boston Eye Group to discuss this matter.