Keratoprosthesis Patient Management
Information for Physicians
We make continuing improvements and modifications to the Boston KPro and highly recommend that KPro users receive training on the most current surgical methods and implantation of the device. KPro courses are offered each year at the American Academy of Ophthalmology Annual Meeting and other major cornea meetings. Training is also available by observation at Mass. Eye and Ear.
The information on this page is intended for the referring physicians and specialists trained in the surgical and postoperative care of patients with Boston Keratoprosthesis (Boston KPro) implants.
Page last updated 7/11/2019
Surgery and Patient Care
- Standard preoperative medical assessment
- General anesthesia or monitored intravenous analgesia
- Antibiotics IV recommended at the time of surgery, e.g., cefazolin 1.0 g., if no allergy.
- The surgery time is usually about an hour and a half.
- Boston Keratoprosthesis surgery is readily performed by ophthalmologists with experience in corneal surgery.
The patient should be seen the following day, after e.g. one week, one month, every two months for the first year, then every three months. If problems, modify schedule.
NOTE: Keratoprosthesis requires a more detailed postoperative follow up regimen than standard keratoplasty. Successful outcome requires patient compliance, more frequent follow up visits and more demands on physician time.
- Prednisolone acetate 1% drops, initially 4 times daily, tapered over 6 months according to degree of inflammation.
- Peribulbar injection of triamcinolone, e.g. 20-40 mg may be used if needed for inflammation after KPro implantation. (Recommended after YAG laser membranotomy.)
- Cephazolin 1.0 g or a fluoroquinolone IV (if no allergy) during surgery.
- Moxifloxacin or gatifloxacin four times daily postoperatively, tapering to once daily after two weeks, to be continued for life
- Vancomycin drops (14 mg/ml+0.005% BAK) once daily, postoperatively for life. Must be made up by hospital or compounding pharmacy. Stable for 2 months at room temperature.
- Alternatives for long-term topical prophylaxis (after two weeks postoperative), instead of a fluoroquinolone and vancomycin, are polymyxin B/trimethoprim (Polytrim) solution, used once daily, used for life.
- Amphotericin B drops 0.15% twice daily for a week every 3 months as a prophylactic antifungal “burst” may be desirable in regions of high risk for fungal infections.
- Topical glaucoma medications are effective after KPro implantation, but prostaglandin analogues should be avoided in the early postoperative period
- Oral carbonic anhydrase inhibitors are equally effective in KPro eyes as in other postoperative indications.
Note: It is difficult to assess IOP in KPro eyes, and finger palpation is the only available method. The optic nerve head (cup to disk ratio) should be observed and recorded at every visit (3 month intervals) and formal visual field testing be performed every 6 month.
Close collaboration with a glaucoma specialist is advised.
Soft Contact Lenses:
- Patients with a keratoprosthesis should wear an appropriate extended wear soft contact lens, which should be cleaned or replaced per the contact lens manufacturer’s instructions.
- If lens deposits occur (in poorly blinking eyes), a hybrid contact lens (soft periphery, rigid center) can provide a clear visual axis.
Close collaboration with your Contact Lens Service is advised.
Sterile keratolysis: Sterile keratolysis is recognized by slit lamp biomicroscopy, but may be found earlier by high resolution optical coherence tomography, which is recommended every 6 months after surgery. Sterile keratolysis has been associated with the presence of retroprosthetic membrane and chronic uveitis. Surgical and postoperative approaches that ensure good corneal wound apposition and reduce postoperative inflammation, respectively, will reduce retroprosthetic membrane formation and subsequent keratolysis. Contact lens wear is essential to reduce the risk of keratolysis after KPro. Consider a microbial cause in every case but if culture negative, sterile keratolysis may be treated with patch graft or replacement of the KPro.
Microbial keratitis: Infection of the donor corneal graft surrounding the keratoprosthesis most commonly occurs around and beneath the KPro front plate. Diagnosis and treatment are standard, but serial examination is essential to recognize the small subset of patients who subsequently develop intraocular infection. The risk of microbial keratitis after KPro is reduced by continuous contact lens wear (to reduce epithelial defect), and daily use of two antibiotics with different mechanisms of action, and combined broad antimicrobial spectrum.
Retroprosthetic membrane: Patients with poor corneal wound closure and those with intraocular inflammation after KPro are at greatest risk for membrane formation. Attention to both surgical technique and control of postoperative inflammation are important to prevent and limit retroprosthetic membrane formation. When present and visually significant, a retroprosthetic membrane can be opened with YAG laser as long as no blood vessels have entered the membrane. Energy settings below 2.0 mJ are recommended to avoid damage to the KPro.
After Yag laser treatment, peribulbar injection of 20-40 mg triamcinolone is recommended. Vascularized retroprosthetic membrane requires pars plana surgical approach or KPro replacement with intraoperative excision of the membrane.
Glaucoma: Preexisting glaucoma is very common in patients needing KPro, worsens in a majority of patients postoperatively, and also occurs de novo in many patients postoperatively even when glaucoma was not evident preoperatively. Frequent optic nerve exams (every 3 months) and formal visual field testing (every 6 months) is recommended, along with aggressive treatment of increased intraocular pressure and/or optic nerve cupping and visual field evidence for glaucoma. Topical and systemic anti- glaucoma medications are usually effective at reducing intraocular pressure, but a glaucoma drainage device may often be necessary (e.g., Ahmed valve). Collaboration with a glaucoma expert is strongly recommended.
Sterile vitritis: Vitreous inflammation in the absence of any other signs of infection can occur at any time after KPro implantation, but microbial endophthalmitis should always be considered. In an eye with vitreous cells and no other signs of microbial endophthalmitis, vitritis may be treated by increased frequency of topical corticosteroids and/or peribulbar injection of 20-40 mg of triamcinolone.
Microbial endophthalmitis: Intraocular infection after KPro is usually consecutive to microbial keratitis. Significant vitreous inflammation in the setting of microbial keratitis should always be considered microbial and treated in standard fashion by a vitreoretinal surgeon with vitreous biopsy and intraocular antibiotics +/- an antifungal agent, depending on clinical suspicion. However, microbial endophthalmitis after KPro may also occur without signs of corneal infection, and when suspected, should be referred immediately to a vitreoretinal specialist for vitreous tap and intraocular antibiotics.
Retinal detachment: Reported rates of retinal detachment after Boston keratoprosthesis vary widely, with the highest incidences in patients with autoimmune disorders and after chemical injuries. When a vitrectomy is indicated at the time of keratoprosthesis implantation, collaboration with an experienced vitreoretinal surgeon is recommended. Peripheral retinal examination after Boston keratoprosthesis is difficult, but wide-field retinal imaging cameras can visualize retinal periphery well beyond what can be seen with indirect ophthalmoscopy, and should be utilized at least annually after keratoprosthesis implantation. Although retinal detachment repair can in many cases be successful anatomically, with the vitreoretinal surgeon working directly through the Boston keratoprosthesis, the functional results after retinal detachment in patients with a Boston keratoprosthesis are typically poor. Therefore, the best approach to retinal detachments after Boston keratoprosthesis appears to be prevention: a pars plana vitrectomy at the time of keratoprosthesis implantation when indicated by pre-existing vitreoretinal pathology, annual imaging with wide-field fundus photography after keratoprosthesis implantation, and aggressive repair of significant vitreoretinal pathology once identified after keratoprosthesis surgery.
Patient Evaluation and Selection
The Boston Keratoprosthesis (KPro) is designed as an “artificial cornea” that can be used in patients with severe corneal opacity.
The Boston KPro type I is used after standard penetrating keratoplasty has failed or when such a transplant would be unlikely to succeed. Thus, keratoprosthesis implantation is a procedure designed to help patients whose corneal diseases are the most difficult to treat.
The Boston KPro type II click-on design is used for patients with corneal scarring/opacity with poor blink mechanisms, severe dry eye, and/or severe cicatricial conjunctival scarring sufficient to preclude either successful corneal transplantation or successful retention of a contact lens after Boston KPro type I implantation.
The Boston KPro Snap-on design Type I consists of 3 components: a front plate made of clear polymethyl methacrylate (PMMA), a back plate made of titanium or PMMA, and titanium locking ring that locks the device in place around a corneal donor graft, The Boston KPro when fully assembled has the shape of a collar-button. The front plate acts as a lens and is provided in aphakic version compatible with a variety of axial lengths (16.0 mm to 31.00mm) or in pseudophakic version when an intraocular lens is present and assumed to target emmetropia.
The Boston KPro Click-on design Type I consists of only two components: a front plate made of clear polymethyl methacrylate (PMMA), and a back plate made of titanium that locks the device in place around a corneal graft.
Note the titanium components do not prevent MRI imaging.
- Patients with at least one failed corneal transplant, with poor prognosis for further grafting, or severe corneal opacity and vascularization with poor prognosis for corneal transplantation.
- Patients with vision worse than 20/200 (and opposite eye with vision less than 20/40).
- Patients with no retinal detachment or extreme optic nerve cupping.
- Patients with intact nasal light projection to exclude end stage glaucoma.
- If patient has glaucoma, consider simultaneous Ahmed shunt.
- If patient’s eye is pseudophakic, consider retaining the IOL and use Boston KPro for pseudophakia.
- If patient’s eye is phakic, do simultaneous open-sky cataract extraction and use KPro indicated for aphakia (chosen according to axial length of the eye).
Patient evaluation typically 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.
- Visual acuity, checked with hard contact lens when necessary.
- Accuracy of light projection (lack of central fixation, and/or lack of nasal projection may indicate end-stage glaucoma)
- Intraocular pressure
- Evaluation of blink mechanism and tear secretion
- Signs of chronic inflammation
- Whether eye is phakic, pseudophakic or aphakic
- Optic nerve cupping, macular abnormalities
- Ultrasound A-scan (to determine KPro optical power for implantation into aphakic eyes) Ultrasound B-scan (to exclude retinal detachment)
Other considerations include estimation of likely patient compliance and ability to obtain medications and make follow-up appointments. Autoimmune diseases, e.g., mucous membrane pemphigoid, Stevens Johnson syndrome, and severe connective tissue diseases, present significantly higher risks than other indications. Published outcomes in children are worse than in adults. The potential for late visual loss should be discussed with the parents or caretakers and carefully considered before implantation in a child. Keratoprosthesis implantation in a child should be performed only when all other aspects of care are optimized.
If the eye is pseudophakic, order a pseudophakic powered keratoprosthesis and plan to keep the intraocular lens in place to prevent vitreous prolapse. Please provide the axial length of the patient’s eye when ordering aphakic Kpro.
The Boston Keratoprothesis is the most commonly used artificial cornea in the United States and throughout the world. Currently 52 international countries are using the Boston Keratoprothesis:
- Czech Republic
- Hong Kong
- Kingdom of Bahrain
- New Zealand
- Saudi Arabia
- Sri Lanka
- South Africa
- United States