Keratoprosthesis - Patient Evaluation and Selection
Information for Referring Physicians
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 link 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 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.
To make an appointment, please call 617-573-3240
Click here to view Boston Keratoprosthesis bibliography.
Past last updated 7/11/2019