Introduction
Keratoprosthesis is a surgical procedure in which a severely damaged or opaque natural cornea is replaced with an artificial corneal device. Unlike traditional corneal transplantation—which involves implanting donor tissue from a recently deceased individual—keratoprosthesis uses a synthetic device to restore vision when conventional grafts are likely to fail.
Indications for Artificial Corneal Implantation
Artificial corneas are generally used in severe bilateral cases resulting from:
• Congenital anomalies
• Corneal ulcers, opacities, or scarring
• Corneal trauma or chemical burns
• Failure of previous corneal grafts due to immune rejection or opacification
• Conditions with low success rates for natural grafts, such as:
o Severe dry eye
o Ocular surface diseases (e.g., Stevens–Johnson syndrome, ocular pemphigoid)
o Caustic injuries
Candidates typically have visual acuity less than 20/400 and bilateral severe impairment.
Types of Artificial Corneas
1. Boston Keratoprosthesis (KPro)
The Boston KPro is composed of:
• An anterior optical cylinder (housing the vision lens)
• A posterior plate
• A titanium locking ring connecting the two parts
A donor corneal graft is placed between the two components, then sutured into the patient’s eye. The donor tissue used is not required to be optically clear, as vision is achieved through the central optical cylinder.
There are two main variants:
• Type I: Implanted with eyelids left open and mobile
• Type II: Requires surgical fusion of the eyelids before implantation, reserved for severe surface diseases
2. Osteo-Odonto-Keratoprosthesis (OOKP)
Also known as “Tooth-in-Eye Surgery”, this technique is used in extreme cases where other prosthetic corneas are contraindicated.
• A tooth (usually from the patient) is extracted, and a cavity is drilled into it to house a synthetic lens
• The tooth-lens complex is implanted into the patient’s cheek or jaw for several months to allow tissue integration
• It is then removed and surgically implanted into the eye
3. AlphaCor (PHEMA-Based Keratoprosthesis)
This device uses PHEMA (poly-2-hydroxyethyl methacrylate), a biocompatible plastic, to support the vision lens. It does not require donor cornea or tooth structure for fixation.
Complications of Keratoprosthesis
1. Retroprosthetic Membrane Formation
o Occurs in up to 65% of cases
o Caused by inflammation or immune response
o Treated effectively using YAG laser in one or more sessions
2. Endophthalmitis (Intraocular Infection)
o A serious complication with a 2.7% annual incidence per patient
o Can result in total vision loss and prosthesis failure
3. Glaucoma (Elevated Intraocular Pressure)
o Occurs in 15–60% of cases
o Often pre-existing but exacerbated postoperatively
o IOP measurement is challenging with prostheses in place
o Treated with topical or oral hypotensive medications
Conclusion
Keratoprosthesis offers a life-changing option for patients with severe corneal disease when traditional transplantation fails. However, the procedure carries significant risks and requires careful patient selection, meticulous postoperative monitoring, and multidisciplinary management to ensure long-term visual rehabilitation and ocular health.