An artificial cornea is a corneal device used in corneal transplantation to replace a diseased or damaged cornea. Corneal transplantation is a surgical procedure that replaces a natural, cloudy cornea or corneal parts, with donor tissue/cornea.
A corneal transplant is often successful in a significant portion of recipients. The human donor tissue remains the best option for corneal transplantation. However, some patients undergo graft rejection (once or more) or have certain corneal diseases that do not respond well to the different types of corneal transplantations (whether full-thickness or partial-thickness). These conditions include ocular surface diseases like Stevens-Johnson syndrome, congenital aniridia, severe dry eye, limbal stem cell deficiency, and following a chemical burn. Therefore, surgeons often will recommend artificial corneas to restore vision.
Artificial corneas have been around for more than 50 years, and recent developments have made the devices reliably successful. Examples of artificial corneas include the Dohlman, AlphaCor, Boston KPro (Type 1 & 2), Fyodorov-Zuev Kpro, and Osteo-odonto-keratoprosthesis.
- Dohlman - This device combines artificial materials with a donor cornea for compatibility.
- Osteo-odonto-keratoprosthesis - It is used to treat severe ocular surface disorders and is implanted via a complex surgical procedure involving several steps.
- Fyodorov-Zuev keratoprosthesis - It is made from a titanium plate with two large openings and designed in a way that the aqueous humor flows anteriorly.
- Boston KPro - It is the most popular keratoprosthesis for transplantation because it is made of a material that does not opacify (cloud). The Boston KPro consists of two pieces with a collar button and is made of polymethylmethacrylate, a transparent thermoplastic with a titanium locking ring. Type 1 is used in eyes with normal blinking and sufficient tear secretion while Type 2 is used in eyes with severe dry eye disease and ocular surface diseases (end-stage)
- AlphaCor - It is a device made from poly-2-hydroxyethyl methacrylate and uses a two-stage surgical procedure to implant the device into the patient’s eye. It utilizes the patient's own tissue to allow the device to get integrated into the ocular tissues. This device has been withdrawn from the US market because it results in serious complications like retinal detachment.
Also Known As
Preparation and Expectation Before Surgery
This office procedure will last at least 3 hours, including the surgical and recovery times, and the patient should return home the same day.
Types, Purpose & Procedure
Once the device has been assembled, the surgeon follows the procedure used in full-thickness corneal transplantation (penetrating keratoplasty). Most patients are placed under local anesthesia. Infants and young children, however, use general anesthesia.
In the procedure:
- The surgeon fixes the artificial cornea to a ring of donor corneal stroma
- S/he uses a femtosecond laser to create an 8-mm corneal pocket at about 100 Î¼m above the endothelium. If a laser device is not available to create the pocket, commercial non-laser devices can be used.
- The surgeon makes a 3.5 Î¼m trephination incision and transplants the device into the previously created corneal pocket using standard corneal transplant methods. The device measures 7 mm in diameter with a 4 mm central optic.
- The surgeon places a hydrophilic bandage lens over the entire surface to eliminate many ocular surface issues common with corneal transplants.
Risks, Side Effects & Complications
Patients with severe dry eyes or inflammation have more significant risks because a membrane can grow behind the artificial cornea and affect vision. A laser beam can open up the membrane and eliminate the need for further surgery.
Tissue around the artificial cornea's stem can dissolve (though this is rare), leading to fluid leakage from the eye. Fluid leaking from the eye can result in infection and loss of vision. In this case, surgery may be repeated.
Complications may include:
- Worsening glaucoma
- Increased intraocular pressure
- Extrusion of the keratoprosthesis
- Corneal melting in chemical burn patients
- Endophthalmitis (inflammation of the anterior eye)
- Expulsive hemorrhage (sudden low intraocular pressure)
- Retinal detachment (retina pulls away from the layer underneath)
- Retroprosthetic membrane (can lead to corneal melt and affect visual acuity)
After Care, Recovery & Results
Patients are given the necessary prescriptions and post-operative care instructions. Long-term topical and oral medications are required to keep away or treat resultant complications like glaucoma and infections. Patients need to be monitored closely postoperatively to address the risk of complications that may lead to a total loss of vision, especially from glaucoma and endophthalmitis.
Patients are required to attend a follow-up appointment the following day after surgery. The next follow-up appointments will take place a week later and every three months in the first year of the procedure. Vision often stabilizes within a month or two and remains unchanged even up to follow-up at 50 months.
Research indicates that 92% of patients who undergo a keratoprosthesis transplant achieve a 20/200 or better visual outcome.