AlphaCor: An Artificial Cornea for Treating Corneal Blindness

AlphaCor is a synthetic, one-piece artificial cornea developed to address the needs of patients with corneal blindness who are unsuitable for or have a high risk of failure with traditional donor corneal grafts. It was FDA-approved in August 2002. 

Composition and design

Made from poly(2-hydroxyethyl methacrylate) (PHEMA), a hydrophilic polymer.

Consists of a central transparent optic surrounded by a white porous skirt, allowing for biointegration by tissue ingrowth.

The optic and skirt are chemically identical but differ in water content and physical properties.

The entire device measures 7.0 mm in diameter, 0.6 mm in thickness, and is designed with specific curvatures to provide the appropriate refractive power when implanted.

Available in two powers: AlphaCor-A (for aphakic patients) and AlphaCor-P (for phakic or pseudophakic patients).

The unique design of AlphaCor is relatively non-invasive, minimizing mechanical stress and allowing for intraocular pressure estimations, visual field examinations, and intraocular examinations. 

Surgical procedure

AlphaCor implantation requires a two-stage procedure performed with at least 3 months between each stage. Stage I involves placing the device in a corneal pocket, removing tissue behind the optic, and closing the wound. During Stage II, tissue in front of the optic is removed, exposing the central optic as a full-thickness replacement while the skirt remains integrated. 

Patient selection

Successful outcomes depend on appropriate patient selection. It is suitable for severe corneal disease with a poor outlook for traditional grafts, such as those with failed grafts or deep vascularization. Contraindications include severely dry, disordered, or inflamed eyes, poor tear film, meibomianitis, blepharitis, collagen vascular disease, conjunctival scarring, and recurrent inflammation like anterior uveitis. 

Outcomes and complications

Early results indicated anatomical stability and improved vision. Device retention rates were 92% at 6 months, 80% at 1 year, and 62% at 2 years in protocol cases. The mean visual acuity gain was 2.5 ± 3.1 lines. Complications can include stromal melting (most common), optic deposition, and retroprosthetic membrane formation. Earlier studies linked corneal melts to ocular herpes simplex infection, making it a contraindication, although later data suggested this might not be the case. 

Note:

The Boston Keratoprosthesis (KPro) has replaced the AlphaCor in some practices, including at the University of Iowa.

Newer is the KeraKlear KPro (K³) which is a foldable and injectable single-piece artificial cornea with no back plate or locking ring. It is made of clear flexible and strong proprietary biocompatible acrylic material, similar to what is used in intraocular lenses. This keratoprosthesis is designed to be implanted into an intracorneal stromal pocket by femtosecond laser, forming a clear window in an opacified cornea. It requires a single-stage procedure without the need for a carrier cornea. 

The image above demonstrating the benefit of the KeraKlear over penetrating keratoplasty. (a) Corneal transplant (PKP) 8 mm diameter full-thickness incision. (b) KeraKlear artificial cornea 3.5 mm diameter. The KeraKlear can also be implanted as an artificial lamellar graft.

Surgery can be conducted under either local anaesthesia (peribulbar or retrobulbar injection) or general anaesthesia.

This information is part of an educational series only. For medical advice or a diagnosis, consult a medical professional who is a corneal specialist.