Keratoprostheses for corneal blindness: a review of contemporary devices

Figures & data

Figure 1 Pintucci KPro.

Notes: (A) Pintucci KPro device. (B) First stage – insertion of Pintucci device into submuscular pouch for vascular ingrowth. (C) First stage – covering the ocular surface with buccal/labial mucosa. (D) Second stage – implantation of the retrieved device into the eye (2–3 months after the stage 1). (E) Second stage – creating an opening in the buccal mucosa to expose the optic. (F) Postoperative appearance of a successful Pintucci KPro. All pictures of this figure are the courtesy of Dr Qureshi Maskati.
Abbreviation: KPro, keratoprosthesis.

Table 1 Historical kertaoprostheses

Keratoprostheses
Author (year)	Materials and design	Summary
Pellier de Quengsy (1789)^Citation14	Silver-rimmed convex glass disk	It is considered the first design of KPros, but no account of implantation was mentioned.
Nussbaum (1853)^Citation14,Citation15	Glass device in collar-stud design	Nussbaum performed heroic experiments on himself by implanting wood, glass, iron, copper, and other materials and noted that glass was non-irritable. He implanted his device in rabbits and humans, which was retained for 3 years and 7 months, respectively.
Heuser (1860)^Citation16	Quartz	Heuser implanted a device made of quartz in a blind girl, which was retained for 6 months with good visual recovery.
Abbate (1862)^Citation16	Glass disk with surrounding skirt made of rubber and casein	Abbate developed a KPro with the skirt made of natural polymers and the optic with glass. He implanted it in animals, which was extruded in a short time. Although failed, his experiments emphasized the importance of integration of skirt into the eye.
Salzer (1900)^Citation16	Quartz disk with platinum ring and flanges	One of the successful early models of KPro that lasted up to 1 year in humans. Salzer made the observations that the optic should be lighter than glass and prosthetic rim should be made of a bio-integrable material.
Stone (1953–1958)^Citation17,Citation18	PMMA disk	Perforated disks implanted into the corneal lamellae were retained for more than 3 years.
Cardona (1969)^Citation19	PMMA – nut and bolt	It was a widely used KPro model. The PMMA skirt is positioned retrocorneally, which forms the nut, and the threaded optic makes up the bolt. Optic was elongated and could be adjusted in length by rotation through the threading so that it can stay projected beyond conjunctival surface. The optic was detachable, thus it facilitated the treatment of retroprosthetic membrane.
Choyce (1967–1978)^Citation20	Perspex CQ – one-piece and two-piece designs	This device was similar to Cardona KPro with a longer core, but was implanted in intralamellar or penetrating fashions. With the initial KPro devices, skirt was implanted first followed by insertion of the threaded optic at a later stage. The implant was covered by either corneal or sclero-corneal graft. The later models were made in a single-piece design and were implanted in two stages. In the first stage, the device was implanted into the eye having the optic covered by corneal tissue. After a period of maturation, the optic was exposed by excision of the overlying tissue. Lens extraction, iridectomy, and core vitrectomy were also performed.
Dohlman (1974)^Citation21	PMMA collar button	It consists of one front and one back plate made of PMMA. The front plate contains the optical stem. The back plate was made of black PMMA in some devices. In preliminary models, the back plate was fused to the front plate by using methylene chloride. In later models, the back plate was threaded to the optic. The device was first inserted into a full-thickness donor cornea through a central hole in the cornea. Then the corneal button along with device is sutured to the host cornea similar to keratoplasty.
Reudemann (1974)^Citation22	Silicone-satellite KPro	This interesting KPro was made of a satellite-shaped optic having a Dacron skirt glued to its sides. The implant was inserted through a limbal incision with the broader side of the optic positioned inside the anterior chamber and the smaller portion of the optic pushed out through a central corneal opening until the Dacron skirt adheres to the cornea. Eventually a fibrotic membrane develops and holds the device against the cornea. Sutures were not used to secure the device.
Cardona (1983)^Citation23	Through and through	A peripherally pigmented PMMA optical cylinder, intended to reduce the glare, was carried on a Teflon skirt. The cylinder was inserted through the cornea, whereas the skirt was anchored to the sclera. Normally, the complex was reinforced with Dacron and supported by donor sclera or autologous tissues like periosteum or eyelid skin (after removing tarsal plate and orbicularis and fascia). Device extrusion rate was 25%.^Citation23
Girard (1983)^Citation24	Modified Cardona’s nut and bolt with Dacron or Proplast skirt	Cardona’s nut-and-bolt principle was applied to this device, but the skirt material was taken from Dacron or Proplast. Surgical technique was improved by performing iridectomy, lens removal, and core vitrectomy. Prosthesis was covered with Tenon’s capsule and conjunctiva. The optic was exposed after 3 months by excision of the conjunctiva. Device extrusion was reduced to 10%, but other complications remained.^Citation24
Polack (1983)^Citation25	Ceramic (optic and skirt made of aluminum oxide–corundum)	The skirt and optic for this epicorneal device were made of ceramic. The principle of the device is to rest the skirt on the cornea and pass the threaded optical cylinder through the central hole (threaded) of the skirt and also cornea. Lens extraction, iris removal, and generous vitrectomy were performed. The entire device was covered with periosteum or Tenon’s capsule and conjunctiva for 1 week or 2 weeks, after which, by excising the overlying tissue, the optic is exposed. In some cases, the device was also implanted through the lids.
Caldwell (1997)^Citation26	PTFE skirt with polyurethane elastomer optic	The skirt was made of a six-pronged porous PTFE polymer (Gore-Tex), which was inserted into the intralamellar corneoscleral pocket.
Worst–Singh–Andel (1995)^Citation26,Citation27	Champagne cork KPro (optic made of glass or polycarbonate)	It is a collar-stud device containing an anterior plate connected to a progressively enlarged cone-shaped optic. The optic is inserted through the central corneal aperture. The intraocular pressure helps to press the optic against the cornea, thus creating a seal. The external plate contains fenestrations, through which steel wires are passed through to anchor the device to the sclera. Their study had poor follow-up results.^Citation26 Singh implanted the device in the nasal paralimbal sclera, and also used nylon sutures to anchor the device to the rectus muscles.^Citation27
Pintucci (1995)^Citation28,Citation29	Dacron skirt with elongated PMMA optic	Dacron fabric capable of biocolonization was incorporated into a medical-grade PMMA optical cylinder. The device is implanted in two stages. In the first stage, the ocular surface of the diseased eye is prepared, keratinized tissue is removed, and a patch of buccal mucosa is grafted, which forms the new ocular surface. In the same sitting, the device is implanted into the submuscular pouch of the contralateral lower lid for connective tissue ingrowth. Two months later, in the second stage, the device is extracted from the submuscular pocket and implanted into the eye under the buccal mucosa. The iris and lens were removed during this procedure. The optic projects through an opening in the buccal mucosa. The authors claim favorable results on a 15-year follow-up with Pintucci KPro.^Citation29

Abbreviations: KPro, keratoprosthesis; PMMA, polymethylmethacrylate; PTFE, polytetrafluoroethylene.

Figure 2 AlphaCor keratoprosthesis.

Notes: (A) AlphaCor device. (B) First stage – insertion of AlphaCor within the corneal lamellar pocket. A 3 mm central zone part of the posterior lamella is trephined. (C) Second stage – the external portion of the optic is exposed by excision of the superior corneal lamella. Adapted by permission from Macmillan Publishers Ltd: Eye. Hicks CR, Crawford GJ, Lou X, et al. Corneal replacement using a synthetic hydrogel cornea, AlphaCor[trade]: device, preliminary outcomes and complications. 2003;17(3):385–392, Copyright ©2003.¹⁰⁹

Figure 3 Boston keratoprosthesis.

Notes: (A) Type-1 device with front plate (optical stem) and titanium back plate. (B) Type-1 device in situ with a bandage contact lens. (C) Type-2 device with extended optical stem and titanium back plate. (D) Type-2 device in situ – projection of the optical stem through the lid. All pictures of this figure are the courtesy of Dr James Chodosh.

Figure 4 Assembly and implantation of Boston type-1 KPro.

Notes: (A) Donor corneal button is trephined to create a central aperture. (B) Corneal graft is placed on the front plate. (C) PMMA back plate covers the graft and titanium ring locks the device. (D) Assembled type-1 device ready for implantation (corneal graft is sandwiched between the front and back plates). (E) Host cornea is excised (excised diameter matches outer diameter of the corneal graft). (F) Implantation of the type-1 KPro. All pictures of this figure are the courtesy of Dr Geetha Iyer.
Abbreviations: KPro, keratoprosthesis; PMMA, polymethylmethacrylate.

Figure 5 Postoperative course of the Boston type-1 KPro.

Notes: (A) Corneal graft melt adjacent to the front plate. (B) Retroprosthetic membrane seen through the optic. (C) OCT scan showing Boston type-1 KPro in situ. Pictures (A) and (B) are courtesy of Dr Geetha Iyer.
Abbreviations: KPro, keratoprosthesis; OCT, optical coherence tomography.

Figure 6 OOKP stage 1 – buccal mucosal graft preparation and transplantation.

Notes: (A) Excision of the BMM. (B) Excised mucosal tissue-fat and muscle are trimmed off. (C) Ocular surface preparation (sclera is bared and corneal epithelium debrided). (D) Mucosal graft transplantation on to the ocular surface.
Abbreviations: OOKP, osteo-odonto-keratoprosthesis; BMM, buccal mucous membrane.

Figure 7 OOKP stage 1 – tooth extraction and preparation of the OOAL lamina.

Notes: (A) Extraction of the tooth with a piece of mandible. (B) Preparation of the tooth (dentine is exposed on one surface, while the alveo-dental ligament is preserved). (C) A central hole is drilled perpendicular to the lamina. (D) A PMMA cylinder is inserted into the lamina.
Abbreviations: OOKP, osteo-odonto-keratoprosthesis; OOAL, alveo-dento-acrylic; PMMA, polymethylmethacrylate.

Figure 8 OOKP lamina and postoperative course after stage 1.

Notes: (A) PMMA optical cylinder – the wide part sits on the dentine surface. (B) Prepared OOAL lamina – rim of acrylic cement can be seen around the optic. (C) A healthy mucous membrane 1 month after the stage 1.
Abbreviations: OOKP, osteo-odonto-keratoprosthesis; PMMA, polymethylmethacrylate; OOAL, alveo-dento-acrylic.

Figure 9 OOKP stage 2 – retrieval of the lamina and implantation into the eye.

Notes: (A) Lamina is recovered from the subcutaneous pocket. (B) Connective tissue is removed from the lamina to expose the dentine side. (C) Buccal mucosa from the eye is reflected to expose the cornea. (D) Central corneal button is excised. (E) Lens extraction (IOL is also removed when present). (F) Open sky core vitrectomy is performed. (G) Lamina is implanted into the eye with wide portion of the optical stem passing through the cornea. (H) Mucosal membrane is replaced over the lamina. Through a central opening in the BMM, the optic projects beyond 1 mm.
Abbreviations: OOKP, osteo-odonto-keratoprosthesis; BMM, buccal mucous membrane; IOL, intraocular lens.

Figure 10 Postoperative course after stage 2.

Notes: (A) A healthy OOKP eye after a successful surgery. (B) CT scan image showing an intact lamina in the OOKP eye.
Abbreviations: OOKP, osteo-odonto-keratoprosthesis; CT, computerized tomography.

Figure 11 Filatov keratoprostheses.

Notes: (A–F) show the previous models. Model (G) is the latest and most successful Iakymenko prosthesis. Reproduced from Iakymenko S. Forty-five years of keratoprosthesis study and application at the Filatov Institute: a retrospective analysis of 1060 cases. Int J Ophthalmol. 2013;6(3):375–380, doi:10.3980/j.issn.22223959.2013.03.22.¹⁰⁶

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