A temporary keratoprosthesis is a device placed to ensure a clear view of the posterior segment during vitreoretinal surgery in eyes with corneal opacity. It is used in cases with significantly reduced corneal transparency, such as corneal blood staining, corneal wounds with severe edema, or corneal foreign bodies from explosive ocular trauma.
Conventionally, for patients with both corneal opacity and vitreoretinal disease, full-thickness penetrating keratoplasty (PKP) was performed first, and posterior segment surgery was delayed for several months until corneal healing and edema resolution. With the advent of the temporary keratoprosthesis, prompt vitreoretinal treatment became possible regardless of the corneal condition.
For severe vitreoretinal pathology (e.g., post-traumatic) associated with corneal opacity, placement of a temporary keratoprosthesis enables safe retinal repair1). The view through a temporary keratoprosthesis is good, often providing a better surgical field than a freshly transplanted corneal graft1).
In 1981, Landers reported the first temporary keratoprosthesis. It consisted of a threaded biconcave optical cylinder made of PMMA, but the cylinder axis was 5 mm long, limiting the wide-field view of the peripheral retina.
In 1989, Eckardt developed a temporary keratoprosthesis made of silicone rubber, designed to be fixed with four nylon sutures. However, the soft material tended to fog during air exchange, and damage from suture tracks made repeated use difficult.
In the early 2010s, the Landers wide-field trunkless model was designed. The cylinder axis was shortened to 1 mm, allowing a wide view of the peripheral retina without an auxiliary lens.
QWhy use a temporary artificial cornea instead of performing corneal transplantation first?
A
In patients with both corneal opacity and vitreoretinal disease, especially in cases of ocular trauma, retinal repair is urgent. Performing full-thickness corneal transplantation first would require several months for corneal healing and edema resolution, during which retinal pathology may deteriorate irreversibly. Using a temporary artificial cornea allows immediate vitreoretinal surgery regardless of the corneal condition, and after surgery, the cornea can be reconstructed with full-thickness corneal transplantation.
The basic design of a temporary artificial cornea is to create a watertight seal using a trunk diameter slightly larger than the corneal trephine diameter. However, it has been reported that efficient sealing is possible even with a device diameter up to 0.3 mm smaller than the trephine diameter.
Tapered shape, compatible with a wide range of trephine diameters
Landers type
Material: Made of rigid PMMA. The central part is composed of PEG (polyethylene glycol).
Advantages: The rigid material protects against suture damage and allows reuse after autoclave sterilization.
Limitations: Low refractive power; a compound lens system (stacking of PMMA rigid lenses) may be required for magnified observation of the macula.
Next-generation model: The wide-field trunkless model ensures a wide peripheral visual field with a cylinder axis of 1 mm, minimizing the need for compound lenses.
Eckardt type
Material: Optically transparent soft silicone with a hydrophilic surface. Good adhesion to the cornea, with less leakage of irrigation fluid during scleral indentation.
Advantages: Provides a wider optical zone and shorter vertical length than the Landers type. High elasticity allows adaptation to irregular corneal defects and excellent peripheral sealing.
Limitations: The soft material tends to fog during air exchange. Reuse is difficult due to damage from suture marks.
The Cobo type is a truncated cone shape made of quartz, and its tapered design allows it to be used with a wide range of trephine diameters. It comes with a stainless steel handle, convenient for fluid and gas injection during intraoperative bleeding.
Intraoperative temporary corneal stabilization is not limited to artificial devices. There are also reports of triple procedures using donor corneal buttons unsuitable for transplantation, or using sutured soft bandage contact lenses as alternatives.
QHow to choose between Landers type and Eckardt type?
A
The Landers type is made of PMMA and is rigid, making it reusable and cost-effective. In contrast, the Eckardt type is made of silicone and is soft, offering better adaptability to irregular corneal defects and good adhesion to the cornea. The Eckardt type is suitable for trauma with corneal lacerations where the corneal defect shape is irregular, while the Landers type is widely used for defects after regular trephination. The next-generation Landers wide-field model combines a wide field of view with reusability.
Combined vitreoretinal surgery: When the posterior segment surgical field cannot be secured due to corneal blood staining, severe corneal edema, or ocular trauma with corneal laceration.
Modified triple procedure: Used to maintain a closed system and secure the surgical field during simultaneous cataract extraction, intraocular lens implantation, and penetrating keratoplasty.
Place the temporary keratoprosthesis in the center of the corneal defect and suture it to the sclera with interrupted 6-0 or 7-0 Vicryl or 9-0 nylon sutures.
After confirming watertight closure, perform vitreoretinal surgery.
After completing vitreoretinal surgery, perform silicone oil or air tamponade.
In cases of ocular trauma, to reduce the risk of allograft rejection, there is also the option of returning the temporary keratoprosthesis to the original corneal button and performing permanent full-thickness corneal transplantation at a later date.
Postoperative visual prognosis strongly depends on the extent of ocular trauma and the severity of retinal pathology. Retinal integrity is the main predictive factor.
In a report by Alvarez et al. (using the Eckardt type), the retinal reattachment success rate was 90% in the non-trauma group compared to 78% in the trauma group. Meanwhile, the visual improvement rate was 67% in the trauma group, exceeding the 47% in the non-trauma group.
In a study of the Landers type involving 107 traumatized eyes, useful visual function was preserved in 86%, visual acuity improved in 80%, and corneal clarity and retinal reattachment were maintained in 72.9%.
Decreased corneal graft clarity: Due to corneal neovascularization and endothelial cell loss secondary to postoperative inflammation.
Intraocular pressure abnormalities: Persistent postoperative hypotony is common in severely traumatized eyes and may require permanent silicone oil tamponade.
Phthisis bulbi: Recorded as the final outcome in severe cases.
While some reports indicate that performing full-thickness corneal transplantation within 8 weeks after trauma increases graft failure, others suggest that timely retinal reattachment within 1 month after trauma determines visual prognosis. The timing of permanent full-thickness corneal transplantation should be decided on a case-by-case basis.
QHow does the view through a temporary keratoprosthesis compare to that through a corneal transplant?
A
The view through a temporary keratoprosthesis is good, and in many cases, it provides a better surgical field than a newly transplanted corneal graft 1). This is because fresh corneal grafts are not optimally transparent due to postoperative edema, whereas the keratoprosthesis is made of optically designed transparent material. Therefore, temporary keratoprosthesis is superior to full-thickness corneal transplantation for ensuring fundus visibility during vitreoretinal surgery.
