To evaluate whether the artificial cornea can play a stable role in restoring vision, its long-term presence rate is a prerequisite. Because of this, the dissolution of the surrounding tissue and the prolapse of the artificial cornea after the artificial cornea implantation have been one of the problems puzzling researchers and clinicians.
For a reason, let's start with the types of artificial corneas.
At present, Boston artificial cornea, which is made of PMMA material, is widely used internationally. In 1992, FDA approved it for use in the United States. Among them, Boston I is the most widely used in clinical practice, and its effect is also good.
However, this kind of artificial cornea has a high requirement for the ocular surface, so it is mainly used in the cases of multiple corneal transplantation failures abroad. In addition, this kind of surgery still needs a corneal allograft as a carrier of artificial cornea.
and! The incidence rate of corneal lysis after Boston artificial cornea surgery is as high as 1.5% ~ 17%. Although improved design, wearing soft corneal contact lenses and oral collagenase inhibitors are used to prevent corneal lysis, it is still difficult to avoid patients with extremely poor ocular surface conditions.
AlphaCor artificial cornea, another kind of artificial cornea made of pHEMA hydrogel material, was once highly praised by people in the industry because it can be implanted surgically in a manner similar to corneal transplantation, without corneal graft.
However, after multi center clinical application, it was found that the incidence rate of corneal stroma melting and artificial corneal fiber exudate membrane formation was high, and the 2-year survival rate was low. Similarly, this kind of artificial cornea requires high ocular surface conditions and is not suitable for long-term vision restoration of patients with severe corneal blindness.
and! Compared with Boston artificial cornea, the probability of dissolution of surrounding tissues is higher. It is reported that AlphaCor artificial cornea can even reach 60%, and more than half of them may be dissolved.
In view of the failure experience of the above two kinds of artificial corneas, the research and development team and doctors of Mihm artificial cornea began to think: how to ensure the safety and stability of Mihm artificial cornea in patients' eyes?
As for stability, in addition to the biocompatibility of artificial cornea as a congenital condition, the acquired reinforcement must also be indispensable. Therefore, they chose autologous ear cartilage reinforcement.
Review of literature shows that artificial cornea reinforcement materials include allogeneic sclera, autologous anterior tibial periosteum, and autologous ear cartilage.
The autologous anterior tibial periosteum is complex to obtain, and the hardness is not enough, and the long-term effect is poor.
Although the selection of allograft sclera is relatively simple and convenient, it has the problem of allograft rejection with cornea, and after a long time of ethanol treatment and storage, it will completely destroy the cell components, become soft, and the tissue is easy to deform.
Therefore, in the clinical application of Mihm artificial cornea, the most common method is to use autologous ear cartilage reinforcement.
Ear cartilage is often used for nose plastic surgery and tarsal replacement surgery. As its own living tissue, active chondrocytes have been effectively preserved, with a high survival rate after surgery, good biocompatibility and stability, good elasticity, moderate hardness, easy shaping, and no rejection. Compared with the bone tooth type artificial cornea, ear cartilage is simple to obtain, and there is no complications such as displacement of the lens column caused by bone absorption.
Of course, in order to make the operation more effective, some doctors also used other combined methods for tissue dissolution and leakage, and achieved good results.
In the Clinical Study on Experimental Aspiration of Mihe Domestic Corneal Prosthesis in Animals, the author wrote that the preventive measures for tissue dissolution and leakage also include: conjunctival covering during operation to rapidly establish ear cartilage blood supply circulation and form biological healing with corneal tissue.
In the case of severe conjunctival defect and scarring, lip mucosa transplantation should be flexibly used to improve the ocular surface integrity and promote tissue vascularization.
Compared with the allograft corneal carrier in Bosoton artificial cornea, it mainly relies on aqueous humor to provide nutrition to maintain its epithelial integrity. Mihe artificial cornea promotes vascularization of the ocular surface as soon as possible by covering the conjunctiva or labial mucosa to maintain the nutrition supply of the anterior lamellar tissue, thereby reducing the possibility of tissue dissolution.
Therefore, ear cartilage reinforcement combined with conjunctival covering is an important measure to prevent aqueous humor leakage and artificial cornea prolapse.
In a word, in the process of keratoprosthesis transplantation, the ear cartilage reinforcement scheme helps to improve the stability and safety of keratoprosthesis in the eye, and adds a guarantee for the restoration of vision of patients. We also believe that, with the continuous improvement of Mihm artificial cornea and the continuous progress of surgical technology, Mihm artificial cornea will have more extensive indications, more convenient implantation process and more stable long-term effects in the future!