|Year : 1973 | Volume
| Issue : 3 | Page : 112-116
Keratoprosthesis : A clinical study
Dhanwant Singh, DC Bansel, Avtar Singh
Government Medical College and Rajendra Hospital, Patiala, India
Government Medical College and Rajendra Hospital, Patiala
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Singh D, Bansel D C, Singh A. Keratoprosthesis : A clinical study. Indian J Ophthalmol 1973;21:112-6
Advances in the field of Keratoplasty have over come the problem of majority of corneal blind persons. Still there are many persons where this method has failed or is likely to fail to restore their eye sight. The advent of plastic corneal prosthesis is an effort to benefit such individuals. In the past over ten to fifteen years many types of keratoprosthesis have been tried by various people with varying degree of success. ,,,,,,,,,,,,
The object of this paper is to report our limited experience with this technique. We are not aware of any such work having been carried out in this country prior to this study.
Indigenously prepared Cardona type penetrating keratoprosthesis was used. It consisted of a 2.5 mm long refracting cylinder of 2.0 mm diameter with an intra-lamellar fenestrated thin disc of 5.5 mm diameter [Figure - 1],[Figure - 2],[Figure - 3]. It was made of pure polymethylmethacrylate having neutral pH and no free radicles on its surface. The radius of curvature of the anterior surface of the optical cylinder was 7.8 mm and that of the prosterior curvature was 7 mm.
The results are shown in [Table - 1]. In all five operations were done on four patients where the keratoplasty had either failed or was likely to fail. In case number one bilateral blindness existed since the age of 2 months due to dense vascularised total corneal opacities of both the eyes. Keratoplasty had failed in the other eye. In case number two the cornea was opaque with the surface irregular, loose and degenerated. Here also previous keratoplasty had failed. The cornea was irregularly thin and had precarious vitality. In the third case the eye had been previously operated for glaucoma and cataract. The operation of glaucoma seemed to have been done at an advanced stage of glaucoma. There was a dense corneal opacity. In case number four the cornea showed bullous keratopathy following cataract operation. In cases numbering one, three and four the keratoprosthesis has been well retained in the cornea over a period of two to three years follow up. [Figure - 4],[Figure - 5]. The eyes are quiet and the keratoprosthesis have retained their transparency. One uniform feature of all the cases has been the growth of fibrous membrane behind the optical cylinder of the keratoprosthesis, which reduced, whatever chance was there of the visual improvement. In case number four this posterior fibrous membrane was excised with knife needle, but it regrew quickly.
In case number two, the keratoprosthesis was extruded after eight months. A second operation was done using a full thickness corneal graft to cover the keratoprosthesis. The corneal transplant necrosed and the keratoprosthesis extruded after three months of reoperation leaving the eye ball still intact because of the posterior corneal hole having been filled with fibrous tissue. The visual improvement in all the successful cases was only marginal.
| Discussion|| |
Three criteria are used to evaluate the results of prostho-keratoplasty. 1. Tolerance of the implant by the ocular tissues. 2. Maintenance of transparency by the keratoprosthesis. 3. Functional improvement.
The indigenously available pure polymethylmethacrylate used for the manufacture of keratoprosthesis in this study has been well tolerated by the eye. Out of the four patients three have retained it without any side effects for over a period of two to three years while it had extruded in one case (25%). In this case the cornea was of a specially low vitality and thin. Even at the time of operation the anterior flap of the cornea appeared to be of doubtful vitality and integrity. According to Cardona, thicker the recipient corneal layers anterior to the intralamellar anchor plate of the prosthesis, the greater the tolerance. Cardona  has also reported the extrusion rate of 21.317o in his series.
In all the cases in this study the keratoprosthesis has maintained transparency of its substance. The follow up in one case is over more than three years. The special climatic conditions of extremes of cold, heat and dryness and also the interaction of tissue fluids have not affected the transparency of the keratoprosthesis.
The poor visual results obtained were due in part to the selection of very poor risk eyes and in part to the growth of a retrocorneal fibrous membrane which covered the posterior surface of the keratoprosthesis. This was also a frequent complication encountered by Cardona.  According to him if the posterior surface of the cornea and the posterior surface of the implant lie at the same level, scar tissue covering posterior face of the implant may result. Stone  however reported that he prevented the development of this posterior membrane by replacing the aqueous humour with a two percent solution of sodium citrate pre-operatively. This prevented the precipitation of a fibrous matrix in the opening. According to him endothelial cells required this fibrin scaffolding to grow across the opening.
The visual improvement reported by Castroviejo et al  and Polack in majority of their patients ranged from 20/200 to counting fingers at two feet due to the same reasons.
Many improvements in the design of the keratoprosthesis and the operation technique are being tried to overcome these drawbacks. 
| Summary|| |
The study consists of implantation of Cardona type through and through corneal transplants made of polymethylmethacrylate in four cases. They have been followed over a period of two to three years. The transplant has been extruded in one case while well tolerated and transparent in three cases.
| Acknowledgement|| |
This study was undertaken with the grant provided by the Indian Council of Medical Research.
| References|| |
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5]
[Table - 1]