Our research began in 1985. In 1986 Dr. Paulo Ferrara realized that to keep the implant in place it was necessary a big hole in the center of the lens what resulted in an annular prostheses. Since then we started trying several annular shapes and diameters and from these researches we concluded that the best project is the one we are using nowadays, made of PMMA, with a total diameter of 5,0 mm, arch length ranging from 90 to 210 degree and thickness ranging from 100 to 400 micra.

The rings were implanted in rabbit eyes, through a free hand dissection technique, at 50% depth of measured central corneal thickness. The eyes were examined for 12 months and the animals were sacrificed so that their eyes could be submitted to hystopathological exams. The hystopathological results revealed excellent tolerance of the cornea to the prostheses since there were only slight inflammatory reaction surrounding the implant and no evidence of extrusion.

The techniques traditionally used for the implant of corneal prostheses, free hand dissection and keratectomy with a microkeratome showed some negative points, such as interface deposits, delay in refractive stability, besides the high costs of the microkeratomes and slow learning curves. In order to improve the ring implantation technique, reducing its complications and making it accessible to a large number of anterior segment surgeons, Dr. Paulo Ferrara developed in 1994 a stromal tunnel and ring implantation technique, which completely eliminates the disadvantages of the conventional techniques.

In 1995 Dr. Paulo Ferrara implanted the first patient who had undergone penetrating keratoplasty and radial keratotomy. This patient was forwarded to the Cornea Service at Hospital Sao Geraldo in UFMG (Federal University of Minas Gerais) for a new transplantation. We decided, with formal authorization of the patient, to test the ring before performing the penetrating keratoplasty. The result was satisfactory, yielding ametropia correction and perfect corneal tolerance to the orthesis. After a 6-year follow-up, the patient has good uncorrected and corrected visual acuity, the shape is more regular and the refraction is stable.

The excellent tolerance to the implant by the transplanted cornea gave us the necessary confidence to apply the technique in keratoconic corneas. Therefore we decided, in 1996, to implant the rings in patients intolerant to contact lenses that had the penetrating keratoplasty indicated.