A satisfying visual function can be restored in early stages of the disease by the use of rigid gas permeable contact lenses (RGP). However, as the disease keeps progressing, intolerance or fitting problems frequently occur. The cornea often becomes too steep to provide a stable fit for the contact lens. The mechanism of action is that the irregularities of the keratoconic cornea are compensated by the tear film between the back surface of the contact lens and the front surface of the cornea.
In light of modern treatment options such as MyoRing, a cornea transplantation is considered the last resort of keratoconus treatment. Here, the affected cornea is replaced with the cornea of a human donor. The connection between the remaining corneal periphery and the transplanted donor cornea is achieved by sutures. This treatment requires a long rehabilitation period of at least 12 months. Even after successful transplantation, only a minority of eyes are able to provide a sufficient vision without rigid contact lenses.
Crosslinking is one of the most important innovations in the treatment of keratoconus of the past decade. This treatment stiffens the cornea and therefore prevents the disease from progressing in a significant number of cases. Crosslinking cannot achieve an improvement of vision. It is therefore the treatment of choice in the very early stages, where vision is still good but there is a considerable risk of progression of the disease.
Corneal crosslinking is a 2-step procedure:
1st step: Introduction of riboflavin into the corneal tissue. Riboflavin is a B2 Vitamin which is introduced into the cornea as yellow eye drops. The substance mediates the crosslinking of collagen in the cornea when irradiated by means of UV-A light. The riboflavin can be introduced into the corneal tissue either via an intact epithelial layer (epi-on) or after removing the epithelium (epi-off). The epithelium is the surface cell layer of the cornea which acts as a barrier for riboflavin penetration. Most surgeons remove the epithelium before soaking the cornea via Riboflavin eye drops (epi-off). Most studies show, that epi-off is more effective than epi-on. Epi-off has the disadvantage of significant postoperative pain for several days.
2nd step: Irradiation of the cornea by means of UV-A light of 365nm wavelength and 5.4 J/cm2 total energy transfer in order to achieve sufficient stiffening of the cornea and to prevent further progression of the disease. A minimum thickness of 400 microns at the thinest point of the cornea is required to perform this step safely. A corneal thickness of less than 400 microns results in a significant risk of destroying the endothelial layer at the back surface of the cornea, which is responsible for keeping the cornea clear and transparent.
Ring segments (ICRS) are incomplete ring implants offered for improving the patient’s visual function. Some 20 years ago, these kinds of implants represented the first relevant technology for improving vision without performing corneal transplantation. Ring segments have to be implanted into the cornea via a circular tunnel and require suturing of the otherwise gaping wound. Since ICRS are designed as incomplete rings, they cannot prevent the progression of the disease and therefore often require additional crosslinking. This design is also responsible for postoperative complications such as extrusion. Given their comparably limited effective range and their postoperative complication rate, ring segments (ICRS) can be considered obsolete nowadays in light of the modern MyoRing technology.
MyoRing keratoplasty, also referred to as CISIS (Corneal IntraStromal Implantation System), is the remodeling of the geometrically altered cornea by inserting a complete ring implant (MyoRing) into the cornea in order to achieve both, improvement of vision and termination of the progression of the disease. The MyoRing is placed between two corneal layers just 300 microns beneath the surface. The tiny wound is self-sealing and requires no suture - it simply heals within several hours. Since the MyoRing is a complete ring, it can stabilize the cornea and avoid typical complications of ring segments. The MyoRing technology is characterized by particularly high effectiveness and safety. It was developed by Dr. Daxer in order to overcome the problems of ring segments.
The table provided above displays a comparison of the distinct treatment methods.