How can CISIS / MyoRing stop the progression?

CISIS / MyoRing can stop the progression of keratoconus as, based on its unsplitted structure; it can absorb the forces inside the cornea. The progression of keratoconus is the result of a biomechanical weakness inside the tissue. There are two possible ways of how to strengthen the cornea in order to stop the progression of the disease:

1. Crosslinking: Strengthening of the cornea by hardening the tissue itself on an ultra-structural kevel; Therefore, the tissue is able to absorb the stress inside the cornea without inducing further irregular deformation.

2. CISIS / MyoRing mechanically supports the cornea without changing the tissue structure itself. The MyoRing can absorb the mechanical stress inside the tissue which acts within the plane of the MyoRing. Therefore, in contrast to MyoRing, Ring segments and splitted rings (see illustration below) cannot stop the progression of the diseaseas as they possess margins and the progressive forces (red arrows) only lead to their separation.

Progressive forces (red arrows)

In analogy to this principle, one can think of the ceiling of a room on which rests a heavy weight. As soon as the ceiling cannot support the heavy weight any longer, it bends towards the inside of the room. In this scenario, the ceiling would suffer from a keratoconus. Now, there are two ways of strengthening the ceiling in order to avoid this from happening.

Firstly, the ceiling of the room could be made out of a more stable material; one could change the very material of the ceiling, so to speak. Consequently, it could carry the additional weight placed upon it. For example, one could use a ceiling made out of steal instead of wood. This is the exact analogy which applies as far as corneal crosslinking is concerned.

Secondly, the ceiling could be supported by an additional ceiling beam. Thus, this beam could absorb the additional forces. This ceiling beam is the analogy of the MyoRing (CISIS). Naturally, an interrupted ceiling beam (ring segments) could not execute a similar function.

A scientific analysis of the biomechanical effect

A scientific analysis of the biomechanical effect (weakening or strengthening of the tissue) of several distinct therapies, including CISIS shows that CISIS strengthens the cornea 300% (Daxer A. Biomechanics of Corneal Ring Implants. Cornea 2015; 1493-1498). This means that even though a cornea weakened by keratoconus measures, for example, 400µm, after CISIS it acts as if it measured 1200µm. This is a significant strengthening which is able to stop the progression of the disease. In comparison, a normal cornea without keratoconus measures around 550µm and an untreated cornea suffering from keratoconus is considerably thinner.

The opposite illustration summarizes these findings. One can see that laser therapies (LASIK, PRK, SMILE) weaken the cornea because of the tissue they remove. Ring segments minimally weaken the cornea (the radial cut creates a potential weak point). In contrast, the MyoRing which is implanted during CISIS strengthens the cornea threefold and crosslinking fourfold. While CISIS can achieve an additional rather significant improvement of visual acuity, this is not possible in crosslinking.