cisis

CISIS/MyoRing - Stop of progression

MyoRing keratoplasty (CISIS) can stop the progression of keratoconus. Based on its complete and continuous structure it can absorb the forces inside the cornea. In general, there are two possible ways of how to strengthen the cornea and stop the progression of the disease:

1. Corneal Crosslinking: Strengthening of the cornea by stiffening the tissue itself on an ultra-structural level;

2. CISIS/MyoRing keratoplasty: Supporting the cornea without changing the tissue structure itself. Since the MyoRing is a closed and complete ring, it can absorb the forces inside the tissue.

Progressive forces (red arrows)

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

First, 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. For example, one could use a ceiling made out of steel instead of wood. This is an analogy for corneal crosslinking.

Second, the ceiling could be supported by an additional ceiling beam. Thus, this beam could absorb the additional forces. This ceiling beam is an analogy for the MyoRing. Naturally, an interrupted ceiling beam (= a ring segment) 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 (MyoRing keratoplasty) shows that the MyoRing strengthens the cornea by 300% (Daxer A. Biomechanics of Corneal Ring Implants. Cornea 2015; 1493-1498). This means, that even though a cornea weakened by keratoconus measures e.g. 400µm after MyoRing insertion, 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 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, an implanted MyoRing strengthens the cornea threefold and crosslinking fourfold. While a MyoRing can additionally achieve a rather significant improvement of visual acuity, this is not possible with crosslinking.

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