A satisfying visual function can be restored in early stages of the disease by the use of hard contact lenses. However, as the disease keeps progressing intolerance to contact lenses develops rather frequently. Furthermore, oftentimes the cornea becomes too steep as to provide a stable fit of the contact lens.
As soon as contact lenses cannot be worn anymore, given the aforementioned intolerance, traditionally, a cornea transplant is performed. The opposite image displays one such surgery. A cornea transplant requires a rather long period of recovery which frequently surpasses an entire year; the sutures remain inside the cornea during this period of time and, occasionally, rather strong irritations of the eye as well as further complications might occur. Moreover, the results of a cornea transplant may vary considerably and are mostly dissatisfying. The reason is that the donor material cannot be selected according to optical and structural parameters. Thus, the sewing in of the cornea cannot be adjusted to them either. Consequently, the range of variation is rather wide. Mostly, even after a cornea transplant has been performed the structure of the cornea remains highly irregular. A satisfying visual function can usually only be achieved if the cornea transplant is combined with hard contact lenses. One further therapy which succeeds in restoring the patients’ visual acuity after a cornea transplant is CISIS / MyoRing. See section “CISIS case studies” for further information.
One therapy which is capable of stopping the progression of the disease is “corneal crosslinking” (CXL). CXL is available for more than 15 years now and can be considered a milestone in keratoconus therapy. It allows stopping the disease in an early stage in order to preserve a good natural vision. However, CXL does not provide visual rehabilitation of any kind, but rather the progression of the disease is stopped. Thus, this therapy only makes sense in early stages of the disease, while visual acuity is still good. During CXL an appropriate dose of riboflavin is applied to the corneal tissue before the cornea is exposed to a certain dose of UV Light. In combination with intense UV-A radiation, riboflavin strengthens the corneal tissue and, consequently, the cornea. CXL requires a minimal corneal thickness of 400µm in order to avoid permanent damages to the endothelium by intensive UV radiation. The endothelium is attached to the backside (inner side) of the cornea and is essential to the maintenance of the cornea’s transparency. The parameter of a corneal thickness of at least 400µm applies to the so-called epi-off technique. The epithelium has to be removed before this procedure is performed in order to secure a sufficient influx of riboflavin into the cornea. The removal of the epithelium causes strong post-operative pains which last up to several days after surgery. The so-called epi-on technique during which the epithelium stays in place to avoid post-operative pains was evaluated as ineffective in qualified studies. In this procedure the concentration of riboflavin does not suffice for an effective treatment as the epithelium comprises a barrier against the influx of riboflavin. However, a sufficient concentration of riboflavin is not only necessary for an effective strengthening of the corneal tissue via UV radiation, but also it poses an important protection against radiation and, consequently, the damage of the rather sensitive endothelium.
Ring segments (ICRS), such as Keraring, Ferrararing and Intacts are offered for improving the patient’s visual function. These segments are implanted into the cornea. In early stages of the disease they can achieve a certain improvement of visual acuity, however, compared to modern therapies they have a rather insufficient degree of predictability of results and, given that they have margins, post-operative complications, such as extrusions are rather frequent. Segments cannot stop the progression of keratoconus. Given their rather limited effective range and a rather high frequency of post-operative complications, ring segments (ICRS) can be considered obsolete nowadays.
CISIS is the insertion of the MyoRing between two corneal layers by means of a particular technology in order to improve the vision AND to stop progression. The MyoRing is a complete-ring inlay with particular features. It is a rather new approach to keratoconus therapy with, nevertheless, already almost 10 years of follow-up period. This technology overcomes the problems associated with ring segments (ICRS) and shows excellent long-term results while it lacks also relevant complications. No other currently available therapy is able to achieve comparable long-term results as the ones in the hand of CISIS-trained surgeons. CISIS / MyoRing can no longer be performed if the corneal thickness is less than 350µm. In this case, the only remaining option is a cornea transplant.
The table provided above displays a comparison of the distinct treatment methods.
The following scheme is a depiction of modern and optimal steps which can be taken in keratoconus treatment.