What is Keratoconus?


Keratoconus is a progressive eye disease which is characterised by a degenerative thinning and irregular bulging of the cornea. Since the quality and regular shape of the cornea is crucial for good vision, keratoconus leads to a gradual vision loss. Its characteristic feature is the cone-shaped bulging of the cornea, as illustrated in the adjacent picture.

In Europe and North America, keratoconus affects one out of 1000 to 2000 inhabitants. In Europe some 1 million eyes are expected to suffer from keratoconus. The rarity of this disease may be one of the reasons why medical experience in keratoconus therapy is mostly limited to a few standardised treatment methods. In endemic regions such as the Middle East and some parts of Asia and South America, keratoconus is much more common. Genetic and environmental factors appear to play a leading role in the onset and development of this disease. 

In Europe, most cases of keratoconus are diagnosed at the age of 18 to 25. Depending on its course of development, the disease may also be diagnosed at an earlier or later age. This mostly happens when a patient starts to complain about worsening vision despite wearing eyeglasses. Today, keratoconus is primarily diagnosed by means of topographical methods (e.g. Pentacam).

As can be seen in the adjacent picture of keratoconus taken with Pentacam, the curvature of the cornea is not symmetrically aligned around the corneal centre, but has a decentralised cone-like and steep shape. This is the most common form of keratoconus. Additionally, there are also centralised forms of keratoconus, which are characterised by an unusually steep corneal surface and dramatically reduced corneal thickness.

The severity of the disease is generally determined by the degree of bulging (steepness) and thinning of the cornea. The thickness of a normal cornea is around 550 micrometres. As keratoconus progresses, corneal thickness gradually decreases over time; patients often also have intermittent bouts of acute worsening of the symptoms. To halt the progression of the disease by means of crosslinking, the cornea needs to have a minimum thickness of 400 micrometres. The minimum thickness for MyoRing treatment is 350 micrometres. In eyes with a corneal thickness of less than 350 micrometres, the cornea can only be transplanted.

What treatment methods are usually provided?

Corneal transplant

In the early phase of the disease, good vision can still be achieved by hard contact lenses. When the disease progresses, however, the eyes often become intolerable to contact lenses: the shape of the cornea is so steep that the contact lenses lose their stability and good fit. The traditional approach in such cases is corneal transplantation, as illustrated in the adjacent picture. Corneal transplants take a relatively long time to heal (more than a year), with sutures remaining inside the cornea and often leading to severe irritations in the eye as well as other discomfort. Moreover, the results of corneal transplantation tend to vary considerably and are often highly inadequate. Many patients complain about poor visual acuity. The reason is that the donor material cannot be selected on the basis of optical and structural criteria, and so the insertion of the donor cornea cannot be adjusted as needed. One viable method to halt the progression of the disease is corneal crosslinking (CXL). However, CXL does not restore the patient’s vision and the cornea also retains its characteristic cone-like shape. This treatment is only helpful and reasonable in the early stages of the disease when progression is confirmed. Vision can also be restored by ring segments, which are implanted into the cornea. In the early stages, these segments may often improve vision to some degree; but the results are poorly predictive and post-operative complications (e.g. extrusions) are quite common as these segments have open ends (edges) and the “cornea-segment system” is not biomechanically balanced. Ring segments are unable to stop the progression of keratoconus. Nowadays, ring segments cannot be considered state of the art treatment of keratoconus anymore. Nevertheless, many of such treatments are still performed worldwide, in particular in under-developed countries.

Why MyoRing?


CISIS (Corneal IntrStromal Improvement Surgery) is a new and highly effective technology for the treatment of keratoconus. Since 2007, several thousand interventions for CISIS treatment of keratoconus have been successfully performed in specialised eye centres in Europe as well as more than 20 countries outside Europe. CISIS is the most technically advanced, most effective and safest therapy of keratoconus currently available.

In CISIS, a closed ring (MyoRing) with specific properties is inserted between two layers of the cornea at a depth of 0.3 mm beneath the surface. The MyoRing improves the corneal geometry in patients with keratoconus and converts the irregular corneal surface into a smooth and regular one. The MyoRing with its regular shape endows the irregularly shaped cornea with regular geometrical features, which significantly improves visual acuity for keratoconic patients. Because the MyoRing is inserted into a “pocket” between two corneal layers and has no open ends or edges typical of ring segments, this leads to highly predictable results and an extremely low rate of complications. All studies and biomechanical calculations indicate that the MyoRing, owing to its closed structure, is able to halt the progression of keratoconus. CISIS is effective in mild to highly advanced stages of keratoconus, as long as the cornea has a minimum thickness of 350 micrometres. In eyes with a corneal thickness of less than 350 micrometres, the only available option is corneal transplant surgery.

How can MyoRing stop the progression of keratoconus?

The progression of keratoconus is the result of the biomechanical weakness of the dieseased cornea.  Generally there a 2 possibilities to strengthen the cornea in order to stop progression:

1st Hardening the corneal tissue itself on an ultrastructural level by means of corneal crosslinking (CXL). 

2nd To support the cornea my adequate mechanical means without changing the tissue itself. Such a support is the MyoRing. Since the MyoRing is a closed and complete ring it can take up all the progression related forces (F) actiing on the tissue. Incomplete rings and Segments of course cannot do that - the progression would just result in a separaration of the endings (Daxer A. Biomechanics of corneal ring implants. Cornea 2015;1493-1498).

In analogy to these considerations one can take the ceiling of a room inside a house under a heavy load from the next floor. If the ceiling is unable to take up the load and the ceiling is bending into the room - the ceiling suffers from "keratoconus".  Now there are 2 options to avoid that: 

First, one can exchange the material of the ceiling to a stronger one. That process would be equivalent to crosslinking.

Second, one can support the ceiling by a ceailing beam. This allows to separate the load on the ceiling in two compartments and to take up the heavy load better. The ceiling beam is equivalent to the MyoRing. An interrupted ceiling beam, corresponding to segments or incomplete rings, can of course not take up the load.

A scientific analysis of the biomechanical conseuqences (weakening or strengthening) of different treatment methods shows that MyoRing can strengthen the cornea by some 300%. This is a significant strengthening of the cornea. It means that even if the cornea has an anatomical thickness of 400 microns, it behaves biomechanically as having some 1200 microns. This is a lot and certainly enough to stop progression. For comparison: A normal cornea has a corneal thickness at the thinnest point of about 550 microns.

The graph shows these informations. One can see, that Laser Vision Corrections (LASIK, PRK, SMILE) weaken the cornea as a result of the related tissue removal. Segments and incomplete rings (ICRS) show only a very small weakening because of the radial cut, which remains a weak point. In contrast to ICRS, CISIS/MyoRing strengthens the cornea considerably by a factor of 3. Crosslinking (CXL) by the way shows even a 4-fold increase in corneal strength. While MyoRing, however, results also in significant visual rehabilitation - this is not the case when using CXL.

Superior long-term results

CISIS/MyoRing allows a remarkable improvement of visual acuity. This improvement remains also in the long-term. Long-term results are available of up to 8 years after treatment and show a stop of progression. In fact this stop of progression of the disease is often even accompanied by a little but statistically significant improvement of visual acuity over the years. It is possible with MyoRing to achieve both, visual rehabilitation AND stop of progression. One can even speak of something like "curing" of keratoconus.

The graphs show the visual acuity of the treated eyes one year (postop1) and 5 years (postop2) after treatment as a function of the severity of the disease. The severity of the disease is shown on the horizontal axis as the preoperative visual acuity in logMAR scale. logMAR 0 means optimal 20/20 visual acuity, logMAR 1 means bad 20/200 visual acuity and logMAR 2 means just "fingercounting". UDVA means uncorrected visual acuity (a, without glasses or contact lenses) and CDVA means visual acuity measured with the best spectacle correction (b). The dotted line shows the theoretically optimal correction to 20/20 visual acuity. The other 2 straight lines are linear regressions of the one year (interrupted) and five year (full) results. The vertical scale shows the improvement of UDVA and CDVA in lines.

It is easy to recognize that CISIS can result in a remarkable improvement of visual acuity and a stabilization of the disease which results even in continuous improvement of vision year by year. This is indicated by the behavior which shows the 5 years regression line (full) significantly closer to the optimal correction line (dotted) than the 1 year regression line (interrupted).

Therefore, the treatment does not only result in remarkable improvement of visual acuity but also in a stop of progression of the disease which shows even little continuous improvement of the patients vision year by year (Antiprogression) if performed according to a strictly defined treatment scheme (Daxer A. Ettl A, Hörantner R. Long-term results of MyoRing treatment of keratoconus. J Optometry 2016 (epub ahead of print)).

Long-Term Stability: The individual postoperative course after mooring implantation demonstrates the impressive long-term stability. One can see in the graph on the right that there is not only a remarkable improvement of visual acuity one year after treatment but also a clear stop of progression of the disease. On a more detailed view there is even still a an improvement in most cases between year 1 and year 5 after treatment. Collectively speaking there is still a statistically significant improvement between year one and year 5 (Antiprogression). Therefore "healing of keratoconus" may be an appropriate term for that treatment effect.

Explanation: Three months after treatment the visual acuity has usually remarkably improved and the status can be considered as fairly stable (Daxer A, Mahmoud H, Venkateswaran SR. Intracorneal continous ring implantation for keratoconus: One-year follow-up. J Cataract Refract Surg 2010;36:1296-1302). Since the MyoRing is a completely closed continuous ring characterized by a high stiffness, the normal intraocular pressure pushes the cornea in a natural way continuously against the regular circumference of the MyoRing inside the cornea. This process results in an continuous elimination ("ironing") of the still existing small irregularities of the cornea. The cornea therefore continuously looses the still existing small irregularities (higher order aberrations) and the good visual acuity still improves significantly over time (Daxer A., ESCRS 2014, 2015). It is therefore obvious why incomplete structures as support inside the cornea such as ICRS (Segments, incomplete rings) cannot achieve that results.

The best possible result in any given case!

In contrast to conventional corneal implant techniques such as intra-corneal ring segments or incomplete rings which are captured in corneal tunnels and which allow the surgeon access to only one degree of freedom (implant thickness), the MyoRing intra-corneal implant, implanted into a pocket which is usually larger in diameter than the diameter of the MyoRing, gives the surgeon access to all 3  theoretically possible degrees of freedom of corneal implant surgery (implant thickness, implant diameter and implant position). Therefore, this superior kind of surgery allows the surgeon to achieve the best possible result in every given case.

In particular the possibility to optimize the position of the MyoRing implant relative to the optical axis within the 9 mm corneal pocket is of outmost clinical importance for the following reason: A concentric preparation of a corneal tunnel around the postoperative optical axis is not possible since the  postoperative optical axis is not known preoperatively and the postoperative optical axis is also different to the optical axis preoperatively. In other words, nobody knows the right placement of an intra-corneal implant preoperatively.Therefore segments are always on the wrong place!  A misalignment of 0.5 mm can reduce the visual result significantly. Therefore, it is important to have the possibility as in MyoRing technology, to exactly adjust the MyoRing position intra-operatively according to the real postoperative optical axis when the implants is already in place!

Without using these kinds of optimisation possibilities of MyoRing treatment the mean improvement of uncorrected visual acuity in mild to advanced keratoconus cases is about 6 lines (logMAR) and therefore similar to that of segments. These results can even be significantly enhanced to more than 10 lines (logMAR) in average when utilizing the optimization potential of MyoRing by a trained MyoRing surgeon.

As the MyoRing is a full  (360°) ring implant with no free ends, relevant complications  (e.g. extrusions, etc) are in contrast to ring segments almost zero (<0.1%) in the hands of a DIOPTEX trained surgeon.

central cone
central cone
non-central cone
non-central cone

Also it is not required to use a complex nomogram. The mechanism of action does not distinguish between central and non-central keratoconus or mild and advanced cases but gives always the best possible result. The unique mechanism of action as a result of the complete and closed structure of the MyoRing "automatically" corrects the affected part of the cornea no matter where the cone is (see Topos above). Therefore MyoRing implantation is effective in central and non-central keratoconus, in mild and advanced cases, in post LASIK keratectasia as well as in insufficient results after corneal transplantation.

Case studies

The following case studies, which were selected on the basis of didactic criteria, shall assist eye doctors who treat patients with keratoconus to identify the right treatment approach and assess the results to be expected. In the following the following cronyism are used: UDVA…uncorrected visual acuity, CDVA…corrected visual acuity.

MyoRing for Keratoconus

 Stage II keratoconus in both eyes

A 37-year-old female patient from Switzerland presented for CISIS treatment with a mild form of keratoconus. Prior to the MyoRing treatment, the patient’s refractive power and visual acuity were:

Right eye   CDVA           0.8         with         +0.25 s -1.75 c x 75°        I               UDVA           0.5

Left eye CDVA           1.0         with         -0.25 s -2.0 c x 105°         I             UDVA           0.6

Five months after MyoRing treatment, the patient had the following refractive power und visual acuity:

Right eye    UDVA           1.0

The patient is highly satisfied and perfectly capable of managing her daily tasks without any vision aids at all.


Stage II keratoconus in the right eye

A 26-year-old patient with mild keratoconus underwent CISIS treatment in his right eye. Prior to the intervention, the patient had the following refractive power and visual acuity:

Right eye    UDVA     0.6 no improvement with glasses

One year after CISIS treatment, the patient had the following finding:

Right eye    UDVA     1.0


Stage IV keratoconus in both eyes

A 35-year-old patient suffering from highly advanced keratoconus in the left eye underwent CISIS treatment. Before the intervention he had:

Right eye    CDVA     0.4         and           UDVA  0.3

Left eye      CDVA     0.15      with         -15.75s -7.25c x 115°    I     UDVA     0.05

The patient did not present for a follow-up exam in my practice. He was satisfied with the result and transmitted the data obtained from his ophthalmologist in Italy by email:

Left eye      UDVA    0.5.


Stage III keratoconus in the right eye

An Austrian patient came to my practice to have his glasses adjusted when he was 19 years old. At that time he had no identifiable abnormalities:

Right eye    CDVA     1.0     with     -1.25s - 1.25c x 160°

Left eye      CDVA     1.0     with     -1.75s -0.5c x 25°

Since his corneal topography was not examined, he was not diagnosed with keratoconus.

Three years later, the patient again presented at my practice because he felt that his vision had deteriorated - this time with clinically manifest keratoconus. He had the following refractive power and visual acuity:

Right eye    UDVA     0.5     Glasses do not improve vision

Left eye      UDVA     1.0     with -2.0s -1.25c x 20°

Today, six years after CISIS treatment of the right eye, the patient constantly has the following right eye findings:

Right eye     CDVA     0.9     with     +0.5s -1.25c x 10°     I     UDVA     0.8

The patient is satisfied. He has not yet experienced progression in his left eye.


Stage III keratoconus in the right eye

A patient presented with the following findings prior to undergoing treatment:

Right eye    CDVA     0.05     with     -8.0s -1.5c x 20°     I     UDVA     counting fingers

Left eye      CDVA     0.8       with     -2.5s -1.5c 135°      I     UDVA     0.4

CISIS was performed in the right eye.

The patient’s ophthalmologist in Germany reported the following post-operative data from his satisfied patient six months after the intervention:

Right eye    UDVA     0.7


Stage III keratoconus in both eyes

A 23-year-old Austrian female patient with keratoconus underwent CISIS treatment in both eyes. Her findings before the intervention were as follows:

Right eye     UDVA     0.2     no improvement with glasses

Left eye       UDVA     0.3     no improvement with glasses

Three years after CISIS, she has the following constant refractive power and visual acuity in both eyes:

Right eye     CDVA     0.7     with     -4.0s     I     UDVA     0.4

Left eye       CDVA     0.8     with     -1.25s   I     UDVA     0.7


Stage III keratoconus in the left eye

A 40-year-old Austrian male patient with keratoconus in both eyes underwent CISIS treatment in the left eye. Before the intervention, his left eye findings were:

Left eye      CDVA     0.1     with     -16.5s -5.75c x 155°

One year after CISIS, the patient had the following findings

Left eye     CDVA     0.5     with     -6.75s -3.25c x 140°     I     UDVA     0.3


MyoRing after unsuccessful corneal transplantation

A big problem after corneal transplantation is that in most of the cases the patients still have bad visual acuity and require often hard contact lenses to be able to achieve a somehow acceptable vision. In such cases after unsuccessful corneal transplantation MyoRing implantation can be successfully applied to bring the patient good vision without the need of wearing hard contact lenses which are often not well tolerated by that patients.

Condition after corneal transplant surgery for keratoconus in both eyes

A patient who had undergone corneal transplant surgery in both eyes for keratoconus treatment presented at my practice with the following clinical findings:

Right eye     0.7     with     -11.0s -3.25c x 165°     I     UDVA     counting fingers

Left eye       0.3     with     -2.0s - 8,0c x 55°          I     UDVA     counting fingers

The patient wore a hard contact lens in the right eye, which he tolerated well, but had problems with it in the left eye. A MyoRing was therefore added to his left-eye transplant.

One year after CISIS, the patient had the following findings:

Left eye       0.8     with     -0.25s -1.75c x 15°     I    UDVA     0.7


Condition after corneal transplant surgery for keratoconus treatment in both eyes

A patient, who had undergone corneal transplant surgery in both eyes for keratoconus treatment, presented at my practice with the following clinical findings:

Right eye     0.6     with     -11.0s -2.25c x 85°     I     UDVA     counting fingers

Left eye       0.8     with      -8.75s -2.25c x 145°  I     UDVA     counting fingers

The patient was wearing hard contact lenses, which he tolerated well in the left eye. In the right eye, which was intolerant to contact lens wear, a MyoRing was added to the transplant.

One year after CISIS, the patient had the following right eye findings:

Right eye     0.7     with     plano -1.75c x 145°     I     UDVA     0.6


MyoRing after Post-LASIK Keratectasia

A big problem in the treatment of post-LASIK Keratectasia is how to stop further deterioration of the vision and the progression of the disease. Corneal Crosslinking can achieve strengthening of the tissue only in the anterior part of the stroma in a decreasing manner down to some 200 to 300 microns depth. After LASIK, however, the anterior part of the stroma (flap) is however biomechanically not adherent anymore to the remaining stroma and strengthening the flap does not mean strengthening of the cornea. MyoRing implantation is therefore the only method which is able to stop the progression in post-LASIK keratectasia. In addition it can also sufficiently improve the vision in that disease. 

Post-LASIK keratectasis in both eyes

A patient had undergone LASIK treatment four years prior to presenting at my practice. Because he had developed post-LASIK keratectasia in both eyes, CISIS treatment was performed in either eye.

Prior to CISIS, the patient had the following findings:

Right eye     0.6     with     -0.25s -0.75c x 150°     I     UDVA     0.5

Left eye       0.5     with     -8.5s - 3.0c x 15°          I     UDVA     0.2

Six months after CISIS in both eyes, the patient’s visual acuity was as follows:

Right eye     UDVA     0.9 

Left eye       UDVA     0.5