In addition to glasses or contact lenses, there are also other more or less invasive procedures by which the corneal curvature can be modified. The most common of these treatment methods are those where corneal tissue is ablated by laser to correct the radius of the corneal curvature as needed. For further details please read the information provided in section Scientific Background.
The most common laser method is LASIK, where a broad flap is cut into cornea. This flap is folded backwards to expose the deeper-lying corneal tissue and direct the laser beam on this tissue for ablation (black, ablated tissue). After laser ablation, the flap is pulled back into its original position an the corneal surface takes on its new geometry. In the myopic eye, more corneal tissue is ablated from the centre than from edges to flatten the corneal surface. this method has the disadvantage that the flap does not heal and therefore n longer supports corneal stability. Hence corneal stability is sustainably weakened an impaired, which may lead to a severe post-operative long-term complication called post LASIK keratectasia. The biomechanically effective thickness, an indicator of corneal stability, is therefore much smaller than the anatomical thickness of the cornea. the best way to treat post LASIK keratectasia currently is CISIS / MyoRing. Both the visual acuity is significantly improved and the progression of vision deterioration is stopped. See case study case examples.
A much safer method is laser ablation of the corneal surface (PRK, LASEK). While this method also weakens the cornea, namely by the amount of tissue ablated for vision correction, the destabilising effect is far less pronounced because no flap needs to be cut; hence severe long-term complications rarely occur. The disadvantage of PRK and LASEK over LASIK is that LASIK causes no or only little post-operative pain, whereas LASEK and PRK may cause the patient considerable pain. Ideally, LASEK / PRK is used in myopia to about 8 diopters.
This is due to the specific alignment of nervous fibres in the cornea. A more recent but increasingly adopted method is shifted from the cornea into the inner eye. This method (as described in more detail under Scientific Background) tends to result in sever long-term complications. On account of these long-term complications, including cataract, glaucoma and corneal decompensation, this method should actually not - or only very restrictively - be applied. It is strictlly contraindicated in relatively young patients as the complications potential of PIOL tend to increase over time.
Another possibility is to remove the natural lens from the eye and replace it by an artifical lens. Since this results in the inability of the eye to accommodate for distance and nearness, and because the risk of lens capsule turbidity is higher in younger patients, this method (lens replacement) should not be applied in patients under 50 years of age. For elderly patients, it is a good option to correct higher refractive errors by surgery
CISIS gives excellent results in cases not suitable for Laser Vision Correction! Whereas laser treatment irreversibly removes corneal tissue in order to flatten the central part of the cornea and correct myopic vision, CISIS adds volume (MyoRing) to the peripheral tissue. This causes the collagen lamellae of the cornea to make a “detour” around the MyoRing, which also flattens the central part of the cornea and corrects myopic vision – but without sacrificing corneal tissue. The MyoRing is therefore a fully reversible method. The light-grey line in the picture represents the shape of the cornea prior to the insertion of the MyoRing, the darker line the corneal shape after the procedure. The two smaller rounded shapes are cross sections of the MyoRing.
Since the MyoRing is designed as a fully closed ring with very specific properties (rigid yet flexible with shape memory effect), it allows to correct myopic vision in the range of -1 to -25 dioptres effectively, safely, and reversibly. Given the fact that this method is a biomechanical correction of myopia where the corneal geometry needs time to adjust to a new balance around the MyoRing, it may take several weeks until final visual acuity is achieved; patients need to take this into account in their workplace.
Since the MyoRing rests inside a fully closed corneal gap, corneal stability is not compromised like after LASIK treatment. As described in further detail under Scientific Background, the lamellar pocket inside the cornea that takes up the MyoRing has biomechanically neutral properties; inserting the MyoRing into the cornea even increases the biomechanical stability of the cornea by a factor of 2. While in LASIK the biomechanically relevant thickness of the cornea is less than the anatomical thickness, the opposite is the case in CISIS. The MyoRing strengthens the cornea in such a way that the biomechanically relevant thickness of the cornea (d) is usually even greater than the anatomical thickness.