Corneal intrastromal implantation surgery (CISIS) is a minimally invasive approach to refractive surgery with intracorneal implants.1 The technique uses a flexible, ring-shaped intracorneal implant (MyoRing; Dioptex GmbH, Linz, Austria; Figure 1), which is inserted into a closed intracorneal pocket made with the PocketMaker microkeratome (Dioptex GmbH; Figure 2). The pocket is located 300 µm under the surface of the cornea. This procedure may be a feasible alternative to LASIK or intraocular surgery in patients with moderate to high myopia. We have also applied CISIS for the treatment of keratoconus.
Once implanted, the MyoRing is a permanent fixture within the eye; however, the procedure is easily reversible if the patient is unhappy with the results or in the event that a secondary intraocular procedure is required. Exchanging the implant may also be necessary in the case of residual refraction. After removal of the implant, the refraction returns to the patient's preoperative values. Implantation of the MyoRing, as well as removal or exchange, is quick and easy to perform.
The mechanism of action for CISIS is that volume added in the periphery leads to a new biomechanical equilibrium of the cornea, thereby flattening its center. CISIS generates a closed pocket by cutting only parallel to the direction of the collagen fibrils. In contrast to LASIK, corneal biomechanical stability remains unaffected.
Once the PocketMaker is fixated to the eye with a suction ring, the microkeratome's vibrating diamond blade is placed in the cutting plane to create an intrastromal corneal pocket up to 9 mm in diameter. The cut is made at 300 µm, and the pocket is closed around the entire circumference except in the area of a 2- to 3-mm incision tunnel. The PocketMaker is removed from the eye, and the flexible MyoRing is inserted into the pocket via the small incision tunnel (Figure 3).
The dimension of the MyoRing varies according to the intended refractive correction (diameter range, 5–8 mm; thickness range, 100–400 µm). The implant is made of PMMA, and its flexibility is the result of the particular shape. Figure 4 shows the MyoRing in situ 3 days after implantation. This implant appears like a hard contact lens; however, to the naked eye, it is less visible.
If the MyoRing must be removed or exchanged, the only tools needed are a spatula and forceps. In all instances that I removed the MyoRing, the patient's refraction returned to preoperative levels, and no lines of BCVA were lost compared with the preoperative prescription. Patients were even able to wear contact lenses just as they had prior to surgery.
CISIS is a safe and effective procedure that has the added benefit of biomechanical stability. Because CISIS does not require flap creation, the stability of the cornea remains unchanged. This may be considered an advantage compared with LASIK; however, I still use LASIK or LASEK as my first line of treatment for patients with myopia less than 8.00 D. Additionally, if the patient has a large pupil, I will consider phakic IOL implantation before I perform CISIS. The typical candidate for the MyoRing presents with myopia higher than 8.00 D; however, CISIS may be used in patients with myopia ranging from -1.00 to -20.00 D.
One of my favorite cases of CISIS is that of a 39-year-old man with a preoperative refraction of -13.00 -3.00 X 170. At the patient's follow-up visits at 1, 3, and 6 months, he was emmetropic. He did not report any side effects, such as glare or problems with night vision. This patient did not require enhancement by exchanging the MyoRing for another one to achieve emmetropia. Because there is some interindividual variation of refractive result in a number of patients, depending on the patient's corneal thickness and stiffness, it may be necessary in these cases to exchange the MyoRing for another to achieve emmetropia. Such a procedure is, however, quick and easy to perform.
We have also been using CISIS for the treatment of keratoconus with and without ultraviolet-A collagen crosslinking before inserting the MyoRing. Ten advanced keratoconus cases have been treated so far. Follow-up is less than 1 year; however, the results are encouraging. This new technology has achieved tremendous reductions of keratometry values and significantly improved BCVA and UCVA. The MyoRing implant, easily positioned and repositioned within the pocket, provides optimized refractive results for treating keratoconus. Repositioning the implant may be performed according to the patient's postoperative refraction and topography. In my opinion, no other technology for the treatment of refractive errors is as simple as CISIS.
Albert Daxer, MD, PhD, is an Associate Professor of Ophthalmology, Department of Ophthalmology, Medical University in Innsbruck, Austria, and runs the Daxer Eye Center, Linz, Austria. Dr. Daxer states that he has a patent or part ownership and is an owner or shareholder in Dioptex GmbH. He may be reached at e-mail: firstname.lastname@example.org.