Combined treatment for keratoconus

Aug 01, 2011

Stopping progression and improving visual and refractive results

There have been, in recent years, some technological advances that have led us to two approaches: (a) corneal regularization based either on intracorneal ring (ICR) implantation4 or limited topography-guided excimer laser customized ablation treatment (T-CAT)5 or toric phakic intraocular lenses (IOLs); (b) corneal stabilization using corneal collagen crosslinking (CXL).6

In our study we examined nine keratoconic patients (14 eyes) [3 males (6 eyes) and 6 females (8 eyes)] who all completed at least one year of follow-up. Uncorrected visual acuity (UCVA), best spectaclecorrected visual acuity (BSCVA), refraction, topographic findings, and adverse events were assessed.

All procedures were performed by the same surgeon (Efekan Coskunseven) at Dunya Eye Hospital, Istanbul, Turkey. The mean patient age was 25.21±1.76 years (range, 22 to 28 years ) All patients demonstrated clear central corneas and contact lens intolerance. Corneal thickness was at least 400 micron at the thinnest corneal point. Patients were excluded if any of the following criteria applied after the preoperative examination:

If there is no increase in visual acuity after RGP or hybird contact lens trial. Even if the patient has contact lens intolerance we must try the contact lenses just to see how much the visual acuity will increase.

The ACD (from endothel) is less than 2.8 mm. Mostly high myopic cases have deep anterior chamber but we should always consider the fact that after ICR implantation ACD will decrease.

Other exclusion criteria are history of herpes, keratitis, corneal dystrophies, diagnosed autoimmune disease, systemic connective tissue disease, acute or grade IV keratoconus, and endothelial cell count of less than 1000 cells/mm2 . The mean interval between ICR and CXL was 7 months and the mean interval between CXL and ICL toric implantation was 8.4 months. Preoperative and postoperative visual acuity, refraction, pachymetry and topography results were evaluated and the mean follow-up period was 7.2 months.

ICR implantation: The implantation of small arc-like polymethyl methacrylate (PMMA) segments is a minimally invasive surgical option for keratoconic corneas or ectatic corneas occurring after laser in situ keratomileusis. There are different types of intracorneal rings, depending on their curvature, width and zone of implantation. Kerarings (Mediphacos, Belo Horizonte, Brazil) are newly developed segments made of PMMA that are characterized by a triangular crosssection that induces a prismatic effect on the cornea. Their apical diameter is 5 mm and the flat basis width is 0.6 mm with variable thickness (0.15 to 0.30 mm thickness with 0.5 mm steps) and arc lengths (90, 120, 160 and 210 degrees). The optical zone provided by Keraring segments is 5.0 mm in diameter. Today 6 mm optical zone Keraring SI6 new segment is also available with 6 mm optical zone to avoid halo and glare.

The surgical procedure was performed under sterile conditions and topical anaesthesia. Purkinje reflex was chosen as the central point and was marked using a Wavelength Allegretto Biomicroscope (Allegretto 400 Hz laser platform, Wavelight Laser Technologie AG). A 5 mm marker was used to locate the exact ring channel. Corneal thickness was measured during surgery using ultrasonic pachymetry (Sonogage, Cleveland, Ohio, USA) along the ring location markings. Tunnel depth was set at 80% of the thinnest corneal thickness on the tunnel location in the femtosecond laser. An incision was made on the steepest topographic axis.

One or two segments were implanted according to the distribution of the ectatic area on the corneal surface, whereas the thickness of the segment was determined using the distribution of the ectatic area and the spherical equivalent (SE).

It is known that spherical and astigmatic correction need to be considered when implanting phakic toric IOL lenses. So, we planned to regularize corneal irregularity not to correct spherical refraction in our study. We evaluated the corneal thickness to choose the appropriate ring thickness. A 60 kHz IntraLase Femtosecond Laser (Abbott Medical Optics, Santa Ana, California, USA) was used to create the ring channels. The mean interval between ICR and CXL was 7 months.