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Cataract & Refractive General Opthalmology Glaucoma Retina All Courses
Peer Review | Nov/Dec '14

Management of Keratectasia With Intrastromal Corneal Ring Segments

Ruju Rai, MD; Wyatt B. Messenger, MD; and Balamurali K. Ambati, MD, PhD, MBA

Corneal ectasia is a condition in which thinning of the normally dome-shaped cornea produces an abnormal cone-shaped bulge that leads to myopia and astigmatism. It can occur due to a primary disease process (ie, keratoconus, pellucid marginal degeneration) or secondary to iatrogenic causes (ie, after corneal and refractive surgery).1-4 Historically, the stepwise management for this malady has entailed molding with rigid gas permeable contact lenses as the first-line treatment, followed by keratoplasty as the second-line treatment if the contact lens cannot be tolerated by the patient and/or fails to achieve adequate refractive correction.1-5 However, over the past decade, intrastromal corneal ring segments (ICRSs) have emerged as a viable intermediary option for delaying or precluding the necessity of a transplant.1,3,6,7

DESIGN AND INSERTION

ICRSs are polymethyl methacrylate semicircular inserts that remodel the corneal contour by acting as spacers between the collagen layers, elevating the midperipheral anterior cornea while flattening the central anterior cornea by shortening its arc length.8-10 They are implanted into channels within the deep stroma that are created either by mechanical dissection via manual blade or photodisruption via femtosecond laser; the latter technique is faster and easier to perform and may have a lower rate of adverse sequelae.11-14 Device types vary by cross-sectional shape, diameter, arc length, and thickness,15-17 while nomograms for their surgical placement vary by eligibility criteria, number of segments, incision location, tunneling method, and channel size.18-21 The best candidates for ICRS implantation are patients who have sufficient corneal thickness (minimum of 450 μm at the 7-mm optical zone), have a clear optical zone without central or paracentral scarring, and are willing to wear corrective lenses as needed after surgery.2,5,22

SAFETY AND EFFICACY

Most of the existing literature on outcomes of ICRSs is limited to observational studies and case reports. ICRS implantation is a relatively low-risk procedure, but it can be associated with occasional complications.23-26 Intraoperative complications typically consist of technical errors (eg, incomplete channel creation, channel or segment malposition, and perforation),14,23,24,26-28 whereas postoperative complications fall along a large spectrum of potential issues (eg, ring segment extrusion or displacement,28 corneal melt,29,30 sterile or infectious keratitis,31-33 neovascularization,34 edema,35 lipid-like biodeposits,36 glare, halos,5,37 and chronic pain38). In terms of efficacy, the majority of publications demonstrate an increase in contact lens tolerance, along with significant and sustained improvements in visual, refractive, and topographic indices.6,7,24,25,27,39-45 However, the data are inconsistent in regard to the predictability of results according to preoperative characteristics such as keratometry and visual acuity,3,4,46 underscoring the need to develop more accurate nomograms based on empirical mathematical modeling that accounts for biomechanical10,47,48 and aberrometric49,50 properties in addition to standard parameters.

INDICATIONS AND FUTURE DIRECTIONS

Promising advances have been made recently toward expanding the versatility of ICRSs. In addition to common indications like keratoconus,1,5,27,51,52 pellucid marginal degeneration,53-55 and post-LASIK ectasia,41, 56-60 ICRSs have also been employed for residual astigmatism after PRK,57 radial keratotomy,61 and penetrating keratoplasty62-64; in patients who have undergone radial keratotomy or penetrating keratoplasty, the manual tunneling method is preferable to femtosecond laser. Moreover, ICRSs have been piggybacked in various permutations with PRK,65-68 phakic IOLs,69 and corneal collagen crosslinking66-68,70-73 for an augmented effect on visual function. Corneal collagen crosslinking, which strengthens and stabilizes the lamellar architecture, is particularly synergistic with ICRSs, given its ability to slow down the rate of ectasia progression.1,67,68,70,71 As future research enhances our knowledge about the corneal response to ICRS implantation, as well as the utility of ICRSs for novel applications and as a part of combination therapy, the role of ICRSs within the scope of keratopathies will continue to evolve.4 For now, ICRS implantation is a safe and effective tool that should be considered when seeking a minimally invasive, adjustable,74 and reversible75 intervention for reducing spherocylindrical error and corneal irregularity.


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40. Levinger S, Pokroy R. Keratoconus managed with intacs: one-year results. Arch Ophthalmol. 2005;123(10):1308-1314.
41. Kymionis GD, Tsiklis NS, Pallikaris AI, et al. Long-term follow-up of Intacs for post-LASIK corneal ectasia. Ophthalmology. 2006;113(11):1909-1917.
42. Coskunseven E, Kymionis GD, Tsiklis NS, et al. One-year results of intrastromal corneal ring segment implantation (KeraRing) using femtosecond laser in patients with keratoconus. Am J Ophthalmol. 2008;145(5):775-779.
43. Torquetti L, Berbel RF, Ferrara P. Long-term follow-up of intrastromal corneal ring segments in keratoconus. J Cataract Refract Surg. 2009;35(10):1768-1773.
44. Kaya V, Utine CA, Karakus SH, et al. Refractive and visual outcomes after Intacs vs ferrara intrastromal corneal ring segment implantation for keratoconus: a comparative study. J Refract Surg. 2011;27(12):907-912.
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74. Pokroy R, Levinger S. Intacs adjustment surgery for keratoconus. J Cataract Refract Surg. 2006;32(6):986-992.
75. Alio JL, Artola A, Ruiz-Moreno JM, et al. Changes in keratoconic corneas after intracorneal ring segment explantation and reimplantation. Ophthalmology. 2004;111(4):747-751.

Ruju Rai, MD

Ruju Rai, MD, is a Pre-Residency Clinical/Research Fellow at Ambati Lab, John A. Moran Eye Center, in Salt Lake City, Utah. Dr. Rai states that she has no financial interest in the products or companies mentioned.

Wyatt B. Messenger, MD

Wyatt B. Messenger, MD, is a Pre-Residency Clinical/Research Fellow at Ambati Lab, John A. Moran Eye Center, in Salt Lake City Utah. Dr. Messenger states that he has no financial interest in the products or companies mentioned.

author
Balamurali K. Ambati, MD, PhD, MBA

Balamurali K. Ambati, MD, PhD, MBA, is a Professor of Ophthalmology and the Director of Cornea Research at the John A. Moran Eye Center of the University of Utah in Salt Lake City, Utah. Dr. Ambati states that he has no financial interest in the products or companies mentioned. He may be reached at (801) 213-3707; bala.ambati@utah.edu.

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