functional improvement of vision is lower than for eyes with flatter keratometry values. In such cases, despite the use of Intacs, a corneal transplant may be unavoidable. If required, penetrating or lamellar keratoplasty may be performed after Intacs placement.
Ectasia After LASIK
Ring segments have also been used for the postoperative management of corneal ectasia after LASIK. As in the treatment of keratoconus, few surgical options are available to treat corneal ectasia. Use of an excimer laser to remove additional tissue is generally considered contraindicated. A lamellar graft or penetrating keratoplasty may result in significant morbidity, such as irregular astigmatism, delayed recovery of vision, and tissue rejection. In limited early trials that used Intacs to treat postLASIK ectasia, myopia was reduced and UDVA was improved. However, the long-term effect of such an approach for managing post-LASIK ectasia is still being evaluated. Use of Intacs for post-LASIK ectasia is an off-label treatment.
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. Rabinowitz Y. INTACS for keratoconus and ectasia after LASIK. Int Ophthalmol Clin. 2013; 53(1)27–39.
Uses for Intrastromal Corneal Ring Segments After LASIK
Corneal ring segments have been used to correct residual myopia following LASIK with good initial results. In such cases, a nomogram adjustment is necessary to reduce the risk of overcorrection. This procedure may be useful in patients whose stromal bed is not sufficient to support a second excimer laser ablation. Conversely, after ring segments have been removed from patients whose vision did not improve satisfactorily (eg, due to undercorrection or induced astigmatism), LASIK has been performed with good success. The flap is created in a plane superficial to the previous ring segment channel.
Boxer Wachler BS, Christie JP, Chandra NS, Chou B, Korn T, Nepomuceno R. Intacs for keratoconus. Ophthalmology. 2003;110(5):1031–1040.
Güell JL, Velasco F, Sánchez SI, Gris O, Garcia-Rojas M. Intracorneal ring segments after laser in situ keratomileusis. J Refract Surg. 2004;20(4):349–355. Kymionis GD, Siganos CS, Kounis G, Astyrakakis N, Kalyvianaki MI, Pallikaris IG. Management of post-LASIK corneal ectasia with Intacs inserts: one-
year results. Arch Ophthalmol. 2003;121(3):322–326.
Rapuano CJ, Sugar A, Koch DD, et al. Intrastromal corneal ring segments for low myopia: a report by the American Academy of Ophthalmology. Ophthalmology. 2001;108(10): 1922–1928.
Siganos CS, Kymionis GD, Kartakis N, Theodorakis MA, Astyrakakis N, Pallikaris IG. Management of keratoconus with Intacs. Am J Ophthalmol. 2003;135(1):64–70.
Orthokeratology
Orthokeratology, or corneal refractive therapy, refers to the overnight use of rigid gas-permeable contact lenses to temporarily reduce myopia. The goal of this nonsurgical method of temporary myopia reduction is to achieve functional UDVA during the day. The contact lens is fitted at a base curve that is flatter than the corneal curvature. Temporary corneal flattening results from the flattening of corneal epithelium. The 2002 FDA approval of the rigid contact lens for overnight orthokeratology was for the temporary reduction of naturally occurring myopia between –0.50 and – 6.00 D of sphere, with up to 1.75 D of astigmatism.
Orthokeratology is most appropriate for highly motivated patients with low myopia who do not want refractive surgery but who want to avoid use of contact lenses and spectacles during the day. These contact lenses do not treat astigmatism or hyperopia. Prospective patients should be informed that in clinical trials, approximately one-third of patients discontinued contact lens use and most patients (75%) experienced discomfort at some point during contact lens wear. Complications of
orthokeratology include induced astigmatism, induced higher-order aberrations, recurrent erosions, and infectious keratitis. Infectious keratitis—the most serious complication—can be bilateral and seems to be more common in children and teenagers. It may be caused by a number of pathogens, including Pseudomonas, Acanthamoeba, Staphylococcus, and Nocardia species.
According to the American Academy of Ophthalmology, the prevalence and incidence of complications associated with orthokeratology, such as bacterial and parasitic keratitis, have not been determined. Sufficiently large, well-designed, controlled studies are needed to provide a more reliable measure of the risks of treatment and to identify risk factors for complications. See BCSC Section 3, Clinical Optics, for further discussion of orthokeratology.
Berntsen DA, Barr JT, Mitchell GL. The effect of overnight contact lens corneal reshaping on higher-order aberrations and best-corrected visual acuity. Optom Vis Sci. 2005;82(6): 490–497.
Mascai MS. Corneal ulcers in two children wearing Paragon corneal refractive therapy lenses. Eye Contact Lens. 2005;31(1):9–11. Saviola JF. The current FDA view on overnight orthokeratology: how we got here and where we are going. Cornea. 2005;24(7):770–771. Schein OD. Microbial keratitis associated with overnight orthokeratology: what we need to know. Cornea. 2005;24(7):767–769.
US Food and Drug Administration. Paragon CRT. PMA P870024/S043. June 13, 2002. Available at www.accessdata.fda.gov/scripts/cdrh/cfdocs/cftopic/pma /pma.cfm?num=P870024S043. Accessed August 5, 2013.
Van Meter WS, Musch DC, Jacobs DS, et al. Safety of overnight orthokeratology for myopia: a report by the American Academy of Ophthalmology. Ophthalmology. 2008; 115(12):2301–2313.
Watt K, Swarbrick HA. Microbial keratitis in overnight orthokeratology: review of the first 50 cases. Eye Contact Lens. 2005;31(5):201–208.