In most studies, the implantation of Intacs was performed in patients with keratoconus who had clear central corneas and suffered from contact-lens intolerance.1-3 Boxer Wachler et al4 reported that the severity of corneal damage ranged from forme fruste to advanced cones with scarring. The FDA approved the Intacs procedure for patients more than 20 years old who have experienced progressive deterioration in their vision, who have clear central corneas with a minimal thickness of 450µm at the proposed incision site, and for whom corneal transplantation is the only remaining option to improve visual function.Placement of Segments
Only 0.25-, 0.30-, and 0.35-mm segments are available in the US. The size and positioning of the segments used varied across the studies. Boxer Wachler et al4 used a thick ring segment inferiorly and a thin segment superiorly. Ring segment size depends upon the amount of myopia present (eg, the larger the refractive error, the larger the segment size required) and the thickness of the cornea.
Colin et al2 reported using 0.45mm superiorly and 0.25mm inferiorly, although Siganos et al1 reported using two 0.45-mm segments in all patients. Kymionis et al5 used two 0.45-mm segments and noted that a smaller segment size for the inferior cornea may decrease the likelihood of perforation in thin corneas, a common occurrence in patients with keratoconus and pellucid marginal degeneration. The depth of insertion reportedly ranged from 66% to 77% of the thinnest corneal measurement.COMPLICATIONS
Theoretical complications associated with Intacs implantation include infection, inflammation, segment migration, expulsion, and perforation. Boxer Wachler et al4 described one eye that suffered a superficial channel dissection with anterior Bowman's perforation. A segment was successfully implanted that day using a deeper channel. Mild inflammatory reactions were noted in two eyes. Segment migration and externalization were found 1 day after surgery in one eye with severe keratoconus. This segment was explanted, followed by the second segment in the same eye and the pair in the fellow eye (the fellow eye also had severe keratoconus). Foreign body sensation was noted in a total of three eyes, and all required explantation of the Intacs.4
In some studies, mild-to-moderate intralamellar channel deposits were noted.1,3 Additionally, one eye showed neovascularization at the wound site at 2 months postoperatively, but the condition did not progress.1 Segment migration may occur when segments are positioned too close to the wound site.6EFFECT ON REFRACTIVE ERROR AND
Intacs placement should decrease myopia and flatten keratometric values, but its effect on astigmatism remains less clear. However, some patients achieved a decrease of 2.43D in refractive myopia with a significant improvement in refractive astigmatism following the implantation of Intacs.4 Siganos et al1 found a mean reduction of 1.82D in spherical equivalent, with no significant change in refractive astigmatism. Colin et al3 reported a mean increase of two lines of BSCVA over baseline and the largest reduction in manifest refractive cylinder (2.70D).
With keratometry, all authors reported a flattening of central corneal curvature. Colin et al3 found an average flattening of 4.00D using keratometry, as well as a qualitative reduction of corneal ectasia as seen with topographic mapping. Siganos et al1 reported a mean reduction in mean keratometry value of 1.94D.CHANGE IN BSCVA
Although the treatment goal for this procedure is to stabilize the progression of the disease, an improvement in best-corrected vision would certainly be beneficial, and any loss of BSCVA must be avoided. In one study,4 three of 74 eyes lost two or more lines of BSCVA, although 33 of 74 gained two or more lines of BSCVA. The same study noted the greatest improvement in BSCVA in eyes with corneal scarring when compared with those with no corneal scarring.
Siganos et al1 reported that, of 33 eyes, four lost one to two lines of BSCVA, and the remaining eyes experienced a one- to six-line improvement. A separate study's patients achieved a mean improvement of two lines at 12 months.1 Colin et al3 reported a mean increase of two lines of BSCVA over baseline.THE BOTTOM LINE
The use of Intacs in patients with keratoconus appears to be a cost-effective alternative to penetrating keratoplasty. The appropriate size and placement of Intacs in keratoconus patients require further evaluation. Combinations varied across these studies. It must be established whether Intacs segments actually inhibit the progression of keratoconus as well as delay the need for a penetrating keratoplasty procedure or eliminates the need for the procedure completely. nCo-Editor and Reviewer
Tracy Swartz, OD, MS, states that she holds no financial interest in any product or company mentioned herein. Dr. Swartz may be reached at (615) 321-8881; firstname.lastname@example.org.Panel Members
Helen J. Abdelmalak, OD, is a resident in optometry at the Wang Vision Institute in Nashville, Tennessee. She states that she holds no financial interest in any product or company mentioned herein. Dr. Abdelmalak may be reached at (615) 321-8881; email@example.com.
Jay S. Pepose, MD, PhD, is Professor of Clinical Ophthalmology at Washington University, St. Louis, Missouri. He states that he holds no financial interest in any product or company mentioned herein. Dr. Pepose may be reached at (636) 728-0111; firstname.lastname@example.org.
Arun Gulani, MD, is Assistant Professor, Department of Ophthalmology; Director of Refractive Surgery; and Chief, Cornea and External Disease for the University of Florida at Jacksonville. He states that he holds no financial interest in any product or company mentioned herein.
Dr. Gulani may be reached at (904) 504-0090; email@example.com. Walid Haddad, MD, is a cornea fellow at the Wang Vision Institute in Nashville, Tennessee. He states that he holds no financial interest in any product or company mentioned herein. Dr. Haddad may be reached at (303) 470-8388; firstname.lastname@example.org.
Paul Karpecki, OD, FAAO, is Clinical Director of Cornea, Cataract, and Refractive Surgery at the Moyes Eye Institute in Kansas City, Kansas. He states that he holds no financial interest in any product or company mentioned herein. Dr. Karpecki may be reached at (816) 746-9800; email@example.com.
Ming Wang, MD, PhD, states that he holds no financial interest in any product or company mentioned herein. Dr. Wang may be reached at (615) 321-8881; firstname.lastname@example.org.
Keming Yu, MD, PhD, is a cornea fellow at the Wang Vision Institute in Nashville, Tennessee. He states that he holds no financial interest in any product or company mentioned herein. Dr. Yu may be reached at (615) 321-8881; email@example.com.