Comparison of single-segment and double-segment Intacs for keratoconus and post-LASIK ectasia

Am J Ophthalmol. 2006 May;141(5):891-5. doi: 10.1016/j.ajo.2005.12.027. Epub 2006 Mar 20.


Purpose: To evaluate the efficacy of single-segment Intacs and compare with double-segment Intacs in subjects with post-LASIK ectasia and keratoconus.

Design: Retrospective comparative analysis.

Methods: setting: Boxer Wachler Vision Institute, Beverly Hills, California, USA. study population: Thirty-seven eyes of 28 patients with keratoconus and post-LASIK ectasia classified into two groups: single-segment group (17 eyes, 11 patients) and double-segment group (20 eyes, 17 patients). Both groups were matched for age, visual acuity (uncorrected, UCVA; best spectacle-corrected, BSCVA), refractive error (sphere, cylinder, spherical equivalent), and keratometry (K) value (flat, steep, average) by t test for equality of means. intervention: Single- or double-segment Intacs procedure with axis of incision for insertion in the steep axis of manifest refraction. main outcome measure: Improvement of acuity, refractive error, K values, and inferior-superior (I-S) ratio.

Results: There was more improvement in UCVA in the single-segment group (nine lines) than the double-segment group (2.5 lines), P < .01; in BSCVA in the single-segment group (2.5 lines) than the double-segment group (<1 line), P < .01; in steep K values in the single-segment group (2.76 diopters +/- 2.68) than the double-segment group (0.93 diopters +/- 2.01), P = .02; and in I-S ratio in the single-segment group (9.51 +/- 7.49) than the double-segment group (4.22 +/- 4.82), P = .01; and greater cylinder decrease after Holladay vector analysis in the single-segment group (5.69 diopters +/- 3.10) than the double-segment group (1.58 diopters +/- 3.09), P < .01.

Conclusions: Single-segment Intacs improved both UCVA and BSCVA by differential flattening of inferior meridian and steepening of superior meridian as reflected by change in I-S ratio.

Publication types

  • Comparative Study

MeSH terms

  • Adult
  • Corneal Stroma / physiopathology
  • Corneal Stroma / surgery*
  • Corneal Topography
  • Dilatation, Pathologic / etiology
  • Dilatation, Pathologic / surgery
  • Follow-Up Studies
  • Humans
  • Keratoconus / physiopathology
  • Keratoconus / surgery*
  • Keratomileusis, Laser In Situ / adverse effects*
  • Polymethyl Methacrylate
  • Postoperative Complications*
  • Prostheses and Implants*
  • Prosthesis Implantation / methods*
  • Retrospective Studies
  • Treatment Outcome
  • Visual Acuity


  • Polymethyl Methacrylate