title: Reversibility and exchangeability of intrastromal corneal ring segments.
abstract: OBJECTIVE
  To evaluate the effect of removal and/or exchange of intrastromal corneal ring segments (ICRS, Intacs); specifically the risk factors, degree of reversibility, and visual outcomes.
  
  
  METHODS
  Gimbel Eye Centres, Calgary, Edmonton, and Vancouver, Canada.
  
  
  METHODS
  Prospective cohort data were collected on 71 eyes that had ICRS placement by 3 surgeons at the Gimbel Eye Centres between August 1998 and July 1999. Data included patient symptoms, best spectacle-corrected visual acuity, uncorrected visual acuity (UCVA), manifest refraction, reason for removal or replacement, keratometry, corneal topography, and complications.
  
  
  RESULTS
  Twenty-four eyes (33.8%) had exchange or removal procedures because of underresponse, 20 eyes; overresponse, 2 eyes; and induced astigmatism and shallow placement, 1 eye each. Secondary procedures were removal and replacement, removal with subsequent laser in situ keratomileusis, and segment repositioning. Two risk factors for secondary surgery were identified: high preoperative refractive astigmatism and postoperative spherical equivalent greater than +/-0.5 diopter (D). The 6 eyes that had ICRS removal stabilized to within +/-0.25 D of the original refractive error with no surgically induced astigmatism within 1 to 7 weeks (mean 4 weeks) and had a final UCVA of 20/20 or better. In the 15 eyes that had ICRS exchange procedures, the UCVA improved by at least 1 line and median UCVA improved from 20/40 to 20/20.
  
  
  CONCLUSIONS
  Preliminary data from this study indicate that removal of segments resulted in reversal of the refractive effect.
authors.affiliation: Department of Ophthalmology, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Stanley M
authors.initials: SM
authors.lastname: Chan
authors.forename: Hamza N
authors.initials: HN
authors.lastname: Khan
mesh_terms: D000328:Adult; D015331:Cohort Studies; D003319:Corneal Stroma / Q000503:physiopathology / Q000601:surgery*; D019781:Corneal Topography; D020878:Device Removal; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D019904:Polymethyl Methacrylate; D011446:Prospective Studies; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D012086:Reoperation; D012307:Risk Factors; D014792:Visual Acuity
chemical_list: D019904:Polymethyl Methacrylate