title: Forward light scatter and visual acuity before and after intrastromal corneal ring segment implantation at different stages of keratoconus.
abstract: OBJECTIVE
  To assess forward light scatter (stray light) before and after intrastromal corneal ring segment (ICRS) implantation at different stages of keratoconus and to examine correlation between postoperative stray light and visual acuity (VA).
  
  
  METHODS
  In 27 eyes of 27 subjects with keratoconus, stray light was determined using the compensation comparison technique before and 6 months after ICRS implantation. Monocular corrected distance VA (CDVA) was measured using a high-contrast logMAR letter chart. Corneal higher-order aberrations (HOAs), contrast sensitivity (CS) and minimum corneal thickness (CT) were also measured.
  
  
  RESULTS
  Mean CDVA was 0.42 ± 0.28 preoperatively and 0.24 ± 0.15 logMAR postoperatively (p < 0.01). Mean corneal coma-like aberration decreased postoperatively (RMS 0.55 ± 1.18 μm, p < 0.01). Minimum CT increased 25.31 ± 18.59 μm (p < 0.01). Mean preoperative and postoperative stray light were 1.36 ± 0.31 and 1.48 ± 0.32 log units, respectively (p < 0.01). Mean changes produced in stray light (worsening) were 0.03 ± 0.21 (p > 0.05) for stage I, 0.13 ± 0.14 (p = 0.013) for stage II and 0.18 ± 0.21 (p = 0.023) for stage III. Significant positive correlation (r = 0.47, p = 0.01) was detected between postoperative stray light and postoperative CDVA such that as stray light increased, CDVA worsened (higher logMAR values). Postoperative stray light was neither associated with HOAs, CS nor minimum CT.
  
  
  CONCLUSIONS
  Stray light values in these patients with keratoconus were higher than normal preoperatively. In eyes with stage II and III keratoconus, stray light increased 6 months after ICRS placement. Higher postoperative stray light was correlated with a worse visual acuity outcome.
authors.affiliation: Applied Vision Research Group, Faculty of Optics and Optometry, Complutense University of Madrid, Madrid, Spain.
authors.forename: María Cinta
authors.initials: MC
authors.lastname: Puell
authors.affiliation: Applied Vision Research Group, Faculty of Optics and Optometry, Complutense University of Madrid, Madrid, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Carballo-Álvarez
mesh_terms: D000293:Adolescent; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology; D003315:Cornea / Q000503:physiopathology; D003319:Corneal Stroma / Q000601:surgery*; D057108:Corneal Wavefront Aberration / Q000503:physiopathology; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology / Q000601:surgery*; D008027:Light; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D057234:Preoperative Period; D011446:Prospective Studies; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D012542:Scattering, Radiation; D014792:Visual Acuity / Q000502:physiology*
keywords: forward scatter; intrastromal corneal ring segment; keratoconus; stray light; visual acuity