title: Screening subclinical keratoconus with placido-based corneal indices.
abstract: OBJECTIVE
  To assess in a sample of normal, keratoconic, and keratoconus (KC) suspect eyes the performance of a set of new topographic indices computed directly from the digitized images of the Placido rings.
  
  
  METHODS
  This comparative study was composed of a total of 124 eyes of 106 patients from the ophthalmic clinics Vissum Alicante and Vissum Almería (Spain) divided into three groups: control group (50 eyes), KC group (50 eyes), and KC suspect group (24 eyes). In all cases, a comprehensive examination was performed, including the corneal topography with a Placido-based CSO topography system. Clinical outcomes were compared among groups, along with the discriminating performance of the proposed irregularity indices.
  
  
  RESULTS
  Significant differences at level 0.05 were found on the values of the indices among groups by means of Mann-Whitney-Wilcoxon nonparametric test and Fisher exact test. Additional statistical methods, such as receiver operating characteristic analysis and K-fold cross validation, confirmed the capability of the indices to discriminate between the three groups.
  
  
  CONCLUSIONS
  Direct analysis of the digitized images of the Placido mires projected on the cornea is a valid and effective tool for detection of corneal irregularities. Although based only on the data from the anterior surface of the cornea, the new indices performed well even when applied to the KC suspect eyes. They have the advantage of simplicity of calculation combined with high sensitivity in corneal irregularity detection and thus can be used as supplementary criteria for diagnosing and grading KC that can be added to the current keratometric classifications.
authors: Department of Mathematics, University of Almería, Almería, Spain.
authors: Darío
authors: D
authors: Ramos-López
authors: Andrei
authors: A
authors: Martínez-Finkelshtein
authors: Gracia M
authors: GM
authors: Castro-Luna
authors: Neus
authors: N
authors: Burguera-Gimenez
authors: Alfredo
authors: A
authors: Vega-Estrada
authors: David
authors: D
authors: Piñero
authors: Jorge L
authors: JL
authors: Alió
mesh_terms: D000328:Adult; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography / Q000295:instrumentation*; D004867:Equipment Design; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007640:Keratoconus / Q000175:diagnosis* / Q000453:epidemiology; D008297:Male; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D012372:ROC Curve; D013030:Spain / Q000453:epidemiology