title: Evaluation of corneal elevation and thickness indices in pellucid marginal degeneration and keratoconus.
abstract: OBJECTIVE
  To determine and compare corneal elevation and thickness indices, thereby formulating a reliable index to distinguish eyes with pellucid marginal degeneration (PMD) from keratoconus eyes and normal (control) eyes.
  
  
  METHODS
  LV Prasad Eye Institute, Hyderabad, India.
  
  
  METHODS
  Initial model-building retrospective study.
  
  
  METHODS
  Anterior and posterior corneal elevations and thickness indices were obtained from the Orbscan IIz topographer. These values were analyzed and compared between PMD patients, keratoconus patients, and control subjects.
  
  
  RESULTS
  Of the indices, the mean values of anterior elevation (AE), ratio of the AE to the anterior best-fit sphere, ratio of the average power values of nasal quadrant to the average power values of inferior quadrant, and difference between maximum keratometry (K) and minimum K were significantly different between the 3 groups (P<.05). The highest area under the receiver-operating-characteristic (AROC) curve in discriminating PMD from keratoconus was for asphericity (0.974; cutoff ≥-0.07; sensitivity 93.3%; specificity 90.6%) followed by the ratio of average power values of the nasal and temporal quadrants to the average power values of the inferior and superior quadrants (Avg NT((D))/IS((D))) (0.959; cutoff ≥1.005; sensitivity 96.7%; specificity 90.6%). The PMD index (AROC curve, 0.935), with a cutoff of 3.45 or higher had 90% sensitivity and 93.7% specificity to distinguish PMD from keratoconus and had 100% sensitivity and 100% specificity to distinguish PMD from control eyes, with a cutoff of 2.46 or higher (AROC curve, 1.000).
  
  
  CONCLUSIONS
  The PMD index appeared to be highly sensitive and specific for diagnosing PMD. Asphericity and Avg NT((D))/IS((D)) were clinically relevant in discriminating PMD from other groups.
authors.affiliation: From the Cornea and Contact Lens Department (Tummanapalli, Mandathara, Rathi, Sangwan), LV Prasad Eye Institute, Hyderabad, India; the School of Optometry and Vision Science (Maseedupally), University of New South Wales, Sydney, Australia. Electronic address: shyamsunder@lvpei.org.
authors.forename: Shyam Sunder
authors.initials: SS
authors.lastname: Tummanapalli
authors.affiliation: From the Cornea and Contact Lens Department (Tummanapalli, Mandathara, Rathi, Sangwan), LV Prasad Eye Institute, Hyderabad, India; the School of Optometry and Vision Science (Maseedupally), University of New South Wales, Sydney, Australia.
authors.forename: Vinod
authors.initials: V
authors.lastname: Maseedupally
authors.affiliation: From the Cornea and Contact Lens Department (Tummanapalli, Mandathara, Rathi, Sangwan), LV Prasad Eye Institute, Hyderabad, India; the School of Optometry and Vision Science (Maseedupally), University of New South Wales, Sydney, Australia.
authors.forename: Preeji
authors.initials: P
authors.lastname: Mandathara
authors.affiliation: From the Cornea and Contact Lens Department (Tummanapalli, Mandathara, Rathi, Sangwan), LV Prasad Eye Institute, Hyderabad, India; the School of Optometry and Vision Science (Maseedupally), University of New South Wales, Sydney, Australia.
authors.forename: Varsha M
authors.initials: VM
authors.lastname: Rathi
authors.affiliation: From the Cornea and Contact Lens Department (Tummanapalli, Mandathara, Rathi, Sangwan), LV Prasad Eye Institute, Hyderabad, India; the School of Optometry and Vision Science (Maseedupally), University of New South Wales, Sydney, Australia.
authors.forename: Virender S
authors.initials: VS
authors.lastname: Sangwan
mesh_terms: D000328:Adult; D019540:Area Under Curve; D003315:Cornea / Q000473:pathology*; D003316:Corneal Diseases / Q000175:diagnosis*; D019781:Corneal Topography; D004108:Dilatation, Pathologic / Q000175:diagnosis; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis*; D008297:Male; D009929:Organ Size; D012372:ROC Curve; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult