title: A novel zernike application to differentiate between three-dimensional corneal thickness of normal corneas and corneas with keratoconus.
abstract: OBJECTIVE
  To evaluate a novel Zernike algorithm to differentiate 3-dimensional (3-D) corneal thickness distribution of corneas with keratoconus (KC) from normal corneas.
  
  
  METHODS
  A retrospective development and evaluation of a diagnostic approach.
  
  
  METHODS
  Corneal tomography with Scheimpflug imaging was performed in normal (43 eyes) and KC (85 eyes) corneas. Axial and tangential cone location magnitude index (axial CLMI and tangential CLMI, respectively) of the anterior and posterior surface were calculated. The aberrations of the anterior corneal surface were analyzed with Zernike polynomials. Pachymetric Zernike analyses (PZA) were used to map the 3-D thickness distribution of the cornea. Logistic regression was performed to develop a diagnostic procedure for KC using CLMI, PZA, and aberrations. A receiver operating characteristic curve was constructed for each regression model. Corneal volume was also compared between normal and KC corneas. Only the central 5 mm zone was used for all analyses.
  
  
  RESULTS
  Among the PZA coefficients, second- and third-order root mean squares of PZA coefficients were the best predictors of KC corneas (P < .0001). Among the CLMI variables, axial CLMI of anterior and tangential CLMI of posterior surface were the best predictors of KC (P < .0001). Among the Zernike corneal aberration coefficients, second- and third-order root mean squares of coefficients were the best predictors of KC (P < .0001). Sensitivity and specificity of Zernike corneal aberrations, CLMI, and PZA logistic regression model were similar (P > .05).
  
  
  CONCLUSIONS
  The entire 3-D corneal thickness was mapped with Zernike. The PZA method was comparable to CLMI and anterior corneal wavefront aberrations in detecting KC.
authors.affiliation: Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.
authors.forename: Rohit
authors.initials: R
authors.lastname: Shetty
authors.affiliation: Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.
authors.forename: Himanshu
authors.initials: H
authors.lastname: Matalia
authors.affiliation: Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.
authors.forename: Purnima
authors.initials: P
authors.lastname: Srivatsa
authors.affiliation: Imaging, Biomechanics and Mathematical Modeling Solutions, Narayana Nethralaya, Bangalore, India.
authors.forename: Arkasubhra
authors.initials: A
authors.lastname: Ghosh
authors.affiliation: Cleveland Clinic Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio; Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio.
authors.forename: William J
authors.initials: WJ
authors.lastname: Dupps
authors.affiliation: Imaging, Biomechanics and Mathematical Modeling Solutions, Narayana Nethralaya, Bangalore, India. Electronic address: asroy27@yahoo.com.
authors.forename: Abhijit
authors.initials: A
authors.lastname: Sinha Roy
mesh_terms: D000328:Adult; D000465:Algorithms; D003315:Cornea / Q000033:anatomy & histology / Q000473:pathology*; D063171:Corneal Pachymetry / Q000379:methods*; D019781:Corneal Topography; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D021621:Imaging, Three-Dimensional; D007640:Keratoconus / Q000175:diagnosis*; D008297:Male; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult