title: Characterization of the thickness of different corneal zones in glaucoma: effect on dynamic contour, Goldmann and rebound tonometries.
abstract: OBJECTIVE
  To characterize five models of corneal thickness circular zoning in a sample of healthy controls and a sample of patients with primary open-angle glaucoma (POAG) and to determine their effect on Goldmann (GAT), dynamic contour (DCT) and rebound tonometers (RT).
  
  
  METHODS
  The study participants were 122 controls and 129 cases. Five corneal thickness zoning models (A, B, C, D and E) were constructed. The partitioning pattern consisted of a circle centred at the corneal apex and several concentric rings, until the limbus; the contours of each ring followed the geometry of the corneal contour of each participant. In Model A, the central circle was 1 mm in diameter and five concentric rings were established. Mean was obtained for each zone for both samples and compared between them using a t-test. The effect on the tonometers of central cornel thickness (CCT) and mean thickness of the zones generated was determined through several linear regression models (one per tonometer and per sample).
  
  
  RESULTS
  According to a t-test, cases and controls differ in zones I [mean difference (MD): 17.93 μm], V (MD: 25.52 μm) and VI (MD: 31.78 μm) of model A (higher values in the cases sample). RT was affected by CCT (controls: B = 0.089; cases: B = 0.081). DCT was affected by zone IV of model A (controls: B = -0.029; cases: B = -0.012). GAT was affected by CCT (controls: B = 0.043; cases: B = 0.025) and zone III of model A (controls: B = -0.045; cases: B = -0.033).
  
  
  CONCLUSIONS
  Our results highlight the importance of the thickness of other regions of the cornea different from its main centre in discriminating between healthy controls and patients with POAG and in IOP measurements made using DCT, GAT and RT.
authors.affiliation: Department of Ophthalmology, Hospital Clínico San Carlos, Universidad Complutense de Madrid, Madrid, SpainInstiuto de Tecnología del Conocimiento, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Federico
authors.initials: F
authors.lastname: Saenz-Frances
authors.forename: Luis
authors.initials: L
authors.lastname: Jañez
authors.forename: Lara
authors.initials: L
authors.lastname: Borrego-Sanz
authors.forename: Jose Maria
authors.initials: JM
authors.lastname: Martinez-de-la-Casa
authors.forename: Laura
authors.initials: L
authors.lastname: Morales-Fernandez
authors.forename: Enrique
authors.initials: E
authors.lastname: Santos-Bueso
authors.forename: Julian
authors.initials: J
authors.lastname: Garcia-Sanchez
authors.forename: Julian
authors.initials: J
authors.lastname: Garcia-Feijoo
mesh_terms: D019540:Area Under Curve; D003315:Cornea / Q000033:anatomy & histology / Q000473:pathology*; D063171:Corneal Pachymetry; D003430:Cross-Sectional Studies; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006068:Gonioscopy; D064368:Healthy Volunteers; D006801:Humans; D007429:Intraocular Pressure; D009929:Organ Size; D012680:Sensitivity and Specificity; D014065:Tonometry, Ocular / Q000295:instrumentation*
keywords: Goldmann applanation tonometry; corneal thickness; dynamic contour tonometry; glaucoma; rebound tonometry