title: Preliminary tests and construction of a computerized quantitative surgical keratometer.
abstract: OBJECTIVE
  To construct a simple, computer-based, quantitative surgical keratometer to measure a 3.0 to 4.0 mm central region of the corneal surface.
  
  
  METHODS
  Laboratorio de Optica Oftalmica, Instituto de Física de São Carlos (IFSC-USP), São Paulo, Brazil.
  
  
  METHODS
  A high-intensity fiber-optic-illuminated ring pattern (Placido disk) is projected on the cornea. Reflected images are captured by a charge-coupled device camera mounted on a Zeiss microscope beam splitter and then digitized by a frame grabber installed on an IBM-compatible personal computer. Simple algorithms based on image-processing techniques were implemented for border detection. A calibrating curve based on 4 spherical surfaces was used to calculate diopter values at 360 points at each examination. Results were plotted on the computer monitor using diopter value versus angle (1 through 360 degrees) graphs. Preliminary measurements of 14 healthy corneas were compared with the equivalent radial distance points measured on an EyeSys corneal topographer.
  
  
  RESULTS
  Mean deviation was 0.05 mm for radius of curvature, 0.24 diopter for power, and 5 degrees for cylinder.
  
  
  CONCLUSIONS
  The keratometer provided precise measurements for corneal shape control during surgery.
authors.affiliation: Instituto de Física de São Carlos-USP, Brazil.
authors.forename: L
authors.initials: L
authors.lastname: Carvalho
authors.forename: S A
authors.initials: SA
authors.lastname: Tonissi
authors.forename: J C
authors.initials: JC
authors.lastname: Castro
mesh_terms: D000328:Adult; D000465:Algorithms; D001251:Astigmatism / Q000175:diagnosis; D003315:Cornea / Q000033:anatomy & histology* / Q000601:surgery; D004867:Equipment Design; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D008297:Male; D013508:Ophthalmologic Surgical Procedures / Q000295:instrumentation*