title: A computer-interfaced vertometer system for contact lenses.
abstract: BACKGROUND
  The conventional vertometer (lensometer) is difficult to use for accurate measurement of contact lenses whose back vertex power (BVP) varies across the optic zone. BVPs of multifocal rigid and soft contact lenses have previously been measured using a conventional vertometer incorporating the Scheiner principle, which makes use of two light paths equidistant from the center of the lens.
  
  
  METHODS
  We have developed a computer-based vertometer system based on the Scheiner principle which can be used to produce a profile of BVPs across rigid and soft contact lenses. A computer interface to the vertometer allows rapid acquisition of readings and software-based ray tracing derives in-air dioptric power readings across the optic zone at specific ray heights.
  
  
  RESULTS
  Results are presented for soft and rigid, and spherical and aspheric surface contact lenses.
  
  
  CONCLUSIONS
  The system improves the measurement resolution of a standard vertometer and shows an acceptable level of precision and accuracy for most applications.
authors.affiliation: Centre for Eye Research, School of Optometry, Queensland University of Technology, Brisbane, Australia. m.collins@qut.edu.au
authors.forename: M
authors.initials: M
authors.lastname: Collins
authors.forename: A
authors.initials: A
authors.lastname: Goode
authors.forename: B
authors.initials: B
authors.lastname: Davis
authors.forename: A
authors.initials: A
authors.lastname: Tait
mesh_terms: D003261:Contact Lenses / Q000592:standards*; D055095:Optics and Photonics / Q000295:instrumentation*; D009907:Optometry / Q000295:instrumentation; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014584:User-Computer Interface