• Melanie Corbett
  • Nicholas Maycock
  • Emanuel Rosen
  • David O’Brart


Reflection-based topography systems use the cornea as a convex mirror and view the first Purkinje image. Keratometers use two pairs of images in perpendicular meridian at a diameter of about 3 mm and is a highly accurate measure of the central curvature of regular corneas. Photokeratoscopes view the reflected image of the black and white concentric rings of a Placido disc, providing qualitative shape information across a large area of the cornea.

Videokeratoscopes analyse the position of the edges of the Placido rings in meridians around 360°, giving about 10,000 data points. Reconstruction algorithms applied to each point on the two-dimensional mire image generate a three-dimensional interpretation of the corneal shape. The accuracy centrally is approximately 0.15D, which drops more peripherally and in irregular corneas.


Corneal topography Corneal shape Corneal elevation Corneal curvature Corneal power Keratometer Placido disc Photokeratoscope Videokeratoscope Topography mires Topography algorithms Topography accuracy Three-dimensional topography 


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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Melanie Corbett
    • 1
  • Nicholas Maycock
    • 2
  • Emanuel Rosen
    • 3
  • David O’Brart
    • 4
  1. 1.Imperial College Healthcare NHS TrustLondonUK
  2. 2.University Hospital Coventry and WarwickshireCoventryUK
  3. 3.ManchesterUK
  4. 4.Department of OphthalmologySt. Thomas HospitalLondonUK

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