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Corneal Topography
Medicoach International Academy
 It is a non invasive imaging technique for mapping the
corneal surface.
 It allows three dimensional evaluation of corneal tissue.
 It provide both quantitative and qualitative evaluation of
cornea.
 It is also known as Photokeratoscopy or
Videokeratoscopy
Indication
 Pre and post refractive surgery.
 Diagnosis of corneal disorder.
 Early screening of keratoconus.
 Confirmation of post-operative astigmatism.
 Contact lens fitting
 ICL fitting
 Orthokeratology
 C3R
 Pre-Operative IOL selection
 Post keratoplasty astigmatism evaluation.
Principle of topography
 Placido disc based system
 Non placido disc based system
1.Scanning slit
2.Scheimpflug photography
Instrument Design
1.Instrument with small target and short working distance
 It is a small instrument
 Provide maximum corneal coverage
 In this focusing and alignment error is more
2.Instrument with larger target and larger working
distance
 This minimise focussing and alignment error
 But provide lesser corneal coverage
Parts of Topography
 Projection device:
To create image of cornea by projecting placido disc.
 Video Camera:
Capture reflected image of plasido disc.
 Computer
Analyse reflected image ,Calculate topographic data
and display .
Keratograph Algorithm
 It is the process of building a topographic map of cornea
from keratoscopic data.
1. Capture image of video keratoscopic ring.
2. Measurement of angular size of point
3. Reconstruction of corneal surface
4. Calculate the power and other data
5. Present measured data as a topogram
Procedure
 Patient is seated comfortably in front of the instrument.
 Enter the patient data.
 Focus the instrument by aligning crosshairs in the centre
of pupil.
 Project alternative black and white concentric ring on to
the cornea.
 Camera take the pictures of the reflection.
 Measure angular points on the ring.
 Computer analyse the reflected images and display result
as colour coded maps.
Corneal Topographic Maps
 Topogram
It is the method of displaying data from corneal topography
system
 Different topographic system generate different types of maps.
Display option of topographic data
1. Numerical power plot
2. Simulated Keratometric view
3. Profile view
4. Photokeratoscopic view
5. Surface elevation map
6. Colour coded maps
Numerical power plot
Simulated keratometric view
Surface elevation map
Colour Coded maps
Colour code Interpretation
Green and yellow Normal cornea
Hot/warm
colours(red and its
hues)
Steeper cornea
Cool colours(blue
and its hues)
Flatter cornea
Interpretation
 Round or oval - Normal cornea
 Bow-tie pattern -Astigmatism
 Vertical bow-tie -With the rule astigmatism
 Horizontal bow-tie -Against the rule astigmatism
 Asymmetrical bow-tie -Keratoconus
 Kissing pigeon pattern -Pellucid marginal degenaration
and advanced keratoconus
Asymmetrical bow tie
Kissing pigeon pattern
Diagnosis if keratoconus
 K value - the average keratometric value of central 2 to
4 rim.
 I-S value - average of dioptric power of five points
measured along inferior and superior cornea.
K value I-S value
Normal <47.2D <1.40
Keratoconus
suspect
47.2 to 48.7 1.4 to 1.9
Keratoconus >48.7 >1.9
Commercially Available Topographic
System
 Corneal modelling system(CMS)
 Topographic modelling system(TMS)
 Orbscan
 Pentacam
 CMS
 It is the fist fully automatic corneal topography system
 Consist of 32 alternatively black and white ring placido disc for
analysing cornea
 Also useful for measuring corneal thickness
TMS
 It consist of 31 alternatively black and white ring placido disc
system
 For analysing 7000 data points on cornea
Orbscan
 it is a newer technology which allow mapping of anterior and
posterior surface of cornea.
 It use a hybrid technique by combining advantages of placido disc
system and slit scanning system
Pentacam
 It is the gold standard anterior segment topography device .
 It use rotating scheimpflug technology to evalute anterior and
posterior corneal surface.
Thankyou

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TOPOGRAPHY .pdf

  • 2.  It is a non invasive imaging technique for mapping the corneal surface.  It allows three dimensional evaluation of corneal tissue.  It provide both quantitative and qualitative evaluation of cornea.  It is also known as Photokeratoscopy or Videokeratoscopy
  • 3. Indication  Pre and post refractive surgery.  Diagnosis of corneal disorder.  Early screening of keratoconus.  Confirmation of post-operative astigmatism.  Contact lens fitting  ICL fitting  Orthokeratology  C3R  Pre-Operative IOL selection  Post keratoplasty astigmatism evaluation.
  • 4. Principle of topography  Placido disc based system  Non placido disc based system 1.Scanning slit 2.Scheimpflug photography
  • 5. Instrument Design 1.Instrument with small target and short working distance  It is a small instrument  Provide maximum corneal coverage  In this focusing and alignment error is more 2.Instrument with larger target and larger working distance  This minimise focussing and alignment error  But provide lesser corneal coverage
  • 6. Parts of Topography  Projection device: To create image of cornea by projecting placido disc.  Video Camera: Capture reflected image of plasido disc.  Computer Analyse reflected image ,Calculate topographic data and display .
  • 7. Keratograph Algorithm  It is the process of building a topographic map of cornea from keratoscopic data. 1. Capture image of video keratoscopic ring. 2. Measurement of angular size of point 3. Reconstruction of corneal surface 4. Calculate the power and other data 5. Present measured data as a topogram
  • 8. Procedure  Patient is seated comfortably in front of the instrument.  Enter the patient data.  Focus the instrument by aligning crosshairs in the centre of pupil.  Project alternative black and white concentric ring on to the cornea.  Camera take the pictures of the reflection.  Measure angular points on the ring.  Computer analyse the reflected images and display result as colour coded maps.
  • 9. Corneal Topographic Maps  Topogram It is the method of displaying data from corneal topography system  Different topographic system generate different types of maps. Display option of topographic data 1. Numerical power plot 2. Simulated Keratometric view 3. Profile view 4. Photokeratoscopic view 5. Surface elevation map 6. Colour coded maps
  • 10. Numerical power plot Simulated keratometric view
  • 12. Colour Coded maps Colour code Interpretation Green and yellow Normal cornea Hot/warm colours(red and its hues) Steeper cornea Cool colours(blue and its hues) Flatter cornea
  • 13. Interpretation  Round or oval - Normal cornea  Bow-tie pattern -Astigmatism  Vertical bow-tie -With the rule astigmatism  Horizontal bow-tie -Against the rule astigmatism  Asymmetrical bow-tie -Keratoconus  Kissing pigeon pattern -Pellucid marginal degenaration and advanced keratoconus
  • 16. Diagnosis if keratoconus  K value - the average keratometric value of central 2 to 4 rim.  I-S value - average of dioptric power of five points measured along inferior and superior cornea. K value I-S value Normal <47.2D <1.40 Keratoconus suspect 47.2 to 48.7 1.4 to 1.9 Keratoconus >48.7 >1.9
  • 17. Commercially Available Topographic System  Corneal modelling system(CMS)  Topographic modelling system(TMS)  Orbscan  Pentacam
  • 18.  CMS  It is the fist fully automatic corneal topography system  Consist of 32 alternatively black and white ring placido disc for analysing cornea  Also useful for measuring corneal thickness TMS  It consist of 31 alternatively black and white ring placido disc system  For analysing 7000 data points on cornea
  • 19. Orbscan  it is a newer technology which allow mapping of anterior and posterior surface of cornea.  It use a hybrid technique by combining advantages of placido disc system and slit scanning system Pentacam  It is the gold standard anterior segment topography device .  It use rotating scheimpflug technology to evalute anterior and posterior corneal surface.
  • 20.