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Published byAlan Bryan Modified over 9 years ago
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Corneal Topography using Orbscan : Basics and interpretation
Dr Gaurav Prakash MBBS, MD, FICO, FRCS(Glasgow) Cornea and Refractive Surgeon, NMC Eye Care , NMC Specialty Hospital , Abu Dhabi , UAE
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Orbscan IIz Complete corneal analysis : Topography Pachymetry
Anterior surface Posterior surface
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Orbscan IIz Combines two principles Placido disc Scanning slit
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Normal appearing corneas
Placido disc Normal appearing corneas Normal Inferior steeping Irregular cornea
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Principle of Placido Placido rings The location of the placido rings in relation to the camera is already known. The radial slope of the surface at the point of reflection can be determined by ray tracing. Used for keratometric analysis camera
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Scanning slit technology
Uses a series of light slits (40 slits) passing over the cornea at an angle of about 45° to the camera.
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Scanning slit technology
The scanning slit triangulates the area between the reflected beam and camera axis to determine the edge. Overall analysis of reflected beams determines ‘floats’. Difference in two edges created by the same beam , adjusting for time delays, determines the depth. Projector camera
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Best fit sphere Best fit sphere is created to match surface points on
anterior and posterior corneal surfaces.
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Analysis techniques Use pseudocolor codes as your friends .
Red is dangerous Look for abnormal patterns Bow tie asymmetry , focal change in color
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Map Reading (Quad Map) Anterior Elevation Map Posterior Elevation Map
Statistics and Data Curvature Map Pachymetry Map
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Map Reading Highest Point Lowest Point
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Map Reading Lowest Point Highest Point
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Pachymetry = Thickness of Cornea
Map Reading Pachymetry = Thickness of Cornea THINNEST Area THICKER Area
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Keratometry = steepness of Cornea
Map Reading
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21 years old female . -2.5 D . Can she undergo lasik ?
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Orbscan : normal
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30 year old male UCVA 6/6 , H/o Sx done 3 years back
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Orbscan : post lasik
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32 years old male , UCVA : 6/24 , BCVA : 6/12 . Mild myopia .
H/o Surgery 8 years back
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Orbscan : Post Lasik Ectasia
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Progressively worsening BSCVA in a young male; high astigmatism
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Steep vertical axis, centrally thin cornea , high posterior float : Keratoconus
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Progressively worsening BSCVA in a young male; high astigmatism
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Bow tie appearance , Extended thin zone inferiorly : Pellucid marginal degeneration
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What’s wrong here ??
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Inverse Bow Tie
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UCVA : 6/60 , BSCVA : 6/36 ; BCVA with RGP : 6/12
UCVA : 6/60 , BSCVA : 6/36 ; BCVA with RGP : 6/12. What problem the patient is having ?
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Post keratoplasty, Graft host thickness disparity, high astigmatism
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Post lasik , success story ???
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Central Island
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Whats wrong for this post lasik 28 year old male ?
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Irregular corneal flap post lasik
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Posterior float anamoly
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Another one from the blue
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normal
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Is this a go ahead ?
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Fellow eye
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Remember , the best way to master topography Is to see more
Feel free to ask your queries at Thanks
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