corneal topography using orbscan : basics and interpretation dr gaurav prakash mbbs, md, fico,...
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Corneal Topography using Orbscan : Corneal Topography using Orbscan : Basics and interpretationBasics and interpretation
Dr Gaurav Prakash Dr Gaurav Prakash MBBS, MD, FICO, FRCS(Glasgow)MBBS, MD, FICO, FRCS(Glasgow)
Cornea and Refractive Surgeon, Cornea and Refractive Surgeon, NMC Eye Care , NMC Eye Care ,
NMC Specialty Hospital , NMC Specialty Hospital , Abu Dhabi , UAEAbu Dhabi , UAE
www.gauravprakash.comwww.gauravprakash.com
Orbscan IIzOrbscan IIz
Complete corneal analysis Complete corneal analysis ::
TopographyTopography PachymetryPachymetry Anterior surfaceAnterior surface Posterior surfacePosterior surface
Orbscan IIzOrbscan IIz
Combines two Combines two principlesprinciples
Placido disc Scanning slit
Placido discNormal appearing corneas
Normal Inferior steeping
Irregular cornea
Principle of PlacidoPrinciple of Placido
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
Placido rings camera
Scanning slit technologyScanning slit technology
Uses a series of light slits (40 slits) passing over the cornea at an angle of about 45° to the camera.
Scanning slit technologyScanning slit technology The scanning slit The scanning slit
triangulates the area triangulates the area between the reflected between the reflected beam and camera axis beam and camera axis to determine the edge.to determine the edge.
Overall analysis of Overall analysis of reflected beams reflected beams determines ‘floats’.determines ‘floats’.
Difference in two Difference in two edges created by the edges created by the same beam , adjusting same beam , adjusting for time delays, for time delays, determines the depth.determines the depth.
Projector camera
Best fit sphereBest fit sphere
Best fit sphere isBest fit sphere is
created to matchcreated to match
surface points onsurface points on
anterior and anterior and posteriorposterior
corneal surfaces.corneal surfaces.
Analysis techniquesAnalysis techniques
Use pseudocolor codes as Use pseudocolor codes as your friends .your friends .
Red is dangerousRed is dangerous
Look for abnormal Look for abnormal patterns patterns
Bow tie asymmetry , focal Bow tie asymmetry , focal change in colorchange in color
Anterior Elevation Map Posterior Elevation Map
Curvature Map Pachymetry MapStatistics and Data
Map Reading (Quad Map)
Highest Point Lowest Point
Map Reading
Lowest PointHighest Point
Map Reading
THINNEST Area THICKER Area
Pachymetry = Thickness of CorneaMap Reading
Map Reading Keratometry =
steepness of Cornea
21 years old female . -2.5 D . Can she undergo lasik ?
Orbscan : normal
30 year old male UCVA 6/6 , H/o Sx done 3 years back
Orbscan : post lasik
32 years old male , UCVA : 6/24 , BCVA : 6/12 . Mild myopia . H/o Surgery 8 years back
Orbscan : Post Lasik Ectasia
Progressively worsening BSCVA in a young male; Progressively worsening BSCVA in a young male; high astigmatismhigh astigmatism
Steep vertical axis, centrally thin cornea , high Steep vertical axis, centrally thin cornea , high posterior float : Keratoconusposterior float : Keratoconus
Progressively worsening BSCVA in a young male; Progressively worsening BSCVA in a young male; high astigmatismhigh astigmatism
Bow tie appearance , Extended thin zone Bow tie appearance , Extended thin zone inferiorly : Pellucid marginal degenerationinferiorly : Pellucid marginal degeneration
What’s wrong here ??What’s wrong here ??
Inverse Bow Tie Inverse Bow Tie
UCVA : 6/60 , BSCVA : 6/36 ; BCVA with RGP : 6/12. What UCVA : 6/60 , BSCVA : 6/36 ; BCVA with RGP : 6/12. What problem the patient is having ?problem the patient is having ?
Post keratoplasty, Graft host thickness disparity, high Post keratoplasty, Graft host thickness disparity, high astigmatismastigmatism
Post lasik , success story ???
Central Island
Whats wrong for this post lasik 28 year old male ?
Irregular corneal flap post lasik
Posterior float anamoly
Another one from the blue
normal
Is this a go ahead ?
Fellow eye
Remember , the best way to master topography
Is to see more
Feel free to ask your queries [email protected]
Thanks