corneal topography using orbscan : basics and interpretation dr gaurav prakash mbbs, md, fico,...

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 atdrgauravprakash@gmail.com

Thanks