Corneal Topography using Orbscan Basics and interpretation Dr

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 www. gauravprakash. com

Orbscan IIz Complete corneal analysis : ü Topography ü Pachymetry ü Anterior surface ü Posterior surface

Orbscan IIz Combines two principles Placido disc Scanning slit

Placido disc Normal appearing corneas Normal Irregular cornea Inferior steeping

Principle of Placido n n n 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 technology Uses a series of light slits (40 slits) passing over the cornea at an angle of about 45° to the camera.

Scanning slit technology n n n 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

Best fit sphere is created to match surface points on anterior and posterior corneal surfaces.

Analysis techniques Use pseudocolor codes as your friends. N Red is dangerous Look for abnormal patterns Bow tie asymmetry , focal change in color

Map Reading (Quad Map) Anterior Elevation Map Curvature Map Posterior Elevation Map Statistics and Data Pachymetry Map

Map Reading Highest Point Lowest Point

Map Reading Highest Point Lowest Point

Map Reading THINNEST Area Pachymetry = Thickness of Cornea THICKER Area

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; high astigmatism

Steep vertical axis, centrally thin cornea , high posterior float : Keratoconus

Progressively worsening BSCVA in a young male; high astigmatism

Bow tie appearance , Extended thin zone inferiorly : Pellucid marginal degeneration

What’s wrong here ? ?

Inverse Bow Tie

UCVA : 6/60 , BSCVA : 6/36 ; BCVA with RGP : 6/12. What problem the patient is having ?

Post keratoplasty, Graft host thickness disparity, high astigmatism

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 at drgauravprakash@gmail. com Thanks