Topography Flashcards
How does it work
Placido disk models use K reflection to map the cornea. Distorted mires= scarring
The cornea reflects like a convex (minus) mirror. Creates a minified, upright virtual image.
More minification means
Higher reflective power= steeper
Normalized scale
Tailors the color/diopter values to individual maps. Useful for same eye.
Round vs oval shape
round- very little astigmatism
oval- Small amount of K cyl
Two types of curvature maps
Axial
Tangential
Axial
Curvature map
Data is smoothed or averaged.
Assumes center of curvature is on optic axis
Best for picking base curves
Caution interpreting power in the periphery- tells you that the cornea is getting flatter NOT that it is decreasing in power.
What map is Best for picking base curves
Axial
Colors on curvature maps
Hot –> Cool
Tells you that the cornea is getting flatter. Looks like diopters are decreasing, but just means its flat.
Colors on refractive power
Hot –> hotter
Tells you that the peripheral cornea is increasing in diopters because of the aberrations.
Gives true power everywhere using ray tracing methods.
center of curvature for axial and tangential map
Axial- Optic axis
Tangential- True center of curvature.
Tangential map
Point by point.
Center of curvature is measured from true center.
Good at locating disease.
Caution interpreting power in the periphery- tells you that the cornea is getting flatter NOT that it is decreasing in power.
Map useful for pre/post surgery eval
Refractive power map
Ex: LASIK and ortho K
Elevation map gives corneal
Shape
What map is based on the best fit sphere
Elevation map
Elevation map is useful for
Disease location and predicting NaFl patterns
