Axial maps are the original mapping method of early topographers. Axial maps are spherically biased (they assume the cornea is spherical in shape), limiting their usefulness. Additionally they do not show peripheral flattening
Local Curvature Maps
True (local) Curvature maps show the cornea's shape far better than Axial maps. Other names for this mapping technique are Instantaneous or Tangential curvature. Local curvature maps will follow the natural flattening of the corneal periphery. Notice how this Lasik map shows the high curvature of the transition zone between the ablated area and the non ablated area.
Refractive maps of this cornea show the refractive power of the cornea according to Snell's law. The warmer colors have higher refractive powers than the cooler colors.
Spherical Offset Elevation Mapping
The SPHERICAL OFFSET scale allows the user to compare the cornea against a user specified spherical curve. The differences between the cornea and the sphere are mapped in micron steps. On the Lasik on the left, the cool colors are below the 43.8 D reference sphere, the warm colors are above the reference sphere. Height mapping is offered in three ways: 1.) vertex tangent method displays the differences (in microns) of the cornea from a sphere centered on the axis, i.e. tangent to the vertex. 2.) the three point reference method allows you to position the reference sphere so that the sphere is forced to pass through three selected points. 3.) the vertex to point method place the vertex of the reference sphere wherever you specify.
All height data is shown with a user adjustable color scale. Profile graphs are displayed in semi-meridian, meridian and circular format with 3D wire frame display. The graph below displays the cornea's depth below the 43.8 D sphere.
Corneal Aberrometry maps display the aberations from the corneal surface. This map is useful in diagnosing the effect of low and high order aberration.
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