Total Cornea Refractive Power Map; Differences Between The Various Topography Maps Of Pentacam - OCULUS Pentacam Interpretation Manual

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Total Cornea Refractive Power map

This map (Figure 7) uses ray tracing to calculate the refractive power of the cornea. It takes into
account how parallel light beams are refracted according to the relevant refractive indices (1.376
and 1.336), the exact location of refraction and the slope of the surfaces. The location of refraction
is a determinant of surface slope, since the anterior and posterior surfaces have slightly differing
principal planes due to corneal thickness. In this way the map takes effects "A", "B", "C" and
"D" into account. Its results are more realistic than any other, but they will deviate from normal
(sagittal) SimK values so they cannot be used in conventional IOL formulas.
Figure 6: Calculation of power according to Snell´s law taking the different refractive
indices and the different principal planes of the anterior and posterior corneal
surfaces into account
Figure 7: Total Corneal Refractive Power map calculated by two spheric surfaces
of anterior r = 8 mm and posterior r = 6.58 mm and pachimetry
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Differences between the various topography maps of Pentacam

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