OCULUS Pentacam - Page 130

128
Front elevation near min RP*
elevation upper limit
(μm) (μm)
mean +1.0 --
+SD +2.1 +3.1
+2 SD +4.2 +5.2
+3 SD +6.2 +7.2
The lower right map [elevation (back)] (Figure 157) shows the elevation of the back surface in μm
relative to the BFTEF over an 8 mm zone. The eccentricity of the ellipsoid is fixed at 0.45 (Q-value
= -0.20) and the principal radii are again varied for the best least square fit of the surface. Plus (+)
values are above the reference surface and negative values (-) are below, and are all given in μm.
Normal values for back elevations near the minimum RP (Table 7) and maximum elevations at any
location on the back surface (Table 8) are given.
Back elevation near min RP*
elevation upper limit
(μm) (μm)
mean +6.8 --
+SD +4.2 +11.0
+2 SD +8.4 +15.2
+3 SD +12.6 +19.4
The asphericity quotient (Q-value) and eccentricity (ε) describe the shape of the elliptical surface
(Q = - ε
2
). These and the computed Zernike as well as the Seidel Longitudinal SA for a 6 mm zone are
shown in Table 9.
Variables indicating shape and SA of cornea front surface*
Q-value Eccentricity (ε) Zernike (4,0) -- SA Seidel Longitudinal SA (D)
-0.54 +0.73 (Q = -ε
2
) 0.00 0.00
-0.26 +0.51 (Q = -ε
2
) +0.19 +1.03
0.00 0.00 +0.38 +2.10
+0.26 0.51 (Q = -ε
2
) +0.59 +3.24
+0.54 0.73 (Q = -ε
2
) +0.81 +4.46
Table 5: Front elevation near min RP
(*N = 1243 normal eyes,
internal, unpublished data
by J. T. Holladay)
Table 6: Maximum front elevation
(*N = 1243 normal eyes,
internal, unpublished data
by J. T. Holladay)
Table 7: Back elevation near min RP
(*N = 1243 normal eyes,
internal, unpublished data
by J. T. Holladay)
Table 8: Maximum back elevation
(*N = 1243 normal eyes,
internal, unpublished data
by J. T. Holladay)
Table 9: Variables indicating the shape and SA of the corneal front surface
(* All variables are computed over a 6 mm corneal zone based on an
anterior corneal apical radius of 7.71 mm, a corneal index of refraction
of 1.376 and a wavelength of 0.555 µm, using an elliptical model.)
Maximum front elevation*
elevation upper limit
(μm) (μm)
mean +1.0 --
+SD +1.3 +4.3
+2 SD +2.6 +5.5
+3 SD +3.8 +6.8
Maximum back elevation*
elevation upper limit
(μm) (μm)
mean +8.5 --
+SD +3.3 +11.8
+2 SD +6.5 +15.0
+3 SD +9.8 +18.3
17 Holladay Report & Holladay EKR65 Detail Report