Low_resolution_Thesis_CDD_221009_public - Visual Optics and ...

REFRACTIVE SURGERY PMMA MODEL
Ablation depth (microns)
0
-10
-20
-30
-40
-50
3 D
6 D
12 D
-60
-6 -4 -2 0 2 4 6
Radial coordinate (mm)
Fig. 3.2. Ablation profiles of three PMMA ablated flat surfaces for three nominal
refractive myopic corrections (3, 6 and 12 D). Optical zone diameters were 7 mm for
the 3-D and 6-D corrections and 5 mm for 12 D. These patterns were obtained by
profilometry on ablated flat surfaces. These ablation patterns are not affected by
ablation efficiency changes and represent the actual patterns for the cornea
programmed into the laser system.
3.4.2. Ablation patterns from flat surfaces and from spherical surfaces
Figure 3.2 shows the profiles of three ablated PMMA flat surfaces, for three different
corrections and optical zones. These ablation patterns are not affected by ablation
efficiency changes and represent the actual patterns programmed into the laser system.
It should be noted that the ablation depth depends both on the attempted correction
and optical zone, and therefore two different corrections (i.e. 6 and 12 D) may result in
similar central ablation depths.
Fig. 3.3. Best fitting conic of the actual corneal ablation pattern -crossescorresponding
to the 12-D PMMA ablation pattern of Fig. 3.2, compared with the
theoretical Munnerlyn and parabolic patterns -solid line- for the same correction and
depth. The Munnerlyn pattern is calculated with the parameters of a typical
preoperative cornea (radius 7.8 mm and asphericity -0.2).
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