Fig. 18.1
(a) Preoperative Pentacam image of an eye with the manifest refraction of −12.0 −1.0 @ 165°. (b) Same eye 1 week postoperatively. The manifest refraction (MR) is +0.25 −0.5 @ 120°. There is a distinct elevation of the posterior corneal surface. (c) After 3 months both the refraction and the topography remain unchanged: +0.25 +0.25 @ 100°
Fig. 18.2
(a) Another example of high myopia combined with astigmatism. MR = −14.0 −2.0 @ 10°. (b) Three months after surgery with primary under-correction for sphere and cylinder the MR is −2.0 −1.25 @ 30°. The posterior float is virtually unchanged. (c) Anterior curvature difference map (right column) between pre-op (left column) and 3 months post-op (middle column). Also note that despite very high correction the residual corneal power is well above 37 D
This procedure was performed on corneas with minimum CCT of not less than 500 μm, ensuring that at least 250 μm of residual stromal bed is left and at least 100 μm cap thickness. The lenticule diameter (i.e., optical zone) was adjusted according to the scotopic pupil diameter and the residual stroma. Therefore, there should be a balance between the residual stromal bed thickness, pupil diameter, and lenticule diameter.
As the machine’s settings have the tendency of undercorrection, we adjusted our nomogram to add about 5–15 % of the manifest refraction according to the patients’ age. However, some patients were intentionally undercorrected due to age considerations, high numerical sum of sphere and cylinder (higher than 14), or insufficient corneal thickness. In some cases we had to compromise the astigmatism correction in order to salvage the correction of very high spheres.
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