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J Refract Surg. 2012 Feb;28(2):139-43. doi: 10.3928/1081597X-20111115-01. Epub 2011 Nov 21.

Is topography-guided ablation profile centered on the corneal vertex better than wavefront-guided ablation profile centered on the entrance pupil?

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London Vision Clinic, London, United Kingdom.



To illustrate the hypothesis that corneal vertex centration is superior to entrance pupil centration when guiding an ablation by wavefront.


In one case example of therapeutic retreatment for treatment zone decentration after primary radial keratotomy (RK) centered on the entrance pupil (line of sight), both a whole-eye wavefront-guided ablation profile (WASCA data) and a topography-guided ablation profile (Atlas data) were generated using the CRS-Master (Carl Zeiss Meditec) and compared. The patient had a large vertical angle kappa. Corneal topography demonstrated that the zone of flattening was decentered superiorly with reference to the corneal vertex and the patient reported severe night vision disturbances.


The wavefront-guided profile, centered on the line of sight, was symmetrical because the wavefront was dominated by spherical aberration induced by the primary RK treatment. On the other hand, the topography-guided profile, centered on the corneal vertex, was asymmetric with an inferior region of ablation, which would logically improve the topographic decentration. The topography-guided profile was chosen for photorefractive keratectomy using the MEL 80 excimer laser (Carl Zeiss). Ten months after the procedure, the treatment zone was topographically well centered on the corneal vertex. Whole-eye higher order root-mean-square (RMS) was reduced by 43% and corneal higher order RMS was reduced by 61%. The patient reported large subjective improvement in the quality of vision and marked reduction in night vision disturbances.


This case provides evidence that wavefront data centered on the entrance pupil center may not represent the patient's view and the treatment zone should preferably be centered on the corneal vertex rather than the entrance pupil center.

[Indexed for MEDLINE]

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