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Manual keratometry and videokeratography after photorefractive keratectomy
Purpose:
To examine the relative accuracy of manual keratometry and videokeratography in eyes treated by photorefractive keratectomy (PRK).
Setting:
Eye Clinic, Cantonal Hospital, Lucerne, Switzerland.
Methods:
Results of manual keratometry and videokeratography were compared with those of subjective refraction in 128 eyes before and 6 months after PRK.
Results:
Six months after PRK, the mean subjective refraction of all eyes decreased more than the mean corneal dioptric power measured with videokeratography (P <.0001). The change in the mean subjective refraction compared with the corresponding difference in the mean manual keratometry of all eyes was also significant (P <.0001).
Conclusions:
This study confirmed an earlier observation that there is a disparity between the change in refraction and the reduction in corneal power measured by videokeratography and with the manual keratometer. Topographical changes from PRK and the subsequent wound-healing processes are likely to falsify objective measurements. The keratometric value in the center of the cornea, since it is not measured by manual keratometry and videokeratography, may actually be lower.