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[The optical power of the corneal epithelium. In vivo evaluation]
J M Legeais1, F Mayer, J J Saragoussi
1Service d'Ophtalmologie de l'Hôtel-Dieu de Paris, Université de Paris VI, INSERM U 86.
Purpose:
The refracting power of the corneal epithelium is relatively unknown. We measured the keratometric refracting power of the cornea on 15 eyes of patients undergoing photorefractive keratectomy with and without epithelium.
Materials:
The readings were performed with a videokeratoscope TMS-1. Three readings were averaged to obtain the mean and standard deviations.
Results:
By removing the epithelium, there was an increase in corneal refracting power. The mean change was +1.19 D (standard deviation +/- 0.36 D) at 1 mm of the center of the cornea. On all patients the optical power of the cornea increased after epithelium removal.
Conclusion:
The curvature of the Bowman membrane is steeper than the cornea with epithelium. A change in the thickness of the epithelium is related to a modification of the optical power of the cornea. The optical role of the epithelium is to compensate surface irregularities of the Bowman membrane and could explained in part the hyperopia in the first months after excimer laser.