Epithelial and stromal changes induced by intacs examined by three-dimensional very high-frequency digital ultrasound

PURPOSE: To examine epithelial and stromal layers by three-dimensional very high-frequency (VHF) digital ultrasound scanning before and after implanta tion of Intacs (intracorneal ring segments [ICRS]). METHODS: Three-dimensional scanning was performed in five eyes before and 3 months after Intacs insertion. Digital signal processing techniques provid ed high-resolution B-scan imaging and I-scan traces for high-precision (1-m um) three-dimensional pachymetry. Thickness maps of individual corneal laye rs were constructed of the epithelium, stroma, and full cornea before and a fter surgery. Difference maps for epithelium and stroma were produced to ex amine anatomical changes in the thickness profile induced in each layer and correlate these to refractive changes. RESULTS: B-scan examination revealed stromal and epithelial anatomy anterio r and adjacent to the Intac. Ring depth could be measured topographically. There was stromal lamellar displacement by the ring segments that produced a concave anterior stromal groove within an annulus central to the ring. Ep ithelial filling of this concavity was shown in three dimensions in such a way as to produce orthogonally asymmetrical flattening of the corneal surfa ce, thus potentially accounting for induced astigmatism. Mapping of the cen tral stroma demonstrated thickening, potentially also accounting for astigm atic changes ascribable to orthogonal asymmetry. CONCLUSIONS: VHF digital ultrasound scanning provided imaging and three-dim ensional thickness mapping of corneal layers, enabling anatomical evaluatio n of the changes induced in the cornea by Intacs.