Epithelial Maps In Highly Aberrated Corneas

In transepithelial excimer laser treatments, the masking of the stromal irregularities is advantageous, since the volume removal based on the laser pulse between epithelium and stroma is in the ratio of 1.0 to 0.8. Nevertheless, a removal error arises due to the non-consideration of the epithelial thickness. The aim is to measure epithelial thickness in highly aberrated corneas and to calculate the expected ablation error if ignoring the actual epithelial map.

Medical University Vienna

In 20 highly aberrated corneas with an RMS HOA (Root Mean Square Higher Order Aberration) of 1.0 to 3.0 Eq.D (Equivalent Diopters), the epithelial map was determined with the anterior chamber OCT MS-39® (Schwind). The central and average epithelial thicknesses for the central 3 and 6 mm were evaluated. The fluctuations of the epithelial thickness were determined for the individual meridians and combined into an overall epithelial irregularity factor. The results were compared with a uniform epithelial gradient of 55 μm centrally to 65 μm in the 8 mm radius.

 

The central epithelial thicknes are represented in scatter plots, as well as the distribution of the average epithelial thickness in relation to the 3 and 6 mm zones. In addition, the RMS HOA of the corneal surface is compared to the total epithelial irregularity factor.

Disregarding of a high central deviation from the standard epithelial thickness as well as epithelial irregularities with high amplitudes influence the ablation accuracy.