Phototherapeutic Keratectomy in Salzmann Nodular Degeneration With “Optical Cornea Plana”

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Abstract

Purpose:

Typically, we observe an unintended hyperopic shift after phototherapeutic keratectomy (PTK). Despite a clear optical axis, elevations of the mid-peripheral cornea often lead to remarkable visual impairment in Salzmann nodular degeneration (SND). The aim of this study was to analyze the effect of mechanical pannus removal and PTK on the corneal curvature in SND.

Methods:

Fifteen eyes of 10 patients with visual impairment caused by SND were treated with combined pannus removal and PTK using a masking fluid. Mean age was 53 years. We analyzed best-corrected visual acuity, central corneal power (in diopters, D), spherical equivalent (in D), and irregularity of corneal topography (Index of Surface Variance, Pentacam).

Results:

Best corrected visual acuity before PTK was 0.64 (median) and improved to 0.85 (median) after the surgical procedure. Mean spherical equivalent was reduced by 1.82 ± 1.4 D from +2.53 D preoperatively to +0.75 D postoperatively (P = 0.001). Mean central corneal power increased by 3.18 ± 3.5 D from 39.8 ± 4.6 D preoperatively to 43 ± 1.7 D postoperatively (P = 0.013). Topographic irregularity normalized from 83.9 ± 53.7 (27–204) to 33.3 ± 14.3 (20–56; Index of Surface Variance) (P = 0.016).

Conclusions:

In SND, asymmetric tear film pooling caused by nodules located in the mid-periphery of the cornea may lead to an “optical cornea plana,” which results in a marked hyperopic shift accompanied with high irregular astigmatism. Pannus removal combined with excimer laser PTK may restore visual performance, at least in part, because of a myopic shift and regularization of the corneal curvature.

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