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Improved effectiveness of trans-epithelial phototherapeutic keratectomy versus topography-guided ablation degraded by epithelial compensation on irregular stromal surfaces
Session Title: Surface Ablation II
Session Date/Time: Tuesday 08/10/2013 | 16:30-18:00
Paper Time: 17:21
Venue: Main Lecture Hall (Ground Floor)
First Author: : G.Carp UK
Co Author(s): : D. Reinstein T. Archer M. Gobbe
To demonstrate the improved effectiveness of trans-epithelial phototherapeutic keratectomy (PTK) where topography-guided ablation is degraded by epithelial compensation for localized irregularities.
London Vision Clinic, London, UK
Artemis very high-frequency digital ultrasound (VHFDU) scanning was performed on 5 eyes (4 patients) after LASIK in which a short nasal flap was created, but the ablation performed, resulting in irregular astigmatism and double vision. The stromal ablation pattern of a trans-epithelial PTK ablation was modeled and compared to topography-guided ablation simulations. Artemis-assisted trans-epithelial PTK procedures were performed in 3 eyes (2 patients), the other 2 patients remained untreated.
In all cases, Artemis VHFDU demonstrated a crevice on the stromal surface caused by ablation on the underside of the flap nasally, which had been compensated for by epithelial thickening, thus masking a significant proportion of the stromal surface irregularity from corneal surface topography. The trans-epithelial PTK ablation pattern appeared logically to reduce the ridge nasal to the crevice whereas topography-guided ablation patterns demonstrated poor targeting of the stromal ridge. Artemis-assisted trans-epithelial PTK succeeded in greatly reducing the stromal irregularity resulting in a smoother epithelial thickness profile and a significant improvement in topography and visual symptoms. In one eye, the irregularity was compensated for fully by the trans-epithelial PTK with the patient reporting 95% subjective improvement in double vision. One patient (two eyes) reported virtually no change in visual symptoms despite significant anatomical regularization due to the partial nature of epithelial compensation demonstrating that multiple procedures may be required.
Compensatory epithelial remodeling masks stromal irregularities from the corneal surface meaning that topography-guided (or wavefront-guided) ablations may not provide an adequate treatment option and may potentially worsen the irregularity. The effectiveness of trans-epithelial PTK will depend on the proportion of epithelial masking due to remodeling, related to the rate of change of curvature of the stromal surface.
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