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Yan Li, Nehal M. Samy El Gendy, David Huang; Optical Coherence Tomography Guided Transepithelial Phototherapeutic Keratectomy for Anterior Corneal Opacities. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3376.
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To use optical coherence tomography (OCT) to guide transepithelial phototherapeutic keratectomy (PTK) of anterior corneal stromal opacities.
Anterior corneal stromal opacity (stromal dystrophies and scars) cases suitable for transepithelial PTK treatment were recruited. Preoperatively, pachymetry (8 radials, 1024 axial scans each, 6mm diameter) and 3-demensional (3D) volumetric (101 raster scans, 512 axial scans each, 6mm x 6mm scan size) OCT scans centered on the cornea were obtained with a Fourier-domain OCT (RTVue). An algorithm was developed to simulate the effect of transepithelial ablation using the OCT data. An excimer laser (VISX S4) was used to deliver PTK and refractive ablation based on OCT measurements (corneal opacity depth, epithelial thickens and stromal thickness) and the refraction. Postoperatively, OCT measurements, refraction and vision were recorded to evaluate the surgical outcome.
Nine eyes of 8 patients had OCT-guided PTK and refractive ablation procedures and were followed-up for at least 3 months. The operated eyes gained an average of 4.5-line in uncorrected visual acuity and 2.0-line in best spectacle corrected visual acuity to 20/29. The laser ablations were deeper than nominal settings by 19.6%. The laser ablation efficiency was lower centrally than that peripherally, accounting for an 8.2% (% laser depth setting) central island height. The spherical equivalent refractive change (D) was related to epithelial thicknesses measured by OCT, in addition to the refractive ablation setting: Refractive change = -0.29 + 0.1405*(PTK depth - CET) - 0.159*(CET-PET) Where CET and PET were the central and peripheral epithelial thicknesses (µm). Postoperative OCT agreed well with simulated PTK performed on preoperative OCT data, based on both en face and cross-sectional views in terms of the pattern of residual opacities.
3D OCT could be used to predict residual stromal thickness, refractive change, central island formation, and opacity reduction after PTK. This could help the surgeon plan PTK and refractive ablations to optimize visual outcome.
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