Effects Of Alcon’S Streamlight Transepithelial Ablation On Stromal Tissue Reduction And Postoperative Epithelial Remodeling

To correlate planned vs. achieved ablation depth in the corneal stroma after the StreamLight transepithelial laser ablation (tPRK).

Memira eye center, Tromsø, Norway

Forty eyes of 40 patients, mean aged 37.9±16.0 years were treated for myopia and astigmatism with mean spherical equivalent -2.55±1.3 D, using tPRK. Corneal optical coherence tomography (OCT) was used to obtain stromal- and epithelial thickness maps (STMs and ETMs), preoperatively and 6 months after the surgery. Planned stromal laser ablation depth map was derived from laser ablation software and divided into central 2 mm zone and 3 concentric rings, to match the STM and ETM reports. The achieved stromal reduction was calculated by subtraction of post- from pre-operative STM of the ablation area. Induced changes in ETM caused by epithelial remodeling were found by subtraction of the preoperative from the postoperative ETM in the same area.

Nineteen eyes with 6 months followup were available for evaluation: Mean planned and achieved central ablation depths were 44,26 and 52,13 µm, respectively, with mean difference of 7.86 µm (p= 0.14) (17.6%). The mean differences within paracentral 2-5- and 5-7-mm rings were 3.28 (p= 0.28) and 0.79 µm (p= 0.39), respectively. Mean pre- and postoperative central epithelial thicknesses were 54.81 and 60.31 µm, respectively, with a mean gain of 5.50 µm (p< 0.001) (10,0%). Total corneal thickness reduction compensated for the mean central epithelial thickness gain, was 46.63 µm, resulting in a difference between the mean planned central ablation depth and the mean total corneal thickness reduction of 2.37 µm (p= 0.37) (4,0%).

Measured mean central stromal tissue reduction after StreamLight tPRK was 7.86 µm higher than the planned ablation depth. However, when the achieved stromal reduction was compensated by the epithelial thickness gain, the difference between the planned and achieved total central corneal thickness reduction was brought down to 2.37 µm. It appears that this finding points out that the planned ablation depth of the treatment accounted for the postoperative epithelial remodelling, to achieve the desired outcomes.