Evaluating Cone Stromal Ablation Depth Using Different Strategies In Customized Surface Ablation In Keratoconus

58 eyes of 58 mild to moderate keratoconus patients were evaluated using 3 different simulation approaches. 1. Treating all the manifest refraction plus the corneal higher order aberrations (HOAs). 2. Treating all HOAs with up to 40% of cylinder and up to 40% of sphere up to 50 microns of cone stromal ablation (Athen’s protocol). 3. Treating all HOAs and only the sphere and cylinder which are embedded in the HOAs ablation, as calculated using the Schwind Amaris ORK CAM software. All models were simulated on the ORK software with optical zones (OS) varying from 5.5 mm to 7.0 mm. The stromal ablation depth over the cone was calculated for all possible outcomes.  

The cone ablation depth in approach 1 was 49.6 ± 19.8 µ, 60.9 ±24.3 µ, 70.1 ± 28.2 µ, and 82.1 ± 32.3 µ at OZ of 5.5, 6.0, 6.5, and 7.0 mm, respectively (P<0.01). The Athen’s protocol yielded 29.12 ± 9.3 µ, 38.2 ± 10.0 µ, 44.5 ± 10.9 µ, and 50.6 ± 13.7 µ, (P<0.01), while approach # 3 yielded 17.6 ± 6.1 µ, 22.7 ± 10.6 µ, 26.3 ± 11.7 µ, and 29.9 ± 13.2 µ,for OZ of 5.5 to 7.0 mm, respectively (P>0.05).

Treating only the sphere and cylinder embedded into the HOAs ablation treatment provides not only with the slimmest ablation depth over the cone, but also the lowest increase in ablation depth with enlargement of optical zone. The adoption of this approach would ensure the best overall strategy in customized ablation, whether topography or wavefront-guided, on keratoconus eyes.