Targeting Higher Order Aberrations Alone in Keratoconus: A Tissue-Saving Alternative to Established Protocols.
TL;DR
Treating only the sphere and cylinder embedded into the HOA ablation treatment profile leads not only to the slimmest ablation depth over the cone and ablation volume, but, more importantly, it provides the lowest increase in ablation depth with enlargement of the OZ.
Abstract
Purpose
To evaluate cone stromal ablation depth with varying optical zones using different customized ablation strategies in keratoconus.
Methods
This retrospective computational analysis assessed 59 eyes from 59 patients with mild to moderate keratoconus using three different simulation approaches. The first approach involved treating the full manifest refraction along with the corneal higher order aberrations (HOAs). The second approach, following the Athens Protocol, targeted all HOAs with up to 70% correction of the cylinder and sphere, limiting cone stromal ablation to 50 µm at an optical zone (OZ) of 5.5 mm. The third approach treated all HOAs and included only the sphere and cylinder embedded within the HOA ablation profile, as calculated by the ORK CAM software for the SCHWIND AMARIS (SCHWIND eye-tech-solutions GmbH). All models were simulated on the ORK module, with OZ ranging from 5.5 to 7 mm. The primary outcome measure was the mean stromal ablation depth over the cone and was calculated for all possible scenarios.
Results
In approach #1, the mean cone stromal ablation depths and ablation volumes were 49 ± 28, 58 ± 34, 68 ± 40, and 77 ± 46 µm, and 1,074 ± 626, 1,460 ± 863, 1,906 ± 1,113, and 2,448 ± 1,451 nl for an OZ of 5.5, 6, 6.5, and 7 mm, respectively (P < .001). Approach #2 yielded mean depths and volumes of 33 ± 13, 38 ± 15, 44 ± 17, and 50 ± 19 μm, and 686 ± 266, 939 ± 371, 1,240 ± 489, and 1,592 ± 669 nl, respectively (P < .001). In approach #3, the corresponding depths and volumes were 15 ± 6, 17 ± 7, 19 ± 7, and 21 ± 8 µm and 279 ± 89, 377 ± 118, 491 ± 146, and 626 ± 205 nl, respectively, across the same OZ range (P < .001). There was a significant difference in mean cone stromal ablation depths and ablation volumes among the three approaches across all OZs, with approach #3 consistently demonstrating the lowest ablation depths and ablation volumes (P < .001). Furthermore, the rate of increase in mean stromal ablation depth over the cone with expanding OZ size was minimal in approach #3.
Conclusions
Treating only the sphere and cylinder embedded into the HOA ablation treatment profile leads not only to the slimmest ablation depth over the cone and ablation volume, but, more importantly, it provides the lowest increase in ablation depth with enlargement of the OZ.