Exploring A Novel Approach To Irregular Astigmatism: A Small Aperture Lens With Toric Correction

IC-8 Apthera (Bausch + Lomb) is a presbyopia-correcting intraocular lens (IOL) that uses the pinhole effect to extend the depth of focus, which can also be used in challenging cases. While reports indicate the suitability of a small aperture in irregular astigmatism, the remaining regular component may still affect vision. The potential benefits of combined small-aperture and toric correction were explored.

David J. Apple Center for Vision Research, Department of Ophthalmology, University of Heidelberg, Germany.

Scheimpflug topography results of patients with irregular astigmatism were evaluated. Elevation maps were extracted and entered into a customized eye model build using ray-tracing software. Pseudophakia was simulated with a +20D IOL, and the optical quality was assessed under three conditions: (1) standard toric correction, (2) the small aperture without a toric surface, or (3) the small aperture with the toric surface. A standard toric range was applied. The root mean square (RMS) of monochromatic aberrations and the Strehl ratio were calculated to determine the eye’s optical function. The Strehl ratio ranges from 0 to 1, with 1 indicating the highest attainable image quality.

Standard toric correction showed low efficiency, with an average cylinder power of 3.0 ± 1.3D applied. Under the toric-IOL condition, RMS was 0.59 ± 0.24 µm, and the Strehl ratio was 0.11 ± 0.10. A small-aperture lens improved the Strehl ratio (0.26 ± 0.25) and reduced RMS (0.17 ± 0.08 µm), but its remaining part demonstrated a significant correlation with Pentacam asymmetry indices (R2 = 0.58 to 0.78, p<0.05). Combining the small-aperture lens with a toric surface further reduced RMS (0.13 ± 0.07 µm) and improved the Strehl ratio (0.79 ± 0.17). Statistical comparisons among the three approaches showed significant differences favoring the combined correction. 

The small-aperture lens may mitigate the effects of irregular astigmatism in cases where standard toric correction is inefficient. However, its efficacy can be further enhanced by combining it with additional toric correction, leading to improved optical quality and potentially enhancing visual outcomes of patients with irregular astigmatism.