Small-aperture intraocular lens tolerance to induced astigmatism

Robert Edward Ang

Department of Cornea and Refractive Surgery, Asian Eye Institute, Makati City, Philippines

Purpose: This prospective, single-site study aimed to assess the corresponding change in monocular visual acuity with induced astigmatic defocus in subjects implanted with a small-aperture intraocular lens (IOL).
Patients and methods: Ten subjects with a mean age of 65.1 years were recruited. Eleven eyes of these 10 subjects were implanted (9 unilaterally, 1 bilaterally) with an IC-8 small-aperture IOL. Baseline manifest refraction and best-corrected distance visual acuity were measured with a Snellen chart (Tumbling E chart). Astigmatic defocus was induced in the same axis as the manifest sphere-cylinder refraction or at 180° for a spherical refraction. Cylinder defocus was reduced in 0.50 D steps from -2.50 D, and distance visual acuity was measured at each level of defocus.
Results: Mean distance visual acuity was 0.08 logarithm of minimum angle of resolution (logMAR) ±0.08 (20/24) at 1.50 D of defocus, 0.18 logMAR ±0.08 (20/30) at 2.00 D of defocus, and 0.24 logMAR ±0.07 (20/35) at 2.50 D of defocus. Eight out of 10 subjects achieved 20/25 or better vision with 1.50 D of cylinder defocus, and all subjects were 20/30 or better. Ten out of 11 subjects were 20/40 or better with 2.50 D of defocus.
Conclusion: The IC-8 IOL shows good tolerance to astigmatic defocus with minimal effect on visual acuity. Overall, 20/25 or better distance acuity was maintained through 1.50 D cylinder defocus.

Keywords: multifocal intraocular lenses, extended depth of focus lenses, refractive errors, cataract