Aspheric IOLs provide better night vision, according to study
May 6, 2009
Aspheric intraocular lenses (IOLs) are premium lens implants used in cataract surgery and refractive lens exchange (RLE).
Manufacturers of aspheric IOLs say that because these lenses more closely mimic the shape of the eye's natural lens (that is removed during these procedures), aspheric IOLs cause fewer aberrations and provide sharper vision than conventional spherical IOLs.
Few studies, however, have compared visual outcomes of aspheric and spherical IOLs of the same material and made by the same company in a way that would definitively show whether an aspheric IOL indeed provides better vision than a conventional spherical lens implant in the same individual.
Aspheric IOLs vs. spherical IOLs: Study design
Researchers in Japan conducted a study of 41 patients who had cataracts in both eyes and underwent bilateral cataract surgery.
After the cloudy lenses were removed, one eye of each patient received an aspheric IOL (Tecnis ZA9003) and the other eye received a spherical IOL (AR40e). All lenses used in the study were foldable acrylic IOLs manufactured and marketed by Abbott Medical Optics (Santa Ana, CA).
Patients were examined two days, one week and one month after surgery. Main outcomes measured included:
- Best-corrected visual acuity (BCVA)
- Contrast sensitivity under low-light (15 lux), moderate-light (70 lux) and bright-light (180 lux) conditions
- Corneal and total higher-order aberrations (HOA)
- Amount of IOL decentration and tilt
- Pupil diameter under dark (3 lux) and bright light (250 lux) conditions
Aspheric IOLs vs. spherical IOLs: Results
Analysis of the data revealed the following results:
- Contrast sensitivity under low-light (scotopic) conditions was significantly better in eyes with aspheric IOLs than eyes with spherical IOLs.
- Eyes with aspheric IOLs had fewer total aberrations than eyes with spherical IOLs.
- There was no significant difference in contrast sensitivity between eyes with aspheric IOLs and eyes with spherical IOLs in moderate-light and bright-light conditions.
- There was no significant difference in BCVA or any other measures considered in the study between eyes with aspheric IOLs and eyes with spherical IOLs.
Conclusions
Based on the results of the study, the researchers concluded that the aspheric Tecnis ZA9003 foldable acrylic IOL yielded significantly lower total higher-order aberrations and better contrast sensitivity under scotopic (low-light) conditions than the spherical foldable acrylic IOL made by the same company.
Additional studies are needed to determine if these same advantages of aspheric IOLs are apparent with intraocular lenses made by other manufacturers.