Study finds aspheric IOLs provide better contrast sensitivity than spherical IOLs
July 15, 2009
Researchers in Italy have found that aspheric intraocular lenses (IOLs) used in cataract surgery produce better contrast sensitivity than conventional spherical IOLs.
Their findings suggest aspheric IOLs may produce noticeably better vision for tasks in low-light conditions, such as driving at night.
Aberrations and visual performance
The quality of vision after cataract surgery is influenced by optical abberations of the eye. Spherical aberration, in particular, can cause glare and halos around lights during tasks such as night driving.
Spherical aberration and other optical abberations of the eye — also called "higher-order aberrations," or HOA — usually cannot be corrected by eyeglasses or contact lenses.
Recently, several manufacturers of lens implants used in cataract surgery and refractive lens exchange (RLE) have introduced aspheric IOLs designed to reduce spherical aberration and improve visual performance.
Unlike conventional spherical IOLs, which have the same curvature across the entire lens surface, aspheric IOLs have a surface curve that becomes flatter toward the lens periphery. This gradually changing curve is designed to more closely mimic the performance of the eye's natural lens and reduce spherical aberration.
Aspheric vs. spherical IOLs: Study design
In the Italian study, 100 people with bilateral cataracts were randomly assigned to receive either aspheric or spherical IOLs in both eyes.
Two brands of aspheric IOLs and two brands of spherical IOLs were included in the study. The aspheric IOLs were the AcrySof SN60WF (Alcon) and the Tecnis Z9000 (Abbott Medical Optics). The spherical IOLs were the AcrySof SN60AT (Alcon) and the Sensar AR40e (Abbott Medical Optics).
Participants had the same type of IOL implanted in both eyes.
All eyes were evaluated for a period of two years after surgery. Quality of vision was assessed via visual acuity, contrast sensitivity and wavefront aberration measurements.
Aspheric vs. spherical IOLS: Study results
After analyzing the study data, the researchers found:
- Both types of aspheric IOLs evaluated in the study reduced total spherical aberration, compared to the spherical IOLs.
- Though there was no significant difference in best spectacle-corrected visual acuity (BSCVA) among the four groups of eyes, eyes receiving either of the aspheric IOLs exhibited significantly better contrast sensitivity than eyes receiving the spherical IOLs.
Conclusions
The researchers concluded that both the aspheric AcrySof IOL and the aspheric Tecnis IOL provide "improved functional vision" compared to spherical IOLs, and this is due to their ability to reduce spherical aberration.
Results of the study suggest that though aspheric IOLs may not produce significantly better visual acuity in bright daylight conditions, they may offer noticeably superior vision in low light conditions such as night driving.