Depth of Focus Comparison Between Acrysof IQ and Acrysof Natural IOLs

Cataract is prevalent throughout the world and IOLs are routinely implanted after the extraction of the cataractous lens. It is the most frequently performed surgery in the United States with an estimated 2-3 million procedures performed annually. With the aging population on the rise, as well as the increasing popularity of refractive intraocular lenses, the number of intraocular surgeries continues to rise.

Over the years, evolution of IOLs has broadened surgeon's armamentarium following cataract extraction. Traditionally spherical IOLs have been routinely implanted following cataract extraction for the correction of aphakia. Even though these IOLs improved the patient vision to 20/20 in most of the times, they did nott address the spherical aberration of the optical system.

Normally the cornea has a positive spherical aberration. Spherical aberration means that the light rays falling on the eye's periphery are either more (positive spherical aberration) or less (negative spherical aberration) refracted than the axial rays. Such aberration usually affects the functional vision of the patient such as contrast sensitivity, depth of focus (ability to see far, near and intermediate) and the perception of glare and haloes. Corneal spherical aberration is adequately neutralized by the negative spherical aberration of the crystalline lens until the age of 40. (1) When the cataractous lens is removed, the corneal spherical aberration is no longer neutralized and the optical system will have now a net positive spherical aberration.

Conventional IOLs implanted after phacoemulsification result in a spherical aberration of approximately 0.08 µm adding to the already positive corneal aberration of the eye. (2, 3) In order for the patient to reach the optimal functional vision, efforts have led to the development of the aspheric IOLs. Aspheric IOLs compensate for the positive spherical aberration of the cornea. They have been shown to improve the functional vision and optical quality in pseudophakic patients. (4, 5)

Acrysof IQ, an aspheric IOL was introduced after gaining FDA approval in May 2006. Its shares the basic design features of the Acrysof Natural IOL with the modifications of its optic design to acquire a posterior prolate surface reducing its central thickness. Unlike the cornea, it introduces negative spherical aberration (0.2 µm) that lowers the spherical aberration of the eye.(6) It has been reported to provide better contrast sensitivity, quality of vision and fewer aberration with the aspheric IOL compared to the conventional (spherical) IOL.(6,7,8) However, some studies have found that conventional (spherical) IOLs have better depth of focus than aspheric IOLs allowing the patient to achieve better intermediate and near vision.(5) Conversely, Mester et al found no difference in depth of focus between both IOLs.(7)

The purpose of this study is to evaluate and compare depth of focus and visual outcomes in eyes receiving the aspheric Acrysof IQ and those receiving the spherical Acrysof Natural IOL after routine cataract extraction.