Modified prolate IOL compensates for changes due to aging

Eugene, OR-The Tecnis Z9000 modified prolate IOL (AMO) improves functional vision by eliminating positive ocular spherical aberration, which increases by 0.15% a year, according to Mark Packer, MD, FACS.

"The term 'functional vision' describes the impact of sight on the quality of life," explained Dr. Packer, clinical assistant professor, Casey Eye Institute, Oregon Health & Science University, Eugene. "Recognizing faces and facial expressions, reading the newspaper, driving at night, performing vocational tasks, and participating in recreational pursuits all bear a relation to functional vision for ophthalmic patients.

An important component of functional vision is contrast sensitivity. Dr. Packer said that contrast sensitivity declines with age even without the presence of ocular pathologies such as cataract, glaucoma, or age-related macular degeneration.

Retinal image quality

"It has been shown that spherical aberration of the human lens increases with age, but the amount of spherical aberration in the human cornea remains constant or tends to increase only slightly with age," he continued. "A young lens counteracts much of this defect by inducing negative spherical aberration, whereas the aging lens fails to compensate for corneal aberrations."

One drawback with conventional spherical IOLs is that they have positive spherical aberration, he said. Because of this, the contrast sensitivity of pseudophakic patients is no better than that of their age-matched counterparts who do not have cataract, Dr. Packer added.

"Patients who have undergone a previous IOL surgery show statistically significant elevations of fourth-order spherical aberration and total wavefront variance for pupil sizes greater than 5 mm compared with normal subjects," he said.

Modified prolate IOL concept