Accommodating and Multifocal IOLs
In past years, intraocular lenses (IOLs) were fixed focus (monofocal) only, usually fixed for distance vision. They were used to treat cataracts in a Clear Lens Exchange (CLE). The other alternative was monovision, which corrects one eye for distance and the other for near vision.
Accommodation Lost With the Lens
The problem with removing the eye’s lens is that accommodative ability goes with it. Accommodation is done by the lens, with the ciliary muscles on each side of it controlling its curvature. They increase its curvature for light coming from far objects, and flatten it for light coming from nearby objects. This is because light from far objects needs less refraction (bending) than light from near objects, in order to focus clearly on the retina.
Accommodation happens naturally and automatically as we switch our focus. A monofocal lens has no accommodative ability.
IOLs to Mimic Accommodation
The FDA has approved two multifocal IOLs (ReZoom® and ReSTOR™) and one accommodating IOL (Crystalens). Using three different technologies, they provide focused vision in distance, near and mid-ranges, and are used to correct both cataracts and presbyopia.
Crystalens, marketed by Bausch & Lomb, is controlled by the same muscles that previously controlled the natural lens. The muscles move it forward to mimic steeper curvature (near vision) and backwards to mimic flatter curvature (distance vision). To the person with Crystalens implants, there is subjectively no difference in how the eyes feel. The Crystalens design provides the best night vision of the three multi-distance IOLs. This is especially valuable for people who do a lot of night driving.
On June 30, 2008, Bausch & Lomb announced that FDA approval had been given to their fourth generation Crystalens, called Crystalens HD™. It has been reshaped to give clearer close-up vision without sacrificing any clarity of intermediate or far vision.
Tecnis, by Abbott, is an IOL designed to restore vision to full clarity. It is especially suited to see in low-light situations, like driving at night or walking outside in foggy weather. The Tecnis IOL comes in three varieties:
- Tecnis® 1-Piece IOL
- Tecnis® Acrylic IOL
- Tecnis® CL IOL
Ask your ophthalmologist about which Tecnis IOL is best for your eyes. Each has different advantages.
ReZoom, by Advanced Medical Optics, Inc., is a multifocal IOL that provides five zones of focus. Unlike Crystalens, it is not controlled by the eye muscles, but is stationary. Distance and midrange vision are corrected immediately, but glasses may be needed for near vision, such as reading. There is generally no period of adjustment to ReZoom IOLs. There may be some night glare from lights, such as headlights, so this may not be the best choice if you do a lot of night driving.
ReSTOR, by Alcon, Inc. is another multifocal lens that is stationary. It is made of a proprietary substance named Acrysof®. It provides good distance and near vision by stepping the focusing power gradually across the surface of the lens. Mid-range vision may be less clear than with ReZoom or Crystalens, and glasses may be required for that range, (computer use or other vision at about arm's length). Like ReZoom, this lens may cause halos around lights and may not be the best choice for people who do a lot of night driving.
Please refer to this chart for help in understanding the differences between IOLs.
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