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Standard lens implants are single-focus lenses ("monofocal" lenses). Monofocal lenses have for decades been the default lenses used to replace a cloudy natural lens during cataract surgery. Following surgery with monofocal lenses, if distance vision is clear, then objects within arm's reach are blurry (viewing a computer monitor, cell phone, wrist watch, restaurant menu, etc).

The Crystalens is one of a new class of lenses that uses the eye's own focusing muscles to adjust focus from distance to near, enabling a wider range of vision than what monofocal lenses provide. The newest-generation Crystalens, the AO, became available in January 2010. The aspheric optic enables slightly improved night vision compared to older models, but preserves focus across a rather wide focal range.

To understand the full benefit of the Crystalens in comparison to older-style monofocal lens implants, it is important to understand the principles of accommodation and accommodative amplitude.

This lens responds to the "pull" of the focusing muscles within the eye, slightly shifting its position in response to close focusing or accommodative effort. For distance viewing (when the ciliary muscles are relaxed), the lens sits slightly further back in the eye. When focusing on a near target (and ciliary muscles are contracting or under tension), the lens optic is moved slightly more forward in the eye, causing a focus shift. See the graphic at bottom of page for a visual demonstration.

The Crystalens is not a perfect replacement for the eye's natural lens; at best earlier versions had accommodative capacity in the range of about 1.5 diopters (close focus clearly to about 26"). The Crystalens affords improved distance, intermediate and near vision compared to monofocal IOLs. Reading glasses may still be necessary for sustained reading of small print.

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