A Lens Implant with Adjustable Focus
The Crystalens™ implant is intended to accommodate or adjust for close focus. It is not a perfect replacement for the eye’s natural lens; at best it can accommodate to a limited extent (about 1.5 diopters), slightly less than the accommodative capacity of the young adult eye (about 4.0 diopters). However, it can certainly allow improved distance, intermediate and near vision compared to previous monofocal lens designs. Glasses may still be necessary for sustained reading of small print.
The Crystalens enables people over 50 to:
- Reduce or eliminate pre-existing near- or far-sightedness, and
- Restore a significant amount of close-focusing capability
The combination of clear distance, intermediate and near vision creates the potential to see clearly without glasses at all these ranges!
Crystalens Technology
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.
How does the Crystalens Work?
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.
A Crystalens can be placed only at the time of initial cataract or lens replacement surgery. The Crystalens is placed within a thin membranous sheath called the lens capsule, which is connected to the ciliary muscle (focusing muscle of the eye) by tiny fibers called zonules. The capsular bag thus functions to suspend and support the lens implant in a fashion analogous to a hammock.
Dr. David Wallace is a highly skilled lens implant surgeon. He has treated thousands of Los Angeles cataract patients. He has treated many cataract patients, as well as those seeking clear lens replacements.
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Recover Clear Vision at Far and Near
In our busy, multi-tasking world, we want to — need to — see perfectly at many different distances. We all read, use cell phones, tablet devices, desktop computers. We read newspapers, magazines, books, and the tiny print on prescription medication bottles when necessary. We enjoy athletic pursuits and sports, most of which benefit from exceptional vision at far distance. When we drive, we want to see freeway signs hundreds of yards away, and our dashboard, and occasionally check email or texts on our phones (OK, when we’re stopped, or parked, officer :->).
So as good as monofocal IOLs may be, they’re not close to a perfect solution. We still have not developed the perfect, adjustable-focus IOL to replace the natural young human lens, but multifocal IOLs add a whole set of features and benefits that are not possible with monofocal IOLs.
Multifocal IOLs work by having concentric zones of different focus, alternating far and near. This affords very good distance and reading clarity. These lenses do need to optically split the incoming light into two points of focus, so they do cause some reduction in contrast sensitivity (fine detail detection in low light). And the concentric rings do cause a bit of halo to be perceived around point sources of light at night such as headlights, taillights and street lights. The overwhelming majority of people that have had multifocal IOLs implanted are extremely happy with their overall visual function, and don’t mind these imperfections, which they perceive to be minor. Whether you will be an optimal candidate for multifocal IOL care will be assessed and discussed at your comprehensive cataract and IOL consultation.
The Tecnis Multifocal
The Tecnis Multifocal IOL is designed to afford very good focus at both distance and near. Nearly 9 out of 10 patients are able to enjoy a glasses-free vision after they receive the Tecnis Multifocal IOL.
The Tecnis Multifocal has its multifocal optic on the rear lens surface. By comparison, The ReSTOR (see below) is designed with its multifocal optic on the front IOL surface.
The ReSTOR Multifocal
The ReSTOR lens has a design similar to single-focus lenses. The difference is that the center section of the front optical surface has concentric rings of differing focus, alternating for distance and near, as shown in images at right and below. Outside the zone of alternating rings, sharp distance vision is provided by the peripheral portion of the lens, like the upper part of a bifocal. The very center of the lens is tuned for near clarity, like the reading portion of a bifocal. The multiple concentric rings effect a much broader range of focus than a monofocal IOL, through both refractive and diffractive optics.
The ReSTOR lens incorporates aspheric optics for optimized distance viewing, and night driving clarity; and has an effective “add” (reading range correction) that is well-suited to common near vision tasks.
With any combination of a particular product (like a lens implant) and a service (like lens implantation surgery and refractive services) there is a wide range of information available. Some of the information is accurate, some is inaccurate, and some is anecdotal. The anecdotal category is typically difficult to evaluate.
Dr. David Wallace is a highly skilled lens implant surgeon. He has treated many Los Angeles cataract patients. He has treated many cataract patients, as well as those seeking clear lens replacements.
