Basic and mixed multifocal IOLs
Since standard monofocal IOLs can only provide clear distance vision and require patients to wear reading glasses for close vision, presbyopia-correcting IOLs with multifocal designs are approved to offer clear vision at multiple distances. There are three brands of multifocal IOLs that are FDA-approval: AcrySof IQ ReSTOR, ReZoom and Tecnis.
The original version of AcrySof IQ ReSTOR changes the way light is directed when it falls on its different zones to achieve vision at multiple distances, while the newer version provides better intermediate vision. ReZoom is actually an upgrading of the Array IOL and uses different zones within concentric rings for multiple focuses. Tecnis also uses a diffractive lens design and has gained both satisfying distance vision and near vision. In the future, toric designs may be applied to multifocal IOLs, so as to provide additional astigmatism correction.
Even though their candidates only account for 5% to 10% of all cataract patients, some surgeons are still considering the idea of mixing and matching IOLs. For instance, they may use the new version of AcrySof IQ ReSTOR to enhance intermediate vision in one eye and the original ReSTOR to bring sharper near vision in the other eye. This is exactly an application of monovision.
If monovision is applied to single vision IOLs, the traditional problems such as uncoordinated eyes may occur, which leads to amblyopia or lazy eye. Since multifocal IOLs themselves can provide vision at multiple distances, monovision with multiple IOLs can maintain stereopsis and avoid amblyopia. Several combinations of different types of IOLs are reported to provide high rates of independence from eyeglasses.
Multifocal IOLs are not suitable for extreme perfectionists, since their expectations can hardly be met. In fact, some people are not good candidates for multifocal IOLs. People requiring great night vision should not receive multifocal IOLs, because these IOLs may cause night glare and halos. Multifocal IOLs should still exclude people with high level of astigmatism, retinal diseases, perfect near vision or low to moderate degrees of myopia.
There are also many people who are favored to receive multifocal IOLs. For patients’ eye conditions, those with good general health and active lifestyles, individuals having presbyopia and people with high level of myopia are more likely to get enough satisfaction. People who are easy-going and realistic in their expectations as well as those are willing to accept tradeoffs are also good candidates for multifocal IOLs.
After receiving an IOL implantation, the patient should visit the doctor periodically, in case of some implant-related changes. Another important factor that the patient should know is that multifocal IOLs require out-of-pocket fees, because most Medicare and insurance plans only cover standard IOLs.
Approved and investigational accommodation IOLs
As we know, some people above 40 can not see clearly at multiple distances, which is caused by the lens’ natural aging and becoming rigid to move smoothly. Among all of the IOLs, accommodation IOL such as the Crystalens has a special design to treat the described presbyopia. An accommodation IOL provides sharp vision by shifting its position with the action of eye muscle and movement, rather than by simply replacing the natural lens. Accommodation IOLs belong to presbyopia-correcting IOLs, so that patients can get multiple distance vision from them.
Firstly approved in 2003, the Crystalens is the only IOL that uses accommodation technology. Bausch & Lomb now is marketing several versions of Crystalens. The newest version claims that it has better near vision and lower side effects.
Among the four types of presbyopia-correcting IOLs, Crystalens IOL is unlike the other three types, which are called multifocal IOLs. Multifocal IOLs perform just like multifocal lenses that the patient should look through an appropriate zone to get certain distance vision. However, IOLs are much smaller than contact lenses, so that these divided zones on IOL are too small to provide clear single vision. Using accommodation, Crystalens can always maintain one focusing zone for any distance vision. A disadvantage of Crystalens IOL is that it provides a narrowed range of focus.
Patients should be aware that neither monovision IOLs nor presbyopia-correcting IOLs can provide perfect vision. Even standard monofocal IOLs may bring night glare and halos. This situation is also true for Crystalens IOLs, which suit people with both presbyopia and cataract. In addition to common complications, Crystalens is reported to bring potential astigmatism and posterior capsule clouding.
Besides Crystalens, there are several types of accommodation IOLs that are still under tests. Approved in Europe, the Synchrony IOL is undergoing clinical trials in US. Synchrony has been proved to bring fewer visual distortion and better intermediate distance vision than ReSTOR. Another type is Tetraflex, which has a square-edged, acrylic optic.