Intraocular Lens - Monofocal V. Multifocal
Author: Sherman Winston Reeves, M.D., M.P.H., Reviewed by: Richard L. Lindstrom, M.D. 

Definition

An intraocular lens (IOL) is a prosthetic lens implant that is placed in the eye after a cataract is removed or during refractive lens exchange surgery. These lenses are made of plastic or silicone and stay permanently in the eye after removal of the eye’s natural crystalline lens. Intraocular lenses may be either monofocal or multifocal. Monofocal lenses have a single zone of clear focus, usually set for excellent distance vision, but require the use of reading glasses for near tasks, like reading or sewing. Others, called multifocal lenses, have several zones of clear vision and allow for both distance and near correction.

How do monofocal and multifocal lenses work?

When light enters a monofocal lens, it is bent to a focus point. As the power of the lens becomes stronger, its ability to bend light more sharply is increased. Since the lens is monofocal, the light can only be bent to one focus point at a time. With monofocal IOLs, the light is bent by the lens so that it will form a focus point on the retina of the eye. A surgeon can choose an IOL that focuses light best coming from distant objects, or a stronger powered IOL that focuses light better from near objects. However, light cannot be focused from both distant and near objects at the same time with a monofocal lens. Most patients choosing a monofocal lens choose to have good distance focus, and use reading glasses to help with near vision tasks.

Monofocal lens bending light from a distant object to a single focus point	A more powerful monofocal lens bends light from a near object to a single focus point

Multifocal lenses, however, incorporate both distance and near powered lenses into one lens. The lower powered zones bend light coming from distant objects to a single focal point on the retina. The higher powered zones bend light from near objects to the same focal point on the retina. Thus, different zones of lens power work together to provide simultaneous near and distance vision.

A multifocal lens can bend light from distant objects and near objects to a single focal point simultaneously

Several types of multifocal IOL lenses are currently available for implantation in the eye. The ReZoom™ lens and the ReStor™ lens are two commonly used lenses that work by the multifocal lens principle. Each lens incorporates ring-shaped zones of differing optical power to provide a multifocal effect.

ReZoom Multifocal Lens	ReStor Multifocal Lens

A third lens, the Crystalens™, works in a different manner to provide a multifocal effect. By moving forward in the back of the eye on small hinges, the lens can change its power in the eye, similar to the process of accommodation of the eye’s natural lens. Hence, the crystalens is called an accommodating lens, and can provide both near and distance focus.

Crystalens accommodating lens

What are the Pros and Cons of Monofocal lenses?

There are several positive features of monofocal intraocular lenses (IOLs). First, the latest generation of monofocal IOLs which employ aspheric lens technology offer the sharpest image of any available IOL. Examples of aspheric IOLs are the Tecnis™ IOL, the AcrySoft IQ™ IOL and the Sofport™ IOL. Due to their aspheric design, these lenses provide excellent contrast sensitivity and an extremely high quality of vision in a variety of lighting conditions. Individuals who require excellent distance vision, such as golfers, or those who frequently drive at night may be well suited with an aspheric monocular IOL. People who have some forms of eye disease, such as macular degeneration or glaucoma may also benefit from an aspheric monocular IOL. For these individuals, the compromised state of the retina or nerves of the eye should be assisted by forming the sharpest image possible on the retina, such as that with an aspheric lens. Lastly, monofocal lenses are typically covered by insurance and Medicare, such that the choice of this lens usually requires no additional out-of-pocket payment from a person undergoing eye surgery.

However, only one zone of clear vision can be chosen with a monofocal lens. Most people choose to have their monofocal lens set for distance vision and use reading glasses for near tasks. Alternatively, a monofocal lens can be set for near vision, but glasses or contact lenses are then required to see objects clearly at a distance. A blending of these two approaches is also available for individuals undergoing cataract surgery or natural lens replacement in both eyes. In this approach, called monovision, the monofocal IOL placed one eye can be set for distance and the IOL placed in the other eye targeted for near. While 85% of people can adapt to monovision correction, a small percentage of people, however, may feel off-balance with this approach.

What are the Pros and Cons of Multifocal lenses?

The main advantage offered by multifocal lenses is the opportunity to become less dependent on reading glasses for near activities. For many people, presbyopia, the loss of the eye’s ability to zoom from distant to near objects, is very frustrating. Activities that were once easily enjoyed without glasses, such as reading or sewing, now require that a pair of reading glasses always be available. For people frustrated by the need for reading glasses, multifocal lenses offer a good alternative.

For example, in the FDA trial of the ReSTOR multifocal lens, 84% of ReSTOR patients achieved simultaneous 20/25 distance vision, which is a single line away from perfect 20/20 vision, and near vision which allowed newsprint to be easily read. However, only 23% of patients with monofocal IOL lenses in the same study were able to achieve those levels of distance and near vision simultaneous. The clinical trials for the ReZoom multifocal IOL and crystalens accommodating IOL also demonstrated markedly better simultaneous near and distance vision with these lenses compared to traditional monofocal IOLs.

The trade-off for simultaneous distance and near vision with multifocal lenses is a higher amount of optical aberrations produced by the lenses multifocal optics. Typically, these aberrations are perceived as glare in certain low lighting situations and halos around light sources at night. Most people with multifocal lenses find these aberrations to be only mildly annoying. In fact, the brain tends to adapt to them with time. However, full adaptation may take several months. Additionally, multifocal lenses usually need to be implanted in both eyes before full adaptation can occur. Also, since the optics of these lenses split the light, the image formed on the retina is slightly less perfect than that which can be formed by an aspheric monofocal IOL. Hence, a small amount of image quality may also be sacrificed to gain the multifocal effect. The vast majority of people with multifocal implants are very happy with them and would chose to have them placed again. However, a small minority of patients do not adapt to the lenses well or are very bothered by the glare and halos that can occur with them. Your surgeon will discuss the pros and cons of these lenses with you and help you make the best choice about what kind of lens you should have implanted.