• What are cataracts?
• What are the symptoms of cataracts?
• Who is at risk for cataracts?
• What causes cataracts?
• How are cataracts diagnosed?
• How are cataracts treated?
• Additional resources

Before intraocular lenses (IOLs) were developed, people had to wear very thick eyeglasses or special contact lenses to be able to see after cataract surgery. Today several IOL types are available to help people enjoy improved vision. Discuss these options with your Eye M.D. to determine the IOL that best suits your vision needs and lifestyle.

How IOLs work
Like your eye’s natural lens an IOL focuses light as images, received from the cornea and pupil at the front of the eye, onto the retina, the sensitive tissue at the back of the eye that relays images through the optic nerve to the brain. Most IOLs are made of a flexible, foldable material and are about one-third of the size of a dime.  Like the lenses of prescription eyeglasses, your IOL will contain the appropriate prescription to give you the best vision possible. Read below to learn about how IOL types correct specific vision problems.

Which IOL is right for you?

• Before surgery your eyes are measured to determine your IOL prescription, and you and your Eye M.D. decide which IOL type will be best for you, in part depending on how you feel about wearing glasses for reading and near vision.
• The type of IOL implanted will affect how you see when not wearing eyeglasses. Glasses may still be needed by some people for some activities.
• If you have astigmatism your Eye M.D. will discuss toric IOLs and related treatment options with you.

IOL types

Monofocal: This IOL type has been in use for several decades.

• Monofocals are set to provide best corrected vision at near, intermediate or far distances.
• Most people who choose monofocals have their IOLs set for distance vision and use reading glasses for near activities. On the other hand, a person whose IOLs were set to correct near vision would need glasses to see distant objects clearly.
• Some who choose monofocals decide to have the IOL for one eye set for distance vision, and the other set for near vision, a strategy called “monovision.” The brain adapts and synthesizes the information from both eyes to provide vision at intermediate distances. Often this reduces the need for reading glasses. People who regularly use computers, PDAs or other digital devices may find this especially useful. Individuals considering monovision may have a trial with monovision contact lenses to learn how well they can adapt to monovision. Those who require crisp, detailed vision may decide monovision is not for them. People with appropriate vision prescriptions may find that monovision allows them see well at most distances with little or no need for eyeglasses.
• Presbyopia is a condition that affects everyone at some point after age 40, when the eye’s lens becomes less flexible and makes near vision more difficult, especially in low light. Since presbyopia makes it difficult to see near objects clearly, even people without cataracts need reading glasses or an equivalent form of vision correction.

Multifocal or accommodative: These newer IOL types reduce or eliminate the need for glasses or contact lenses.

• In the multifocal type, a series of focal zones or rings is designed into the IOL. Depending on where incoming light focuses through the zones, the person may be able to see both near and distant objects clearly.
• The design of the accommodative lens allows the eye’s ciliary muscles to move the IOL forward and backward, thus allowing the focus to change much as it would with a natural lens and enabling near and distance vision.
• The ability to read and perform other tasks without glasses varies from person to person but is generally best when multifocal or accommodative IOLs are placed in both eyes.
• Usually 6 to 12 weeks are required after surgery on the second eye for the brain to adapt and for full visual improvement to be realized with either of these IOL types.

Considerations with multifocal or accommodative IOLs

• For many people, these IOL types reduce but do not eliminate the need for glasses or contact lenses. For example, a person can read without glasses, but the words appear less clear than with glasses.
• The effectiveness in a specific person may depend on the size of his/her pupils and other eye health factors. People with astigmatism can ask their Eye M.D. about toric IOLs and related treatments
• Side effects such as glare or halos around lights, or decreased sharpness of vision (contrast sensitivity) may occur, especially at night or in dim light. Most people adapt and are not bothered by these effects, but those who frequently drive at night or need to focus on close-up work may be more satisfied with monofocal IOLs.

Toric: This is a monofocal IOL with astigmatism correction built into the lens.

• Astigmatism: This eye condition distorts or blurs the ability to see both near and distant objects. With astigmatism the cornea (the clear front window of the eye) is not round and smooth (like a basketball), but instead is curved like a football. People with significant degrees of astigmatism are usually most satisfied with toric IOLs.
• People who want to reduce (or possibly eliminate) the need for eyeglasses may opt for an additional treatment called limbal relaxing incisions, which may be done at the same time as cataract surgery or separately. These small incisions allow the cornea’s shape to be rounder or more symmetrical.

Protective filters: IOLs include filters to protect the eye’s retina from exposure to UV and other potentially damaging light radiation. The Eye M.D. selects the filters that will provide appropriate protection for the patient’s specific needs.

Other important considerations

• If, after healing completely from the initial cataract removal and IOL implantation, a person needs further correction to achieve the best vision possible, the Eye M.D. may recommend additional surgery to exchange an IOL for another type, implant an additional IOL, or make limbal relaxing incisions in the cornea. Other laser refractive surgery may be recommended in some cases.
• People who have had previous refractive surgery such as LASIK need to be especially carefully evaluated before receiving IOLs because the ability to calculate the correct IOL prescription (PDF 650K) may be affected by the previous refractive surgery.

Last reviewed and updated in March 2010,
by the American Academy of Ophthalmology.