Intraocular Lens Implant
A cataract is an opacity in the human lens. When the cataract is removed, it has to be replaced by an artificial intraocular lens (IOL). This allows us to correct pre-existing refractive errors, including myopia, hyperopia, astigmatism and presbyopia.
A. Types of lenses
There are 4 major types of intraocular lenses (IOL).
Monofocal IOL
Monofocal IOL gives high quality clear vision for a single focus. Depending on your needs, you can choose to have good distance vision or good reading (near) vision. The downside to a monofocal IOL is that glasses are still required after surgery. If you choose to have clear distance vision, then reading glasses are required for near work. If you choose to have good reading vision, then glasses for driving and distance vision are required.
Some patients may benefit from having monofocal IOLs implanted in both eyes but each eye has a different focus. This is known as monovision and usually the master eye is targeted for distance vision and the other eye for intermediate/near vision. Near vision is reading at about 30–40cm and intermediate vision is reading at 50–70cm.
Multifocal IOL
Due to their unique design, multifocal IOLs can give good distance, intermediate and near vision without the need to wear glasses. They are particularly suited for individuals who have to switch from one visual task to another at different distances rapidly and find wearing glasses a chore.
However, multifocal IOLs can cause glare, starburst and haloes in low lighting, e.g. driving at night and may not be suited for everyone. They are also not recommended if there is another co-existing eye problem. Current multifocal or trifocal designs have gone through many iterations and improvements over the years and the symptoms of glare and haloes with them is now much less disturbing.
Extended Depth of Focus IOL (EDOF)
Another option is an extended depth of focus (EDOF) IOL. New generations of EDOF IOLS now allow a patient to see well for far as well as at intermediate distances with minimal risk of visual disturbances like glare and haloes. What this means in practice is that with these lenses implanted and hitting the correct target refraction, a patient can see well for far and intermediate without glasses ie computers, iPads, food on the table, larger fonts on the mobile phone, etc.
Toric IOL
Toric IOLs correct astigmatism and are incorporated into a monofocal, EDOF and multifocal IOL platforms. Indeed, it is absolutely essential to correct all pre-existing astigmatism to ensure precise outcomes with good vision post-operatively regardless of which of these three IOLs are chosen.
This type of IOL is recommended if you have significant regular astigmatism. Astigmatism is a condition of the eye in which the transparent cornea is shaped like a part of an egg rather than a sphere and is present in many people. Accurate placement of a toric IOL during surgery is crucial for good outcomes. It is equally important to rest quietly especially in the first hour after cataract surgery and not undergo vigorous high impact physical exercise for the first two week to reduce the possibility of unwanted rotation of the toric lens implant. If there is significant rotation of the IOL after surgery, a second surgery may be needed to move the IOL back to its correct location.
- Very Good
- Poor
- Poor
- Good
- Fair
- Good
- Good
- Good
- Fair
- Good quality of vision with spectacles
- less spectacle dependence
- less spectacle dependence
- Reading glasses required
- Risk of glare and haloes, especially at night.
- Decreased contrast sensitivity especially in low light conditions
- Need period of adaptation
- Less risk of glare and haloes
- May need glasses for near
- All
- Individuals who have healthy eyes without previous refractive surgery
- Individuals who want to reduce their dependence on glasses for far and near vision
- Individuals who want to have good distance and intermediate vision without glasses
- None
- Individuals who have had previous refractive surgery e.g. LASIK
- Vocational drivers
- Individuals with certain existing eye conditions
- Individuals who do not wish to wear reading glasses
B. The visual correction patients can expect
Intraocular lens implants (IOLs) are implanted into the empty cataract lens bag after the cataract has been removed. This allows the surgeon to correct all types of existing refractive error; eg myopia, hyperopia, astigmatism and presbyopia. Indeed, this means that cataract surgery with IOL implantation will allow most patients to significantly improve their eyesight.
The choice of which IOL to use though can be confusing, when a patient and indeed a surgeon is faced with the plethora of available lenses.
