An intraocular lens (or IOL) is an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract. They usually consist of a plastic lens with plastic side struts called haptics to hold the lens in place within the capsular bag .
Insertion of an intraocular lens is the most commonly performed eye surgical procedure; cataracts are the most common eye disease. The procedure can be done under local anesthesia with the patient awake throughout the operation which usually takes less than 30 minutes in the hands of an experienced ophthalmologist.
There are foldable intraocular lenses made of acrylic or silicone which can be rolled up and inserted through a tube with a very small incision not requiring any stitches; inflexible lenses (typically made of PMMA) require a larger incision.
Unlike the natural lens, the curvature of current intraocular lenses cannot be changed by the eye. Standard intraocular lenses provide good distance vision and the patient needs reading glasses for near vision. Newer bifocal intraocular lenses give distance vision in one area and near vision in another area of the vision field.
There is also an FDA approved lens called Crystalens whose position can be changed by the ciliary muscles of the eye, allowing for natural focusing. The downside is in added expense of the lens and the need for a larger corneal incision for implantation.
Introcular lenses for correcting refractive errors
Intraocular lenses has been used since 1999 for correcting larger errors in near sighted (myopic), far sighted (hyperopic) and astigmatic eyes. This type of IOLs are also called PIOLs (phakic intraocular lenses) Most IOLs has not yet been approved by FDA, but many are under investigation, and some of the risks that FDA has found so far during a three year study of the Artisan lens, produced by Ophtec USA Inc, are:
- a yearly loss of 1.8 % of the endothelial cells,
- 0.6 % risk of retinal detachment,
- 0.6 % risk of cataract (other studies has showed a risk of 0.5 - 1.0 %), and
- 0.4 % risk of corneal swelling.
Other risks include:
- 0.03 - 0.05 % eye infection risk, which in worst case can lead to blindness. This risk exists in all eye surgery procedures, and is not unique for IOLs.
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glaucoma,
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astigmatism,
- remaining near or far sightedness,
- rotation of the lens inside the eye within one or two days after surgery.
One of the causes of the risks above is that the lens can rotate inside the eye, because the PIOL is too short, or because the sulcus has a slightly oval shape (the height is slightly smaller than the width).
Types of PIOLs
PIOLs can be either spheric or toric - the latter is used for astigmatic eyes. The difference is that toric PIOLs has to be inserted in a specific angle, or the astigmatism will not be fully corrected, or it can even get worse.
PIOLs can also be inserted in two different ways - either in front of your iris, or in between your natural lens and your iris.
The procedure
The first thing you as a patient do is meet an eye surgeon (and probably a optician), and they will evaluate your eyes. You must fulfill certain requirements, such as:
- Your eyes must not have changed significantly in the last few years, which means that younger people cannot undergo PIOL surgery, since their eyes are still growing.
- Your eyes must have a normal pressure (i.e. you cannot have glaucoma).
- The iris must be normal.
- The size of your pupil must be within a certain range.
- You must not have retinal detachment.
After this evaluation, the eye surgeon decides the size of the PIOL - this is a very important, and also difficult task. If the lens is of incorrect length, then it can rotate inside your eye, causing astigmatism, and/or damage to your natural lens. It can also block the natural flow of fluid inside your, causing glaucoma. The size is usually estimated, by measuring white-to-white, and there guesstimate the sulcus-to-sulcus. However, the surgeon can perform 3D ultrasound biomicroscopy with for example Artemis for a completely accurate measurement. 3D ultrasound is to traditional 2D ultrasound like computer assisted tomography is to x-ray. Therefore, 3D ultrasound examination is strongly recommended, since the white-to-white guesstimate does not have a strong correlation with sulcus-to-sulcus - neither for myopic, nor for hyperopic. About 1 % of sulcus-to-sulcus estimates based on white-to-white are so wrong that serious complications can arise.
The lens is ordered from the manufacturer, and it takes a number of weeks, and then it is time for the actual surgery. You will get either pupil dilating drops (if the lens is fitted behind the iris), or pupil constricting drops (if the lens is fitted in front of the iris). You will also get local anaesthetics in the eye, and tranquilizing medicines, if you want. After a while, when the medicines has started to work, you will enter the operating room. You will sit in a chair which reclines like a dentists chair, and your eye will be swabbed with disinfectant. Your face will be covered with a cloth, with a hole for your eye. You eye will be held open so that you cannot blink during the surgery. The surgeon starts by making the incisions the he/she may or may not need, and then the actual insertion of the lens is done. After the lens is inserted, the surgeon checks that the incisions do not leek fluid, and you are done.
An "emergency release valve" is done by making one large or two smaller holes in the iris, in case the pupil is blocked, in order to avoid glaucoma. This is either done surgically with a knife after the lens is inserted, or with a laser a couple of weeks before the lens surgery.
No pain at all is felt during the procedure, and the only things which can be felt as unpleasant is the bright light from the microscope that the surgeon uses. The nurse sprays the eye with a sterile saline solution, so the eye does not dry. Afterwards, you will be instructed to keep your eye clean, and avoid infectuous environments (such as saunas, swimming pools), and to take you eye drops - antiinflammatory and antibiotics. You must not lift heavy things, do anything that elevates your blood pressure, or participate in contact/extreme sports.
IOL manufacturers
Here is a list of some of the manufacturers, and which material they use in their IOLs:
Acrylic:
Silicone:
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AMO (Advanced Medical Optics) produces the Verisyse™ lens.
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Tekia Inc. produces the Kelman Duet lens.
- The Vision Membrane phakic IOL is produced by Vision Membrane Technologies Inc., Apollo Optical Systems LLC, and Millennium Biomedical Inc.
Other:
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Staar produces the Visian ICL™ lens, in a material called Collamer®.
More information about PIOLs
History
Sir Harold Ridley was the first to successfully implant an intraocular lens on November 29, 1949, at St Thomas' Hospital at London.
See also
Last updated: 05-23-2005 01:14:22
