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An intraocular lens (IOL) is an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract, or as an alternative to refractive surgery when this procedure is contraindicated. It usually consists 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 (FDA) approved lens called Crystalens whose position can be changed by the ciliary muscles of the eye, allowing for natural focusing. The drawback is the added expense of the lens and the need for a larger corneal incision for implantation.

History

Sir Harold Ridley was the first to successfully implant an intraocular lens on November 29, 1949, at St Thomas' Hospital at London. That first intraocular lens was manufactured by the Rayner company of Brighton, East Sussex, England from Perspex CQ made by ICI.

Phakic, aphakic and pseudophakic IOLs

  • Phakia is the presence of the natural crystalline lens.
  • Aphakia is the absence of the natural crystalline lens, either from natural causes or because it has been removed.
  • Pseudophakia is the substitution of the natural crystalline lens with a synthetic lens. Pseudophakic IOLs are used in cataract surgery.

The root of these words comes from the Greek word phakos 'lens'.

Intraocular lenses for correcting refractive errors

Intraocular lenses have been used since 1999 for correcting larger errors in myopic (near-sighted), hyperopic (far-sighted), and astigmatic eyes. This type of IOL is also called PIOL (phakic intraocular lens). Most PIOLs have not yet been approved by FDA, but many are under investigation, and some of the risks that FDA have been found so far during a three year study of the Artisan lens, produced by Ophtec USA Inc, are:

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.
  • glaucoma,
  • 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 either in front of the iris or in between the natural lens and the iris.

Intraocular contact lenses

Very different from contact lenses that are placed on the surface of the eye, an intraocular contact lens, also known as an implantable contact lens, is a small corrective lens that is surgically placed in the eye's posterior chamber behind the iris and in front of the lens to correct higher amounts of myopia and hyperopia.

The procedure

An eye examination or pre-operative evaluation by an eye surgeon is necessary to confirm the presence of a cataract and to determine if the patient is a suitable candidate for surgery. The patient must fulfill certain requirements, such as:

  • The eyes must not have changed significantly in the last few years, which mean that younger people cannot undergo PIOL surgery, since their eyes are still growing.
  • The eyes must have a normal pressure (i.e. cannot have glaucoma).
  • The iris must be normal.
  • The size of the pupil must be within a certain range.
  • The patient 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 the eye, causing astigmatism, and/or damage to the natural lens. It can also block the natural flow of fluid inside the eye, causing glaucoma. The size is usually estimated, by measuring white-to-white, and estimating the ciliary sulcus diameter. 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, requiring a number of weeks before the surgery. The patient will receive either pupil dilating drops (if the lens is to be fitted behind the iris), or pupil constricting drops (if the lens is to be fitted in front of the iris). The patient will also get local anesthetics in the eye, and tranquillizing medicines, if desired. Once the medicines have taken effect, the patient will enter the operating room and be seated in a chair which reclines like a dentist's chair, and the eyelids, and surrounding skin will be swabbed with disinfectant. The face will be covered with a cloth, with a hole for the eyes. The eye will be held open with a speculum so that the patient cannot blink during the surgery. The surgeon starts by making the incisions that 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 leak fluid, and the patient is 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 can be done in two ways: either surgically by first lifting up the front layer of the iris and cut away a small portion, and then make a small hole in the pigment/back layer of the with a suction device - called iridectomy. The other alternative is with a laser a couple of weeks before the lens surgery - called laser peripheral iridotomy.

The hole is larger when done surgically, and some of the negative effect are that it can be seen by others (aesthetics), and that light can fall into the eye through the new hole creating visual disturbances (blurry images on top of the normal view). In the case of visual disturbances, the eye and brain often learns to compensate and ignore the disturbances over the couple of months. One negative effect with laser peripheral iridotomy is that the hole can heal, which means that the hole ceases to exist, meaning there is no "emergency release valve". Therefore, the surgeon often makes two holes, so that at least one hole is open.

No pain at all is felt during the procedure, and the only discomfort is from 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, the patient will be instructed to keep the eyes clean, and avoid infectious environments (such as saunas, swimming pools), and to take eye drops - anti-inflammatory and antibiotics for the time it takes the eye to heal completely. The eye will be mostly recovered within a week, and complete recovery should be expected in about three weeks. The patient must not lift heavy things, do anything that elevates the blood pressure. Also, the patient should avoid contact/extreme sports within the next several months.

IOL manufacturers and materials

There are many different manufacturers of intraocular lenses.

Acrylic:

Silicone:

  • AMO (Advanced Medical Optics) produces the Verisyse™ lens.
  • 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.
  • The PRL™ Phakic Refractive Lens is produced by Medennium, distributed by IOLTech.

Other:

  • Staar produces the Visian ICL™ lens, in a material called Collamer®.

More information about PIOLs

See also

Notes

References

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Corrective lenses | Lenses

Intraokularlinse | Lente Intraocular

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Intraocular lens".

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