Intraocular lens

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 a form of refractive surgery to change the eye's optical power. It usually consists of a small plastic lens with plastic side struts, called haptics, to hold the lens in place within the capsular bag inside the eye. IOLs were traditionally made of an inflexible material (PMMA), although this has largely been superseded by the use of flexible materials. Most IOLs fitted today are fixed monofocal lenses matched to distance vision. However, other types are available, such as multifocal IOLs which provide the patient with multiple-focused vision at far and reading distance, and adaptive IOLs which provide the patient with limited visual accommodation.

Insertion of an intraocular lens for the treatment of cataracts is the most commonly performed eye surgical procedure. The procedure can be done under local anesthesia with the patient awake throughout the operation. The use of a flexible IOL enables the lens to be rolled for insertion into the capsule through a very small incision, thus avoiding the need for stitches, and this procedure usually takes less than 30 minutes in the hands of an experienced ophthalmologist. The recovery period is about 2–3 weeks. After surgery, patients should avoid strenuous exercise or anything else that significantly increases blood pressure. They should also visit their ophthalmologists regularly for several months so as to monitor the implants.

IOL implantation carries several risks associated with eye surgeries, such as infection, loosening of the lens, lens rotation, inflammation, night time halos. Though IOLs enable many patients to have reduced dependence on glasses, most patients still rely on glasses for certain activities, such as reading.

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. It is said that idea of implanting an intraocular lens came to him after an intern asked him why he was not replacing the lens he had removed during cataract surgery. The first lenses used were made of glass, they were heavy and were prone to shatter during YAG laser capsulotomy. Plastic materials were used later, when Harold Ridley noticed that they were inert, after seeing pilots of World War II with pieces of shattered windshields in their eyes. The intraocular lens did not find widespread acceptance in cataract surgery until the 1970s, when further developments in lens design and surgical techniques had come about. Currently, more than a million IOLs are implanted annually in the United States.

Materials used for intraocular lenses
Polymethylmethacrylate (PMMA) was the first material to be used successfully in intraocular lenses. British ophthalmologist Sir Harold Ridley observed that Royal Air Force pilots who sustained eye injuries during World War II involving PMMA windshield material did not show any rejection or foreign body reaction. Deducing that the transparent material was inert and useful for implantation in the eye, Ridley designed and implanted the first intraocular lens in a human eye.

Advances in technology have brought about the use of silicone and acrylic, both of which are soft foldable inert materials. This allows the lens to be folded and inserted into the eye through a smaller incision. PMMA and acrylic lenses can also be used with small incisions and are a better choice in people who have a history of uveitis, have diabetic retinopathy requiring vitrectomy with replacement by silicone oil or are at high risk of retinal detachment. Acrylic is not always an ideal choice due to its added expense. New FDA-approved multifocal intraocular lens implants allow most post operative cataract patients the advantage of glass-free vision. These new multifocal lenses are not a covered expense under most insurance plans (In the United States, Medicare decided to stop covering them in May 2005) and can cost the patient upwards of $2800 per eye. Latest advances include IOLs with square-edge design, non-glare edge design and yellow dye added to the IOL.

In the United States, a new category of intraocular lenses was opened with the approval by the Food and Drug Administration in 2003 of multifocal and accommodating lenses. These come at an additional cost to the recipient beyond what Medicare will pay and each has advantages and disadvantages.

Multifocal IOLs - provide for simultaneous viewing of both distance vision and near vision. Some patients report glare and halos at night time with these lenses.

Accommodating IOLs - allow for both distance vision and midrange near vision. These IOLs are typically not as strong for closer vision as the multifocal IOLs.

To incorporate the strengths of each type of IOL, eye surgeons are increasing using a multifocal IOL in one eye to emphasize close reading vision and an accommodating IOL in the other eye for further midrange vision. This is called "mix and match." Distance vision is not compromised with this approach, while near vision is optimized.

Other IOLs include:


 * Blue Light Filtering IOLs filter the UV and high-energy blue light present in natural and artificial light, both of which can cause vision problems.
 * Toric IOLs (1998) correct astigmatic vision.

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), and the crystalline lens is not removed.

More commonly, aphakic IOLs (that is, not PIOLs) are implanted via Clear Lens Extraction and Replacement (CLEAR) surgery. During CLEAR, the crystalline lens is extracted and an IOL replaces it in a process that is very similar to cataract surgery: both involve lens replacement, local anesthesia, both last approximately 30 minutes, and both require making a small incision in the eye for lens insertion. People recover from CLEAR surgery 1–7 days after the operation. During this time, they should avoid strenuous exercise or anything else that significantly raises blood pressure. They should also visit their ophthalmologists regularly for several months so as to monitor the IOL implants. CLEAR has a 90% success rate (risks include wound leakage, infection, inflammation, and astigmatism). CLEAR can only be performed on patients ages 40 and older. This is to ensure that eye growth, which disrupts IOL lenses, will not occur post-surgery.

Once implanted, IOL lenses have three major benefits. First, they are an alternative to LASIK, a form of eye surgery that does not work for people with serious vision problems. Effective IOL implants also entirely eliminate the need for glasses or contact lenses post-surgery. Cataract will not return, as the lens has been removed. The disadvantage is that the eye's ability to change focus (accommodate) has generally been reduced or eliminated, depending on the kind of lens implanted.

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:
 * a yearly loss of 1.8% of the endothelial cells,
 * 0.6% risk of retinal detachment,
 * 0.6% risk of cataract (other studies have shown 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.
 * 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).

NuLens Ltd. is currently in patient trials with a new Accommodative Intraocular Lens (IOL) technology with the potential to provide over 10 diopters of accommodative power. With an IOL that sits on top of the collapsed capsular bag, the NuLens Accommodative IOL may be the first intraocular lens to provide real, comfortable, and lasting accommodation for near, intermediate and far distances.

Types of PIOLs
Phakic IOLS (PIOLs) can be either spheric or toric—the latter is used for astigmatic eyes. The difference is that toric PIOLs have to be inserted in a specific angle, or the astigmatism will not be fully corrected, or it can even get worse.

According to placement site in the eyes phakic IOLs can be divided to:


 * Angle supported PIOLs: those IOLs are placed in the anterior chamber. They are notorious for their negative impact on the corneal endothelial lining, which is vital for maintaining a healthy dry cornea.


 * Iris supported PIOLs: this type is gaining more and more popularity. The IOL is attached by claws to the mid peripheral iris by a technique called enclavation. It is believed to have a lesser effect on corneal endothelium.


 * Sulcus supported PIOLs: these IOLS are placed in the posterior chamber in front of the natural crystalline lens. They have special vaulting so as not to be in contact with the normal lens. The main complications with this type is their tendency to cause cataracts and/or pigment dispersion.

Accommodating IOLs
One of the major disadvantages of conventional IOLs is that it is primarily focused for distance vision. Though patients who undergo a standard IOL implantation no longer experience clouding from cataracts, they are unable to accommodate, or change focus from near to far, far to near, and in distances in between. Accommodating IOLs interact with cilliary muscles and zonules, using hinges at both ends to “latch on” and move forward and backward inside the eye using the same mechanism for normal accommodation. These IOLs have a 4.5-mm square-edged optic and a long hinged plate design with polyimide loops at the end of the haptics. The hinges are made of an advanced silicone called BioSil that was thoroughly tested to make sure it was capable of unlimited flexing in the eye. There are many advantages to accommodating IOLs. For instance, light comes from and is focused on a single focal point, reducing halos, glares, and other visual aberrations. Accommodating IOLs provide excellent vision at all distances (far, intermediate, and near), projects no unwanted retinal images, and produces no loss of contrast sensitivity or central system adaptation. Accommodating IOLs have the potential to eliminate or reduce the dependence on glasses post-cataract surgery. For some, accommodating IOLs may be a better alternative to refractive lens exchange (RLE) and monovision.

The FDA approved Eyeonics Inc.’s accommodating IOL, Crystalens AT-45, in November 2003. Bausch & Lomb acquired Crystalens in 2008 and introduced a newer model called Crystalens HD in 2008. Crystalensis the only FDA-approved accommodating IOL currently on the market and it is approved in the United States and Europe.

Studies and Peer Reviews:

In a September 2004 FDA trial involving 325 patients :


 * 100% could see at intermediate distances (24" to 30") without glasses; the distance for most of life's activities
 * 98.4% could see well enough to read the newspaper and the phone book without glasses.
 * Some patients did require glasses for some tasks after implantation of the crystalens
 * Vision was restored to 20/40 or better in 88% of patients compared to 35.9% of patients who received normal IOLs.


 * In 2006, a 12 month study by Cummings et al. investigated contrast sensitivity and near visual acuity in patients who had received a Crystalens AT-45 versus those who received a standard IOL. Effectiveness was measured in terms of near, intermediate, and distance visual acuities and safety was evaluated by assessing complications.  The study concludedthat contrast sensitivity was not reduced compared to those receiving standard IOLs and provided good visual acuity at all distances in pseudophakic patients.  There were no adverse complications reported.  However, this study lacked a long-term follow up.
 * Pepose et al. (2007) tested the combination of a multifocal IOL in one eye and an accommodating IOL in the other eye. The group found that any combination of Crystalens in one or both eyes was better for intermediate vision. ReSTOR (multifocal IOL) is better for near vision.  The Crystalens and ReSTOR combination had better mean intermediate and near vision overall.
 * Macsai et al. (2006) conducted a multicenter, nationwide study evaluating the visual outcomes of 112 cataract patients implanted with Crystalens IOL (n=56) versus standard monofocal IOLs (n=56).  The Crystalens group demonstrated significantly better visual acuity compared to the monofocal patient group, as well as better distance and near vision 6 months post-operation.
 * In overall FDA clinical results on uncorrected binocular vision in 124 patients, 92 per cent had distance vision of 20/25 or better, 98 per cent had intermediate vision of 20/25 or better, and 73 per cent had near vision of 20/25 or better 11 to 15 months after surgery. In addition, 73.5 per cent either did not wear spectacles or wore them most none of the time.
 * However, at this time, there no long-term, well-designed clinical trials to support the accommodating technology of the Crystalens IOL.

Criticisms:
 * The main concern with accommodating IOLs is that there are no long-term, large-scale studies involving its use in patients. Such clinical studies using objective measurement techniques must be done to fully support the claim that accommodating IOLs can restore accommodative vision to the presbyopic eye.


 * Though it is rare, potential complications include capsular bag contraction and posterior capsule opacification.


 * It is more difficult to implant an accommodating IOL (due to the attachment of hinges) and recovery time may be longer than with a standard IOL.


 * Patients should expect that his or her accommodative abilities will not be restored to perfect or near perfect function. Though vision is significantly improved, the degree of improvement will not be the same for all and some will still need glasses after surgery.


 * Accommodating IOLs are expensive-Insurance companies do not cover these technologically advanced IOLs because its long-term efficacy still remains to be fully elucidated.

Candidates:

Generally, patients over 50 with cataract problems and no serious eye diseases are good candidates for the procedure. The patient must have functional ciliary muscles or zonules for haptics positioning. In addition, the pupils must dilate adequately, as the IOL will induce glares in low-light environments if the pupils dilate too large. Accommodating IOLs are beneficial not only for patients with cataracts, but also those who wish to reduce their dependency on glasses and contacts due to myopia, hyperopia and presbyopia.

Post-operative care is similar to that of normal IOLs. However, patients must include ophthalmologic exercises such as puzzles and word games as a part of their daily regimen in order to tone up their ciliary muscles and attain the maximum benefit from the accommodating lenses. These exercises should be done consistently for 3–6 months and the patient's performance be monitored by their eye care professional.

Other promising multifocal/accommodating IOLs currently in clinical trials include Accommodative 1CU (HumanOptics, Erlangen, Germany), Smartlens (Medennium, Irvine, CA), and dual optic accommodating lenses such as Sarfarazi (Bausch and Lomb, Rochester, NY) and Synchrony (Visiogen, Inc., Irvine, CA).