intraocular lens intraocular lens an intraocular lens (iol) is a lens implanted in the eye usually as part of a treatment for cataracts or for correcting other vision problems such as short sightedness and long sightedness, a form of refractive surgery. if the natural lens is left in the eye, the iol is known as phakic, otherwise it is a pseudophakic, or false lens. both kinds of iols are designed to provide the same light-focusing function as the natural crystalline lens. this is an alternative to lasik. intraocular lensa posterior chamber iol (with haptics)icd-9-cm13.72meshd054120ops-301 code5-984 a phakic iol iols usually consist of a small plastic lens with plastic side struts, called haptics, to hold the lens in place in the capsular bag inside the eye. iols were originally made of a rigid material (pmma), although this has largely been superseded by the use of flexible materials, such as silicone. most iols fitted today are fixed monofocal lenses matched to distance vision. however, other types are available, such as a multifocal intraocular lens that provides multiple-focused vision at far and reading distance, and adaptive iols that provide limited visual accommodation. multifocal iols can also be trifocal iols or extended depth of focus (edof) lenses. more than six million lenses are implanted annually as of 2009. the procedure can be done under local or topical anesthesia with the patient awake throughout the operation. the use of a flexible iol enables the lens to be rolled for insertion into the capsular bag through a very small incision, thus avoiding the need for stitches. this procedure usually takes less than 30 minutes in the hands of an experienced ophthalmologist, and 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 visit their ophthalmologists regularly for 3 weeks to monitor the implants. iol implantation carries several risks associated with eye surgeries, such as infection, loosening of the lens, lens rotation, inflammation and nighttime halos, but a systematic review of studies has determined that the procedure is safer than conventional laser eye treatment. though iols enable many patients to have reduced dependence on glasses, most patients still rely on glasses for certain activities, such as reading. these reading glasses may be avoided if multifocal iols, trifocal iols or edof lenses are used. medical uses intraocular lenses have been used since 1999 for correcting larger errors in near-sighted, far-sighted, and astigmatic eyes. this type of iol is also called phakic intraocular lens (piol), as it is implanted without removing the patient's natural crystalline lens. phakic iol appear to be less dangerous than excimer laser surgery (lasik) in those with significant nearsightedness. more commonly iols 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, last approximately 30 minutes, and 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 visit their ophthalmologists regularly for several weeks to monitor the iol implants. clear has a 90% success rate (risks include wound leakage, infection, inflammation, and astigmatism). clear can be performed only on patients ages 40 and older. this is to ensure that eye growth, which disrupts iol lenses, will not occur post-surgery. once implanted, iols have three major benefits. first, they are an alternative to the excimer laser procedure (lasik), a form of eye surgery that does not work for people with serious vision problems. effective iol implants also eliminate the need for glasses or contact lenses post-surgery for most patients. the 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. some of the risks that fda have been found so far during a three-year study of the artisan 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 to iols.) glaucoma, astigmatism, remaining near or far sightedness, rotation of the lens inside the eye one or two days after surgery. one of the causes of the risks above is that the lens can rotate inside the eye if the piol is too short, if the eye was incorrectly measured, or because the sulcus has a slightly oval shape (the height is slightly smaller than the width). toric iols must be powered and aligned inside the eye on a meridian that corrects the patient's preexisting astigmatism. again, these lenses can rotate inside the eye postoperatively or be placed incorrectly by the operating surgeon. either way, the patient's preexisting astigmatism may not be corrected completely or may even increase. when standard iols are implanted with a clear procedure, in substitution of the patient's crystalline, astigmatism is typically not corrected, as astigmatism is mainly attributable to a deformation of the cornea. toric iols may be used during the clear procedure to correct astigmatism. the surgeon can ascertain the astigmatic, or steepest, meridian in a number of ways, including manifest refraction or corneal topography. manifest refraction is the familiar test where the eye doctor rotates lenses in front of the eye, asking the patient, "which is better (or clearer), this one or this one?" corneal topography is considered a more quantitative test, and for purposes of aligning a toric iol, most surgeons use a measurement called simulated keratometry (simk), which is calculated by the internal programming of the corneal topography machine, to determine the astigmatic meridian on the surface of the cornea. the astigmatic meridian can also be identified using corneal wavefront technology or paraxial curvature matching. type of surgery implants with or without removal of natural crystalline phakia is the presence of the natural crystalline lenses. phakic iol (piol) refers to an intraocular lens implanted without removal of the patient's original crystalline lens, and this is performed solely to correct refractive error in the presence of a clear crystalline lens. aphakia is the absence of the natural crystalline lens. the aphakic state is usually due to surgery to remove a cataractous lens, but post-surgical aphakia is rare nowadays because of the ubiquity of intraocular lenses. rarely, aphakia can be post-traumatic or congenital in nature. aphakic iol refers to a lens implanted secondarily in an eye already aphakic from previous surgery or trauma some time ago. pseudophakia is the substitution of the natural crystalline lens with an iol, as is often done after cataract extraction or to correct refractive error. pseudophakic iol refers to a lens implanted during cataract surgery, immediately after removal of the patient's crystalline lens. many aphakic and pseudophakic iols such as anterior chamber iols or 3 piece posterior chamber iols can be used interchangeably. the exception are one piece iols, which must be placed within the capsular bag at the time of cataract surgery and hence cannot be used as secondary implants. location of implant before surgery (natural crystalline lens, left). after surgery (implanted pciol, right). an anterior chamber iol (aciol) posterior chamber iol (pciol). this is by far the most common type of implanted lens after cataract surgery in the united states. anterior chamber iol (aciol). a less-common type of intraocular lens, which is sometimes used if a pciol is not an option for a patient or if the situation requires a phakic iol (piol). pseudophakic iols pseudophakic iols are lenses implanted during cataract surgery, immediately after removal of the patient's crystalline lens. monofocal monofocal iols are standard lenses used in cataract surgery. one of the major disadvantages of these conventional iols is that they can only be focused for one particular distance - either optical infinity (rendering the eye emmetropic) or a fixed finite distance (rendering the eye myopic). patients who undergo a standard iol implantation no longer experience clouding from cataracts, but they are unable to accommodate (change focus from near to far, far to near, and to distances in between). this is not a concern for most cataract surgeries, as they are primarily performed on elderly people that are already completely presbyopic. however, it can be a problem for patients that are not yet presbyopic (or are in the early stages of presbyopia) undergoing refractive lens exchange for the sake of correcting refractive errors. monovision, in which one eye is made emmetropic and the other myopic, can partially compensate for the loss of accommodation and enable clear vision at multiple distances. more versatile types of lenses (multifocal and accommodating iols) were introduced in 2003 in the united states, with the approval by the food and drug administration. these come at an additional cost to the recipient beyond what medicare will pay and each has advantages and disadvantages. multifocal main article: multifocal intraocular lens multifocal iols attempt to provide simultaneous viewing of distance vision and near vision. trifocal iols can provide intermediate vision. many multifocal iol designs attempt to achieve this simultaneous viewing focus using a concentric ring design, which alternates distance and near focal points. however, many concentric ring multifocal lenses used today are prone to glare and mildly compromised focus at all ranges of vision. people who have a multifocal iol after their cataract is removed may be less likely to need additional glasses compared with people who have standard monofocal lenses. however, people receiving multifocal lenses may experience more visual problems than with monofocal lenses. the most common adverse visual effects from multifocal iols include glare, halos (rings around lights), and a loss of contrast sensitivity in low-light conditions. adjustable lens an adjustable iol is unlike any other lens as its prescription power can be adjusted after surgery once all healing is complete. all other iols require surgeons to use pre-surgery measurements to determine a patient's post-surgery lens power. the drawback of this is that pre-surgery measurements are taken while a patient still has cataracts, and they can't account for minuscule shifts that occur during healing. an adjustable iol allows surgeons to implant it and then, once healing is complete, use an ultra violet light delivery device to fine tune it until it suits the patient. an early example being the (rxsight) light adjustable lens (lal). the eyes and lenses must not be exposed to random ultraviolet light before and during the adjustment process, and protective glasses must be worn from the operation until the lens is locked. when the eye has healed, which is usually 2 to 4 weeks after iol implantation, refraction adjustment is done. a prescription is formulated for the patient and customization of the iol's refractive power is done by exposing either the centre or the periphery of the lens to a metered dose of uv light, with the help of a contact lens on the cornea. this exposed part will swell slightly, adjusting the lens surface curvature. meridional exposure can be done in much the same way to correct for astigmatism. several exposures can be made for fine tuning, spaced over several days. once the lens has been optimised a final exposure of the whole lens is made to lock the changes, after which the lens will no longer be adjustable and can be used outdoors. accommodating main article: multifocal intraocular lens some newer lens designs attempt to allow the eye to regain some partial focusing ability in order to change focus from distance to near (accommodation). however, many accommodating iols used today only achieve a very limited improvements in near vision which reduced over time. accommodative intraocular lenses may also have a slightly higher risk of developing posterior capsule opacification (pco), though there is some uncertainty around this finding. pco is a common side-effect of many cataract surgeries and is easily treatable with a one-time laser capsulotomy procedure (see below). accommodating iols interact with ciliary muscles and zonules, using hinges at both ends to "latch on" and