move forward and backward inside the eye using the same mechanism as 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. an accommodating lens made by eyeonics, now bausch & lomb, was approved by the us fda in 2003. the crystalens has two hinged struts on opposite edges which displace the lens along the optical axis when an inward transverse force is applied to the haptic loops at the outer ends of the struts (the components transferring the movement of the contact points to the device), and it springs back when the force is reduced. it is implanted in the eye's lens capsule, where the contractions of the ciliary body which would focus the eye with the natural lens are used to focus the implant. toric a toric iol is a type of toric lens used to correct preexisting corneal astigmatism at the time of cataract surgery. astigmatism can also be treated with limbal relaxing incisions or an excimer laser procedure. about 40% of americans have significant astigmatism and thus may be candidates for a toric iol. cataract surgery with implantation of a toric iol is essentially the same as cataract surgery with a conventional iol. like toric contact lenses, toric iols have different powers in different meridians of the lens, and they must be positioned on the correct meridian to reverse the preexisting astigmatism. if the toric iol is not on the correct meridian, it may need to be repositioned in a second procedure. multifocal toric standard toric iols are monofocal, permanently focused on distant objects. multifocal toric iols are also available. these lenses provide the patient not only with correction of preexisting astigmatism, but also with multiple-focused vision at far and reading distance extended depth-of-focus extended depth-of-focus (edof) is an intraocular lens technology for treating presbyopia. where multifocal iols have two or more focal points, edof lenses form a single elongated focal point to enhance depth of focus. the intention is to reduce glare, halos, and other photic phenomena which occur with multifocal iols. a possible drawback is decrease in image quality due to aberrations. edof iols have often been combined with multifocus designs, which has caused some confusion. it has been suggested that lenses combining more than one optical design be termed "hybrid iols" the principle on which they work is to form a single, axially elongated focal point, unlike monofocal lenses which have a single focal point, and multifocal lenses which have two or more stacked discrete focal points. the elongated zone of focus is intended to prevent the overlapped out-of-focus images of the multifocal lens which cause the halo effect. when matched correctly to the eye, these lenses are intended to have little effect on distance vision, and improve middle distance and near vision. in practice they have been satisfactory for intermediate distances, but not good enough for near vision. spherical aberration and the pinhole effect have been use to produce the elongated focal zone. phakic iols main article: phakic intraocular lens phakic iols (piols) are intraocular lenses which are placed in an eye that still contains a natural human crystalline lens. piols are sometimes referred to as an 'implantable contact lenses' (icls). as with other iols, piols can be either spheric or toric. toric piols have to be aligned with the meridian of astigmatism; toric iol misalignment or rotation can lead to residual or even greater astigmatism postoperatively. depending on their attachment site to the eye, piols can be divided into three categories: angle-supported piols, placed in the anterior chamber. they are notorious for their negative impact on the corneal endothelial lining, which is vital for maintaining a healthy clear cornea. iris-fixated piols, attached by claws to the mid-peripheral iris by a technique called enclavation. it is believed to have a lesser effect on corneal endothelium. the main complication with this type is their tendency to cause endothelial cell reduction. sulcus-supported piols, placed in the posterior chamber in front of the natural crystalline lens. this type of piols is gaining more and more popularity. they have special vaulting so as not to be in contact with the normal lens. the main complication with older versions was a small possibility of cataract formation. in 2006, a centrally perforated icl (i.e., the hole-icl) was created to improve aqueous humour circulation. blue-light filtering iols 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; however too much filtering of blue light can increase depression, especially in the winter months (sad). the trademarked "natural yellow" material is available in three hydrophilic iols. dr. patrick h. benz of benz research and development created the first iol material to incorporate the same uv-a blocking and violet light filtering chromophore that's present in the human crystalline lens in order to attempt to protect the retina after cataract extraction of the natural crystalline lens. a cochrane review found little evidence of important differences between blue‐light filtering and non‐blue‐light filtering lenses for protecting the macula (back of the eye) after cataract surgery. this may have been due to studies being too small and too short‐term to provide reliable results. posterior capsule opacification