Two main types of surgical procedures are in common use throughout the world. The first procedure is phacoemulsification (phaco) and the second involves two different types of extracapsular<unk>  extraction (ECCE). In most surgeries, an intraocular lens is inserted. Foldable lenses are generally used for the 2–3 mm phaco incision, while non-foldable lenses are placed through the larger extracapsular incision. The small incision size used in phacoemulsification (2–3 mm) often allows "sutureless" incision closure. ECCE uses a larger incision (10–12 mm) and therefore usually requires stitching, and this in part led to the modification of ECCE known as manual small incision<unk>  (MSICS).<unk>  extraction using intracapsular<unk>  extraction (ICCE) has been superseded by phacoemulsification and ECCE, and is rarely performed. Phacoemulsification is the most commonly performed<unk>  procedure in the developed world. However, the high cost of a phacoemulsification machine and of the associated disposable equipment means that ECCE and MSICS remain the most commonly performed procedure in developing countries.<unk>  is commonly done as day care rather than in-patient procedure as there is some evidence that day surgery has similar outcomes and is cheaper than hospitalisation and overnight stay. Types of surgery<unk> , using a temporal approach phacoemulsification probe (in right hand) and "chopper" (in left hand) being done under the operating microscope at a US Navy medical center<unk>  recently performed, foldable IOL inserted. A small incision and very slight hemorrhage are visible to the right of the still dilated pupil. There are a number of different surgical techniques used in<unk> : * Phacoemulsification (phaco) is the most common technique used in developed countries. It involves the use of a machine with an ultrasonic handpiece equipped with a titanium or steel tip. The tip vibrates at ultrasonic frequency (40,000 Hz) and the lens material is emulsified. A second fine instrument (sometimes called a "cracker" or "chopper") may be used from a side port to facilitate cracking or chopping of the nucleus into smaller pieces. Fragmentation into smaller pieces makes emulsification easier, as well as the aspiration of cortical material (soft part of the lens around the nucleus). After phacoemulsification of the lens nucleus and cortical material is completed, a dual irrigation-aspiration (I-A) probe or a bimanual I-A system is used to aspirate out the remaining peripheral cortical material. * Manual small incision<unk>  (MSICS): This technique is an evolution of ECCE (see below) where the entire lens is expressed out of the eye through a self-sealing scleral tunnel wound. An appropriately constructed scleral tunnel is watertight and does not require suturing. The "small" in the title refers to the wound being relatively smaller than an ECCE, although it is still markedly larger than a phaco wound. Head-to-head trials of MSICS vs phaco in dense<unk> s have found no difference in outcomes, but shorter operating time and significantly lower costs with MSICS. Nucleus of hypermature<unk>  after ECCE * Extracapsular<unk>  extraction (ECCE): Extracapsular<unk>  extraction involves the removal of almost the entire natural lens while the elastic lens capsule (posterior capsule) is left intact to allow implantation of an intraocular lens. It involves manual expression of the lens through a large (usually 10–12 mm) incision made in the cornea or sclera. Although it requires a larger incision and the use of stitches, the conventional method may be indicated for patients with very hard<unk> s or other situations in which phacoemulsification is problematic. * Intracapsular<unk>  extraction (ICCE) involves the removal of the lens and the surrounding lens capsule in one piece. The procedure has a relatively high rate of complications due to the large incision required and pressure placed on the vitreous body. It has therefore been largely superseded and is rarely performed in countries where operating microscopes and high-technology equipment are readily available. After lens removal, an artificial plastic lens (an intraocular lens implant) can be placed in either the anterior chamber or sutured into the sulcus. * Femtosecond laser-assisted<unk>  has been shown to have no visual, refractive or safety benefit over manual phacoemulsification. Cryoextraction is a form of ICCE that freezes the lens with a cryogenic substance such as liquid nitrogen. In this technique, the<unk>  is extracted through use of a cryoextractor – a cryoprobe whose refrigerated tip adheres to and freezes tissue of the lens, permitting its removal. Although it is now used primarily for the removal of subluxated lenses, it was the favored form of<unk>  extraction from the late 1960s to the early 1980s. Intraocular lenses * Intraocular lens (IOL) implantation: After the removal of the<unk> , an IOL is usually implanted into the eye, either through a small incision (1.8 mm to 2.8 mm) using a foldable IOL, or through an enlarged incision, using a poly(methyl methacrylate) (PMMA) lens. The foldable IOL, made of silicone or acrylic material of appropriate power is folded either using a holder/folder, or a proprietary insertion device provided along with the IOL. The lens implanted is inserted through the incision into the capsular bag within the posterior chamber (in-the-bag implantation). Sometimes, a sulcus implantation (in front or on top of the capsular bag but behind the iris) may be required because of posterior capsular tears or because of zonulodialysis. Implantation of posterior chamber IOL (PCIOL) in patients below 1 year of age is controversial due to rapid ocular growth at this age and the excessive amount of inflammation, which may be very difficult to control. Optical correction in these patients without intraocular lens (aphakic) is usually managed with either special contact lenses or glasses. Secondary implantation of IOL (placement of a lens implant as a second operation) may be considered later. New designs of multifocal intraocular lens are now available. These lenses allow focusing of rays from distant as well as near objects, working much like bifocal or trifocal eyeglasses. Preoperative patient selection and good counselling is extremely important to avoid unrealistic expectations and post-operative patient dissatisfaction. Acceptability for these lenses has become better and studies have shown good results in selected patients. In addition, there is an accommodating lens that was approved by the US FDA in 2003 and made by Eyeonics, now Bausch & Lomb. The Crystalens is on struts and is implanted in the eye's lens capsule, and its design allows the lens' focusing muscles to move it back and forth, giving the patient natural focusing ability. Artificial intraocular lenses (IOLs) are used to replace the eye's natural lens that is removed during<unk> . These lenses have been increasing in popularity since the 1960s, but it was not until 1981 that the first U.S. Food and Drug Administration (FDA) approval for this type of product was issued. The development of IOLs brought about an innovation as patients previously did not have their natural lens replaced and as a result had to wear very thick eyeglasses or some special type of contact lenses. Presently, IOLs are especially designed for patients with different vision problems. The main types of IOLs that now exist are divided into monofocal and multifocal lenses. A<unk> . Dictionnaire Universel de Médecine (1746–1748). The monofocal intraocular lenses are the traditional ones, which provide vision at one distance only: far, intermediate, or near. Patients who choose these lenses over the more developed types will probably need to wear eyeglasses or contact lenses for reading or using the computer. These intraocular lenses are usually spherical, and they have their surface uniformly curved. The multifocal intraocular lens is one of the newest types of such lenses. They are often referred to as "premium" lenses because they are multifocal and accommodative, and allow the patient to visualize objects at more than one distance, removing the need to wear eyeglasses or contact lenses. Premium intraocular lenses are those used in correcting presbyopia or astigmatism. Premium intraocular lenses are more expensive and are typically not covered, or not fully covered, by health insurance, as their additional benefits are considered a luxury and not a medical necessity. An accommodative intraocular lens implant has only one focal point, but it acts as if it is a multifocal IOL. The intraocular lens was designed with a hinge similar to the mechanics of the eye's natural lens. The intraocular lenses used in correcting astigmatism are called toric, and have been FDA approved since 1998. The STAAR Surgical Intraocular Lens was the first such lens developed in the United States and it may correct up to 3.5 diopters. A different model of toric lenses was created by Alcon and may correct up to 3 diopters of astigmatism. In order to achieve the most benefit from a toric lens, the surgeon must rotate the lens to be on axis with the patient's astigmatism. Intraoperative wavefront analysis, such as that provided by the ORA System developed by Wavetec Visions Systems, can be used to assist the doctor in toric lens placement and minimize astigmatic errors.<unk>  may be performed to correct vision problems in both eyes, and in these cases, patients are
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