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 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 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