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 patients 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 patients 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
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 patients 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.