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Cataract surgery

2007 Schools Wikipedia Selection. Related subjects: Health and medicine

   Cataract in Human Eye- Magnified view seen on examination with a slit
   lamp
   Enlarge
   Cataract in Human Eye- Magnified view seen on examination with a slit
   lamp

   Cataract surgery is the removal of the lens of the eye that has
   developed a cataract. The natural lens is usually then replaced with an
   artificial intraocular lens. Cataract operations are generally regarded
   as among the safest types of surgery, and although complications can
   occur, well over 90% of operations are successful in restoring useful
   vision.

Types

   Currently, the two main types of cataract extraction performed by
   ophthalmologists are conventional extracapsular cataract extraction
   (ECCE) and phacoemulsification (phaco), usually followed by intraocular
   lens insertion.
     * Cataract extraction using intracapsular cataract extraction (ICCE)
       has been superseded by ECCE & phaco, and is no longer the prefered
       method of cataract removal.
     * Couching is an old historical form of cataract surgery in which a
       small probe was inserted in the eye to push the lens down into the
       posterior chamber. It is no longer performed by Ophthalmologists.

Extracapsular cataract extraction

   Cataract surgery, using a temporal approach phacoemulsification probe
   (in right hand) and "chopper"(in left hand) being done under operating
   microscope at a Navy medical center
   Enlarge
   Cataract surgery, using a temporal approach phacoemulsification probe
   (in right hand) and "chopper"(in left hand) being done under operating
   microscope at a Navy medical centre

   Extracapsular cataract extraction involves the removal of the lens
   while the elastic lens capsule is left partially intact to allow
   implantation of an intraocular lens. There are two main types of
   extracapsular surgery:
     * Conventional extracapsular cataract extraction (ECCE): It involves
       manual expression of the lens through an incision made in the
       cornea or sclera. Although it requires a larger incision and the
       use of stitches, the conventional method is indicated for patients
       with very hard cataracts, lower corneal endothelial cells counts,
       or other situations in which phacoemulsification is problematic.

     * Phacoemulsification (Phaco) involves the use of a machine with an
       ultrasonic handpiece with a titanium or steel tip. The tip vibrates
       at ultrasonic frequency under continuous irrigation to sculpt and
       emulsify the cataract. A second fine steel instrument (sometimes
       called a cracker or chopper) may be used from a side port to
       facilitate cracking or chopping the nucleus into smaller pieces.
       The nucleus emulsification makes it easier to aspirate the
       particles. After phacoemulsification of the lens nucleus is
       completed, an irrigation-aspiration probe or a bimanual system is
       used to aspirate out the remaining peripheral cortical matter.

     * Intraocular lens implantation: Thereafter, an intraocular lens
       (IOL) is usually implanted, either through a small incision using a
       foldable IOL, or through an enlarged incision, using a PMMA
       (polymethylmethacrylate) 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 (PC-IOL) in patients below 1 to 2 years of
       age is relatively contraindicated due to rapid ocular growth at
       this age. Optical correction in these 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 after 2 years of age.

Intracapsular cataract extraction

   Intracapsular cataract extraction (ICCE) involves the removal of the
   lens and the surrounding lens capsule in one piece. The lens is then
   replaced with an artificial plastic lens (an intraocular lens implant)
   of appropriate power which remains permanently in the eye. The
   procedure has a relatively high rate of complications due to the large
   incision required and pressure placed on the vitreous body, thus is
   rarely performed in countries where operating microscopes and
   high-technology equipment are readily available. Cryoextraction is a
   form of ICCE that freezes the lens with a cryogenic substance such as
   liquid nitrogen. Although it is now used primarily for the removal of
   subluxated lenses, it was the favored form of cataract extraction from
   the late 1960s to the early 1980s.

Preoperative evaluation

   An eye examination or pre-operative evaluation by an eye surgeon is
   necessary to confirm the presence of a cataract and to determine if the
   patient is a suitable candidate for surgery. The patient must fulfill
   certain requirements, such as:
     * Reduction of vision should be judged due, at least in large part,
       to the cataract. While the existence of other sight-threatening
       diseases, such as age-related macular degeneration or glaucoma, do
       not preclude the advisability of cataract surgery, outcome
       expectations may need to be adjusted downward.

     * The eyes should have a normal pressure, or any pre-existing
       glaucoma should be adequately controlled on medications. In cases
       of uncontrolled glaucoma, a combined cataract-glaucoma procedure
       (Phaco- trabeculectomy) can be planned and performed.

     * The pupil should be adequately dilated using eyedrops; if
       pharmacologic pupil dilation is inadequate, procedures for
       mechanical pupillary dilatation must be available during the
       surgery.

     * The patients with retinal detachment may be scheduled for a
       combined vitreo-retinal procedure, along with PC-IOL implantation.

Operation procedures

   The surgical procedure in phacoemulsification for removal of cataract
   involves a number of steps, in order: starting with proper anaesthesia,
   exposure using a lid speculum, incision (corneal or scleral),
   viscoelastic injection to stabilise the anterior chamber, capsulotomy,
   hydrodissection, hydrodelineation, ultrasonic emulsification, nuclear
   cracking or chopping (if needed), cortical aspiration, capsular
   polishing (if needed), implantation & centration of IOL, viscoelastic
   removal, wound closure / hydration (if needed).

   The pupil is dilated using drops (if the IOL is to be placed behind the
   iris), to help better visualise the cataract. Pupil constricting drops
   are reserved for secondary implantation of the IOL in front of the
   iris(if the cataract has already been removed without primary IOL
   implantation). Anesthesia may be placed topically (eyedrops) or via
   injection next to (peribulbar) or behind (retrobulbar) the eye. Oral or
   intravenous sedation may also be used to reduce anxiety. General
   anesthesia is rarely necessary, but may be employed for children and
   adults with particular medical or psychiatric issues. The operation may
   occur on a stretcher or an reclining examination chair. The eyelids,
   and surrounding skin will be swabbed with disinfectant. The face is
   covered with a cloth or sheet, with a opening for the operative eye.
   The eyelid is held open with a speculum to minimize blinking during
   surgery. Pain is usually minimal in properly anesthetised eyes, though
   a pressure sensation and discomfort from the bright operating
   microscope light is common. The ocular surface is kept moist using
   sterile saline eyedrops. The incision is fashioned at or near where the
   cornea and sclera meet (corneoscleral junction). Adavantages of smaller
   incision include use of few or no stitches and shortened recovery time.
   . A capsulotomy/ capsulorhexis (rarely known as cystitomy), is a
   procedure to open a portion of the lens capsule. An anterior
   capsulotomy refers to the opening of the front portion of the lens
   capsule, whereas a posterior capsulotomy refers to the opening of the
   back portion of the lens capsule. In an extracapsular surgery, the
   surgeon performs an anterior continuous curvilinear capsulorhexis, to
   create an opening through which the lens nucleus can be emulsified and
   the intraocular lens implant inserted.

   Following cataract removal (via ECCE or phacoemulsification, as
   described above), an intraocular lens is usually inserted. After the
   IOL is inserted, the surgeon checks that the incisions do not leak
   fluid. An eye shield is applied on the operated eye, sometimes
   supplemented with an eye patch.

   Antibiotics may be administered preoperatively, intraoperatively,
   and/or posteroperatively. Frequently a topical corticosteroid is used
   in combination with topical antibiotics postoperatively.

   Most cataract operations are performed under a local anaesthetic,
   allowing the patient to go home the same day.

   In some cases, an "emergency release valve" ( peripheral iridectomy)
   can be made at the same time by making one large or two smaller holes
   in the iris, in case the pupil is blocked, in order to avoid glaucoma.
   This can be done in two ways: either surgically by first lifting up the
   front layer of the iris and cut away a small portion, and then make a
   small hole in the pigment/back layer of the with a suction device -
   called iridectomy. The other alternative is with a laser a couple of
   weeks before the lens surgery - called laser peripheral iridotomy.

   The iridectomy hole is larger when done surgically, and some of the
   negative effect are that it can be seen by others (aesthetics), and
   that light can fall into the eye through the new hole creating visual
   disturbances (blurry images on top of the normal view). In the case of
   visual disturbances, the eye and brain often learns to compensate and
   ignore the disturbances over the couple of months. One negative effect
   with laser peripheral iridotomy is that the hole can heal, which means
   that the hole ceases to exist, meaning there is no "emergency release
   valve". Therefore, the surgeon often makes two holes, so that at least
   one hole is open.

   Afterwards, the patient will be instructed to keep the eyes clean, and
   avoid infectious environments (such as saunas, swimming pools), and to
   take eye drops - anti-inflammatory and antibiotics for the time it
   takes the eye to heal completely. The eye will be mostly recovered
   within a week, and complete recovery should be expected in about three
   weeks. The patient must not lift heavy things, do anything that
   elevates the blood pressure. Also, the patient should avoid
   contact/extreme sports within the next several months.

Complications

   Complications after cataract surgery are relatively uncommon.
     * Many people (up to 50%) can develop a posterior capsular
       opacification (also called an after-cataract). As a physiological
       change expected after cataract surgery, the posterior capsular
       cells undergo hyperplasia, showing up as an thickening,
       opacification and clouding of the posterior lens capsule (which is
       left behind when the cataract was removed, for placement of the
       IOL). It can be easily corrected using a to make holes in the
       capsule for the person to see through. A quick outpatient procedure
       using a Nd-[[YAG laser]] (neodymium-yttrium-aluminium-garnet) may
       be performed to clear the central portion of opacified posterior
       lens capsule ( posterior capsulotomy). This creates a clear central
       visual axis for improving visual acuity. . In very thick opacified
       posterior capsules, a capsulectomy is the surgical procedure
       performed. involving removal of lens capsule tissue, which may be
       required in young children, not amenable to a laser procedure.
     * Posterior capsular tear is a complication during cataract surgery,
       leading to a rupture of the posterior capsule . It needs to be
       managed by a vitrectomy and alternative planning for implanting the
       intraocular lens, either in the sulcus, or sutured to the sclera,
       or in the anterior chamber (in front of the iris).
     * Retinal detachment is an uncommon complication of cataract surgery,
       which may occur soon after, or even months to years later.
     * Endophthalmitis is an infection of the intraocular tissues, usually
       following some form of intraocular surgery, or penetrating trauma.
     * Other complications may include: Swelling or edema of the cornea
       without associated cloudy vision ( pseudophakic bullous
       keratopathy), displacement or dislocation of the intraocular lens
       implant, swelling or edema of the central retina ( cystoid macular
       edema), and unanticipated high refractive error.

   Slit lamp photo of IOL showing Posterior capsular opacification visible
   few months after implantation of Intraocular lens in eye, seen on
   retroillumination
   Enlarge
   Slit lamp photo of IOL showing Posterior capsular opacification visible
   few months after implantation of Intraocular lens in eye, seen on
   retroillumination

History

   The earliest references to cataract surgery are found in Sanskrit
   manuscripts dating from the 5th century BC, which show that Susruta
   developed specialised instruments and performed the earliest eye
   surgery in India . In the Western world, bronze instruments that could
   have been used for cataract surgery, have been found in excavations in
   Babylonia, Greece and Egypt. The first references to cataract and its
   treatment in the West are found in 29 AD in De Medicinae, the work of
   the Latin encyclopedist Aulus Cornelius Celsus.

   The first extracapsular cataract surgery using a sharply pointed
   instrument with a handle fashioned into a trough was described in
   Susrutasamhita. This technique is known to have existed in India as
   described and performed by Susruta sometime in early BC. Another early
   technique to remove cataracts was couching, which involved using a thin
   needle or stick to remove the clouding. This technique is known to have
   existed in Roman times and continued to be used throughout the Middle
   Ages - it has now been superseded by extracapsular cataract surgery.

   In 1748, Jacques Daviel started with modern cataract surgery, in which
   the cataract is actually extracted from the eye. In the 1940s Harold
   Ridley invented the intraocular lens which permitted more efficient and
   comfortable visual rehabilitation possible after cataract surgery.

   In 1967, Charles Kelman introduced phacoemulsification, a technique
   that uses ultrasonic waves to emulsify the nucleus of the crystalline
   lens in order to remove the cataracts without a large incision. This
   new surgery removed the need for an extended hospital stay and made the
   surgery less painful.

   According to surveys of members of the American Society of Cataract and
   Refractive Surgery, approximately 2.85 million cataracts procedures
   were performed in the United States during 2004 and 2.79 million in
   2005 .

   In India, modern surgery with intraocular lens insertion in Government
   and Non Government Organisation (NGO) sponsored Eye Surgical Camps have
   replaced older surgical procedures.

   Retrieved from " http://en.wikipedia.org/wiki/Cataract_surgery"
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   with only minor checks and changes (see www.wikipedia.org for details
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