Cataract surgery
2007 Schools Wikipedia Selection. Related subjects: Health and medicine
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- Cataract extraction using intracapsular cataract extraction (ICCE) has been superseded by ECCE & phaco, and is no longer the prefered method of cataract removal.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
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.
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.