Cataract surgery

Cataract surgery is the removal of the lens of the eye (also called "crystalline") that has developed an opacification, which is referred to as a cataract. Metabolic changes of the crystalline lens fibers over the time lead to the development of the cataract and loss of transparency. Following surgical removal of the natural lens, an artificial intraocular lens implant is inserted (eye surgeons say that the lens is "implanted"). Cataract surgery is generally performed by an ophthalmologist (eye surgeon) at an ambulatory (rather than inpatient) setting, in a surgical center or hospital, using local anesthesia (either topical, peribulbar, or retrobulbar). Well over 90% of operations are successful in restoring useful vision, with a low complication rate. ^[1] Day care, high volume, minimally invasive, small incision phacoemulsification with quick post-op recovery has become the standard of care in cataract surgery all over the world.

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Types

Currently, the two main types of cataract surgery extraction performed by the ophthalmologists are phacoemulsification (phaco) and conventional extracapsular cataract extraction (ECCE). In both types of surgery an Intraocular lens is usually inserted. Foldable lenses are generally used when phaco is performed while non-foldable lenses are placed following ECCE. The small incision size used in phacoemulsification often allows "sutureless" wound closure. ECCE usually require stitching.

Cataract extraction using intracapsular cataract extraction (ICCE) has been superseded by phaco & ECCE, and is only rarely performed.

Couching is a historical method of performing cataract surgery and it is reported to have been used in ancient Egypt. In this procedure, a small probe was inserted into the eye in order to push the lens down into the vitreous cavity. This would improve visual acuity by some degree, but the result was poor. No glasses were even known back in those days. We now know that the lens can spontaneously dislocate into the vitreous cavity in certain diseases including Marfan's Syndrome and Homocystinuria. The dislocations of the crystalline into the vitreous cavity may require surgical intervention to prevent the development of intra-ocular inflammation and increase of the intra-ocular pressure.

Types of surgery

  Extracapsular cataract extraction involves the removal of the almost the entire natural lens while the elastic lens capsule (posterior capsule) is left intact to allow implantation of an intraocular lens^[2]. There are two main types of cataract surgery:

• Phacoemulsification (Phaco) is the preferred method in most cases. It involves the use of a machine with an ultrasonic handpiece 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.

• Conventional extracapsular cataract extraction (ECCE): 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 cataracts or other situations in which phacoemulsification is problematic.

• Intra-capsular extraction is an out-dated method of cataract surgery, rarely performed today.

• Intraocular lens implantation: After the removal of the cataract, an intraocular lens (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 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 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 after 2 years of age. New designs of multi-focal intra-ocular lens are now available. These lenses allow focusing of rays from distant as well as near objects. Pre-operative 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. Brands in the market include: Restore (R), Rezoom (R) and Technis MF (R).

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^[2]. Cryoextraction is a form of ICCE that freezes the lens with a cryogenic substance such as liquid nitrogen^[3]. 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^[4].

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 may be needed during the surgery.

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

• In addition, it has recently been shown that patients taking tamsulosin (Flomax), a common drug for enlarged prostate, are prone to developing a surgical complication known as floppy iris syndrome, which must be correctly managed to avoid the complication posterior capsule rupture; however, prospective studies have shown that the risk is greatly reduced if the surgeon is informed of the patient's history with the drug beforehand, and has appropriate alternative techniques prepared. ^[5].

Operation procedures

The surgical procedure in phacoemulsification for removal of cataract involves a number of steps. Each step must be carefully and skillfully performed in order to achieve the desired result. The steps may be described as follows:

1. Anaesthesia,
2. Exposure of the eyeball using a lid speculum,
3. Entry into the eye through a minimal incision (corneal or scleral)
4. Viscoelastic injection to stabilize the anterior chamber and to help maintain the eye pressurization
5. Capsulorhexis
6. Hydrodissection pie
7. Hydro-delineation
8. Ultrasonic destruction or emulsification of the cataract after nuclear cracking or chopping (if needed), cortical aspiration of the remanescent lens, capsular polishing (if needed)
9. Implantation of the artificial IOL
10. Entration of IOL (usually foldable)
11. Viscoelastic removal
12. Wound sealing / 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 a reclining examination chair. The eyelids and surrounding skin will be swabbed with disinfectant. The face is covered with a cloth or sheet, with an 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 or methylcellulose viscoelatic. The incision is fashioned at or near where the cornea and sclera meet (limbus = corneoscleral junction). Advantages of the smaller incision include use of few or no stitches and shortened recovery time. ^[6][2]. A capsulotomy (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 phacoemulsification, the surgeon performs an anterior continuous curvilinear capsulorhexis, to create a round and smooth 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 incision does not leak fluid. This is a very important step, since wound leakage increases the risk of unwanted microrganisms to gain access into the eye and predispose to endophathalmitis. An antibiotic/steroid combination eye drop is put and an eye shield may be applied on the operated eye, sometimes supplemented with an eye patch.

Antibiotics may be administered pre-operatively, intra-operatively, and/or post-operatively. 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. The use of an eye patch may be indicated, usually for about some hours, after which the patient is instructed to started using the eyedrops to control the inflammation and the antibiotics that prevent infection.

Occasionally, a peripheral iridectomy may be performed to minimize the risk of pupillary block glaucoma. An opening through the iris can be fashioned manually (surgical iridectomy) or with a laser (called YAG-laser iridotomy). The laser peripheral iridotomy may be performed either prior to or following cataract surgery.

The iridectomy hole is larger when done manually than when performed with a laser. When the manual surgical procedure is performed, some negative side effects may occur, such as that the opening of the iris can be seen by others (aesthetics), and the light can fall into the eye through the new hole, creating some visual disturbances . In the case of visual disturbances, the eye and brain often learn to compensate and ignore the disturbances over a couple of months. Sometimes the peripheral iris opening can heal, which means that the hole ceases to exist. This is the reason why the surgeon sometimes makes two holes, so that at least one hole is kept open.

After the surgery, the patient is instructed to use anti-inflammatory and antibiotic eye drops for up to two weeks (*depending on the inflammation status of the eye and some other variables). The eye surgeon will judge, based on each patient's idiosyncrasies, the time length to use the eye drops. The eye will be pretty recovered within a week, and complete recovery should be expected in about a month. The patient should not participate in contact/extreme sports until cleared to do so by the eye surgeon.

Complications

Complications after cataract surgery are relatively uncommon.

• Some people 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 and cellular migration, showing up as a thickening, opacification and clouding of the posterior lens capsule (which is left behind when the cataract was removed, for placement of the IOL). This may compromise the visual acuity and the ophthalmologist can use a device to correct this situation. It can be safely and painlessly corrected using a laser device (YAG laser) to make small holes in the posterior lens capsule of the crystalline. It usually is a quick outpatient procedure that uses a Nd-[[YAG laser]] (neodymium-yttrium-aluminum-garnet) to disrupt and clear the central portion of the opacified posterior lens capsule (posterior capsulotomy). This creates a clear central visual axis for improving visual acuity. ^[7]. In very thick opacified posterior capsules, a surgical (manual) capsulectomy is the surgical procedure performed. * Posterior capsular tear may be a complication during cataract surgery. It refers to a rupture of the posterior capsule of the natural lens. Surgical management may involve anterior vitrectomy and, occasionally, alternative planning for implanting the intraocular lens, either in the ciliary sulcus, in the anterior chamber (in front of the iris), or, less commonly, sutured to the sclera.
• Retinal detachment is an uncommon complication of cataract surgery, which may occur weeks, months, or even years later.
• TASS or toxic anterior segment syndrome is a non-infectious inflammatory condition that may occur following cataract surgery. It is usually treated with topical corticosteroids in high dosage and frequency.
• Endophthalmitis is a serious infection of the intraocular tissues, usually following intraocular surgery, or penetrating trauma. There is some concern that the clear cornea incision might predispose to the increase of endophalmitis but is no conclusive study to corroborate this suspicion.
• Glaucoma may occur and it may be very difficult to control. It is usually associated with inflammation, specially when little fragments or chunks of the nucleus get access to the vitreous cavity. Some experts recommend early intervention when this condition happens (posterior pars plana vitrectomy). In some patients, the intraocular pressure may remain so high that blindness may ensue.
• Other possible complications include: Swelling or edema of the cornea. This condition may be associated with cloudy vision, which may be transient or permanent(pseudophakic bullous keratopathy). Displacement or dislocation of the intraocular lens implant may rarely occur, as well as swelling or edema of the central part of the retina, called macula, resulting in (cystoid macular edema. Unplanned high refractive error (either myopic or hypermetropic) may occur due to error in the ultrasonic ecobiometry (measure of the length and the required intra-ocular lens power).

History

The earliest references to cataract surgery are found in Sanskrit manuscripts dating from the 5th century BC, which show that Sushruta 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. ^{[8] [9] [10]} 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 ancient times and continued to be used throughout the Middle Ages - However, it has now been replaced by extracapsular cataract surgery and, specially, phacoemulsification.

In 1748, Jacques Daviel started with modern cataract surgery, in which the cataract is actually extracted from the eye. In the 1940s Harold Ridley introduced the concept of implantation of the intraocular lens which permitted more efficient and comfortable visual rehabilitation possible after cataract surgery. The implantation of foldable intraocular lens is the procedure considered the state-of-the-art.

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 method of surgery decreased the need for an extended hospital stay and made the surgery ambulatorial. Patients that undergo cataract surgery hardly complain of pain or even disconfort during the procedure. However, patients that have topical anesthesia (as compared to those that have peribulbar block anesthesia) may experience some degree of discomfort.

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 ^[11].

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

See also

• Eye surgery

References