Cataract surgery is the removal of the natural lens of the eye (also called “crystalline lens”) that has developed an opacification, which is referred to as a cataract. Metabolic changes of the crystalline lens fibers over time lead to the development of the cataract and loss of transparency, causing impairment or loss of vision. Many patients’ first symptoms are strong glare from lights and small light sources at night, along with reduced acuity at low light levels. During cataract surgery, a patient’s cloudy natural lens is removed and replaced with a synthetic lens to restore the lens’s 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) in an ambulatory (rather than inpatient) setting, in a surgical center or hospital, using local anesthesia (either topical, peribulbar, or retrobulbar), usually causing little or no discomfort to the patient. Well over 90% of operations are successful in restoring useful vision, with a low complication rate. 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.
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 (2-3mm) often allows “sutureless” wound closure. ECCE utilises a larger wound (10-12mm) and therefore usually requires stitching, although sutureless ECCE is also in use.
Cataract extraction using intracapsular cataract extraction (ICCE) has been superseded by phaco & ECCE, and is rarely performed.
Phacoemulsification is the most commonly performed cataract procedure in the developed world. However, the high cost of a phacoemulsification machine and of the associated disposable equipment means that ECCE remains the most commonly performed procedure in developing countries.
Types of surgery
There are three main types of cataract surgery:
- Phacoemulsification (Phaco) is the preferredÂ Â method in most cases. It involves the use of a machine with an ultrasonicÂ handpiece equipped with a titanium or steel tip. The tip vibrates at ultrasonic frequency (40,000 Hz) and the lens material is emulsified.Â Â A second fine instrument (sometimes called a “cracker” orÂ Â “chopper”) may be used from a side port to facilitate crackingÂ Â or chopping of the nucleus into smaller pieces. Fragmentation into smallerÂ pieces makes emulsification easier, as well as the aspiration of corticalÂ material (soft part of the lens around the nucleus). AfterÂ phacoemulsification of the lens nucleus and cortical material isÂ completed, a dual irrigation-aspiration (I-A) probe or a bimanual I-AÂ system is used to aspirate out the remaining peripheral cortical material.
- ConventionalÂ extracapsular cataract extraction (ECCE): Extracapsular cataractÂ Â extraction involves the removal of almost the entire natural lens whileÂ the elastic lens capsule (posterior capsule) is left intact to allowÂ implantation of an intraocular lens.Â It involves manual expression of the lens through a large (usually 10â€“12Â mm) incision made in the cornea or sclera. Although it requires a larger incision and theÂ use of stitches, the conventional method may be indicated for patientsÂ with very hard cataracts or other situations in which phacoemulsificationÂ is problematic.
- Intracapsular cataract extraction (ICCE) involves the removal of the lens and theÂ Â surrounding lens capsule in one piece. The procedure has a relatively high rate of complications due to the large incision required and pressureÂ placed on the vitreous body. It has therefore been largelyÂ Â superseded and is rarely performed in countries where operating Â Â Â Â microscopes and high-technology equipment are readily available.Â Â After lens removal, an artificial plastic lensÂ (an intraocular lens implant) can be placed in either the anterior chamber or sutured into the sulcus.
Cryoextraction is a form of ICCE that freezes the lens with a cryogenic substance such as liquid nitrogen. In this technique, the cataract is extracted through use of a cryoextractor â€” a cryoprobe whose refrigerated tip adheres to and freezes tissue of the lens, permitting its removal. 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.
Intraocular lens implantation: After the removal of the cataract, an intraocular lens (IOL) is usually implantedÂ Â into the eye, either through a small incision (1.8 mm to 2.8 mm) using aÂ Â foldable IOL, or through an enlarged incision, using a PMMA Â Â Â Â (polymethylmethacrylate) lens. The foldable IOL, made of siliconeÂ Â or acrylicÂ material of appropriate power is folded either using a holder/folder, or a proprietary insertion device provided along with the IOL. The lensÂ implanted is inserted through the incision into the capsular bag within the posterior chamber (in-the-bag implantation). Sometimes, a sulcusÂ implantation (in front or on top of the capsular bag but behind the iris)Â Â may be required because of posterior capsular tears or because ofÂ zonulodialysis.
Implantation of posterior chamber IOL (PCIOL) in patientsÂ below 1 year of age is controversial due to rapid ocular growth at thisÂ age and the excessive amount of inflammation, which may be very difficultÂ to control. Optical correction in these patients without intraocular lens (aphakic) is usually managed with either special contact lenses orÂ Â glasses. Secondary implantation of IOL (placement of a lens implant as aÂ second operation) may be considered later.
New designs of multifocalÂ intraocular lens are now available. These lenses allow focusing of raysÂ Â from distant as well as near objects, working much like bifocal orÂ trifocal eyeglasses. Preoperative patient selection and good counsellingÂ Â is extremely important to avoid unrealistic expectations andÂ post-operative patient dissatisfaction. Acceptability for these lenses has become better and studies have shown good results in selected patients.Â Brands in the market include: ReSTOR (R), Rezoom (R) and Tecnis MF (R).