Cataract surgery is the removal of the natural lens of the eye that has developed a cataract, an opaque or cloudy area. The eye's natural lens is usually replaced with an artificial intraocular lens (IOL) implant.
Over time, metabolic changes of the crystalline lens fibres lead to the development of a cataract, causing impairment or loss of vision. Some infants are born with congenital cataracts, and environmental factors may lead to cataract formation. Early symptoms may include glare from lights, especially at night, blunting of colors in vision and reduced visual acuity at low light levels.
During cataract surgery, the cloudy natural lens is removed from the posterior chamber of the eye, either by emulsification in place or by manual removal. An IOL (intraocular lens) is usually implanted in its place (PCIOL), or less frequently in the cilliary sulcus, to restore clear vision. Cataract surgery is performed by an ophthalmologist in an out-patient setting at a surgical centre or hospital. Local anaesthesia (injection) or topical anesthesia (drops) are normally used. The procedure is usually quick and causes little or no pain and minor discomfort. Recovery sufficient for most daily activities usually takes place in days, and full recovery takes about a month.
Well over 90% of operations are successful in restoring useful vision, and there is a low complication rate. Same day, minimally invasive, small-incision phacoemulsification with quick post-operative recovery has become the standard of care of cataract surgery in much of the world. Manual small incision cataract surgery (MSICS), which is considerably more economical in capital equipment and consumables, and provides comparable results, is popular in the developing world. Both procedures have a low risk of serious complications, and are the definitive treatment for vision impairment due to cataract.
Uses
Cataract surgery is used to remove the natural lens of the eye when it has developed a cataract, (a cloudy area in the lens that causes visual impairment). Cataracts usually develop slowly and can affect one or both eyes. Early symptoms may include faded colours, blurred or double vision, halos around lights, sensitivity to glare from bright lights, and night blindness. Blindness can be the end result. The procedure is normally elective, but lens removal may be part of trauma surgery in cases where the eye is severely injured. The lens is usually replaced by an intraocular implant when this is reasonably practicable, as removal of the lens also removes the ability of the eye to focus at from one distance to another.
Cataracts most commonly occur due to aging, but may also be caused by trauma or radiation exposure, be present since birth, or may develop as a complication of eye surgery intended to solve other health problems. Cataracts form when clumps of proteins or yellow-brown pigment accumulate in the lens, which reduces transmission of light to the retina at the back of the eye. Cataracts can be diagnosed via an eye examination.
Early symptoms of cataract may be improved by wearing appropriate glasses; if this does not help, cataract surgery is the only effective treatment. Surgery with implants generally results in better vision and an improved quality of life: however, the procedure is not readily available in many countries.
Techniques
Two main classes of cataract surgical procedures are currently in common use throughout the world: phacoemulsification, and extracapsular cataract extraction. Intracapsular cataract extraction has been superseded where the facilities for surgery under a microscope are available except for cases where the lens capsule cannot be retained, and couching is no longer used in mainstream medicine.
In phacoemulsification (phaco), the natural lens is fragmented by an ultrasonic probe and removed by suction. A more recent and less common variation of this, femtosecond laser-assisted phacoemulsification surgery, uses a laser to make the corneal incision, execute the capsulotomy, which provides access to the lens, and initiate lens fragmentation, which reduces energy requirements for phacoemulsification. The small incision size used in phacoemulsification generally allows for sutureless incision closure.
In (ECCE), and its variation manual small incision cataract surgery (MSICS), the lens is removed from its capsule and manually extracted from the eye, either whole or after being split into a small number of substantial pieces. The basic version of ECCE uses a larger incision of and usually requires stitches. This requirement led to the variation known as MSICS, which does not usually need stitches as the incision should be self sealing under internal pressure due to its geometry.
Comparative trials of MSICS against phaco in dense cataracts have found no significant difference in outcomes, although MSICS had shorter operating times and significantly lower costs. MSICS has been prioritized as the method of choice in developing countries, because it provides high-quality outcomes with less surgically-induced astigmatism than standard ECCE, no suture-related problems, quick rehabilitation, and fewer post-operative visits. MSICS is generally easy and fast to learn for the surgeon, cost-effective and applicable to almost all types of cataract. ECCE using a large incision has largely become a contingency procedure to deal with complications during surgery and for managing cataracts expected to be difficult extractions.
In most surgeries, an IOL is inserted. Foldable lenses are generally used for the phaco incision, while non-foldable lenses can be placed through the larger extracapsular incision.
(ICCE) is the removal of the lens and the surrounding lens capsule in one piece. The procedure has a relatively high rate of complications in comparison to techniques in which the capsule is retained in place, due to the large incision required, pressure placed on the vitreous body when removing the encapsulated lens, and the removal of the barrier between the chambers of the eye, allowing easier migration of vitreous into the anterior chamber. It has therefore been largely superseded and is rarely performed in countries where operating microscopes and high-technology equipment are readily available. After lens removal by ICCE, an intraocular lens implant can be placed in either the anterior chamber or sutured into the ciliary sulcus. Cryoextraction is a technique used in ICCE to extract the lens using a cryoprobe, the refrigerated tip of which adheres to the tissue of the lens at the contact point by freezing with a cryogenic substance such as liquid nitrogen, facilitating its removal. Cryoextraction may still be used for the removal of subluxated (partially dislocated) lenses.
Couching is the earliest documented form of cataract surgery. It involves dislodging the lens of the eye, removing the cataract from the optical axis, but leaving it inside the eye. The lens is not replaced and the eye cannot focus at any distance.
Phacoemulsification is the most commonly performed cataract procedure in the developed world, but the high capital and maintenance costs of a phacoemulsification machine and of the associated disposable equipment, have made ECCE and MSICS the most commonly performed procedures in developing countries. Cataract surgery is commonly done as an out-patient or day-care procedure, which is less expensive than hospitalisation and an overnight stay, and day surgery has similar medical outcomes.
Pre-operative evaluation An eye examination or pre-operative evaluation is done to confirm the presence of a cataract and to determine the patient's suitability for surgery:
The degree of reduction of vision due largely to the cataract is evaluated. While the existence of other sight-threatening diseases, such as age-related macular degeneration or glaucoma, does not preclude cataract surgery, less improvement may be expected in their presence. In cases of uncontrolled glaucoma, a combined cataract-glaucoma procedure (phaco-trabeculectomy) can be planned and performed. The pupil is checked for dilation using eyedrops; if they do not provide a satisfactory result, injected intracameral mydriatics have been shown to be safe and effective for surgery and fast acting. If pharmacologic pupil dilation is insufficient, procedures for mechanical pupil dilatation may be needed during the surgery. People with retinal detachment may be scheduled for a combined vitreo-retinal procedure, along with IOL implantation. People taking tamsulosin (Flomax), a common drug for enlarged prostate, are prone to developing a surgical complication known as intraoperative floppy iris syndrome (IFIS), which requires appropriate management to avoid posterior capsule rupture. A Cochrane Review of three randomized clinical trials, including over 21,500 cataract surgeries, examined whether routine pre-operative medical testing resulted in a reduction of adverse events during surgery. Results showed performing pre-operative medical testing did not result in a reduction of risk of intra-operative or post-operative medical adverse events, compared to surgeries with no or limited pre-operative testing. Infants with congenital cataracts are more likely to have post-operative inflammation problems, and their eyes grow rapidly and unpredictably, making it challenging to select and fit a posterior chamber IOL in infants younger than seven months that will give satisfactory results later in childhood. A second surgery may be required later.
Contraindications Contraindications to cataract surgery include cataracts that do not cause visual impairment and medical conditions that predict a high risk of unsatisfactory surgical outcomes. such as: Poor general health or a serious medical condition. Surgery will not provide better visual function. Advanced macular degeneration Detached retina. Advanced diabetes that has affected the retina. An infection of the eyes or nearby that could cause endophthalmitis, so should be treated before cataract surgery. The person does not want surgery. Functional vision can be provided by glasses or other visual aids which is sufficient for the person's requirements. Corneal diseases such as glaucoma may be a relative contraindication.
Selection of intraocular lenses
After the removal of a cataract, an intraocular lens is usually implanted to replace the damaged natural lens. A foldable IOL may be implanted through a incision, whereas a rigid poly(methyl methacrylate) (PMMA) lens requires a larger cut. Foldable IOLs are made of silicone, hydrophobic, or hydrophilic acrylic material of appropriate refractive power and are inserted with a special tool. The IOL is inserted through the incision, usually into the capsular bag from which the cataract was removed (in-the-bag implantation). Sometimes, a sulcus implantation—in front of the capsular bag, but behind the iris—may be required because of posterior capsular tears or zonular dialysis (inadequate support for the capsular bag). This requires an IOL with different refractive power because of the placement further forward on the optical axis.
The appropriate refractive power of the IOL is selected, much like a spectacle or contact lens prescription, to provide the desired refractive outcome. Pre-operative measurements, including corneal curvature, axial length, and white-to-white measurements are used to estimate the required power of the IOL. These methods include several formulae and free online calculators which use similar input data. A history of corneal refractive laser surgery such as LASIK surgery, which alters corneal curvature, requires different calculations to take this into account.