Cataract surgery
Cataract surgery | |
---|---|
intracapsular cataract extraction | |
Frequency | Hundreds to thousands per million population per year. |
Outcomes | Restoration of useful vision or significant improvement in most cases |
ICD-9-CM | 13.19 |
MeSH | D002387 |
MedlinePlus | 002957 |
Cataract surgery, also called lens replacement surgery, is the removal of the natural
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 strong glare from lights and small light sources at night and reduced visual acuity at low light levels.[3][4]
During cataract surgery, the cloudy natural lens is removed from the posterior chamber, either by
Well over 90% of operations are successful in restoring useful vision, and there is a low complication rate. Day care, high-volume, minimally invasive, small-incision
Uses
Cataract surgery is the most common application of lens removal surgery, and is usually associated with lens replacement. It is used to remove the natural lens of the eye when it has developed a cataract, a cloudy area in the lens that causes
Cataracts most commonly occur due to aging, but may also be caused by
Early symptoms of cataract may be improved by wearing appropriate glasses; if this does not help, cataract surgery is the only effective treatment.[4] Surgery with implants generally results in better vision and an improved quality of life: however, the procedure is not readily available in many countries.[4][11][12][13]
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 Intracapsular cataract extraction has been superseded where the facilities for surgery under a microscope are available except for cases where the lens capsule cannot be retained, and couching is no longer used in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.[7] The small incision size used in phacoemulsification generally allows for sutureless incision closure.[7]
In extracapsular cataract extraction (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.[9] The basic version of ECCE uses a larger incision of 10–12 mm (0.39–0.47 in) 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.[2] 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.[6] 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.[8] 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.[14]
In most surgeries, an IOL is inserted. Foldable lenses are generally used for the 2–3 mm (0.08–0.12 in) phaco incision, while non-foldable lenses can be placed through the larger extracapsular incision.
Intracapsular cataract extraction (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.[2] After lens removal by ICCE, an intraocular lens implant can be placed in either the anterior chamber or sutured into the ciliary sulcus.[Note 1][7] 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.[15] Cryoextraction may still be used for the removal of subluxated (partially dislocated) lenses.[16]
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.[17]
Phacoemulsification is the most commonly performed cataract procedure in the developed world,[18] 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.[2] Cataract surgery is commonly done as an out-patient or day-care procedure, which is cheaper than hospitalisation and an overnight stay, and day surgery has similar medical outcomes.[19]
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:[2]
- The degree of reduction of vision due largely to the cataract is evaluated. While the existence of other sight-threatening diseases, such as
- In cases of uncontrolled glaucoma, a combined cataract-glaucoma procedure (phaco-trabeculectomy) can be planned and performed.[20]
- The
- People with vitreo-retinal procedure, along with IOL implantation.[25]
- People taking 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;[Note 2][26]
- 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.[27]
- Infants with congenital cataracts are more likely to have post-operative inflammation problems,[28] 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.[29]
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.[2] such as:
- Poor general health or a serious medical condition.[30]
- Surgery will not provide better visual function.[31]
- Advanced macular degeneration[30]
- Detached retina.[30]
- Advanced diabetes that has affected the retina.[30]
- An infection of the eyes or nearby that could cause endophthalmitis, so should be treated before cataract surgery.[31]
- The person does not want surgery.[31]
- Functional vision can be provided by glasses or other visual aids which is sufficient for the person's requirements.[31]
- Corneal diseases such as relative contraindication.[30]
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 1.8 to 2.8 mm (0.071 to 0.110 in) incision, whereas a rigid
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
Monofocal IOLs provide accurately focused vision at one distance only; far, intermediate, or near. People who are fitted with these lenses may need to wear glasses or contact lenses while reading or using a computer. These lenses usually have uniform spherical curvature.[35]
Other designs of multifocal intraocular lens that focus light from distant and near objects, working with similar effect to bifocal or trifocal eyeglasses, are also available. Pre-operative patient selection and good counselling is necessary to avoid unrealistic expectations and post-operative patient dissatisfaction, and possibly a requirement to replace the lens.[36] Acceptability of these lenses has improved, and studies have shown good results in patients selected for expected compatibility.[37]
Cataract surgery may be performed to correct vision problems on both eyes. If both eyes are suitable, people are usually advised to consider
One model of lens designed to change focus using the natural reflexes of the eye has two hinged struts on opposite edges, which displace the lens along the optical axis when an inward transverse force is applied to the haptic loops at the outer ends of the struts—the components transferring the movement of the contact points to the device—while recoiling when the same force is reduced. The lens is implanted in the eye's lens capsule, where the contractions of the ciliary body, which would focus the eye with the natural lens, are used to focus the implant, instead.[2][38]
IOLs used in correcting astigmatism have different curvature on two orthogonal axes, as on the surface of a torus: for this reason, they are called toric lenses. Intraoperative aberrometry[Note 4] can be used to assist the surgeon in toric lens placement and minimize astigmatic errors.[39][40]
The first aspheric IOLs were developed in 2004; they have a flatter periphery than the middle of the lens, improving contrast sensitivity. The effectiveness of aspheric IOLs depends on a range of conditions and they may not always provide significant benefit.[41]
Some IOLs are able to absorb
The light-adjustable IOL was approved by the U.S. Food and Drug Administration (FDA) in 2017.[44] This type of IOL is implanted in the eye and then treated with ultraviolet light to alter the curvature of the lens before fixing it at the final strength.[45]
In some cases, it may be necessary or desirable to insert an additional lens over the already implanted one, also in the posterior capsule. This type of IOL placement is called "piggyback" IOLs and is usually considered when the visual outcome of the first implant is not optimal.[46] In such cases, implanting another IOL over the existing one is considered safer than replacing the initial lens. This approach may also be used in people who need high degrees of vision correction.[47]
Cost is an important aspect of these lenses. Although Medicare covers the cost of monofocal IOLs in the United States, people will have to pay the price difference if they choose more expensive lenses.[48]
Operation procedures
Preparation
Preparation may begin three-to-seven days before surgery, with the pre-operative application of NSAIDs and antibiotic eyedrops.[8] If the IOL is to be placed behind the iris, the pupil is dilated by using drops to help better visualise the cataract. Pupil-constricting drops are reserved for secondary implantation of the IOL in front of the iris, when the cataract has already been removed without primary IOL implantation.[49]
The operation may occur on a stretcher or a reclining examination chair. The eyelids and surrounding skin are swabbed with a disinfectant, such as 10%
Anaesthesia
Most cataract operations are performed under
Phacoemulsification
Femtosecond laser-assisted phacoemulsification surgery is a more recent development which may have fewer adverse effects on the cornea and macula than manual phacoemulsification. The laser is used to make the corneal incision and the capsulotomy, which provides access to the lens, and initiate lens fragmentation, which reduces energy requirements for phacoemulsification. It provides high-precision, effective lens fragmentation at lower power levels and consequent good optical quality. However, as of 2022, the technique has not been shown to have significant visual, refractive, or safety benefits over manual phacoemulsification, and it has a higher cost.[2][53][54]
Entry into the eye is made through a minimal tunnel incision near the edge of the cornea.[7] The incision for cataract surgery has evolved along with the techniques for cataract removal and IOL placement. In phacoemulsification, the width depends on the requirements for IOL insertion. With foldable IOLs, it is often possible to use incisions smaller than 3.5 mm (0.14 in). The shape, position, and size of the incision affect the capacity for self sealing, the tendency to induce astigmatism, and the surgeon's ability to maneuvre instruments through the opening.[55] A more-posterior incision simplifies wound closure and decreases induced astigmatism, but it is more likely to damage blood vessels nearby.[7] One or two smaller side-port incisions at 60-to-90 degrees from the main incision may be needed to access the anterior chamber with additional instruments.[50]
Ophthalmic viscosurgical devices (OVDs), a class of clear, gel-like materials, are injected into the anterior chamber at the start of the procedure, to support, stabilize, and protect the eyeball, to help maintain eye shape and volume, and to distend the lens capsule during IOL implantation.[56] Their consistency allows surgical instruments to move through them, although they do not flow and retain their shape under low shear stress. The OVD will also constrain lens fragments from drifting around in the chamber. OVDs are available in several formulations, which may be combined or used individually as best suits the procedure.[7]
The lens is inside a capsule supported by the ciliary body, between the aqueous and vitreous, behind the opening in the iris.
The cataract's outer (cortical) layer is then separated from the capsule by a gentle, continuous flow or pulsed dose of liquid from a cannula, which is injected under the anterior capsular flap, along the edge of the capsulorhexis opening, in a step called hydrodissection.[58][59][60] In hydrodelineation, fluid is injected into the body of the lens through the cortex against the nucleus of the cataract, which separates the hardened nucleus from the softer cortex shell by flowing along the interface between them. As a result, the smaller hard nucleus can be more-easily emulsified. The posterior cortex serves as a buffer at this stage, protecting the posterior capsule membrane. The smaller size of the separated nucleus allows it to be broken up using shallower and less-peripheral grooving by the phaco tip, and produces smaller fragments after cracking or chopping. The posterior cortex also maintains the shape of the capsule through this stage, which reduces the risk of posterior capsule rupture.[61]
After nuclear cracking or chopping (if needed), the cataract is
Manual small incision cataract surgery (MSICS)
Many of the steps followed during MSICS are similar, if not identical, to those for phacoemulsification; the main differences are related to the alternative method of incision and cataract extraction from the capsule and eye.
The small incision into the anterior chamber of the eye is made at or near the
Extracapsular cataract extraction
Extracapsular cataract extraction (ECCE), also known as manual extracapsular cataract extraction, is the removal of almost the entire natural lens in one piece, while most of the elastic lens capsule (posterior capsule) is left intact to allow implantation of an intraocular lens.[2] The lens is manually removed through a 10–12 mm (0.39–0.47 in) incision in the cornea or sclera. Although it requires a larger incision and the use of stitches, this method may be preferable for very hard cataracts, which would require a relatively large ultrasonic energy input, which causes more heating, as well as in other situations in which phacoemulsification is problematic.[14]
Converting to ECCE to manage a contingency
The most commonly used procedures are phacoemulsification and manual small incision cataract surgery (MSICS). In either of these procedures, it can sometimes be necessary to convert to ECCS to deal with a problem better managed through a larger incision.[14] This may occur in the event of posterior capsule rupture, zonular dehiscence,[Note 8] a dropped nucleus[Note 9] with a nuclear fragment more than half the size of the cataract,[14] problematic capsulorhexis with a hard cataract,[14] or a very dense cataract where the heat developed by phacoemulsification is likely to cause permanent damage to the cornea.[14] Similarly, a change from MSICS to ECCE is appropriate whenever the nucleus is too large for the MSICS incision,[14] as well as in cases where the nucleus is found to be deformed during MSICS on a nanophthalmic eye.[Note 10][14]
Closing the wound
After the IOL is inserted, OVDs that were injected to stabilize the anterior chamber, protecting the cornea from damage and distending the cataract's capsule during IOL implantation, are removed from the eye to prevent post-operative viscoelastic glaucoma, a severe intra-ocular pressure increase. This is done via suction from the irrigation-aspiration instrument and replacement by buffered saline solution (BSS). Cohesive OVDs tend to adhere to themselves, a characteristic that makes their removal easier.[56] Removal of OVDs from behind the implant reduces the risk and magnitude of post-operative pressure spikes or capsular distention.[7] In the final step, the wound is sealed by increasing the pressure inside the globe with BSS, which presses the internal tissue against the external tissue of the incision, holding it closed. The surgeon will check whether the incision leaks fluid, because wound leakage increases the risk of penetration into the eye by microorganisms, thus predisposing it to endophthalmitis. If this does not achieve a satisfactory seal, a suture may be added. The wound is then hydrated, an antibiotic/steroid combination eyedrop is put in, and an eye-shield may be applied, sometimes supplemented with an eyepatch.[7]
Post-operative care
The use of an eye patch may be indicated, usually for some hours after surgery and for a few days while sleeping. A topical corticosteroid or nonsteroidal anti-inflammatory drug (NSAID) is used to control inflammation, in combination with topical antibiotics to prevent infection in the post-operative phase. These are generally self-administered as eyedrops for a few weeks.[7]
Complications
During surgery
Posterior capsular rupture, a tear in the posterior membrane of the natural
Intraoperative floppy iris syndrome has an incidence ranging from around 0.5% to 2.0%.[2] Iris or ciliary body injury has an incidence of about 0.6%-1.2%.[2] Other complications include failure to aspirate all lens fragments, leaving some in the anterior chamber,[71] and incisional burns, caused by overheating of the phacoemulsification tip when ultrasonic power continues while the irrigation or aspiration lines are blocked—the flow through these lines is used to keep the tip cool. Burns to the incision may make closure difficult and can cause corneal astigmatism.[7]
After surgery
Complications after cataract surgery are relatively uncommon. Posterior vitreous detachment (PVD) does not directly threaten vision, but may increase the risk of future vitreoretinal conditions. It may be more problematic in younger eyes because many people older than 60 have already gone through PVD. PVD may be accompanied by peripheral light flashes and increasing numbers of floaters.[74]
Some people develop
Mechanical pupillary block manifests when the anterior chamber gets shallower as a result of the obstruction of the aqueous humour flow through the pupil by the vitreous face or IOL.[85] This is caused by contact between the edge of the pupil and an adjacent structure, which blocks the flow of aqueous through the pupil itself. The iris then bulges forward and closes the angle between the iris and cornea, blocking drainage through the trabecular meshwork and causing an increase in intraocular pressure. Mechanical pupillary block has mainly been identified as a complication of anterior chamber intraocular lens implantation, but has been known to occur occasionally after posterior IOL implantation.[86]
Occasionally, a
Swelling of the
Uveitis–glaucoma–hyphema syndrome is a complication caused by the mechanical irritation of a mis-positioned IOL over the iris, ciliary body or iridocorneal angle.[89]
Other possible complications include
It may be necessary to exchange,[Note 11] remove[Note 12] or reposition[Note 13] an IOL after surgery, for any of the following reasons:[85]
- Capsular block syndrome, the hyper-distention of the lens capsular bag, due to the IOL blocking fluid from draining through the anterior capsulotomy. This may cause a myopic refractive error;[85]
- Chronic anterior uveitis, which is a persistent inflammation of the anterior segment;[85]
- Chronic loss of endothelial cells faster than the rate due to normal aging;[85]
- Iris pigment epithelium loss;[85]
- Physical pain;[85]
- Progressive elongation of the pupil in direction of the IOL's long axis;[85]
- Progressive closing of the anterior chamber angle, due to propagation of anterior synechiae without apparent anterior uveitis;[85]
- Incorrect IOL refractive power;[85]
- Incorrect positioning of the IOL (including decentring, tilt, or rotation), which partially prevents its correct function;[85]
- Damage or deformation of the IOL;[85]
- Unexpected optical results due to defects of the IOL;[85]
- Undesirable optical phenomena reported by the patient due to any other cause.[85]
Risk
Cataract surgery and IOL implantation have the safest and highest success rates of any eye care-related procedures. As with any type of surgery, however, some level of risk remains.[7]
Most complications of cataract surgery do not result in long-term visual impairment, but some severe complications can lead to irreversible blindness.[90] A survey of adverse results affecting Medicare patients recorded between 2004 and 2006 showed an average rate of 0.5% for one or more severe post-operative complications, with the rate decreasing by about 20% over the study period. The most important risk factors identified were diabetic retinopathy and a combination of cataract surgery with another intraocular procedure on the same day. In the study, 97% of the surgeries were not combined with other intraocular procedures; the remaining 3% were combined with retinal, corneal or glaucoma surgery on the same day.[90]
Recovery and rehabilitation
Following cataract surgery, side-effects such as grittiness, watering, blurred vision, double vision, and a red or bloodshot eye may occur, although they usually clear after a few days. Full recovery from the operation can take four-to-six weeks.
With small-incision self-sealing wounds used with phacoemulsification, some of the post-operative restrictions common with intracapsular and extracapsular procedures are not relevant. Restrictions against lifting and bending were intended to reduce the risk of the wound opening, because straining increases intraocular pressure. With a self-sealing tunnel incision, however, higher pressure closes the wound more tightly. Routine use of a shield is not usually required, because inadvertent finger pressure on the eye should not open a correctly structured incision, which should only open to point pressure.[7] After surgery, patients need to prevent contamination by avoiding rubbing their eyes, as well as not using eye makeup, face cream or lotions. Any kind of contact with excessive dust, wind, pollen or dirt should also be avoided. Moreover, people are advised to wear sunglasses on bright days, since the eyes become more sensitive to bright light for a prolonged period after surgery.[93]
Topical anti-inflammatory drugs and antibiotics are commonly used in the form of eyedrops to reduce the risk of inflammation and infection. A shield or eye-patch may be prescribed to protect the eye while sleeping. The eye will be checked to ensure the IOL remains in place, and once it has fully stabilized (after about six weeks), vision tests will be used to check whether prescription lenses are needed.
In some cases, people are dissatisfied with the optical correction provided by the initial implants, making removal and replacement necessary; this can occur with more complex IOL designs, as the patient's expectations might not match with the compromises inherent in these designs, or they might not be able to accommodate the difference in distance and near-focusing of monovision lenses.[36] The patient should not participate in contact or extreme sports, or similar activities, until cleared to do so by the eye surgeon.[95]
Outcomes
After full recovery, visual acuity depends on the underlying condition of the eye, the choice of IOL, and any long-term complications associated with the surgery. More than 90% of operations are successful in restoring useful vision, with a low complication rate.[96] The World Health Organization (WHO) recommends at least 80% of eyes should have a presenting visual acuity of 6/6 to 6/18 (20/20 to 20/60) after surgery, which is considered a good enough visual outcome; the percentage is expected to reach at least 90% with best correction. Acuity of between 6/18 and 6/60 (20/60 to 20/200) is regarded as borderline, whereas a value worse than 6/60 (20/200) is considered poor. Borderline or poor visual outcomes are usually influenced by pre-surgery conditions such as glaucoma, macular disease, and diabetic retinopathy.[97]
Refractive results using power calculation formulae based on pre-operative biometrics leave people within 0.5 dioptres of target (correlates to visual acuity of 6/7.5 (20/25) when targeted for distance) in 55% of cases and within one dioptre (correlates to 6/12 (20/40) when targeted for distance) in 85% of cases. Developments in intra-operative wavefront technology have demonstrated power calculations that provide improved outcomes, yielding 80% of patients within 0.5 dioptres (6/7.5 (20/25) or better).[40]
A ten-year prospective survey on refractive outcomes from a UK National Health Service (NHS) cataract surgery service from 2006 to 2016 showed a mean difference between the targeted and outcome refraction of −0.07 dioptres, with a standard deviation of 0.67, and a mean absolute error of 0.50 dioptres. 88.76% were within one diopter of target refraction and 62.36% within 0.50 dioptres.[98]
According to a 2009 study conducted in Sweden, factors that affected predicted refraction error included sex, pre-operative visual acuity and glaucoma, together with other eye conditions. Second-eye surgery, macular degeneration, age and diabetes did not affect the predicted outcome. Prediction error decreased with time, which is likely due to the use of improved equipment and techniques, including more-accurate
There is a tendency for post-operative refraction to vary slightly over several years. A small overall myopic shift has been recorded in 33.6% and a small hypermetropic shift in 45.2% of eyes with the remaining 21.2% in the study having no reported change. Most of the change occurred during the first year after surgery.[101]
Phacoemulsification via a coaxial incision[Note 14] may be associated with less astigmatism than the average for bimanual incisions,[Note 15] but the difference was found to be small and the evidence statistically uncertain.[102][103]
History
Cataract surgery has a long history in Europe, Asia, and Africa. Couching was the original form of cataract surgery, and was used from antiquity. It is still occasionally found in traditional medicine in parts of Africa and Asia. In 1753, Samuel Sharp performed the first-recorded surgical removal of the entire lens and lens capsule, equivalent to intracapsular cataract extraction. The lens was removed from the eye through a limbal incision.[104]
In 1884, Karl Koller became the first surgeon to apply a cocaine solution to the cornea as a local anaesthetic.[105][106] By the beginning of the 20th century, the standard surgical procedure was intracapsular cataract extraction (ICCE).[7] In 1949, Harold Ridley introduced the concept of implantation of the intraocular lens (IOL) which made visual rehabilitation after cataract surgery a more efficient, effective, and comfortable process.[104]
Intracapsular cryoextraction was the favoured form of cataract extraction from the late 1960s to the early 1980s using a liquid-nitrogen-cooled probe tip to freeze the encapsulated lens to the probe.[17][15][107] In 1967, Charles Kelman introduced phacoemulsification, which uses ultrasonic energy to emulsify the nucleus of the crystalline lens and remove cataracts by aspiration without a large incision. This method of surgery reduced the need for an extended hospital stay and made out-patient surgery the standard.[108] Ophthalmic viscosurgical devices (OVDs), which were introduced in 1972, facilitate the procedure and improve overall safety, particularly of phacoemulsification, by maintaining the shape of the eye at reduced pressure, and protecting the internal tissues of the eye without interfering with the operation.[104]
In the early 1980s,
In 1983 G.T. Keener Jr. introduced a constricting wire loop, L.L. Fry reported the phaco-sandwich technique, and Peter Kansas suggested the phacosection method for reducing the incision required. The sclerocorneal pocket tunnel incision introduced by Kratz allowed manual small incision cataract surgery without phacoemulsification. The introduction of the anterior chamber maintainer (ACM) by Blumenthal in 1987 facilitated a high-pressure and -flow system, for a stable intraocular environment during surgery.[109]
The Vision 2020 initiative succeeded in bringing avoidable blindness to the global health agenda. The causes have not been eliminated, but there have been significant changes to their distribution, which have been attributed to global demographic shifts. Remaining challenges to management of avoidable blindness include population size, gender disparities in access to eye-care, and the availability of a professional workforce.[112]
Recent developments as of 2022 include continuing research into the possibility of lens regeneration and pharmacological approaches to slowing the development of cataracts. Lens implants that help compensate for age-related macular degeneration by magnification have been developed, but require relatively large incisions. Improved management of inflammatory response, use of ray-tracing models, artificial intelligence and a range of new formulae for refraction prediction.[113]
Accessibility
Access to cataract surgery is very variable by country and region. Even in developed countries availability may vary significantly between rural and more densely populated areas.
The global health situation of cataracts is improving but this progress has not reduced the need for cataract surgery, which is still inadequate in large parts of the world. Older people, women, and lower socioeconomic status are associated with higher untreated cataract numbers.[114]
Cataracts have the most uneven global distribution of non-communicable eye diseases, with the burden of cataracts more concentrated in countries with lower socioeconomic status. Blindness is also correlated with a lack of ophthalmologists, and density of ophthalmologists correlates with a higher national income. High-income countries had an average of 76.2 ophthalmologists, and low income countries an average of 3.7 ophthalmologists per million inhabitants. The countries with highest socioeconomic levels tend to have the best cataract surgery outcomes. Low income countries also tend to lack adequate training facilities for surgeons.[114]
Europe
About 4.5 million cataract surgeries were done in the EU Member States in 2016. The rate of surgeries generally varied between 12000 and 4000 per million inhabitants. The highest rate was in Portugal, at 14000 per million and the lowest were Ireland and Slovakia at 2000 per million. The figures are not altogether comparable, as in some countries only surgeries at hospitals are included in the counts. The proportion of out-patient surgeries increased in almost all EU states between 2011 and 2016.[115]
Asia
The estimated distribution of ophthalmologists in Asia ranges from more than 114 per million of population in Japan, to none in Micronesia. South Asia has the highest global age-standardized prevalence of moderate-to-severe visual impairment (17.5%) and mild visual impairment (12.2%). Cataract has traditionally been a major cause of blindness in less-developed countries in the region, and in spite of improvements to the volume and quality of cataract surgeries, the rate of surgery remains low for some of these nations.[116]
Cataracts are common in China; as of 2022, their estimated overall prevalence in Chinese people over 50 years old was 27.45%. The overall cataract-surgery coverage rate was 9.19%. The prevalence of cataract and cataract surgical coverage also significantly varies by region.[117]
India's cataract-surgical rate rose from just over 700 operations per million people per year in 1981, to 6,000 per million per year in 2011, thus getting closer to the estimated requirement of 8,000-8,700 operations per million per year needed to eliminate cataract blindness in the country. The rate's rise was partly linked to factors such as increased efficiency due to improved surgical techniques, application of day-case surgery, improvements in operating theatre design, and efficient teamwork with sufficient staff.[118]
Africa
Cataracts are the main cause of blindness in Africa, and affect approximately half of the estimated seven million blind people on the continent, a number that is expected to increase with population growth by about 600,000 people per year. As of 2005, the estimated cataract-surgery rate was about 500 operations per million people per year. Progress on gathering information on epidemiology, distribution and impact of cataracts within the African continent has been made, but significant problems and barriers limiting further access to reliable data remain.[119]
These barriers relate to awareness, acceptance, and cost; some studies also reported community and family dynamics as discouraging factors. Most of the studies held locally reported that cataract-surgical rate was lower in females. The higher cataract-surgery coverage found in some settings in South Africa, Libya, and Kenya suggest many barriers to surgery can be overcome.[120]
According to the International Agency for the Prevention of Blindness, some sub-Saharan African countries have about one ophthalmologist per million people, while the National Center for Biotechnology Information stated the percentage of adults above the age of 50 in western sub-Saharan Africa who have developed cataract-induced blindness is about 6%—the highest rate in the world.[121]
A mathematical model using survey data from sub-Saharan Africa showed the incidence of cataracts varies significantly across the continent, with the required rate of surgery to maintain a visual acuity level of 6/18 (20/60) ranging from about 1,200 to about 4,500 surgeries per year per million people, depending on the area. Such variations may relate to genetic or cultural differences, as well as life expectancy.[122]
Latin America
A four-year longitudinal study of 19 Latin American countries published in 2010 showed most of the countries had increased their surgery rates over that period, with increases of up to 186%, but still failed to provide adequate surgical coverage. The study also shown a significant correlation between gross national income per capita and cataract-surgery rate in the countries involved.[123]
In a study published in 2014, the
A 2009 study showed that the prevalence of cataract blindness in people 50 years and older ranged from 0.5% in Buenos Aires, to 2.3% in parts of Guatemala. Poor vision due to cataracts ranged from 0.9% in Buenos Aires, to 10.7% in parts of Peru. Cataract-surgical coverage ranged from good in parts of Brazil to poor in Paraguay, Peru, and Guatemala. Visual outcome after cataract surgery was close to conformity with WHO guidelines in Buenos Aires, where more than 80% of post-surgery eyes had visual acuity of 6/18 (20/60) or better, but ranged between 60% and 79% in most of the other regions, and was less than 60% in Guatemala and Peru.[125]
Social, economic and environmental relevance
It has been estimated there were 43.3 million blind people in 2020, and 295 million with moderate and severe visual impairment (MSVI), 55% of whom were female. The age-standardised global prevalence in blindness decreased by 28.5% between 1990 and 2020, but the age-standardised prevalence of MSVI increased by 2.5%. Cataract remained the global leading cause of blindness in 2020.[112]
Cataract impairs vision and lowers quality of life. Improvements in vision help with daily activities, including work productivity and education. Cataract surgery reduces risk of falling and of dementia. It can prevent disability and is very cost effective, so it has large socioeconomic benefits, but the demand is great and the cost remains a large financial burden to public health systems.[114]
The cost of cataract surgery depends on the type of procedure, whether it is provided privately or by a government hospital, whether it is provided by out-patient (day care) or in-patient surgery, and on the economic status of people in the region. Because of the high cost of the equipment, phacoemulsification is generally more expensive than ECCE and MSICS.[6]
A 2021 study found that perioperative procedures before and after surgery differ considerably between various surgeons and institutions, which suggests the possibility for large amounts of unnecessary expenditure worldwide. Standardised best practice perioperative procedures can improve patient safety and have the potential to reduce unnecessary costs and unnecessary diagnostic procedures.[126]
The restoration of functional vision or improvement in vision possible in most cases has a large social and economic impact; patients may be able to return to paid work or continue their previous jobs, and may not become dependent on support from their family or the wider society. Studies show a sustained improvement to quality of life, financial situation, physical well-being, and mental health. Cataract surgery is one of the most cost-effective health interventions, since its economic benefits considerably exceed the cost of treatment.[127][128]
The 1998 World Health Report estimated 19.34 million people were bilaterally blind due to age-related cataracts, and that cataracts were responsible for 43% of all cases of blindness. This number and proportion were expected to increase due to population growth, and increased life expectancy approximately doubling the number of people older than 60 years. The global increase in blindness from cataract is estimated to be at least five million per year; a figure of 1,000 new cases per million population per year is used for planning purposes. The average outcomes of cataract surgery are improving, and consequently, surgery is being indicated at an earlier stage in cataract progression, increasing the number of operable cases. To reduce the backlog of patients, it is necessary to operate on more people per year than the new cases alone.[129]
As of 1998, the rate of surgeries in economically developed countries was about 4,000 to 6,000 per million population per year, which was sufficient to meet demand. India raised the cataract surgery rate (CSR) to over 3,000, but this was not considered to be sufficient to reduce the backlog. Middle-income countries of Latin America and Asia have CSRs of between 500 and 2,000 per million per year, whereas China, most of Africa, and poor countries of Asia had rates of less than 500. In India and South East Asia, the rate required to keep up with the increase is at least 3,000 per million population per year; in Africa and other parts of the world with smaller percentages of older people, a rate of 2,000 may be sufficient in the short term.[129]
In addition to the direct costs, associated surgical complications may require further intervention. In high income countries the environmental costs also tend to be higher. A phacoemulsification surgery in a UK hospital was estimated to cost more than 20 times the greenhouse gas emission of an equivalent surgery in an Indian hospital. Some of the unnecessary costs may be due to regulatory requirements that are based on perceived safety rather than actual safety.[114][130]
Special populations
Congenital cataracts
In general, there is greater urgency to remove dense cataracts from very young children because of the risk of amblyopia. For optimal visual development in newborns and young infants, a visually significant unilateral congenital cataract should be detected and removed before the child is six weeks old, while visually significant bilateral congenital cataracts should be removed before 10 weeks.[3] Congenital cataracts that are too small to affect vision will not be removed or treated, but may be monitored by an ophthalmologist throughout the patient's life. Commonly, a patient with small congenital cataracts that do not damage vision will be affected later in life, though this will take decades to occur.[131]
As of 2015[update], the standard of care for pediatric cataract surgery for children older than two years is primary posterior intraocular lens (IOL) implantation. Primary IOL implantation before the age of seven months is considered to have no advantages over aphakia.
Higher risk for operations on separate occasions
Most patients have bilateral cataracts; although surgery in one eye can restore functional vision, second-eye surgery has many advantages, so most patients undergo surgery in each eye on separate days. Operating on both eyes on the same day as separate procedures is known as immediately sequential bilateral cataract surgery; this can decrease the number of hospital visits, thus reducing risk of contagion in an epidemic. Immediately sequential bilateral cataract surgery also has significant cost savings, and faster visual rehabilitation and neuroadaptation.[Note 16] Another indication is significant cataracts in both eyes of patients for whom two rounds of anaesthesia and surgery would be unsuitable. The risk of simultaneous bilateral complications is low.[135][136]
Other animals
Cataract surgery in small animals such as dogs and cats is a routine ophthalmic procedure with a success rate of around 90%, and is usually better for eyes with relatively recent cataract development. The presence of other ocular problems may reduce the success rate. Procedures are similar to those for humans. General anesthesia is likely to be used,
See also
- Medicine portal
- Media related to Cataract surgery at Wikimedia Commons
- Africa Cataract Project
- Eye surgery – Surgery performed on the eye or its adnexa
- Himalayan Cataract Project – U.S. nonprofit organization
- IOLVIP – Intraocular lens system to compensate for macular degeneration
- Ophthalmology – Field of medicine treating eye disorders
- Phakic intraocular lens implantation in series with the natural lens to correct vision in cases of high refractive errors.[139]
- Refractive lens exchange, or clear lens extraction – Effectively use of the same procedures as for cataract surgery to replace a natural lens with high refractive error when other methods are not effective.
Notes
- ^ Ciliary sulcus: The space between the anterior surface of the ciliary body and the posterior surface of the base of the iris, just in front of the position of the natural lens.
- ^ Posterior capsule rupture: Unintended tearing of the posterior membrane of the lens capsule, which can allow migration of the vitreous into the anterior chamber.
- ^ White -to-white (WTW) measurement of an eye is the horizontal diameter of the cornea, measured across the corneal limbus.
- ^ Intraoperative aberrometry: A tool to take aphakic and pseudophakic refractive measurements during surgery to help optimise IOL power selection and placement.
- ^ Bridle suture: A suture passing through the superior rectus muscle of the eye, used to rotate the eyeball downwards in eye surgery.
- ^ Hydroexpression: Method of removing the lens from the capsule and anterior chamber by carrying it out in a flow of saline solution.
- ^ Viscoexpression: Method of removing the lens from the capsule and anterior chamber by carrying it out in a flow of viscoelastic material.
- ^ Zonular dehiscence: Breaking of the fibrous strands (zonules) connecting the crystalline lens to the ciliary body.
- ^ Dropped nucleus: A cataract nucleus which has fallen through into the vitreous chamber.
- ^ Nanophthalmic: Exceptionally small eyes.
- ^ Exchange: The IOL is replaced with another of the same model.
- ^ Remove: The IOL is removed and replaced with a different model lens or no replacement lens is implanted.
- ^ Reposition: The IOL is surgically moved to another location or rotated.
- ^ Coaxial phacoemulsification uses a single probe to irrrigate, emulsify and aspirate, which is operated through a single incision.
- ^ Bimanual phacoemulsification uses one probe to emulsify and aspirate, and a second that is only used for irrigation.
- ^ Neuroadaptation: Changes in the brain which accommodate the presence of a new substance or condition, such as the admission of more blue light after removal of a yellow tinted cataract, or the inability to adjust the focus of an IOL by the ciliary muscles.
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Further reading
- Frampton G, Harris P, Cooper K, Lotery A, Shepherd J (November 2014). "The clinical effectiveness and cost-effectiveness of second-eye cataract surgery: a systematic review and economic evaluation". Health Technology Assessment. 18 (68). NIHR Journals Library: 1–205, v–vi. PMID 25405576. 18.68.
- Prajna NV, Ravilla TD, Srinivasan S (2015). "Ch: 11. Cataract Surgery". In Debas HT, Donkor P, Gawande A, Jamison DT, Kruk ME, Mock CN (eds.). Essential Surgery. Disease Control Priorities. Vol. 1 (3rd ed.). The International Bank for Reconstruction and Development / The World Bank. from the original on 2022-01-19. Retrieved 2017-08-16.
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