Cataract surgery

Cataract surgery recently performed, foldable IOL inserted. A small incision and very slight hemorrhage are visible to the right of the still dilated pupil.

There are two main types of surgical technique used in cataract surgery: Phacoemulsification and manual extraction.

• Phacoemulsification (phaco) is the most common technique used in developed countries. It involves the use of a machine with an ultrasonic handpiece equipped with a titanium or surgical steel tip which vibrates at ultrasonic frequency (commonly 40,000 Hz) to emulsify the lens tissue. A second instrument (sometimes called a "cracker" or "chopper") may be used from a side port to facilitate breaking the hard cataract nucleus into smaller pieces. Fragmentation into smaller pieces makes emulsification, and the aspiration of cortical material (the soft part of the lens around the nucleus), easier. 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 remove the remaining peripheral cortical material.
• Femtosecond laser-assisted cataract surgery has been reported to be safe, and may have less adverse effect on the cornea and macula than manual phacoemulsification. The laser is used to make the corneal incision, the capsulotomy and to initiate lens fragmentation, which reduces the energy requirements for phacoemulsification. It offers high precision, effective lens fragmentation at lower power levels and good optical quality, but as of 2022 has not been shown to have significant visual, refractive or safety benefit over manual phacoemulsification, and it has a higher cost.[2][22][23]
• Extracapsular cataract extraction (ECCE), also known as manual extracapsular cataract extraction, is the removal of almost the entire natural lens in one piece, while the elastic lens capsule (posterior capsule) is left intact to allow implantation of an intraocular lens.[2] 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, this method may be indicated for patients with very hard cataracts or other situations in which phacoemulsification is problematic.[20]
• The manual small incision cataract surgery (MSICS) technique is an evolution of ECCE where the entire lens is removed from the eye through a self-sealing scleral tunnel wound. A well-constructed scleral tunnel is held closed by internal pressure, is watertight, and does not require suturing. The "small" in the title refers to the wound being relatively smaller than in ECCE, although it is still markedly larger than a phaco wound. Head-to-head trials of MSICS vs phaco in dense cataracts have found no difference in outcomes, but shorter operating time and significantly lower costs with MSICS.[6] MSICS has become the cataract surgery method of choice in the developing world, as it provides high quality outcomes with less surgically induced astigmatism than ECCE, no suture related problems, quick rehabilitation, and few post-operative visits. It is easy and fast to learn for the surgeon, cost effective, simple, and applicable to almost all types of cataract.[8]

Nucleus of a hypermature cataract removed by ECCE

• 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 due to the large incision required and pressure placed on the vitreous body. 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.[7]
  Cryoextraction is a technique used in ICCE in which the cataract is extracted 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.[24] It may still be used for the removal of subluxated lenses.[25]
• Refractive lens exchange is effectively the same procedure used to replace a lens with high refractive error when other methods are not effective. There are risks in addition to cataract procedural risks.[2] A related procedure is the implantation of phakic intraocular lenses in series with the natural lens to correct vision in cases of high refractive errors.[26]

Ophthalmic viscosurgical devices (OVDs) are a class of clear gel-like material used in cataract surgery to maintain the volume and shape of the anterior chamber of the eye, and protect the intraocular tissues during the procedure. They were originally called viscoelastic substances, or just viscoelastics. Their consistency allows the surgical instruments to move through them, but when there is low shear stress they do not flow, and retain their shape. OVDs are available in several formulations which may be combined or used individually as best suits the procedure, and are introduced into the anterior chamber at the start of the procedure, and removed at the end, when they are replaced by a buffered saline solution.[7] The tendency of cohesive OVDs to adhere to themselves helps with removal.[27]

18.5 diopter foldable intraocular lens

Injector for foldable Intraocular lenses. The incision size for this type is 2.8mm

The IOL injector is inserted in the incision and aimed at the capsule

The rolled up lens is ejected from the nozzle int the capsule

The lens unfolds in place

Section diagram of the eye, showing intraocular lens implanted in the posterior lens capsule behind the iris

After the removal of the cataract, an intraocular lens (IOL) is usually implanted into the eye, to provide refractive compensation for the lack of the natural lens. An IOL may be implanted either through a small incision (1.8 mm to 2.8 mm) when using a foldable IOL, or through a larger incision, when using a rigid poly(methyl methacrylate) (PMMA) lens. The foldable IOL, made of silicone, hydrophobic, or hydrophilic acrylic material of appropriate refractive power is folded either using a holder/folder, or a proprietary insertion device provided along with the IOL.[28] The lens implant is inserted through the incision, usually 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. This will require a modification of refractive power because of the more anterior placement on the optical axis.[29]

Other designs of multifocal intraocular lens are also available, which focus light from distant as well as near objects, working with similar effect to bifocal or trifocal eyeglasses. Preoperative patient selection and good counselling is necessary to avoid unrealistic expectations and post-operative patient dissatisfaction, and possibly a requirement to replace the lens.[30] Acceptability of these lenses has improved and studies have shown good results in patients selected for expected compatibility.[31]

A model of accommodating lens 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), and it springs back when the force is reduced. It 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.[32][2]

The intraocular lenses used in correcting astigmatism have different curvature on two orthogonal axes, as on the surface of a torus, and are called toric lenses. The STAAR Surgical Intraocular Lens was the first such lens developed in the United States and it may correct up to 3.5 diopters. A different model of toric lenses was created by Alcon and may correct up to 3 diopters of astigmatism. To achieve the most benefit from a toric lens, the surgeon must place the lens with the axes of curvature to suit the patient's astigmatism. Intraoperative aberrometry,[Note 1] can be used to assist the surgeon in toric lens placement and minimize astigmatic errors.[33][34]

Monofocal intraocular lenses provide accurately focused vision at one distance only: far, intermediate, or near. Patients who are fitted with these lenses may need to wear eyeglasses or contact lenses for reading or using a computer. These lenses usually have uniform spherical curvature.[35][36]

Cataract surgery may be performed to correct vision problems in both eyes, and in these cases, if both eyes are suitable, patients are usually advised to consider monovision. This procedure involves inserting in one eye an intraocular lens that provides near vision and in the other eye an IOL that provides distance vision. Although most patients can adjust to having implanted monofocal lenses with differing focal length, some cannot compensate and may experience blurred vision at both near and far distances. An IOL optimised for distance vision may be combined with an IOL that optimises intermediate vision instead of near vision as a variation of monovision.[28]

The first aspheric IOLs were developed in 2004. They provide better contrast sensitivity by having their periphery flatter than the middle of the lens. The effectiveness of aspheric IOLs depends on a range of conditions, and they may not always provide significant benefit.[37]

Some IOLs provide ultraviolet and high energy blue light absorbption. The natural crystalline lens of the eye filters these potentially harmful frequencies. A Cochrane review of 2018 found that there is unlikely to be a significant difference in distance vision between blue-filtering and plain lenses, and were unable to identify a difference in contrast sensitivity or colour discrimination.[38][39]

Another type of intraocular lens is the light-adjustable IOL, which was approved by the FDA in 2017.[40] This particular type of IOL is implanted in the eye and then treated with ultraviolet light of a certain wavelength in order to alter the curvature of the lens.[41]

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 as an option when the visual outcome of the first implant is not optimal.[42] 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 patients who need high degrees of vision correction.[43]

Whichever type is used, the appropriate refractive power of the IOL must be selected, much like an eyeglass prescription, to provide the desired refractive outcome. Conventionally, preoperative 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 formulas, including Hagis,[44] Hoffer Q,[44] Holladay 1,[44] Holladay 2,[44] and SRK/T.[45] There are also free online calculators using similar input data.[44] A history of LASIK surgery requires different calculations to take this into account.[44] Refractive results using power calculation formulas based on pre-operative biometrics leave patients within 0.5D (diopters) of target (correlates to visual acuity of 6/7.5 (20/25) when targeted for distance) in 55% of cases and within 1D (correlates to 6/12 (20/40) when targeted for distance) in 85% of cases. Developments in intraoperative wavefront technology have demonstrated power calculations that provide improved outcomes, yielding 80% of patients within 0.5 diopters (7/7.5 (20/25) or better).[34]

The cost is another important aspect of these lenses. Although most insurance companies cover the costs of monofocal IOLs, patients may have to pay the price difference if they choose more expensive lenses.[46]

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:

• The degree of reduction of vision due, at least in large part, to the cataract should be 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.[2]
• The eyes should have a normal pressure, or any pre-existing glaucoma should be adequately controlled with medications. In cases of uncontrolled glaucoma, a combined cataract-glaucoma procedure (phaco-trabeculectomy) can be planned and performed.[47]
• The pupil should be adequately dilated using eyedrops; if pharmacologic pupil dilation is insufficient, procedures for mechanical pupil dilatation may be needed during the surgery.[48]
• Patients with retinal detachment may be scheduled for a combined vitreo-retinal procedure, along with PCIOL implantation.[49]
• It has been shown that patients taking tamsulosin (Flomax), a common drug for enlarged prostate, are prone to developing a surgical complication known as intraoperative floppy iris syndrome (IFIS), 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.[50]
• A Cochrane Review of three randomized clinical trials including over 21,500 cataract surgeries examined whether routine preoperative medical testing resulted in a reduction of adverse events during surgery. Results showed that performing preoperative medical testing did not result in a reduction of risk of intraoperative or postoperative medical adverse events, compared to surgeries with no or limited preoperative testing.[51]

Antibiotics may be administered pre-operatively, intra-operatively, and/or post-operatively. Frequently a topical corticosteroid or nonsteroidal anti-inflammatory drug (NSAID) is used in combination with topical antibiotics post-operatively.[7]

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 some hours and while sleeping, after which the patient is instructed to use anti-inflammatory eyedrops to control inflammation and antibiotic eyedrops to prevent infection. Lens and cataract procedures are commonly performed in an outpatient setting; in the United States, 99.9% of lens and cataract procedures were done in an ambulatory setting in 2012.[52][7]

Occasionally, a peripheral iridectomy may be performed to minimize the risk of pupillary block glaucoma.[7] An opening through the iris can be fashioned manually (surgical iridectomy) or with a laser (called Nd:YAG laser iridotomy). The laser peripheral iridotomy may be performed either prior to or following cataract surgery.[53]

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.[53][54]

The two 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.[20]

The surgical procedure in phacoemulsification for removal of cataract involves a number of steps, and is typically performed under an operating microscope. Each step must be correctly performed to achieve the desired result. The steps may be described as follows:

1. Anaesthesia and pupil dilation; Either topical, sub-tenon, peribulbar, or retrobulbar local anaesthesia is used, usually causing little or no discomfort to the patient.[55] Topical anaesthetic agents are most commonly used and may be placed on the globe of the eye as eyedrops prior to surgery and or in the globe during surgery.[56] Local anaesthetic injection techniques include sub-conjunctival injections and or injections posterior to the globe (retrobulbar block) to produce a regional nerve block when it is necessary to prevent movement of the eye.[7] Intravenous sedation may be combined with the topical and injection techniques. General anaesthesia and retrobulbar blocks were historically used for intracapsular cataract surgery, but for small incision surgery and phacoemulsification local and topical anaesthesia is in common use.[2]
2. Site preparation by disinfection of the area surrounding the eye, covering the rest of the face, and exposure of the eyeball using an eyelid speculum;[57]
3. Entry into the eye through a minimal incision;[7] The incision for cataract surgery has evolved along with the techniques for cataract removal and IOL placement. In phacoemulsification the size depends on the requirements for IOL insertion. A more posterior incision simplifies wound closure and decreases induced astigmatism, but is more likely to damage blood vessels. With foldable IOLs it is sometimes possible to use incisions smaller than 3.5 mm. The shape, position and size of the incision all affect the capacity for self sealing, the tendency to induce astigmatism, and the surgeon's ability to maneuver instruments through the opening.[7] One or two smaller side port incisions 60 to 90 degrees from the main incision may be needed to access the anterior chamber with additional instruments.[57]
4. Injection of ophthalmic viscosurgical devices, also known as viscoelastics, into the anterior chamber to support, stabilize and protect the eyeball, to help maintain eye shape and volume, and to distend the lens capsule during IOL implantation.[27]
5. Capsulorhexis; Making a circular opening on the front surface of the lens capsule to access the lens within. In phacoemulsification, an anterior continuous curvilinear capsulorhexis, is used to create a round and smooth edged opening through which the lens nucleus can be emulsified and the intraocular lens implant inserted.[58]
6. Hydrodissection; The cataract's outer (cortical) layer is separated from the capsule by a gentle continuous flow or pulsed dose of liquid from a cannula, injected under the anterior capsular flap along the edge of the capsulorhexis opening;[59][60]
7. Hydrodelineation; An injection of fluid into the body of the lens through the cortex against the nucleus of the cataract separates the hardened nucleus from the softer cortex shell by flowing along the interface between them. The smaller hard nucleus can then be more expeditiously phacoemulsified, while the posterior cortex serves as a buffer protecting the posterior capsule membrane. The smaller size of the separated nucleus requires less deep and less peripheral grooving and produces smaller fragments after cracking or chopping. The posterior cortex also maintains the shape of the capsule which reduces risk of posterior capsule rupture[61]
8. Ultrasonic destruction and aspiration of the cataract after nuclear cracking or chopping (if needed), careful aspiration of the remaining lens cortex (outer layer of lens) material from the capsular bag, and capsular polishing (the removal of all remaining epithelial cells from the capsule), if needed;[62]
9. Implantation of the folded intraocular replacement lens, usually into the remaining posterior capsule, and ensuring that it unfolds correctly. Aligning the IOL in the correct axis to counteract astigmatism is necessary for a toric IOL;[2]
10. Removal of ophthalmic viscosurgical devices; The viscoelastic that was injected to stabilize the anterior chamber, protect the cornea from damage, and distend the cataract's capsule during IOL implantation must be 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). Removal of OVD from behind the implant reduces the risk and magnitude of postoperative pressure spikes or capsular distention;[7]
11. Wound sealing and hydration. The incision is sealed by elevating the pressure inside the globe with BSS which presses the internal tissue against the external tissue of the incision, holding the incision closed. If this does not achieve a satisfactory seal a suture may be added.[7]

Many of the steps are similar and some may be essentially the same as for phacoemulsification, and the main differences are related to the alternative method of incision and cataract extraction from the capsule and eye.

1. Preparation may begin 3 to 7 days before surgery with the preoperative application of NSAIDs and antibiotic eye drops.[8]
2. 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, when the cataract has already been removed without primary IOL implantation. Anaesthesia may be placed topically as eyedrops or via injection next to (peribulbar), or behind (retrobulbar) the eye,[56] or sub-Tenons. Local anaesthetic nerve blocking has been recommended to facilitate surgery.[8] Topical anaesthetics may be used at the same time as a intracameral lidocaine injection to reduce pain during the operation.[56] Oral or intravenous sedation may also be used to reduce anxiety. General anaesthesia is rarely necessary, but may be used for children and adults with medical or psychiatric issues affecting their ability to remain still during the procedure.[56][7]
3. 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% povidone-iodine, and topical povidone-iodine is put in the eye. 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.[57] Pain is usually minimal in properly anaesthetised eyes, though a pressure sensation and discomfort from the bright operating microscope light is common.[7] The ocular surface is kept moist during the procedure using sterile saline eye drops or methylcellulose viscoelastic. Bridle sutures[Note 2] may be used to help to stabilize the eyeball during sclerocorneal tunnel incision and during extraction of the nucleus and epinucleus through the tunnel.[8]
4. The small incision into the anterior chamber of the eye is made at or near the corneal limbus where the cornea and sclera meet, either superior or temporal.[8] Advantages of the smaller incision include use of few or no stitches and shortened recovery time.[2] The "small" incision is small in comparison with the earlier ECCE incision, but considerably larger than the phaco incision. The precise geometry of the incision is important as it affects the self-sealing of the wound and can cause astigmatism by distortion of the cornea during healing. A sclerocorneal or scleral tunnel incision is commonly used, which reduces induced astigmatism if suitably formed.[6][57] A sclerocorneal tunnel is a three phase incision. It starts with a shallow incision perpendicular to the sclera, followed by an incision through the sclera and cornea approximately parallel to the outer surface, and then a beveled incision into the anterior chamber. This structure provides the self-sealing characteristic, as internal pressure presses the faces of the incision together.[8]
5. The depth of the anterior chamber and position of the posterior capsule may be maintained during surgery by ophthalmic viscosurgical devices or an anterior chamber maintainer, which is an auxiliary cannula providing a sufficient flow rate of BSS to keep the shape of the chamber and internal pressure stable.[63][64]
6. A capsulotomy, also known as a cystotomy, is made to open the surface of the lens capsule, using an instrument called a cystotome.[65] The continuous curvilinear capsulorhexis technique is in common use. An anterior capsulotomy refers to the opening of the front portion of the lens capsule, necessary for access for removing the cataract,[66] whereas a posterior capsulotomy refers to an opening of the back portion of the lens capsule, which is not usually necessary or desirable unless it has opacified. [67] The types of capsular openings commonly used in MSICS are the continuous curvilinear capsulorhexis, the can-opener capsulotomy, and the envelope capsulotomy.[63]
7. Manual removal of the cataract lens from the capsule and anterior chamber. Hydroexpression,[Note 3] viscoexpression,[Note 4] or more direct mechanical methods may be used.[63][68][69]
8. Following cataract removal, an intraocular lens is usually inserted into the posterior capsule.[7] When the posterior capsule is damaged, the IOL may be inserted into the ciliary sulcus,[29] or a glued intraocular lens technique may be applied.[70]
9. After the IOL is inserted, the ophthalmic viscosurgery device is aspirated and replaced with BSS and the wound closed. The surgeon checks that the incision does not leak fluid, since wound leakage increases the risk of microorganisms gaining access into the eye and predisposing it to endophthalmitis. An antibiotic/steroid combination eye drop is put in and an eye shield may be applied, sometimes supplemented with an eye patch.[7]

Sometimes it can be necessary to change from a phacoemulsification procedure to ECCE if one of the following occur:[20]

• A posterior capsule rupture or zonular dehiscence[Note 5] or a dropped nucleus[Note 6] with a nuclear fragment more than half the size of the cataract;[20]
• Problematic capsulorhexis with a hard cataract;[20]
• A very dense cataract, where phacoemulsification is likely to cause permanent damage to the cornea.[20]

Similarly, there are occasions when it is appropriate to change from MSICS to ECCE:[20]

• The nucleus turns out to be too large for the MSICS incision;[20]
• During MSICS on a nanophthalmic eye,[Note 7] the nucleus is found to be deformed.[20]

• Posterior capsular rupture is the most common complication during cataract surgery, with a rate of around 0.5% to 5.2%. This is a tear in the posterior capsule of the natural lens.[2] Surgical management may involve anterior vitrectomy and, occasionally, alternative planning for implanting the intraocular lens, either in the ciliary sulcus, (the space between the iris and the ciliary body), in the anterior chamber (in front of the iris), or, less commonly, sutured to the sclera. Posterior capsule rupture can cause lens fragments to be retained, corneal oedema, and cystoid macular oedema. it is also associated with a six-times increase of risk of endophthalmitis and as much as 19 times increase in the risk of retinal detachment.[2][71] Management methods include the Intraocular lens scaffold procedure.[72]
• Suprachoroidal hemorrhage is a rare complication of intraocular surgery where the ciliary arteries bleed into the space between the choroid and the sclera.[73] It is a potentially vision threatening pathology. Risk factors for suprachoroidal hemorrhage include anterior chamber intraocular lens (ACIOL), axial myopia, advanced age, atherosclerosis, glaucoma, systolic hypertension, tachycardia, uveitis, and previous ocular surgery. Immediate and effective management of a suprachoroidal hemorrhage is necessary to protect vision.[7]
• Intraoperative floppy iris syndrome has an incidence of around 0.5% to 2.0%.[2]
• Iris or ciliary body injury has an incidence of about 0.6%-1.2%[2]
• Posterior dislocation of nuclear fragments: In the event of a posterior capsule rupture, fragments of the nucleus can find there way through the tear into the vitreous chamber. It is not always desirable to attempt to recover the fragments and it is rarely successful. The rest of the fragments should generally be stabilised first, and vitreous prevented from entering the anterior chamber. Removal of the fragments may be best referred to a vitreoretinal specialist.[7]
• Failure to aspirate all lens fragments, leaving some in the anterior chamber.[71]
• Incisional burns are caused by overheating of the phacoemulsification tip when ultrasonic power continues while the irrigation or aspiration lines are blocked, as 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]

Complications after cataract surgery are relatively uncommon.

• Posterior vitreous detachment (PVD) does not directly threaten vision. Even so, it is of increasing interest because the interaction between the vitreous body and the retina might play a decisive role in the development of major pathologic vitreoretinal conditions. PVD may be more problematic with younger patients, since many patients older than 60 have already gone through PVD. PVD may be accompanied by peripheral light flashes and increasing numbers of floaters.[74]

Slit lamp photo of IOL showing Posterior capsular opacification (PCO) visible a few months after implantation of intraocular lens in eye, seen on retroillumination

• Some people develop a posterior capsular opacification (PCO), 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 visual acuity and can be safely and painlessly corrected using a laser to a hole in the posterior lens capsule. It usually is a quick outpatient procedure that uses a Nd-YAG laser (neodymium-yttrium-aluminum-garnet) to clear the central portion of the opacified posterior pole of the capsule (posterior capsulotomy).[75] This creates a clear central visual axis for improving visual acuity.[76] In very thick opacified posterior capsules, a surgical (manual) capsulectomy may be needed. A posterior capsulotomy is a factor which must be taken in consideration in the event of IOL replacement as vitreous can migrate toward the anterior chamber through the opening previously occluded by the IOL. Posterior capsule opacification has an incidence of about 0.3% to 28.4%.[2]
• Retinal detachment normally occurs at a prevalence of 1 in 1,000 (0.1%), but patients who have had cataract surgery are at an increased risk (0.5–0.6%) of developing rhegmatogenous retinal detachment (RRD) – the most common form of retinal detachment.[77] Cataract surgery speeds up the rate of vitreous humor liquefaction and this leads to increased rates of RRD.[78] When a retinal tear occurs, vitreous liquid enters the space between the retina and retinal pigmented epithelium (RPE) and presents as flashes of light (photopsia), dark floaters, and loss of peripheral vision.[77]
• Toxic anterior segment syndrome or TASS is a non-infectious inflammatory condition that may occur following cataract surgery. It is usually treated with topical corticosteroids in high dosage and frequency.[79]
• Endophthalmitis is a serious infection of the intraocular tissues, usually following intraocular surgery complications, or penetrating trauma, and one of the most severe. It is rare in cataract surgery due to the use of prophylactic antibiotics There is some concern that the clear cornea incision might predispose to the increase of endophthalmitis but there is no conclusive study to corroborate this suspicion.[80] An intracameral injection of antibiotics may be used as a preventive measure. A meta-analysis showed the incidence of endophthalmitis after phacoemulsification to be 0.092%. The risk is higher with diabetes, advanced age, larger incision procedures,[28] and vitreous communication with the anterior chamber due to posterior capsule rupture, The risk of vitreous infection is at least six times higher than for the aqueous.[81] Typical presentation is within two weeks after the procedure with decreased visual acuity, red-eye, and pain. Hypopyon occurs about 80% of the time. Common infective agents include coagulase-negative staphylococci and Staphylococcus aureus in about 80% of infections. Management includes vitreous humor tap and injection of broad-spectrum antibiotics. Outcomes can be severe even with treatment, and may range from permanently decreased visual acuity to no light perception, depending on the microbiological etiology.[2]
• Glaucoma may occur and it may be very difficult to control. It is usually associated with inflammation, especially when little fragments or chunks of the nucleus get access to the vitreous cavity. Some experts recommend early intervention by posterior pars plana vitrectomy when this condition occurs. In most cases raised post-operative intraocular pressure is transient and benign, usually returning to baseline within 24 hours without intervention. Glaucoma patients may experience further visual field loss or a loss of fixation, and are more likely to experience intraocular pressure spikes.[82] Secondary glaucoma is an important complication of surgery for congenital cataracts. It can occur several years after the cataract surgery, so these patients need lifelong surveillance.[83]
• Mechanical pupillary block; shallowing of the anterior chamber by obstruction of the flow of aqueous humor flow through the pupil by the vitreous face or IOL;[84]
• Elevated intraocular pressure.[84]
• Swelling of the central part of the retina, called the macula, resulting in macular oedema, can occur a few days or weeks after surgery. Most such cases can be successfully treated. Preventative use of nonsteroidal anti-inflammatory drugs has been reported to reduce the risk of macular oedema to some extent.[85]
• Uveitis–glaucoma–hyphema syndrome: This is a complication caused by the mechanical irritation of a mispositioned intraocular lens over the iris, ciliary body or iridocorneal angle.[86]
• Other possible complications include: Swelling or oedema of the cornea, sometimes associated with cloudy vision (pseudophakic bullous keratopathy), which may be transient or permanent. Displacement or dislocation of the intraocular lens implant may occur, but it is rare. Unplanned high refractive error (either myopic or hypermetropic) may occur due to error in the ultrasonic biometry (measurement of the eye length and calculation of the required intraocular lens power). Cyanopsia, in which the patient sees everything tinted with blue, often occurs for a few days, weeks or months after removal of a cataract. Floaters commonly appear after surgery.[39]

It may be necessary to exchange,[Note 8] remove[Note 9] or reposition[Note 10] an IOL after surgery, for any of several possible reasons.[84]

• Capsular block syndrome, which is 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;[84]
• Chronic anterior uveitis, which is a persistent inflammation of the anterior segment;[84]
• Chronic loss of endothelial cells faster than the rate due to normal aging;[84]
• Iris pigment epithelium loss;[84]
• Pain;[84]
• Progressive elongation of the pupil in direction of the long axis of the IOL;[84]
• Progressive closing of the anterior chamber angle due to propagation of anterior synechiae without apparent anterior uveitis;[84]
• Incorrect IOL refractive power;[84]
• Incorrect positioning of the IOL, including decentering, tilt, or rotation that reduces correct function;[84]
• Damage or deformation of the IOL;[84]
• Unexpected optical results due to defects of the IOL;[84]
• Undesirable optical phenomena reported by the patient due to any other cause.[84]

Statistically, cataract surgery and IOL implantation are procedures with the safest and highest success rates in eye care.[7] However, as with any type of surgery, some level of risk remains.

As of 2011, cataract surgery is the most frequent surgical procedure in the United States, with 1.8 million Medicare beneficiaries undergoing the procedure in 2004. This rate is expected to increase as the population ages. Cataract surgery following modern procedures is safe and effective, but not entirely free of risk.[87]

Most complications of cataract surgery do not result in long-term visual impairment, but there are some severe complications that can result in irreversible blindness.[87] 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 over the study period by about 20%. The most important risk factors identified were diabetic retinopathy, and a combination of cataract surgery with another intraocular procedure on the same day. 97% of the surgeries in the study were not combined with other intraocular procedures. 3% were combined with retinal, corneal or glaucoma surgery on the same day.[87]

"Couching for cataract"; Wellcome Collection illustration of Indian doctors performing the technique.

Couching is the earliest documented form of cataract surgery, and one of the oldest surgical procedures. It is a technique whereby the lens is dislodged, and pushed aside, but not removed from the eye, thus removing the opacity, but also the ability to focus. Couching was used for centuries, but it has generally poor outcomes and is currently routinely practiced only in remote areas of developing countries.[98][99]

Cataract surgery was first mentioned in the Babylonian code of Hammurabi 1750 BCE.[100]

The earliest known depiction of cataract surgery is on a statue from the Fifth Dynasty of Egypt (2467–2457 BCE).[100] It is further alleged that a "relief painting from tomb number TT 217 in a worker settlement in Deir el-Medina" shows "the man buried in the tomb, Ipuy,... one of the builders of royal tombs in the renowned Valley of the Kings, circa 1279–1213 BC"[101] as he underwent cataract surgery. It is assumed that the couching technique was used.[100]

Couching was practised in ancient India and subsequently introduced to other countries by the Indian physician Sushruta (c. 6th century BCE),[102] who described it in his work the Compendium of Sushruta or Sushruta Samhita. The Uttaratantra section of the Compendium, chapter 17, verses 55–69, describes an operation in which a curved needle was used to push the opaque "phlegmatic matter" (kapha in Sanskrit) in the eye out of the way of vision. The phlegm was then said to be blown out of the nose. The eye would later be soaked with warm clarified butter and then bandaged. Here is a translation from the original Sanskrit:

vv. 55–56: Now procedure of surgical operation of ślaiṣmika liṅganāśa (cataract) will be described. It should be taken up (for treatment) if the diseased portion in the pupillary region is not shaped like half moon, sweat drop or pearl: not fixed, uneven and thin in the centre, streaked or variegated and is not found painful or reddish.

vv. 57–61ab: In moderate season, after unction and sudation, the patient should be positioned and held firmly while gazing at his nose steadily. Now the wise surgeon leaving two parts of white circle from the black one towards the outer canthus should open his eyes properly free from vascular network and then with a barley-tipped rod-like instrument held firmly in hand with middle, index and thumb fingers should puncture the natural hole-like point with effort and confidence not below, above or in sides. The left eye should be punctured with right hand and vice-versa. When punctured properly a drop of fluid comes out and also there is some typical sound.

vv. 61bc–64ab: Just after puncturing, the expert should irrigate the eye with breast-milk and foment it from outside with vāta-[wind-]alleviating tender leaves, irrespective of doṣa [defect] being stable or mobile, holding the instrument properly in position. Then the pupillary circle should be scraped with the tip of the instrument while the patient, closing the nostril of the side opposite to the punctured eye, should blow so that kapha [phlegm] located in the region be eliminated.

vv. 64cd–67: When pupillary region becomes clear like cloudless sun and is painless, it should be considered as scraped properly. (If doṣa [defect] cannot be eliminated or it reappears, puncturing is repeated after unction and sudation.) When the sights are seen properly the śalākā [probe] should be removed slowly, eye anointed with ghee and bandaged. Then the patient should lie down in supine position in a peaceful chamber. He should avoid belching, coughing, sneezing, spitting and shaking during the operation and thereafter should observe the restrictions as after intake of sneha [oil].

v. 68: Eye should be washed with vāta-[wind-]alleviating decoctions after every three days and to eliminate fear of (aggravation of) vāyu [wind], it should also be fomented as mentioned before (from outside and mildly).

v. 69: After observing restrictions for ten days in this way, post-operative measures to normalise vision should be employed along with light diet in proper quantity.[103]

The removal of cataracts by surgery was introduced into China from India, and flourished in the Sui (581–618 CE) and Tang dynasties (618–907 CE).[104]

The first references to cataract and its treatment in Europe are found in 29 AD in De Medicina, the work of the Latin encyclopedist Aulus Cornelius Celsus, which describes a couching operation.[105]

Galen of Pergamon 2nd century CE, a prominent Greek physician, surgeon and philosopher, performed an operation to remove a cataract affected lens, using a needle-shaped instrument.[106][107] Although many 20th century historians have claimed that Galen believed the lens to be in the exact center of the eye, there is evidence that he understood that the crystalline lens is located in the anterior aspect of the human eye.[108]

The removal of cataracts by couching was a common surgical procedure in Djenné,[109] as in many other parts of Africa.[110]

Couching continued to be used throughout the Middle Ages and is still used in some parts of Africa and in Yemen.[111][99] Couching is an ineffective and dangerous method of cataract therapy, and often results in patients remaining blind or with only partially restored vision.[111] For the most part, it has been replaced by extracapsular cataract surgery, including phacoemulsification.[112]

The lens can also be removed by suction through a hollow instrument. Bronze oral suction instruments have been unearthed that seem to have been used for this method of cataract extraction during the 2nd century CE.[113] Such a procedure was described by the 10th-century Persian physician Muhammad ibn Zakariya al-Razi, who attributed it to Antyllus, a 2nd-century Greek physician. The procedure "required a large incision in the eye, a hollow needle, and an assistant with an extraordinary lung capacity".[114] This suction procedure was also described by the Iraqi ophthalmologist Ammar Al-Mawsili, in his Choice of Eye Diseases, also written in the 10th century.[114] He presented case histories of its use, claiming to have had success with it on a number of patients.[114]^: p318 Extracting the lens has the benefit of removing the possibility of the lens migrating back into the field of vision.[115] A later variant of the cataract needle in 14th-century Egypt, reported by the oculist Al-Shādhili, used a screw to grip the lens. It is not clear how often, if ever, this method was used, as other writers, including Abu al-Qasim al-Zahrawi and Al-Shadhili, appear to have been unfamiliar with this procedure or claimed it was ineffective.[114]^: p319

Beer-type cataract knife and needle, cased, Paris, 1820-1866

A cataract surgery. Dictionnaire Universel de Médecine (1746–1748).

In 1748, Jacques Daviel was the first modern European physician to successfully extract cataracts from the eye, removing the cataract from the capsule through a corneal incision with about 50% success rate.[96] In 1753 the first recorded surgical removal of the entire lens and lens capsule was done by Samuel Sharp. The lens was removed from the eye through a limbal incision.[96] In America, cataract couching may have been performed in 1611,[116] and cataract extraction was most likely performed by 1776.[117] Cataract extraction by aspiration of lens material through a tube to which suction is applied was performed by Philadelphia surgeon Philip Syng Physick in 1815.[118]

King Serfoji II Bhonsle of Thanjavur in India performed cataract surgeries in the early 1800s, documented in manuscripts at the Saraswathi Mahal Library.[119]

At the beginning of the 20th century the standard procedure was intracapsular cataract extraction (ICCE). The work of Henry Smith was influential as he had developed a safe and fast way to remove the lens within its capsule by external manipulation. The capsule forceps, the discovery of enzymatic zonulysis by Joaquin Barraquer in 1957, and the introduction of cryoextraction of the lens by T. Krawicz and Charles Kelman in 1961 helped continue the development of ICCE.[7] Inracapsular cryoextraction using a probe tip cooled by liquid nitrogen to freeze the encapsulated lens to the probe was the favored form of cataract extraction from the late 1960s to the early 1980s.[24][120]

In 1949, Harold Ridley introduced the concept of implantation of the intraocular lens which made more efficient and comfortable visual rehabilitation possible after cataract surgery.[96]

Artificial intraocular lenses (IOLs) are used to replace the eye's natural lens that is removed during cataract surgery. These lenses increased in popularity since the 1960s, but it was not until 1981 that the first U.S. Food and Drug Administration (FDA) approval for this type of product was issued. The development of IOLs was an innovation, as patients previously did not have their natural lens replaced and as a result had to wear very thick eyeglasses or a special type of contact lenses. IOLs can be selected to correct other vision problems, such as toric lenses for correcting astigmatism.[35] IOLs can be classified as monofocal, toric, and multifocal lenses.[2] Also in the 1960s, the development of ultrasound A-scan biometry was a major advance in ocular biometry, which contributed towards accurate prediction of implant refractive strength.[121]

In 1967, Charles Kelman introduced phacoemulsification, a technique that uses ultrasonic energy to emulsify the nucleus of the crystalline lens in order to remove the cataracts by aspiration without a large incision. This method of surgery decreased the need for an extended hospital stay and made out-patient surgery the standard. Patients who undergo cataract surgery hardly complain of pain or even discomfort during the procedure. However patients who have topical anaesthesia, rather than peribulbar block anaesthesia, may experience some discomfort.[122]

Ophthalmic viscosurgical devices (OVDs) were introduced in 1972, and facilitated the procedure, as well as improving safety. An OVD is a viscoelastic solution, a gel-like substance used to maintain the shape of the eye at reduced pressure and to protect the inside structure and tissues of the eye without interfering with the operation.[96]

In the early 1980s Danièle Aron-Rosa and colleagues introduced the neodymium:yttrium-aluminum-garnet laser|neodymium:yttrium-aluminum-garnet (Nd:YAG) laser for posterior capsulotomy.[7]

In 1980 Colvard made the cataract incision in the sclera, which limited induced astigmatism.[63]

Thomas Mazzocco developed the first foldable IOL and implanted it in 1985. Graham Barrett and associates pioneered the use of silicone, acrylics, and hydrogel lenses.[7]

According to Cionni et al 2006, Kimiya Shimizu began removing cataracts using topical anaesthesia in the late 1980s,[7] though Davis, 2016, attributes the introduction of topical anaesthetics to Fischman in 1993.[96]

In 1987, Blumenthal and Moissiev described the use of a reduced incision size for ECCE, They used a 6.5 to 7 mm straight scleral tunnel incision 2 mm behind the limbus, with two side ports.[63]

In 1989 McFarland introduced a self-sealing incision architecture, in 1990 Pallin described a chevron-shaped incision which induces the least astigmatism, and in 1991 Singer described the frown incision, where the ends curve away from the limbus, which produces reduced astigmatism, but more than the chevron.[63]

Toric intraocular lenses were introduced in 1992 and are used worldwide to correct corneal astigmatism during cataract surgery.[35][96] They have been FDA approved since 1998.[33]

In the late 1990s, a further advance was made with optical biometry based on partial coherence infrared interferometry, which gives better resolution and much greater precision, and is also much quicker and more comfortable than ultrasound.[121]

According to surveys of members of the American Society of Cataract and Refractive Surgery, approximately 2.85 million cataract procedures were performed in the United States during 2004 and 2.79 million in 2005.[123]

In 2009 Kosakarn described a method for manual fragmentation of the lens called double-nylon loop. In this technique, the lens is divided into three pieces for extraction, allowing a smaller, sutureless incision of 4.0–5.0 mm, and implantation of a foldable IOL. This technique used less expensive instruments and is suitable for use in developing countries.[63]

As of 2013, instruments are available that use infra-red swept-source optical coherence tomography (SS-OCT), a non-invasive, high-speed method that can penetrate dense cataracts, and collects thousands of scans per second to generate high resolution 2- or 3-dimensional data.[121]

As of 2021, approximately 4 million cataract procedures take place annually in the U.S. and nearly 28 million worldwide, a large proportion in India. That is about 75,000 procedures per day globally.[124]

In the UK the practice of the various National Health Service healthcare providers in referring people with cataracts to surgery varied widely as of 2017, with many of the providers only referring people with moderate or severe vision loss, and often with delays.[125] This is despite guidance issued by the NHS executive in 2000 urging providers to standardize care, streamline the process, and increase the number of cataract surgeries performed in order to meet the needs of the aging population.[126] The national ophthalmology outcomes audit in 2019 found five NHS trusts with complication rates between 1.5% and 2.1%, but since the first national cataract audit in 2010, there had been a 38% reduction in posterior capsule rupture complications.[127]

South Asia has the highest global age-standardized prevalence of moderate to severe visual impairment (17.5%) and mild vision impairment (12.2%). The distribution of ophthalmologists ranges from more than 114 per million of population in Japan to none in Micronesia. Cataract has traditionally been a major cause of blindness in the less developed countries in the region, and although the volume and quality of cataract surgeries have improved, the cataract surgery rate remains low for some of these countries.[128]

The cataracts are common in China, with the overall prevalence in 2022 in Chinese people over 50 years old found to be 27.45% This was split by environment, with rural prevalence at 28.79%, and urban prevalence at 26.66%. Prevalence of cataract varies considerably by age group. From ages 50 to 59 it is 7.88%, from 60 to 69 it is 24.94%, from 70 to 79 it is 51.74%, and over 80 years old it is 78.43%. The overall cataract surgery coverage rate was 9.19%. The prevalence of cataract and cataract surgical coverage also has significant variation by region.[129]

India has raised its cataract surgical rate from just over 700 operations per million people per year in 1981, to 6,000 per million per year in 2011, which is much closer to the estimated rate of 8,000 to 8,700 per million per year needed to eliminate blindness due to cataracts in India. This is partly a combined result of increased efficiency due to improved surgical technique, with surgeons able to do twenty operations per day, application of day case surgery, improvements in operating theatre design, and efficient team work with sufficient staff.[130]

The other aspect is that people apply for surgery in large numbers. This has been achieved by creating a demand for cataract surgery in the community. Social marketing methods were used to make the population more aware of cataracts and that they are a common age-related problem that can be treated effectively at affordable cost. The NGO sector and Indian ophthalmologists have developed methods to deal with local problems, including outreach camps to find those needing surgery, counselors to explain the system, locally manufactured equipment and consumables and a tiered pricing structure, using subsidies where appropriate.[130]

There have been occasional public scandals when multiple patients have been infected and developed endophthalmitis on the same day at some hospitals associated with eye camps in India. Journalists have reported blame being placed on the surgeons, the hospital administration, and other persons, but have not reported on who was responsible for sterilisation of the surgical instruments and theatres involved, whether all infections involved the same micro-organisms, the same theatres, or the same staff. One investigation found bacteria known to be associated with endophthalmia present in the theatre and in the eyes of affected patients, and it was claimed that the hospital had not followed the required protocol for infection control, but the investigation was ongoing. Several instances of surgeons performing more operations per day than officially allowed have also been reported, but it has not been made clear how this could affect sterility of equipment, or how it might plausibly cause infection.[131]

In 2022 the digital news publication Scroll.in requested information on the numbers of patients who had contracted such infections from the central health ministry and were informed that since 2006, 469 people had either been blinded in one eye or had their vision seriously affected after undergoing surgery at eye camps. Further inquiries indicated that the number was at least 519, but the total number of surgeries for that period was not mentioned.[131] Since the number of eye surgeries performed in India is large – as of 2017, India is claimed to be doing about 6.5 million cataract surgeries per year – more than the US, Europe and China put together – this is a very small percentage.[132]

Cataract surgery in Bedele, Ethiopia

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 which is expected to expand with population growth by about 600,000 people per year. The cataract surgery rate is about 500 per million per year as of 2005. Progress has been made on gathering information on epidemiology, distribution and impact of cataracts within Africa, but significant barriers and challenges remain.[133]

These barriers are variously reported as relating to awareness, acceptance and cost, and some studies reported community and family dynamics as barriers. Cataract surgical rate was reported as lower in females in the majority of studies. The higher cataract surgical coverage found in some settings in South Africa, Libya, and Kenya suggest that many barriers to surgery can be overcome.[134]

According to the International Agency for the Prevention of Blindness there is only about one ophthalmologist per million people in some sub-Saharan countries, and according to the National Center for Biotechnology Information the percentage of adults above the age of 50 in western sub-Saharan Africa who are blind because of cataracts is about 6% – the highest rate in the world.[135]

A mathematical model using survey data from sub-Saharan Africa shows that the incidence of cataracts varies significantly across the continent, and therefore that the required rate of surgery to maintain a visual acuity level of 6/18 (20/60) varies significantly from about 1200 to about 4500 surgeries per year per million people. This variation may relate to genetic or cultural differences, and to life expectancy.[136]

As of 2011, 0.78% of the population of Nigeria are blind. More than 43% of these are blind from cataracts and another 9% from aphakia and complications from couching performed by itinerant practitioners. There are about 2.8 ophthalmologists per million population in Nigeria, but the cataract surgical rate is only 300 per million per year, as opposed to the WHO recommendation of 3000 per million per year. Reasons cited for this situation include inadequate blindness prevention programs, lack of political will, shortage of funding, and failure of the government to take responsibility for training and services. Teaching hospitals do not have enough patient surgical load to support training.[99]

Facilities vary from government hospitals where subsidised operations for the disadvantaged may be charged at rates that cover the consumables, to private clinics where state of the art equipment is used and charged at premium rates. Waiting times in government hospitals may be up to two years, but are much shorter at private clinics. An innovation increasing efficient use of facilities is used in some hospitals where two patients are operated on for cataracts in the theatre at the same time.[137] There are also charitable organisations which provide pro bono cataract surgery in rural areas using mobile clinics.

As of 2023 the cataract surgery rate in South Africa is less than half of the estimated requirement of at least 2000 per million population per year needed to eliminate cataract blindness.[138][139] Problems identified by Lecuona and Cook in 2011 include inadequate human resources available to the public sector to provide care for the indigent population.[139] The main barrier to increasing the rate of surgery in South Africa is inadequate surgery capacity. A higher annual rate of cataract surgeries by individual surgeons would improve cost effectiveness and personal skills, and also contribute towards a overall reduction of risk.[139]

Cataract operation in Sao Paulo, Brazil

A four-year longitudinal study of 19 Latin-America countries published in 2010 showed that most of the countries increased their surgery rates over that period, with increases of up to 186%, but still fell significantly short of adequate surgical coverage. There is a good correlation between gross national income per capita and cataract surgery rate over the countries involved.[140]

In a study published in 2014 the weighted mean regional surgery rate was found to have increased by 70% over the period from 2005 to 2012, from 1562 to 2672 cataract surgeries per million inhabitants. The weighted mean number of ophthalmologists per 1 million inhabitants in the region is approximately 62. Cataract surgery coverage varies widely in Latin America, from only 15% in El Salvador to a more satisfactory 77% in Uruguay. Barriers cited include cost of surgery and lack of awareness of the surgical treatment option. The available numbers of ophthalmologists appear to be adequate, but it is not known how many actually perform surgery.[141]

In a third study, published in 2009, 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 World Health Organization (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 worse than 60% in Guatemala and Peru.[142]

Bilateral cataracts in an infant due to congenital rubella syndrome

Congenital cataracts are a lens opacity which is present at birth. They occur in a broad range of severity: some lens opacities do not progress and are visually insignificant, others can produce profound visual impairment. Congenital cataracts may be unilateral or bilateral. They can be classified by morphology, presumed or defined genetic cause, presence of specific metabolic disorders, or associated ocular anomalies or systemic findings.[3]

In general, the younger the child, the greater the urgency in removing a dense cataract, 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 age six weeks, and visually significant bilateral congenital cataracts should be removed before age 10 weeks.[3]

Some congenital cataracts are too small to affect vision, therefore no surgery or treatment will be done. If they are superficial and small, an ophthalmologist will continue to monitor them throughout a patient's life. Commonly, a patient with small congenital cataracts that do not affect vision will eventually be affected later in life; generally this will take decades to occur.[149]

The standard of care as of 2015 for pediatric cataract surgery for children older than two years is primary posterior intraocular lens implantation. Primary IOL implantation before age seven months is considered to have no advantages over aphakia.[150] A 2015 study suggests that primary IOL implantation in the seven month to two years old age groups should be considered in children who require cataract surgery.[150]

Research into the possibility of regeneration of infant lenses from lens epithelial cells has shown interesting results in a small trial study reported in 2016.[151][152]

The capital equipment for phacoemulsification is expensive and requires expert maintenance, and the consumables are also expensive. Quality of outcomes is not sufficiently better than outcomes for manual small incision cataract surgery (MSICS) to justify the difference in cost in a developing world environment.[6]

Most patients have bilateral cataracts and although surgery in one eye can restore functional vision, second eye surgery has many advantages, so most patients undergo surgery in both eyes but 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 which reduces risk of contagion in an epidemic. There are also significant cost savings and faster visual rehabilitation and neuroadaptation. Another indication is significant cataract in both eyes where the person is not a good candidate for having anaesthesia and surgery twice. The risk of simultaneous bilateral complications is low.[153][154]