Cataract surgery


Cataract surgery, also called lens replacement surgery, is the removal of the natural lens of the eye that has developed an opacification, which is referred to as a cataract, and its replacement with an intraocular lens. Metabolic changes of the crystalline lens fibers over time lead to the development of the cataract, causing impairment or loss of vision. Some infants are born with congenital cataracts, and certain environmental factors may also lead to cataract formation. Early symptoms may include strong glare from lights and small light sources at night, and reduced acuity at low light levels.
During cataract surgery, a patient's cloudy natural cataract lens is removed, either by emulsification in place or by cutting it out. An artificial intraocular lens is implanted in its place. Cataract surgery is generally performed by an ophthalmologist in an ambulatory setting at a surgical center or hospital rather than an inpatient setting. Either topical,, or retrobulbar local anesthesia is used, usually causing little or no discomfort to the patient.
Well over 90% of operations are successful in restoring useful vision, with a low [|complication] rate. Day care, high volume, minimally invasive, small incision phacoemulsification with quick post-op recovery has become the standard of care in cataract surgery all over the world.

Types

Two main types of surgical procedures are in common use throughout the world. The first procedure is phacoemulsification and the second involves two different types of extracapsular cataract extraction. In most surgeries, an intraocular lens is inserted. Foldable lenses are generally used for the 2-3mm phaco incision, while non-foldable lenses are placed through the larger extracapsular incision. The small incision size used in phacoemulsification often allows "sutureless" incision closure. ECCE utilises a larger incision and therefore usually requires stitching, and this in part led to the modification of ECCE known as manual small incision cataract surgery.
Cataract extraction using intracapsular cataract extraction has been superseded by phaco & ECCE, and is rarely performed.
Phacoemulsification is the most commonly performed cataract procedure in the developed world. However, the high cost of a phacoemulsification machine and of the associated disposable equipment means that ECCE and MSICS remain the most commonly performed procedure in developing countries.
Cataract surgery is commonly done as day care rather than in-patient procedure as there is some evidence that day surgery has similar outcomes and is cheaper than hospitalisation and overnight stay.

Types of surgery

There are a number of different surgical techniques used in cataract surgery:
ication easier, as well as the aspiration of cortical material. After phacoemulsification of the lens nucleus and cortical material is completed, a dual irrigation-aspiration probe or a bimanual I-A system is used to aspirate out the remaining peripheral cortical material.
Cryoextraction is a form of ICCE that freezes the lens with a cryogenic substance such as liquid nitrogen. In this technique, the cataract is extracted through use of a cryoextractor — a cryoprobe whose refrigerated tip adheres to and freezes tissue of the lens, permitting its removal. Although it is now used primarily for the removal of subluxated lenses, it was the favored form of cataract extraction from the late 1960s to the early 1980s.

Intraocular lenses

In addition, there is an accommodating lens that was approved by the US FDA in 2003 and made by Eyeonics, now Bausch & Lomb. The Crystalens is on struts and is implanted in the eye's lens capsule, and its design allows the lens' focusing muscles to move it back and forth, giving the patient natural focusing ability.
Artificial intraocular lenses are used to replace the eye's natural lens that is removed during cataract surgery. These lenses have been increasing in popularity since the 1960s, but it was not until 1981 that the first U.S. Food and Drug Administration approval for this type of product was issued. The development of IOLs brought about an innovation as patients previously did not have their natural lens replaced and as a result had to wear very thick eyeglasses or some special type of contact lenses.
Presently, IOLs are especially designed for patients with different vision problems. The main types of IOLs that now exist are divided into monofocal and multifocal lenses.
The monofocal intraocular lenses are the traditional ones, which provide vision at one distance only: far, intermediate, or near. Patients who choose these lenses over the more developed types will probably need to wear eyeglasses or contact lenses for reading or using the computer. These intraocular lenses are usually spherical, and they have their surface uniformly curved.
The multifocal intraocular lens is one of the newest types of such lenses. They are often referred to as "premium" lenses because they are multifocal and accommodative, and allow the patient to visualize objects at more than one distance, removing the need to wear eyeglasses or contact lenses. Premium intraocular lenses are those used in correcting presbyopia or astigmatism. Premium intraocular lenses are more expensive and are typically not covered, or not fully covered, by health insurance, as their additional benefits are considered a luxury and not a medical necessity. An accommodative intraocular lens implant has only one focal point, but it acts as if it is a multifocal IOL. The intraocular lens was designed with a hinge similar to the mechanics of the eye's natural lens.
The intraocular lenses used in correcting astigmatism are called toric, and have been FDA approved since 1998. The STAAR Surgical Intraocular Lens was the first such lens ever developed in the United States and it may correct up to 3.5 diopters. A different model of toric lenses is created by Alcon and may correct up to 3 diopters of astigmatism. In order to achieve the most benefit from a toric lens, the surgeon must rotate the lens to be on axis with the patient's astigmatism. Intraoperative wavefront analysis, such as that provided by the ORA System developed by Wavetec Visions Systems, can be used to assist the doctor in toric lens placement and minimize astigmatic errors.
Cataract surgery may be performed to correct vision problems in both eyes, and in these cases, 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 in both eyes, some cannot and may experience blurred vision at both near and far distances. IOLs that emphasize distance vision may be mixed with IOLs that emphasize intermediate vision in order to achieve a type of modified monovision. Bausch and Lomb developed in 2004 the first aspheric IOLs, which provide better contrast sensitivity by having their periphery flatter than the middle of the lens. However, some cataract surgeons have questioned the benefits of aspheric IOLs, because the contrast sensitivity benefit may not last in older patients.
Some of the newly launched IOLs are able to provide ultraviolet and blue light protection. The crystalline lens of the eye filters these potentially harmful rays and many premium IOLs are designed to undertake this task as well. According to a few studies though, these lenses have been associated with a decrease in vision quality.
Another type of intraocular lens is the light-adjustable one which is still undergoing FDA clinical trials. This particular type of IOL is implanted in the eye and then treated with light of a certain wavelength in order to alter the curvature of the lens.
In some cases, surgeons may opt for inserting an additional lens over the already implanted one. This type of IOLs procedures are called "piggyback" IOLs and are usually considered an option whenever the lens result of the first implant is not optimal. In such cases, implanting another IOL over the existent one is considered safer than replacing the initial lens. This approach may also be used in patients who need high degrees of vision correction.
No matter which IOL is used, the surgeon will need to select the appropriate power of IOL to provide the patient with the desired refractive outcome. Traditionally, doctors use preoperative measurements including corneal curvature, axial length, and white to white measurements to estimate the required power of the IOL. These traditional methods include several formulas including Hagis, Hoffer Q, Holladay 1, Holladay 2, and SRK/T, to name a few. Refractive results using traditional power calculation formulas leave patients within 0.5D of target or better in 55% of cases and within 1D or better in 85% of cases. Recent developments in interoperative wavefront technology such as the ORA System from Wavetec Vision Systems, have demonstrated in studies, power calculations that provide improved outcomes, yielding 80% of patients within 0.5D.
Statistically, cataract surgery and IOL implantation seem to be procedures with the safest and highest success rates when it comes to eye care. However, as with any other type of surgery, it implies certain risks. The cost is another important aspect of these lenses. Although most insurance companies cover the costs of traditional IOLs, patients may need to pay the price difference if they choose the more expensive premium ones.

Preoperative evaluation

An eye examination or pre-operative evaluation by an eye surgeon is necessary to confirm the presence of a cataract and to determine if the patient is a suitable candidate for surgery. The patient must fulfill certain requirements such as:
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 carefully and skillfully performed in order to achieve the desired result. The steps may be described as follows:
  1. Anaesthesia; Topical anesthetic agents may be placed on the globe prior to surgery and or in the globe during surgery. Anesthetic injection techniques include sub-conjunctival injections and or injections posterior to the globe to produce a regional nerve block. Intravenous sedation may be combined with the topical and injection techniques. General anesthesia with the patient unconscious from intravenous agents and or inhaled gases is another technique.
  2. Exposure of the eyeball using an eyelid speculum;
  3. Entry into the eye through a minimal incision ;
  4. Viscoelastic This is injected to stabilize the anterior chamber, to help maintain eye pressurization, and to distend the cataract's capsule during IOL implantation.
  5. Capsulorhexis;
  6. Hydrodissection; The cataract's outer cortical layer is dissected, by the injection of a fluid wave, from the capsule, the outer-most skin of the cataract.
  7. Hydrodelineation; The cataract's outer softer epi-nucleus is separated from the inner firmer endo-nucleus by the injection of a fluid wave. The epi-nucleus serves to protect the cataract's capsule during phacoemulsification of the endo-nucleus.
  8. Ultrasonic destruction or emulsification of the cataract after nuclear cracking or chopping, careful aspiration of the remaining lens cortex material from the capsular bag, capsular polishing ;
  9. Implantation of the, usually foldable, intraocular lens ;
  10. Viscoelastic removal; The viscoelastic 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 viscoelastic glaucoma post-operatively. This is done via suction from the Irrigation-Aspiration instrument.
  11. Wound sealing / hydration. The incision is sealed by elevating the pressure inside the globe which presses the internal tissue against the external tissue of the incision forcing closed the incision.
The pupil is dilated using drops to help better visualise the cataract. Pupil-constricting drops are reserved for secondary implantation of the IOL in front of the iris. Anesthesia may be placed topically or via injection next to or behind the eye. Oral or intravenous sedation may also be used to reduce anxiety. General anesthesia is rarely necessary, but may be employed for children and adults with particular medical or psychiatric issues. The operation may occur on a stretcher or a reclining examination chair. The eyelids and surrounding skin will be swabbed with disinfectant. The face is covered with a cloth or sheet, with an opening for the operative eye. The eyelid is held open with a speculum to minimize blinking during surgery. Pain is usually minimal in properly anesthetised eyes, though a pressure sensation and discomfort from the bright operating microscope light is common. The ocular surface is kept moist using sterile saline eye drops or methylcellulose viscoelastic. The discission into the lens of the eye is performed at or near where the cornea and sclera meet. Advantages of the smaller incision include use of few or no stitches and shortened recovery time.
A capsulotomy is a procedure to open a portion of the lens capsule, using an instrument called a cystotome. An anterior capsulotomy refers to the opening of the front portion of the lens capsule, whereas a posterior capsulotomy refers to the opening of the back portion of the lens capsule. In phacoemulsification, the surgeon performs an anterior continuous curvilinear capsulorhexis, to create a round and smooth opening through which the lens nucleus can be emulsified and the intraocular lens implant inserted.
Following cataract removal, an intraocular lens is usually inserted. After the IOL is inserted, the surgeon checks that the incision does not leak fluid. This is a very important step, since wound leakage increases the risk of unwanted microorganisms gaining access into the eye and predisposing it to endophathalmitis. An antibiotic/steroid combination eye drop is put in and an eye shield may be applied on the operated eye, sometimes supplemented with an eye patch.
Antibiotics may be administered pre-operatively, intra-operatively, and/or post-operatively. Frequently a topical corticosteroid is used in combination with topical antibiotics post-operatively.
Most cataract operations are performed under a local anaesthetic, allowing the patient to go home the same day. The use of an eye patch may be indicated, usually for about some hours, after which the patient is instructed to start using the eyedrops to control the inflammation and the antibiotics that 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.
Occasionally, a peripheral iridectomy may be performed to minimize the risk of pupillary block glaucoma. An opening through the iris can be fashioned manually or with a laser. The laser peripheral iridotomy may be performed either prior to or following cataract surgery.
The iridectomy hole is larger when done manually than when performed with a laser. When the manual surgical procedure is performed, some negative side-effects may occur, such as that the opening of the iris can be seen by others, and the light can fall into the eye through the new hole, creating some visual disturbances. In the case of visual disturbances, the eye and brain often learn to compensate and ignore the disturbances over a couple of months. Sometimes the peripheral iris opening can heal, which means that the hole ceases to exist. This is the reason that the surgeon sometimes makes two holes, so that at least one hole is kept open.
After the surgery, the patient is instructed to use anti-inflammatory and antibiotic eye-drops for up to two weeks. The eye surgeon will judge, based on each patient's idiosyncrasies, the time length to use the eye drops. The eye will be mostly recovered within a week, and complete recovery should be expected in about a month. The patient should not participate in contact/extreme sports until cleared to do so by the eye surgeon.

Complications

Complications after cataract surgery are relatively uncommon.
photo of IOL showing Posterior capsular opacification visible a few months after implantation of Intraocular lens in eye, seen on retroillumination

Ancient Babylonia

Cataract surgery was first mentioned in the Babylonian code of Hammurabi.

Ancient Greece

of Pergamon (c. 2nd century AD, a prominent Greek physician, surgeon and philosopher, performed an operation similar to modern cataract surgery. Using a needle-shaped instrument, Galen attempted to remove a cataract-affected lens. Although many 20th century historians have claimed that Galen believed the lens to be in the exact center of the eye, Galen actually understood that the crystalline lens is located in the anterior aspect of the human eye.

India

A form of cataract surgery, now known as 'couching, was found in ancient India and subsequently introduced to other countries by the Indian physician Sushruta, 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 in the eye out of the way of vision. The phlegm was then blown out of the nose. The eye would later be soaked with warm clarified butter and then bandaged. Here is translation from the original Sanskrit:
The removal of cataracts by surgery was also introduced into China from India, and flourished in the Sui and Tang dynasties.

West Africa

The removal of cataracts was a common surgical procedure in Djenné.

Europe and the Islamic world

The first references to cataract and its treatment in Europe are found in 29 AD in De Medicinae, the work of the Latin encyclopedist Aulus Cornelius Celsus, which also describes a couching operation.
Couching continued to be used throughout the Middle Ages and is still used in some parts of Africa and in Yemen. However, couching is an ineffective and dangerous method of cataract therapy, and often results in patients remaining blind or with only partially restored vision. For the most part, it has now been replaced by extracapsular cataract surgery and, especially, phacoemulsification.
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 AD. 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". 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. He presented case histories of its use, claiming to have had success with it on a number of patients. Extracting the lens has the benefit of removing the possibility of the lens migrating back into the field of vision. A later variant of the cataract needle in 14th-century Egypt, reported by the oculist Al-Shadhili, used a screw to produce suction. It is not clear, however, how often this method was used as other writers, including Abu al-Qasim al-Zahrawi and Al-Shadhili, showed a lack of experience with this procedure or claimed it was ineffective.

Eighteenth century and later

In 1748, Jacques Daviel was the first modern European physician to successfully extract cataracts from the eye. In America, an early form of surgery known as cataract couching may have been performed in 1611, and cataract extraction was most likely performed by 1776. 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.
King Serfoji II Bhonsle of Thanjavur in India performed cataract surgeries as documented in manuscripts at the Saraswathi Mahal Library in the early 1800s.
In 1949, Harold Ridley introduced the concept of implantation of the intraocular lens which permitted more efficient and comfortable visual rehabilitation possible after cataract surgery.
In 1967, Charles Kelman introduced phacoemulsification, a technique that uses ultrasonic waves to emulsify the nucleus of the crystalline lens in order to remove the cataracts without a large incision. This new method of surgery decreased the need for an extended hospital stay and made the surgery ambulatory. Patients who undergo cataract surgery hardly complain of pain or even discomfort during the procedure. However patients who have topical anesthesia, rather than peribulbar block anesthesia, may experience some discomfort.
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.
In India, modern surgery with intraocular lens insertion in government- and NGO-sponsored Eye Surgical camps has replaced older surgical procedures. In rare cases, infections have caused blindness among some of the patients in mass free eye camps in India.

Usage in the UK

In the UK the practice of the various NHS 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. 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. 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.