The Cataract Operation

This section provides more information about what is involved in having a cataract operation. It expands on the brief explanation given on the previous page. It includes information about:

The different techniques of cataract removal:

• Phacoemulsification
• Extracapsular Cataract Extraction
• Intracapsular Cataract Extraction

Cataract surgery in children

The History of cataract surgery

To Recap:

• Basically a cataract operation involves removing the cloudy natural lens of the eye and replacing this with a clear plastic lens; called the intra ocular lens implant.
• Nowadays most cataract operations are done using a local anaesthetic and as a day case, i.e. without an overnight stay in hospital.
• Most cataracts are now removed using a technique called 'Phacoemulsification'.

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Phacoemulsification

Phaco (or Phako) means lens

Emulsification means to turn into an emulsion, or to disintegrate a solid into a fluid suspension.

Phacoemulsification has been the most popular surgical technique for the removal of cataract in the UK since the mid 1990's. It offers the advantages of a small incision and more rapid visual recovery following surgery. In routine cases the eye is usually fully recovered and the vision and focus stable after 2 to 3 weeks.

With phacoemulsification the solid core of the lens (cataract) is broken up and disintegrated within the eye. The microscopic lens debris is then sucked out of the eye. Because the cataract is fragmented inside the eye the incision can be kept small. It can be as little as 2 to 3 mms in length, just enough to allow the phacoemulsification instrument to be inserted into the eye. Once the cataract has been removed the artificial lens, the lens implant, is put into the eye. In order to avoid having to make the incision any larger many surgeons use foldable lens implants. As the name suggests these are made from a pliable plastic and are folded to allow them to pass through the small incision. Once inside the eye they unfold and are manoeuvred into place.

The best position for the artificial lens implant is the same location as the natural lens of the eye, i.e. behind the pupil and iris. In order to provide support for the lens implant in this position the thin membranous outer shell of the natural lens is preserved. Eye surgeons call this the 'capsular bag'.

The natural lens of the eye is similar in a size and shape to a smartie (a sweet made by Nestle, formerly Rowntrees). The capsular bag is like the thin outer sugar coating of the smartie that surrounds the chocolate within. In a phaco' cataract operation a small circular opening, usually between 4 and 7 mm in size, is made in the front layer of the capsular bag. This is like removing part of the sugar coating on one surface of a smartie. Saline fluid is then gently flushed around the lens material within the capsular bag to loosen it. The lens material (the cataract) is then disintegrated and removed to leave an empty capsular bag. Every effort in made to preserve the integrity of the posterior (back) layer of the capsular bag. Using the smartie analogy it is as if the chocolate had been removed leaving the sugar coating behind. An empty sugar shell with a small hole in one surface. The lens implant is then put into this empty capsular bag. If the capsular bag breaks then the lens implant may need to be placed in a different location to ensure that it is secure and stable.

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The Phacoemulsification  Instrument and Machine

The phacoemulsification hand piece is about the size and shape of a fountain pen. This is held by the surgeon. At its tip is a needle like probe. This is the bit that is placed into the eye. This needle has a metal core surrounded by a plastic sheath which together have a diameter of 2 - 3 mms; manufactures are though continually trying to further miniaturise the designs. This phaco tip does three things at once. The needle moves backwards and forwards very slightly and very rapidly. The movement is too small to be seen and occurs about 40,000 times per second. It is this oscillation that disintegrates the lens (cataract) immediately adjacent to the needle tip. The disintegrated lens debris is then sucked out of the eye up through the core of the needle. At the same time saline like fluid is infused into the eye from beneath the sheath that surrounds the needle. The volume of fluid entering the eye matches that sucked out and so the eye remains inflated. The fluid flow also cools the needle as the rapid oscillations do generate some heat. The sheath also protects the incision from this heat where the instrument passes into the eye.

The phaco hand piece is connected to a computer driven control box by a cable and tubing. The settings on the control box determine the performance of the hand piece and what is happening within the eye.

Once the hard core of the cataract, called the nucleus, has been removed by the phacoemulsification machine a layer of softer material often remains. This is called soft lens matter or cortex. The phaco hand piece can then be exchanged for another probe that will remove this material. This is a simpler device which just infuses fluid and vacuums up the soft lens matter. This part of the procedure is called aspiration/irrigation. Once this has been completed the artificial lens implant is inserted.

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Extracapsular Cataract Extraction

This procedure was the most popular technique for cataract removal throughout the 1980's and gradually gave way to phacoemulsification in the 1990's. Eye surgeons call this operation ECCE which is an abbreviation of ExtraCapsular Cataract Extraction. It is still employed by some surgeons today and I believe it still has a place in some patients. Some eyes and cataracts have features that can make the phacoemulsification procedure hazardous. An ECCE is then often a reasonable alternative.

In this procedure the main core of the cataract (the lens nucleus) is removed from the eye in one piece, rather than being disintegrated within the eye as occurs with phacoemulsification. To make this possible the wound needs to be larger than for phacoemulsification and may be of the order of 10 mms in length. This cut is usually placed along the upper aspect of the eyeball in an arc. It can be in the periphery of the cornea (the transparent window of the eye) or just above the cornea within the sclera (the white of the eye). Once the lens nucleus has been removed the remaining soft lens matter is sucked out of the eye as with phacoemulsification. The lens implant is also similarly placed within or onto the capsular bag; as described above.

Because of the relatively large incision used in an ECCE sutures are required at the end of the operation in order to close the eye securely. These sutures need to be sufficiently tight and this may distort the curvature of the cornea, the window of the eye. This can induce astigmatism and throw the eye out of focus. This is one reason why sutures may need to be removed once the eye has healed. This can be done at the examination instrument in the outpatient clinic. If the sutures are buried and not causing, and not likely to cause, problems they can be left. Most surgeons use non-dissolving sutures. These are made of nylon thinner than human hair. In fact so thin that if the needle is cut off they float on air! In routine cases the eye is usually fully recovered and the vision and focus stable after 6 to 8 weeks (c.f. 2 to 3 weeks for phaco).

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Intracapsular Cataract Extraction

This form of cataract extraction involves removing the whole lens intact from the eye. The opaque lens is removed still contained within its capsular bag. Using the smartie analogy the smartie (lens) is removed with its sugar coating still intact around it. A large incision, requiring sutures, is needed. The opaque lens (cataract) is grasped either with special forceps or a probe that freezes onto it. The intact lens is then pulled from the eye. Eye surgeons call this procedure an ICCE which is an abbreviation of IntraCapsular Cataract Extraction. It is a technique now rarely used in the UK though it is still used in the developing world. It has a relatively high post-operative complication rate for retinal detachment and cystoid macular oedema. If an intra ocular lens implant is placed after removal of the cataract this is usually positioned in the anterior chamber of the eye between the cornea and the iris.

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Cataract Surgery in Children

Although cataract usually develops in later life it can occur at any age and occasionally does so in a child or baby. Views on how childhood cataract should be treated have changed considerably in recent years.

Up to the age of 7 years vision is still developing. This process involves the wiring up of the nerves from the eye to the visual part of the brain. Sight is actually created within the brain from the signals received from the eyes. The eyes are in a sense only the cameras that collect the image of our surroundings. It is really our brains that do the seeing. If in early childhood anything prevents a clear and focused imaged from reaching the retina (e.g. a cataract) the signals that pass to the brain will be compromised. The nerve connections within the visual part of the brain will then not be stimulated to develop fully. This will result in a "lazy eye". The medical term for this is amblyopia.

Soon after 7 the nerve connection 'set' and thereafter further re-wiring is not possible. However if a visual defect is corrected before age 7 visual development can be reactivated.

When considering whether or not to remove a cataract in a child there are two questions:

• Is the cataract interfering with visual development?
  If the child is less than 7 years old and the vision is reduced due to the cataract then visual development is under threat. It may be necessary to remove the cataract in order to allow visual development to occur. If a significant cataract is left until the child is older it may then not be possible to restore normal vision. This is because the eye will have become "lazy" as a result of poorly developed nerve connections within the brain.
  
  It is now thought that the most critical period for visual development is the very first few weeks of life. Because of this some experts now believe that if a baby is born with dense cataracts (congenital cataract) these should be removed within the first month of life.
  
  As well as removing the cataract it is necessary to bring the eye back into focus, i.e. to produce a clear image on the retina. As for adults intra ocular lens are now put into the eyes of children and the minimum age for this has been falling dramatically over recent years. However for babies and the very young extended wear contact lenses tend to be used instead of an intra ocular lens. An intra ocular lens may though be placed into the eye when the child is a little older and the eye itself has grown larger.
  
• Will removing the cataract restore normal vision?

If an older child has a cataract it is important to determine whether the cataract was present before age 7. If it was then removing the cataract now may not restore normal vision. This is because visual development may have been impaired and the eye may not be capable of normal sight; i.e. the eye may be "lazy". This also applies to an adult where the cataract has been present since early childhood. However if the cataract has become worse since early childhood surgery may still achieve some visual improvement and be worthwhile.

The technique for removing a cataract in a child differs slightly from that in an adult. This because the lens of the eye in a child is much softer than in an adult. It does not have the hard central nucleus of the elderly cataract. The lens material can therefore be sucked out of the eye without the need to disintegrate it first. In other words there is no need for phacoemulsification. The operation can be done by simple aspiration and irrigation. At one time the entire lens was removed in this way but increasingly surgeons nowadays try to preserve the capsular bag (thin outer coat) of the lens. This can then provide support for the insertion of an intra ocular lens implant. Children are very prone to the development of opacity of the posterior capsular. It may therefore be necessary to create a small central hole in the posterior layer of this capsule to ensure continued unobstructed vision following surgery.

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The History of Cataract Surgery

Only during the 17'th and 18'th centuries did it gradually become accepted that a cataract was a problem to do with the lens of the eye. The idea of extracting a cataract, that is removing the opaque lens from the eye, did not become accepted as the best surgical approach until the late 18'th century (1700's). Before this cataract, if it was treated at all, was dealt with using a procedure called 'couching'. This involved stabbing the eye from the front or side with a fine needle like probe. These instruments were often beautifully made but rarely sterile or even clean. The couching needle was then used to push the cataract (the lens) downwards and backwards. This dislocated the lens into the vitreous (the main jelly filled cavity of the eye) often rupturing it in the process. This might allow light to reach the retina at the back of the eye but the eye remained massively out of focus. This would provide a relative improvement in vision if the patient had been completely blind from mature cataract. Unfortunately most cases developed serious complications, e.g. intra ocular infection or retinal detachment and soon went blind again.

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