Cataracts are the most common form of treatable blindness worldwide. According to the World Health Organisation they affect 45 million people worldwide.
What is a Cataract?
Cataract is opacity of the lens inside the eye. It is so-called because a mature cataract, when the entire lens is opaque, causes the pupil of the eye to appear white and historically this was likened to a waterfall in the eye. Normally the lens is a transparent structure, but when the fibres become disorganised and proteins oxidise, transparency is lost.
What Causes Cataracts?
The most significant factor is age. In the UK, approximately a third of people of retirement age have visually significant cataract. It is slightly more common in women. Genetic makeup affects susceptibility to risk factors such as smoking, poor nutrition and alcohol abuse. Cataracts are also linked to exposure to sunlight, radiation, steroids, diabetes and trauma to the eye. About 30% of those with cataract will have some other pre-existing eye disease.
Children and young people can also have cataract. Trauma is the most common cause for cataract in only one eye. Otherwise it may be hereditary, associated with a metabolic disorder, resulting from a maternal infection while in utero - eg, rubella, or some other cause.
How is Vision Affected?
Usually cataract develops earlier in one eye than the other, so symptoms may not immediately be apparent. Symptoms will vary according to the type and location of the opacity in the lens.
The ageing lens yellows, altering colour perception. The yellow tone of Turner's 1 paintings has been attributed by some people to the onset of cataracts.
Early cataract often causes an increase in myopia (short sight). Common problems are variability in the quality of vision according to the light conditions or at different distances, glare from light sources (eg, street lights, car headlamps). There may also be ghosting of images or even multiple images. Vision will gradually deteriorate as the cataract spreads and increases in density.
Why Should Cataracts be Treated?
If left untreated, most cataracts will eventually cause loss of useful vision 2. Even in the early stages, the impact on daily life can be quite severe. The effect on a person's quality of life depends on the demands of the visual tasks undertaken and a person's general expectations. Loss of vision in one eye will hinder the ability to judge distances.
Cataract impedes the view of the interior of the retina which means that signs of other disease may not be detected. A mature cataract may in itself cause problems of raised intraocular pressure and inflammation.
Up to the age of about seven, the visual system in the eye and brain is still developing. The presence of cataract in a child under seven may restrict normal visual development in the eye and brain. If the cataract is removed early enough, there is a good chance that normal vision will develop, provided there is no other relevant eye disease.3
How are Cataracts Treated?
Treatment is by surgery, which these days is considered low-risk. It is the most common elective surgery; there are approximately 200,000 cases each year in the UK and 1.5 million in the USA. Less than 2 in 1,000 patients end up with worse vision after surgery.
Techniques have improved so much that patients no longer have to wait until their cataract is mature or 'ripe.' Normally the impaired lens is replaced with an artificial lens (intraocular lens, or IOL), so thick spectacles4 are no longer required post-operatively.
The patient's quality of life is an important factor in choosing when to consider surgery. Other causes for the symptoms must first be excluded. Examination includes determining any co-existing eye disease, assessment of general health, blood-clotting, blood pressure and blood sugar levels, to gauge any risk factors.
Ultrasound is used to measure the eye in order to determine the power of the IOL to be inserted. This should also take into account the patient's requirements and the state of the other eye. The default is usually to err on the side of slight myopia. Usually the most affected eye is the first to be operated on. If both eyes require surgery, the second eye will only be treated once a satisfactory result of the first eye is assured.
The patient should be counselled as to the likely outcome, taking account of their personal risk factors and any possible complications.
Outline of the Surgical Procedure
Cataract surgery is usually done as a day case. 99.5% of cataract surgery is done under local anaesthetic, the type and route of administration of which depends on the surgeon's preferences. A general anaesthetic is only used for patients who cannot co-operate or are psychologically unable to cope with a local anaesthetic.
The patient wears their own clothes and lies on an articulated table. A cloth is used to cover the patient's face with a hole to reveal the eye for surgery. A nurse will be assigned to reassure the patient and be a contact in case the patient has a need - for example, to move or cough.
The eye is washed with a solution designed to kill any agents on the eye surface which could cause infection inside the eye. A main incision about 2.5mm long is made at the edge cornea such that it will be self-closing from the pressure within the eye. Other 1mm incisions are made to permit access for supplementary surgical instruments used. The hard nucleus of the lens is fractured or emulsified by ultrasonic energy and then sucked out through the main incision5, leaving behind the capsule which contained the lens. The incision is widened to 3mm to insert the IOL which is folded up and opens out when in position. Saline is used to restore pressure in the eye.
The total operation lasts between ten and 30 minutes. The wounds are self-healing and the eye should be stable within about two weeks.
With babies and children, IOLs are becoming more common, but often are not used. In this case, when the affected lens has been removed contact lenses or spectacles are used for optical correction instead. An IOL may be inserted when the child is older.
What Happens after Surgery
A plastic eye-shield is worn for 24 hours, then at night only for one week to protect the eye from accidental rubbing. Steroid and antibiotic eye drops will be prescribed to last for up to three weeks as a precautionary measure. Water should be kept away from the eye for a few days.
Because of the extra light now entering the eye, sunglasses may be necessary initially for comfort. Glare from peripheral light sources may also be experienced as the mirror-like edge of the IOL scatters light.
During the first few weeks the eye may feel gritty and watery and the eyelid may be slightly droopy. Vision may be slightly hazy and variable. The eye should stabilise over a period of between four and six weeks, then glasses can be prescribed if necessary to correct any residual refractive error. In particular, because the IOL is inflexible (unlike the human lens), reading glasses are usually necessary.
Strenuous activities should be avoided for the next one or two months; patients can return to work within between one and four weeks depending on the type of occupation they hold.
The 1997 UK national cataract survey found that six months after surgery, 92% patients where no other ocular pathology was present and 86% of all patients achieved corrected vision of 6/12 or better. The results of a patient self-evaluation survey were that approximately 85% felt their vision was better after surgery and 9% reported no change, whereas 6% thought their vision was worse.
Are There any Possible Complications?
Pre-existing conditions may mean that the surgical procedure or post-operative care has to be adapted or that the eventual outcome is uncertain.
Most complications that occur are minor and transitory as improved surgical techniques have reduced disturbance to the eye. The most common complication is opacification of the lens capsule that remains in the eye, caused by residual lens cells spreading over the surface. About 20 - 50% patients will experience some loss of vision because of this, up to two years after surgery. It can be treated in an outpatient clinic with a laser.
Corneal distortion causing induced astigmatism6 is less likely to occur these days because only a small incision is required. If unexpected or intolerable astigmatism or anisometropia7 does occur, laser surgery may be used to reshape the cornea.
There are a some serious possible complications which may lead to a significant loss of sight, but fortunately these are rare.
History of Treatment
Mention of cataracts and their treatment has been found in many ancient texts. The first known treatment was to use a needle to lance the eye and dislocate the opaque lens, a technique known as couching. In 1753 the first surgical lens extraction was performed - this was before anaesthetics were used. The high plus lenses needed in corrective spectacles caused problems such as a small field of view and a magnified retinal image. When contact lenses became available, these provided a better optical option though often not a suitable one for the majority of patients, who were elderly and found them difficult to handle.
In 1948 the operating microscope enabled the development of microsurgery which was closely followed by the invention of the IOL. The idea of an artificial implant has been attributed to Casanova in the 18th century! Harold Ridley, having observed that perspex fragments embedded in pilots' eyes from shattered plane windows caused little inflammation, devised the IOL and implanted the first one in 1950. At this time surgery usually required waiting until the cataract was severe, or 'ripe.' It was manually removed through a 9mm incision. The design of IOLs continued to evolve, using different acrylic materials and methods of attachment. Because they were not reliable in the long term their use was mainly confined to the more elderly patients.
In 1967 the technique of phacoemulsification was first used, reducing the required incision to 3mm, although until recent years when the folding IOL was invented, the rigid design still dictated a 6mm opening.
Are Cataracts Preventable?
Cataracts are an almost inevitable consequence of age, but they appear sooner in some individuals than others. Avoiding the risk factors will certainly reduce the likelihood of developing cataracts.
As for general well being, a healthy diet should be followed. Intake of lots of fresh, coloured fruit and green vegetables and fish oils rather than animal fats are advised.
Some studies have shown that supplements of vitamins A, C and E plus beta-carotene may reduce the incidence of cataract. It is important not to exceed the recommended daily dose and smokers are advised against taking beta-carotene because of an associated increased risk of cancer. Generally it is thought that in people with poor nutrition, supplements may be beneficial in slowing the rate of progression of cataracts in the early stages, otherwise there is not a proven gain.
Non-steroidal anti-inflammatory drugs (NSAIDs) have been identified as reducing the incidence of cataract, but the risks of using these for this purpose outweigh the benefits.
The Future of Cataract Treatment
Surgical techniques are being improved to be quicker with even smaller incisions so that there is less trauma to the eye. Cataract surgery is so successful that it is already being considered as an alternative means of refractive surgery for those with a high spectacle prescription.
The shape and material of IOLs continues to be developed to reduce unwanted side-effects. Multifocal IOLs are being used to eliminate the need for reading spectacles, but as yet these have the disadvantage of a reduction in the overall quality of vision, greater problems with glare and haloes round lights. An alternative idea is adjustable implants, which should flex within the lens capsule to simulate the eye’s natural accommodative ability.
Another development is an IOL material sensitive to specific UV light. This is so that post-operatively the lens can be 'set' in the shape of the desired lens power.
There are measures to tackle cataracts in the developing world effectively and at low cost. Treating opacity of the lens capsule that may occur post-operatively is expensive, so it is important to design an IOL where this is less likely to happen.