Cataract is the leading cause of blindness worldwide and one of the most common surgical procedures in the UK. In 2019/20, more than 450,000 cataract surgeries were carried out in England. The number will increase because of the changing age profile of our population.

Cataract surgery to remove and replace the affected lens is currently the only effective treatment.

What are Cataracts?

Cataracts occur when the lens, the small transparent tissue inside the eye, scatters light to appear cloudy or milky to others and the optometrist as they look into your eyes.

Cataracts prevent you from either seeing clearly or even at all.

How do cataracts affect vision?

The lens, which sits behind the iris in the front of the eye, helps the cornea focus light onto the retina (the light-sensitive layer at the back of the eye). In healthy eyes, the lens is clear (transparent), allowing light to pass through it and to focus the image onto the retina.

When the lens becomes cloudy because of a cataract, light is prevented from reaching the back of the eye because it is scattered instead, which limits or even blocks a person’s vision.

A cross-section of the eye with letters identifying key areas
  • H in the above diagram shows the lens, which appears cloudy or milky, where someone has cataracts. For a full explanation, see Anatomy of the Eye

Cataracts continue to develop if left untreated and eventually block vision. They usually appear in both eyes – but they may not always develop at the same time or be the same in each eye. In humans, cataracts are progressive, so over time, they will get bigger and denser, and more parts of the lens appear cloudy.

The lens may also turn yellow,  brown or black as part of the accumulated damage, making it difficult for a person to distinguish colours. Some famous artists, including Turner and Monet, experienced this, as evidenced in their later works.

An out-of-focus picture of a dog.
Cataract will cause vision to become blurry

What are the causes of cataracts?

Most cataracts develop as we age (most common in people over 60).

The commonest type of cataract is age-related cataracts (ARC), but not every older person gets cataracts, and many centenarians do not develop cataracts.

Why do cataracts occur with age?

Cataracts most commonly affect older adults (typically people in their sixth decade and older).

The transparency and optical properties of the lens derive from its structure and the proteins it contains. These proteins can be older than our birth age because we make some of them while in our mother’s womb.

It is, therefore, easy to understand that these proteins become damaged with age and do not work as intended causing them to scatter the light that is needed to see.

The lens then appears “cloudy” because of this scattering of light.

For older people, visual impairment is highly correlated with morbidity due to the 2-3 increase in the risk of trips and falls and the consequences that then result.

Factors other than ageing that increase the risk of cataracts

The biggest influence on whether we get age-related cataracts is our environment, health and how we live our lives. Factors other than ageing may increase a person’s chances of developing cataracts, including but not limited to:

  • A family history of cataracts
  • An eye injury or trauma
  • Diabetes
  • Drinking alcohol
  • Eye surgery – for treating glaucoma or another eye condition
  • Kidney dialysis
  • Long-term use of certain medications, such as steroids
  • Other eye conditions – such as retinitis pigmentosa, glaucoma or uveitis
  • Radiation exposure – sunlight, X-rays, for example.
  • Smoking

The World Health Organisation identifies cataract as a preventable disease. The WHO's 2030 target for member states, such as the UK, is to complete coverage for all people over 50, meaning clinical capacity should be increased to meet the population's needs.

We can help ourselves by, for example, stopping smoking, drinking alcohol in moderation, protecting our eyes from the sun, and going for regular eye exams to monitor the appearance and progression of cataracts if and when they occur.

Genetic causes of cataracts

Inherited mutations can cause cataracts. Actually, cataract was the first human disease to be identified as “autosomal dominant” in humans.

In autosomal dominant inheritance, an affected individual has a 50% chance of passing the mutated gene to each of their children. Both males and females can be affected, and if an individual inherits the mutated gene from either parent, they are likely to express the trait or disorder associated with that gene.

What causes childhood cataracts?

Genetic causes are the most common reason for cataracts in babies, infants and children. If left untreated in babies, they will develop severe visual impairment or blindness.

However, childhood cataracts are rare:

  • In the UK, around 2.5 in every 10,000 babies are born with cataracts.
  • This incidence can be as high as 15 in 10,000 births in low-income countries.

Research is advancing, and as we develop our understanding of human genetics, we can better understand the causes of cataracts and other diseases.

Identifying a cataract in a young patient is the easier part, but researching the underlying genetic cause is important and can help to identify the risk of co-morbidities.

Now the prospect of gene therapy for cataract is closer as a potential therapeutic option for the future.

  • Read our blog: research breakthroughs we are funding that owe a debt to the Human Genome Project

Cataract is also a clinical feature of some 200 syndromic genetic diseases indicating that the lens is still very similar in its biology to other tissues in our bodies. In babies and infants, cataracts slow down and change normal visual development and can permanently change the area of the brain responsible for vision.

To avoid such an outcome, the affected lens is removed by surgery.

What are the different types of cataract?

The location and appearance of cataracts are highly variable, and terms such as anterior polar, posterior polar, nuclear, lamellar, coralliform, blue dot (cerulean), cortical, pulverulent and polymorphic are all used to describe them.

There are three categories of age-related cataract (ARC), as follows:

1. Nuclear sclerotic cataracts

These are the commonest type of cataract. They affect the centre (nucleus) of the lens but then gradually extend into other regions of the lens. This type of cataract usually develops slowly with age, and it can take time before vision is affected.

2. Cortical cataracts

Cortical cataracts affect the outer layers of the lens first and not the centre, but then gradually extend to the rest of the lens if untreated.

3. Posterior subcapsular cataracts

Typically, posterior subcapsular cataracts form at the back of the lens (the region closest to the retina), and therefore they impair vision more rapidly. These cataracts also tend to progress faster than the other types. They can especially affect a person’s reading and night vision – causing halo effects and glare around lights.

What are the symptoms of cataracts?

A person may not have any symptoms at first, but cataracts will eventually change their vision as the cataract progresses.

An optometrist can detect cataracts before they affect vision, underlining the importance of regular eye examinations as then the development can be tracked as we age. As cataracts can affect each eye differently, some people will notice different vision in one eye compared to the other.

Cataracts are not painful but can cause blindness if left untreated.

The main symptom of cataract is blurred or hazy vision, which may appear ‘washed out’, with less contrast between black and white. Lighting conditions also affect vision. This can make it gradually more difficult to carry out everyday activities, such as driving, reading, recognising faces or watching TV. When daily activities and lifestyle is adversely affected

  • Cataracts may also cause a variety of other symptoms, including:
  • Double vision – seeing objects in duplicate.
  • Difficulties with colour vision – which may look faded, altered or more yellow.
  • Glare – difficulty seeing in the presence of bright light and lamps sunlight. Or headlights seem too bright.
  • Halos – seeing halos around lights.
  • Problems with night vision – difficulties seeing well at night, with important consequences for driving.

Cataracts gradually get worse over time. Sometimes this progression happens slowly, so the person doesn’t notice any sight loss, but regular eye examinations monitor the changes.

How are cataracts treated?

If a person’s cataracts are at an early stage and their symptoms are mild, small changes such as a stronger prescription or contact lenses and brighter reading lights may help them delay any treatment.

Cataracts usually worsen over time, so there will come a time when surgery should be given serious consideration. This will be when cataracts start to interfere with everyday activities, such as reading or driving.

  • Remember, the DVLA must be notified when a number plate cannot be read 20m (65 feet) away. This is relevant for all eye conditions.  

Surgery is currently the only way to remove a cataract. It involves removing and replacing the lens interior with a new artificial plastic lens (an intraocular lens, or IOL). This restores vision as light can again pass through unhindered by the lens and focused onto the back of the eye by the IOL.

The surgery has a high success rate – improving vision for most people, but this needs to be monitored over time. One factor that may impact outcomes is PCO, explained below.

What is posterior subcapsular opacification (PCO)

However, as with any surgery, there are risks and complications. The artificial lens cannot become cloudy or milky in the same way as the living lens, but light can still be prevented from reaching the retina by the condition called posterior subcapsular opacification (PCO). 

In babies and young children, PCO approaches 100%, and in adults, it is between 20-30%. It is, therefore, important to discuss the risk of PCO and the treatment options at your pre-assessment meeting with the team responsible for your cataract treatment.

PCO is caused by those lens cells that remain after surgery that grow to cover the IOL and the lens sac, scattering the light and preventing it from reaching the retina. In this case, an additional laser treatment is recommended to remove these cells and can restore vision.

PCO usually occurs 2 to 5 years after the initial cataract surgery in adults.

What is cataract surgery?

Cataract surgery is now a relatively straightforward procedure due to a breakthrough in 1950 by Sir Harald Ridley. He noticed that acrylic shards could become embedded in the eye lens without causing rejection when treating fighter pilots during World War II.

Ridley proposed that a plastic lens implant could replace the cataract-containing lens.

The technology has been optimised over the intervening decades to be a very successful treatment for cataract, and today there are two alternative approaches – the “lens in the bag” and the “bag in the lens”.

For children, the Bag-in-the-Lens has significant advantages, and in adults, it also helps prevent PCO.

You should be given an opportunity to discuss the options available to you at the pre-assessment appointment by the clinical team responsible for your treatment.

Surgery is recommended once cataracts affect a patient’s eyesight and quality of life.

What does cataract eye surgery involve?

Once the decision to undergo cataract surgery has been made, there are many tests to be done before surgery can be performed by the ophthalmology team.

For instance, an eye exam to determine the optical requirements of the intraocular lens to be implanted. If you wear contact lenses, these must be removed before the eye exam. The ophthalmological team responsible for your treatment will organise a “pre-assessment appointment”, and you will be provided with all the information you need for the eye exam and for, the operation, and your recovery afterwards.

Preparing for cataract surgery

The pre-assessment appointment will involve a discussion of the following:

  • What happens in the operation,
  • The risks and benefits of cataract surgery,
  • How long a recovery is expected.

As cataract removal is a surgical procedure, your medical history will be considered at this point, and blood tests and an electrocardiogram (ECG) might be required. Advice sheets are available from all NHS Trusts, but you should still ask any follow-up questions to your pre-assessment team, as each individual case is different. 

How long will the surgery take? 

Cataract surgery for adults is usually carried out as a day surgery procedure. Cataract surgery usually takes 30 to 45 minutes, but again this is something to discuss at your pre-assessment meeting with the team responsible for your cataract treatment.

The details of this and what to expect before, during and after surgery should all be explained and discussed at the pre-assessment meeting with the team responsible for your treatment.

NHS patients are usually offered monofocal lenses optimised for either near or distance vision. The options will be discussed fully at the preassessment meeting with the ophthalmology team responsible for the treatment to achieve the best patient outcome.

Some patients may be given other options for the lenses to be implanted, and the pre-assessment team will explain the risks / benefits of such options before making any decision.

Will both eyes be treated at once?

If a person has cataracts in both eyes and is thought to have a low risk of complications, it may be recommended that both eyes are treated on the same day.

Again, this will be discussed at the pre-assessment meeting with the ophthalmology team responsible for your treatment. Otherwise, surgery is usually done 6 to 12 weeks apart to allow one eye to recover at a time.

This may have consequences. For instance, it is your responsibility to make sure that you continue to meet the DVLA's visual standards for driving.

Can cataracts be treated without surgery?

Surgery to replace a cataract is currently the only available clinical option. Still, there is increased interest in non-surgical solutions to delay, halt and even prevent cataracts forming particularly age-related ones. This is because the increased demand caused by the changing age profile of the UK population and the surgical resource this requires means that momentum is building to find non-surgical solutions. Our scientific understanding of cataracts has advanced and alerted the ophthalmic biopharma industry to the possibility of non-surgical alternatives.

A person may delay surgery and have regular check-ups to monitor cataract development and progression and its impact on their sight before deciding to have surgery.

What next after your cataract surgery?

After cataract surgery, you should be able to see things clearly, and your colour perception and contrast sensitivity should be restored or even better than you remember them to have been. Most people will need to wear glasses for some tasks after surgery, such as reading. Once the eye has completely healed, a new prescription for glasses or contact lenses may be needed.

Is cataract surgery painful?

Cataract surgery should be almost painless. The details of the surgery and options for pain relief will be discussed at the pre-assessment meeting.

How long are you off work after cataract surgery?

Patients are usually recommended to wait at least three days before returning to work after their surgery. This important question should be discussed at the pre-assessment meeting when the specifics of your occupation and the potential risks it might pose can be discussed and the best advice suited to you offered by them.

What are the potential risks of cataract surgery?

Cataract surgery is a common, safe and effective type of surgery, although there are risks. The pre-assessment meeting is an excellent opportunity to discuss these risks.

These can include blurred vision, some loss of vision, and detached retina – where the thin layer of tissue at the back of the eye becomes loose.

There is a very small, but not negligible, risk of permanent sight loss due to the operation (1 in 1000).

The biggest risk is the development of posterior capsule opacification (PCO), which then requires laser treatment to correct this complication of cataract surgery (1 in 10). The pre-assessment team will provide this information listen to your concerns, and answer your questions before the patient makes the decision for surgery.

Many centres of excellence provide such information online, e.g. the Moorfields Eye Hospital.

Others will offer a patient advice sheet (e.g. Cataract Operation; Sunderland Eye Infirmary, South Tyneside and Sunderland NHS Foundation Trust).

Dos and Don’ts after cataract surgery

  • Do use eye drops as prescribed: Eye drops after cataract surgery can prevent infection and aid recovery.
  • Do take time to heal: Patients are advised to avoid strenuous activity and rest for the first two or three days following the operation. Consultants can advise on this further.
  • Do protect your eyes from bright lights: wear sunglasses and allow time for your vision to adjust to the extra brightness due to the more efficient, new lens.
  • Do use a protective eye shield or glasses outside: Patients should use their eye shield for at least a week following the procedure. This is especially important during the night, so patients can avoid rubbing their eyes in their sleep.
  • Don’t drive home after the surgery: Patients should arrange a pick-up for the day of the procedure and should not attempt to go immediately after cataract surgery.
  • Don’t wear eye makeup for at least a week after the operation: Particles from eye makeup can cause an infection or inflame the wound, delaying the healing process. All eye makeup must be removed before the operation for these very reasons,

The ophthalmological team will advise further on dos and don’ts after surgery.

How can cataracts be prevented?

Unfortunately, there are no proven ways to absolutely protect the eyes from developing cataracts. There are a few lifestyle changes that might help reduce the risk:

  • Protecting the eyes from the sun – wearing high-quality sunglasses and a wide-brimmed hat can help protect your eyes from ultraviolet (UV) damage.
  • Quit smoking - smoking is bad for your general health and your eyes. When it comes to cataracts, smoking is a risk factor you can control.
  • Managing your health conditions – if you have diabetes, keep your blood sugar under control. People with diabetes are more prone to cataracts.
  • Reducing alcohol intake – drink alcohol in moderation, as there is some evidence that excessive drinking can increase the risk of cataracts.
  • Healthy diet – eat a variety of healthy foods rich in vitamins and antioxidants, including fruits and vegetables, leafy greens, nuts and whole grains.

Latest research on cataracts

Key topics in cataract research include advanced genetic studies, developing a non-surgical treatment for preventing or delaying cataracts, the development of stem cell and gene therapy approaches combined with lens regeneration to replace IOLs, the application of the latest genetic and proteomic technologies to make the multimorbidity connections that will take disease treatment and prevention to a new level.

Whilst the original discovery by Harald Ridley represented a step change in the treatment of cataract, the common complication of cataract surgery called ‘posterior capsule opacification’ still needs to be solved, but the key topics listed above will represent the next step change in the treatment of cataract and human disease.

Fight for Sight UK funds projects in these areas.

Last updated July 2023
Approved by Emeritus Professor Roy Quinlan, Durham University

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