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Cataracts - causes, symptoms, treatment, surgery

Cataracts occur when the normally clear lens of the eye becomes cloudy, restricting the amount of light that reaches the retina, leading to a decrease in vision.

Cataracts tend to develop slowly over a period of years and in the early stages may not produce any symptoms. Without treatment (normally surgery) cataracts will eventually lead to complete blindness. In New Zealand, cataracts are a leading cause of vision loss in older adults.


The lens is mostly made from water and protein – it’s thought cataracts develop because of changes in the proteins, that result in cloudy vision. The most common cause of cataracts is ageing. Cataracts are a natural part of ageing and most elderly people with cataracts are healthy and have no other eye disease. The exact cause of age-related cataracts is unclear

Eye anatomy

Cataracts can also exist at birth (congenital cataracts) and can develop in children (childhood cataracts). The former may be due to a faulty gene while the latter may be associated with infection or trauma during pregnancy. However, cataracts in new-borns and children are rare.

Several other factors may increase the risk of developing cataracts:

  • A family history of cataracts
  • Diabetes
  • Other eye conditions such as uveitis
  • Previous eye surgery or eye injury or inflammation
  • Use of high-dose corticosteroid medication (eg: prednisone, prednisolone) or long-term use of corticosteroids.

Other factors that are possibly linked to the development of cataracts include smoking, drinking too much alcohol, poor diet, and excessive exposure to sunlight.

Cataracts can be classified according to which part of the lens they affect. The location and extent of the cataract also determines the extent of the vision impairment. For example, vision may be significantly impaired if the centre of the lens is affected; however, if the edges of the lens are affected, vision impairment may be barely noticeable. Cataracts can affect one eye at a time or both eyes at the same time. 

Signs and symptoms

Signs and symptoms of cataracts can include:  

  • Cloudy, blurry, fuzzy, foggy, or filmy vision
  • A noticeable cloudiness in the pupil
  • Increased glare from lights, eg: from headlights when driving at night
  • A decrease in distance vision but an improvement in near vision.
  • Double vision (diplopia) or halos around lights
  • Frequent changes in eye prescriptions
  • Impairment of colour vision
  • Poor vision in sunlight.


Diagnosis of cataracts is usually easily made after assessment of the symptoms and examination of the eye, beginning with visual acuity testing for signs of vision impairment. A GP may make an initial diagnosis after examination of the eye with an ophthalmoscope - a hand-held instrument fitted with a lens and light that enables the inside of the eye to be examined. An optometrist will use a slit-lamp biomicroscope, which is a microscope-like instrument that steadies the patient's head to enable closer examination of the eye. Sometimes the cataracts may be so obvious that they can be seen by the naked eye or they may be seen by shining a pen light into the eye.

If cataracts are suspected, a referral to an eye specialist (ophthalmologist) is usually recommended. The eye specialist may carry out more detailed examinations of the eye and vision in order to determine the exact location and extent of the cataracts. They will then recommend appropriate treatment.


The symptoms of early cataracts may be improved with new prescription glasses and stronger lighting. However, once cataracts progress to the point that impaired vision reduces a person’s quality of life and interferes with daily activities surgery is the only effective treatment.

Cataract surgery involves removing the cataract-damaged lens and replacing it with a clear plastic lens known as an intraocular lens (IOL). The aim of surgery is to restore vision (particularly distance vision) as much as possible. IOLs of differing magnifying power can be used to help correct pre-existing short-sightedness (myopia), long-sightedness (hyperopia) or astigmatism.

Cataract surgery is most commonly performed as a day-stay procedure and is usually carried out under a local anaesthetic with a light sedation.

Surgery involves making a small incision in the front of the eye, through which the old lens is removed and a new IOL is inserted. The incisions are usually made using a hand-held microscopic blade but, in recent times, laser cataract surgery has allowed computer-guided, bladeless incisions to be made. Laser cataract surgery should not be confused with laser eye surgery (PRK and LASIK) which is used to correct problems with the eye's ability to focus.

There are two main techniques for the surgical treatment of cataracts:

The surgeon makes a small incision near the border of the cornea and sclera, or in the cornea. A small probe that emits ultrasound waves is inserted into the lens capsule to break the lens into pieces. The pieces are gently suctioned away and the IOL inserted. The much smaller incision required for this technique has the advantage of a reduced healing time. It is the technique most commonly used in New Zealand.

Extracapsular surgery
A 10-12mm incision is made in the front of the eye and the lens is removed. The posterior capsule is left in place to support the new IOL. Once the new lens has been fitted the incision in the eye is closed using tiny, invisible stitches.

If cataracts affect both eyes, only one eye is operated on at a time. It is usually recommended that the eye is well healed before the other eye is treated. This is generally at least one month.


Patients are normally sent home after a few hours of recovery in the clinic or hospital, and when the sedation has worn off. An eye pad is usually positioned over the eye for the first night in order to protect the eye.

It is usual to feel some mild pain and discomfort in the eye after cataract surgery. This can usually be well controlled with medications such as paracetamol.

While it may take a day or two for the eyes to synchronise, people generally report that vision improves quickly, being able to return to normal activities within about two weeks. Distance vision returns but reading glasses will still be required for fine or detailed visual tasks.


Cataract surgery is generally safe and the risk of developing serious complications is small. The most common complication is a condition called posterior capsule opacification (PCO), which involves a skin or membrane growing over the back of the lens implant months or years after surgery causing vision to become cloudy again. PCO can be treated with a simple laser eye surgery to cut away the membrane.

Cataract surgery also carries a risk of infection and bleeding inside the eye and increased risk of retinal detachment. However, most complications can be treated with medication or further surgery.


Cataracts cannot be prevented.  However, certain approaches may delay or reduce the chances of them developing. Wearing sunglasses that protect the eyes from ultraviolet light is recommended. A diet high in fruits and vegetables and quitting smoking are also thought to be beneficial. Optimal management of health conditions that can increase the risk of developing cataracts (eg: diabetes) is also advised. If corticosteroids, are being taken on a long-term basis, it is recommended that the eyes are checked by a GP or optometrist regularly for signs of cataract development.


Mayo Clinic (2016). Cataracts (Web Page). Rochester, NY: Mayo Foundation for Medical Education and Research. [Accessed: 14/07/17]
NHS Choices (2016). Age-related cataracts (Web Page). Redditch: National Health Service (NHS) England. [Accessed: 14/07/17]
NHS Choices (2016). Childhood cataracts (Web Page). Redditch: National Health Service (NHS) England. [Accessed: 14/07/17]
Ocampo Jr, V.V.D. (2017). Senile cataract (age-related cataract) (Web Page). Medscape Drugs and Diseases. New York, NY: WebMD LLC. [Accessed: 14/07/17]
O’Toole, M.T. (Ed.) (2013). Cataract. Mosby’s Dictionary of Medicine, Nursing & Health Professions (9th ed.). St Louis, MI: Elsevier Mosby.

Last Reviewed – July 2017


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