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.
The most common cause of cataracts is ageing. They 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.
Cataracts can affect different areas of the lens and 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 eg: if the centre of the lens is affected, vision may be significantly impaired, 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.
Diagram courtesy of National Eye Foundation
Cataracts most commonly affect people over the age of 60 years. In New Zealand they are a leading cause of vision loss in older adults.
In New Zealand, the most common cause of cataracts is ageing. The lens is made up of approximately 35% protein and 65% water. As people age, degenerative changes in the lens's proteins occur. Over time these changes cause clouding of the lens, making images look blurred or fuzzy.
Ultraviolet light is thought to play a role in the development of these changes, however cataracts can occur for a variety of reasons. The different types of cataracts include:
- Age-related cataracts - mainly occur after 60 years of age.
- Secondary cataracts - occur as the result of another medical condition such as diabetes, an inflammatory eye condition such as uveitis, or an inflammatory skin condition such as eczema. There is some evidence that high blood pressure and glaucoma may also be a cause of cataracts
- Traumatic cataracts - occur as the result of an injury to the eye or lens.
- Congenital cataracts - are present at birth or develop in early childhood. They may be caused by an illness or infection in the mother during pregnancy, or as the result of a genetic defect.
- Toxic cataracts - can result from chemical toxicity or long term use of some medications, such as corticosteroids (eg: prednisone).
Smoking and alcohol have been linked to the development of cataracts and other factors currently being investigated include diets that are high in fat and the long-term use of vitamin supplements.
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)
- 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. 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 slitlamp biomicroscope which 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, better lighting or effective sunglasses. Once cataracts progress surgery is the only effective treatment.
Cataract surgery is usually recommended in cases where cataracts cause impairment of vision to such an extent that daily activities are affected. Surgery may not be recommended if the eye is affected by a pre-existing condition such as glaucoma
, macular degeneration
or diabetec retinopathy.
Cataract surgery involves removing the cataract-damaged lens and replacing it with a clear plastic lens known as an intraocular lens (IOL). The eye is carefully measured prior to surgery so that the appropriate sized intraocular lens can be selected. The aim of surgery is to restore vision (particularly distance vision) as much as possible. Intraocular lenses 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. Anaesthetic eye drops or gel may be used. In rare cases a general anaesthetic may be recommended.
Surgery involves making a small incision in the front of the eye, through which the old lens is removed and a new intraocular lens 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:
A 3mm incision is made in the front of the eye and the lens is broken into tiny pieces by a special machine that emits sound waves. The lens is then suctioned out of the eye capsule. In this procedure the back half of the lens capsule (posterior capsule) is left in place to support the new intraocular lens. 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. With phacoemulsification surgery the incision is so small that stitches may not be required and the incision quickly seals on its own.
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 intraocular lens. Once the new lens has been fitted the incision in the eye is closed using tiny, invisible stitches.
Some people cannot have an IOL fitted due to the presence of another eye disease or have problems during surgery. In these cases a soft contact lens, or high magnification glasses may be recommended.
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. Driving is not permitted after the surgery so arrangements for transport home will need to be made.
Detailed instructions on care of the eye will be given prior to leaving the clinic / hospital. General guidelines include not rubbing, pressing or jarring the eye. Activities such as driving and exercise may be restricted for a period of time after the surgery. It is important to carefully follow the specialist's guidelines for when a return to these activities is permitted. In most cases, driving is permitted within the first week following surgery and a full return to normal daily activities is permitted within two weeks.
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. Eye drops to reduce inflammation and help prevent infection are prescribed for 2 - 3 weeks after the surgery. It is important to take these as directed.
An appointment with the specialist is usually booked for the day after surgery so that the eye can be checked. A further follow up appointment with the specialist is usually arranged for 3 - 4 weeks after surgery to further assess healing and vision.
While it may take a day or two for the eyes to synchronise, people generally report that vision improves quickly. Distance vision returns but reading glasses will still be required for fine or detailed visual tasks. A new prescription for reading glasses is often given at the second follow up visit.
Most people report that colours seem different and that things are much brighter after cataract surgery. If there is difficulty adjusting to this, dark glasses may be recommended for comfort.
The success rate of cataract surgery is high, with over 90% of cases achieving a good result. However complications can occur. There is a small risk of infection (as with any type of surgery) but this is rare and can usually be easily treated.
While cataracts cannot recur after cataract surgery, it is possible for the remaining portion of the lens capsule to become cloudy. This clouding tends to develop slowly over a period of months or years and is sometimes referred to as a secondary cataract. The clouding can be easily treated during an outpatient visit to the specialist. A special laser called a YAG laser is used to make a tiny hole in the lens capsule. This lets light through to the retina, quickly restoring vision.
After cataract surgery there is an increased risk of detachment of the retina. The main symptoms of a detached retina are a sudden shower of black spots in the vision and flashes of light in the eye at night. If a detached retina is suspected, the specialist should be consulted immediately.
Other complications can include fluid build up in the retina, bleeding within the eye, inflammation and swelling of the eye, increased pressure within the eye and drooping of the eyelid. Again, if any of these complications are suspected or symptoms such as pain, redness, or vision disturbances are experienced in the days or weeks after surgery, the specialist should be consulted immediately.
While cataracts cannot be prevented, the chances of them developing may be reduced or delayed. Wearing sunglasses that protect the eyes from ultraviolet light is recommended. A diet high in antioxidants (citrus fruits, potatoes, carrots, green leafy vegetables) is also thought to be beneficial.
If certain medications, such as 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.
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Last Reviewed – June 2013