What is a Cataract?
A cataract is a clouding of the normally clear lens of the eye. When the amount of light that passes through the lens is reduced and scattered by the cataract, images are not correctly focused on the retina at the back of the eye. The result is that vision becomes poor - it can be compared to looking through a frosted or steamed window.
There are many misconceptions about cataract. It is:
- not a film over the eye
- not a cancer
- not spread from one eye to another
- not a cause of irreversible blindness
Cataract formation affects only the lens of the eye and not any of the other important structures, such as the cornea, iris, retina or optic nerve.
A cataract will often worsen to a point where surgery is needed to remove the cloudy lens and replace it with a permanent artificial lens.
Causes and Cataract Development
Cataracts develop as a normal part of the aging process. By the age of 60 about half of all people will have some cataract formation although it may be minor and not noticeable. By 70 years of age almost everyone will have some degree of cataract formation. Other causes of cataract may include family history, medical conditions such as diabetes, injury to the eye, medications such as steroids, various chronic eye diseases, and long-term, unprotected exposure to sunlight.
Cataracts usually develop slowly and at a different rate in each eye. The rate of cataract formation will also vary among individuals - it is not possible to predict how fast cataracts will develop in any given person. Most cataracts associated with aging progress gradually over a period of years.
Common symptoms include:
- a painless blurring of vision
- glare or light sensitivity
- frequent spectacle prescription changes
- double vision in one eye
- needing brighter light to read
- fading or yellowing of colours
- poor night vision
- as the cataract worsens, halos around lights
Diagnosis of Cataract
A thorough eye examination by an ophthalmologist (eye doctor) can detect the presence and extent of a cataract, as well as any other conditions that may be causing blurred vision or discomfort.
The examination will:
- carefully examine the external and internal structures of both eyes
- assess vision with modern tests that determine how much vision has been affected
- determine whether the cataract can be removed successfully
- determine whether any other eye conditions are present and need treatment
Treatment of Cataract
Surgery is the only way to remove the cataract. This surgery may be necessary when vision has worsened to a point where daily activities are effected, or if personal safety is at risk. However if symptoms from a cataract are mild, a change of spectacles may be all that is required. A decision to have a cataract removed should be made only after a discussion with an ophthalmologist.
Cataracts can not be cured by any type of medication, eye exercise, alternative therapy, diet or glasses.
Success of Surgery
Removal of a cataract is the most common eye operation and one of the most common surgical procedures performed in Australia and New Zealand. It has a high rate of success due to the modern methods used by ophthalmologists.
If the eye is healthy, the likelihood is that cataract surgery will restore good vision. Of every 100 operations to remove a cataract, 95 will result in significantly improved vision. Despite the proven benefits of cataract surgery, one should be aware that, like any surgery, there are potential risks. Anyone considering cataract surgery should speak to their ophthalmologist about this.
The lens is contained in a clear membrane called a capsule. With older surgical methods both the lens and capsule were removed. With modern methods the capsule is preserved. This is a significant advance in technique because:
- the capsule can be used to hold and position the artificial lens
- the risks of surgery are fewer
- vision following surgery is usually better
Cataract removal is usually performed under local anaesthesia and light sedation. For some patients general anaesthesia may be recommended. For those who have a local anaesthetic and sedation, they may be able to see movement and light during the surgery but will not be able to see the surgery.
Ophthalmologists primarily use three different methods to remove a cataract. All are performed with the ophthalmologist viewing the eye through a microscope placed above the patient.
This is the most common technique and the procedure takes an hour. A small incision of approximately 3mm is made where the cornea meets the sclera (where the white of the eye meets the clear part). A small probe which vibrates at high frequencies is inserted into the eye to divide the cloudy lens into small pieces. The pieces are then suctioned away leaving only the lens capsule.
An artificial lens is then usually inserted into the lens capsule. The incision is usually so small that often stitches are not required.
This technique is used less commonly but it is effective for those patients whose lens is too hard to remove using phacoemulsification. A 10 to 12mm incision is made where the sclera meets the cornea. The front of the capsule is opened and the lens then removed. An artificial lens is inserted and fixed into position. The incision is then closed with several sutures.
The entire lens and capsule is removed. This is now only used in special cases.
This is also called an intraocular lens or an IOL. It is a transparent plastic disk with a similar shape to a natural human lens. The focus of the lens is fixed and can not change. The strength of the lens chosen for an individual is determined by the ophthalmologist's prescription and made for distance vision.
Most people fitted with IOL's will not need spectacles for distance vision. However, others may require glasses for both distance vision and close vision, such as reading. The use of intraocular lenses has almost eliminated the need to wear thick cataract glasses and contact lenses.
Recovery from Surgery
If the operation has been performed under local anaesthetic, after surgery the patient is moved to a quiet area to recover from the effects of sedation. Most patients are then ready to leave for home within a few hours. Most patients get sufficient pain relief by using over-the-counter products such as paracetamol. Some patients may require more pain relief and are encouraged to see their ophthalmologist.
Within a number of days the ophthalmologist will examine the eye. Recovery is usually rapid. Soon after surgery most people notice their vision has improved although glasses are still needed for reading. If the operation has been an extracapsular extraction then inflammation from the operation may take several days or weeks to settle. Vision may remain hazy or cloudy during that time but slowly improve over the next three months.
Typically, lights will appear intense shortly after the operation and during this time sunglasses may be worn. After the eye has healed and adjusted to the intraocular lens for several weeks, the eye is tested again and a new prescription for glasses may be needed.