Cataract is the loss of transparency of the crystalline lens in the eye. This is most commonly due to ageing but there are other causes including congenital conditions, disease, and trauma. Certain drugs are also implicated in cataract development.

There is a misconception that a cataract can be seen as a "film" growing over the front of the eye. This film is probably not cataract but a pterygium or some opacification involving the cornea. Cataract cannot usually be seen on casual inspection because it is happening in the lens which is just behind the iris and the pupil aperture.

Some noders may have had cataract surgery. It is an extremely successful surgical procedure in which the crystalline lens, which has become cloudy or opaque, is extracted.

This removes almost all the focussing ability of the eye. Up until the 1970's, these patients would then have to be fitted with an enormously thick pair of glasses or (assuming they could tolerate it), a powerful rigid contact lens. Nowadays the extracted lens is replaced by an implanted artificial lens of a similar effectivity.

In our larger cities, it is likely that 60 or more people are having cataract extractions with lens implants on any given weekday.

It all happens something like this. First your opaque lens needs to be removed. In the operating theatre and using local anaesthetic, the ophthalmologist makes a tiny incision at the edge of the cornea to gain access to the cloudy lens through a dilated pupil. With a thin hollow titanium needle attached to a hand-piece containing a piezo-electric crystal which vibrates longitudinally at ultrasonic frequencies, the contents of the cloudy lens are emulsified. An irrigation and aspiration system sucks out the emulsified contents through tiny tubes and your "cataract" ends up in the waste pipe. This process is called phaco-emulsification.

For the moment then, you have no lens.

In the meantime an artificial replacement lens of a certain dioptral strength has been selected and is waiting on the surgical tray. The power of this lens is based on pre-operative measurements including ultrasound scan information. The surgeon delivers this lens by "injecting" it through another hollow needle into the now vacant space left by the recently removed cataractous material. Here it "deploys" by unrolling and will require a bit of skillful nudging into place by the surgeon. The implanted lens has cleverly designed stabilizing attachments which protrude from the edge to keep it in position, just behind the pupil.

In a few more steps, the operation is concluded. Most times, the incision is so small that no sutures are required. Post operative eye drops and follow-up appointments are arranged and the patient may go home about 6 hours after arriving at the hospital. Often the patients are already commenting on their improved eyesight as they are being driven home.

Because the artificial lens is of a fixed shape and not flexible, eyeglasses are often necessary after the operation to provide clear reading vision. To minimise the dependancy on glasses, the surgeon may select intra-ocular lens (IOL) strengths so that one eye is biased for close work and the other for distance vision.

The capsule of the patient's natural lens is left in place behind the implanted lens which increases the success and safety of this operation. Some months or years later, this remaining lens capsule may become opaque, causing a drop in vision. This is addressed by using a YAG laser to form a hole in the now opaque lens capsule which can now be done with relative safety. This is a short procedure, often done in the surgeon's office and once again the result is quite gratifying.

Cataract surgery is often rated as the most successful and effective type of surgery ever. It is a far cry from the days when the surgeon had to peel back most of your cornea to surgically remove your cataract. Old timers will remember family members having to stay in bed with their head "sandbagged" for days on end to prevent movement after the operation. Then came the even more challenging process of getting fitted with a contact lens or glasses which looked like magnifiers.

It is medical technology at its most elegant.

Whilst the average age for cataract surgery is during the eighth decade, the eye-care practitioner may see the first signs of your age-related cataract when you are fifty five. Only through repeat visits can the progress be assessed and it may be another decade before you need to be referred for surgery. Some patients never progress to a point where surgery is required.