What is a cataract?
A cataract is the name given to any degree of opacity that is present
within the normally quite clear natural lens of the eye.
This effects of this can range from none at all (normal vision), 
slight (requiring more frequent changes of spectacles), moderate (objects
appear blurred, even with the correct spectacles) to extremely poor
vision due to a very cloudy natural lens.
(The animated diagram opposite demonstrates what effect a clouding
of the lens has on vision.)
How do I know if I have a cataract?
Most patients with significant cataract notice reduced vision, either
for distance or for reading. Some patients have problems with glare,
either when driving at night or in bright sunshine.
It is important to be aware that these symptoms themselves are not necessarily
due to cataract.
Patients who are over 50 may also develop ageing changes at the back
of their eye which can produce exactly the same symptoms, and of course,
they do not require cataract surgery.
If you have some or all of the above symptoms, you should consult your
optometrist (optician) who has had special training to examine for the
causes of reduced vision. They will usually pass their findings to your
family practitioner who will then decide, with you, on the most appropriate
course of action.
When should a cataract be removed?
It should not be removed just because it is there!
Cataract surgery is major surgery, and like all surgery, it carries
unavoidable risks. Standard cataract surgery carries an approximately
2-3% risk of a complication resulting in a permanent serious loss
of vision. For patients with other ocular or medical problems, these
risks are higher.
For this reason, I do not normally advise surgery unless either the
vision is already significantly affected, or I have documented definite
evidence of progression of the cataract (as then if a complication
does occur, we can be reasonably sure that without surgery, the vision
would have deteriorated any way because of progression of the cataract).
This may mean seeing a patient several times over the course of a
few months to see if the cataract is actually increasing.
In view of these risks, I never advise cataract surgery on both eyes
simultaneously, even if both eyes have significant cataract. I believe
it is safer to separate the two operations by a few days.
As far as the level of impairment of vision that is needed before
I would advise surgery, this depends very much on the individual patient
and their visual requirements. For example, a lorry driver might seem
to have reasonable distance vision on testing, but be unable to drive
because of disabling glare caused by the presence of a small opacity
at the back of the lens that would cause no problems to a non-driver.
Every patient needs to be considered individually, and the issues
fully discussed with them and any appropriate relatives, before a
final decision is made about the timing of surgery.
