Here is some information you need
to know about intraocular lenses
The human lens
The human eye has a natural lens to focus light. When the lens becomes
cloudy this is called a cataract. To clear your vision, the cloudy lens
is removed and replaced with an artificial lens - an intraocular lens
(IOL) or implant.
Removal of the natural lens in your eye may also be appropriate to
correct long or short sightedness (refractive lens removal) even if a
cataract is not present.
In both cases, to avoid the need for thick glasses after surgery, it is
necessary to replace your natural lens with an artificial “intraocular
lens” or implant.
How do we work out the power of
As all eyes are different, we need to work out the power of the lens
for each of your eyes. We need to take several measurements including
keratometry, a measurement of the curvature of your cornea (the clear
window at the front of your eye which also acts as a lens) and the
distance between the front of your eye and the retina, called the axial
length. These measurements are taken with highly sophisticated
equipment and in most cases, are very accurate.
The information obtained from these measurements is fed into computer
calculations, which predict the power of the lens most likely to
achieve focused vision.
How accurate are these predictions?
In most cases, the predictions are accurate but occasionally, an
individual’s eye may not fit the normal pattern, and an unexpected
result may follow. It is therefore not possible to guarantee that
the lens we implant in your eye will give perfect focused vision
without the need for a spectacle correction, even though this is
usually the case. An unexpected result is most common in patients who
are either very long-sighted or very short-sighted or who have had
laser vision correction in the past.
Do these lenses change focus at
No - the lens we place in your eye has a fixed focal distance. In other
words, unless you have a multifocal lens implant or you have
astigmatism (see below), the lens will provide a clear focused image at
only one distance.
If we select the lens for distance vision, then intermediate and near
vision will be out of focus.
If we select a lens for intermediate vision (which would be useful say
for computer work, mobile phones and menus), distance vision will be
compromised and near vision such as reading fine print will also be
So will I
need glasses or not?
The best quality of vision is achieved if both eyes are focused for
distance and glasses are used for intermediate and near. Quality
vision refers to the type of vision you would require to get to the
lowest line of the vision chart in low light situations, and which you
may require for certain activities or occupations eg a jet fighter
pilot or a jeweller.
However, for many people this clarity of vision is not required for
day-to-day activities and patients who are willing to tolerate a degree
of compromise, can usually achieve good functional vision without
glasses. This means they are likely to be able to perform most
activities (such as driving, playing sport, using a computer or mobile
phone) most of the time without glasses, but glasses might be required
for fine print or driving at night.
I really want to be free of
glasses. How do we achieve this?
You can achieve good functional vision, and have a good chance of
spectacle independence for most activities most of the time, with
either monovision or multifocal lens implants.
Monovision means having one eye focused for distance and the other eye
focused for intermediate or near. It sounds strange but most patients
tolerate this extremely well. Many people who do not have cataracts but
have difficulty reading, use contact lenses for monovision and we can
do the same with an intraocular lens. If you do not have significant
cataract, it may be possible for your optometrist to perform a
simulation to determine whether or not monovision after cataract
surgery would suit you.
Multifocal lens implants use a completely different principle, with two
or more distances in focus. Your brain will concentrate on the in-focus
clear object of interest. With multifocal lenses, there is a
chance of being completely spectacle independent but most patients will
be aware of halos around images particularly at night for some time
I have astigmatism - will this
mean I still need glasses?
Astigmatism is when the curvature of your cornea is not spherical - the
cornea is shaped more like a dessert spoon than a soup spoon and light
is not focused uniformly.
There are now special implants which can reduce or eliminate
astigmatism and thereby reduce your dependence on glasse and these can
be used to create monovision as described above or they are also now
available as multifocal implants.
All of these issues require careful consideration and discussion with
your optometrist and me. For us to have the greatest chance of
your expectations, we need to be aware of your visual requirements and
you need to be aware of the advantages and disadvantages and
limitations of the various combinations of intraocular lenses available
and suitable for you.