Any patient undergoing cataract surgery or laser lens surgery in 2016 has to make a choice, “What sort of intraocular lens will I have inside my eye?” Whenever the natural lens of the eye is removed – whether it be therapeutically for cataract reasons; or whether it be simply to decrease the dependence on glasses in someone who is long-sighted, short-sighted or has co-existing astigmatism – they all have to make this very important decision.
If this is you, the choices can be bewildering, but it really comes down to two separate paths you may wish to take. If you want to be truly free of glasses for all activities, then the way to be most certain of this is to use a trifocal intraocular lens in both eyes, keeping both eyes the same (ie. not attempting to use any type of blended or monovision effect; where one eye is deliberately made different to the other).
If you don’t mind wearing simple reading glasses, then you would normally not bother with a trifocal lens – you would be better off with a lens which is termed ‘aspheric monofocal lens’, which may or may not have astigmatism added into it to try to make both eyes normal.
These lenses give excellent clarity of vision with very good optics, because they are not trying to do too much, but they do mean that if the eyes are set for distance then glasses will be needed for computer work and reading.
If you want to walk down the spectacle independence path, then trifocal intraocular lenses are the way to go.
Surprisingly, one thing they are not is a trifocal lens – that is, they are not three lenses in one. They are, in fact, a lens where the optics have been manipulated to try and give a good range of vision from approximately 30cm out to infinity. For example, they don’t let you see 10cm from your nose.
They are called trifocals because they are an improvement on previous generation multifocals. These previous generation multifocals tended to have an area missing at the intermediate range for computer work, so the vision was pretty good for reading, then dipped for computer work, and came back up again for the distance, whereas trifocals manage to give a good range of vision from reading, computer work, looking at the dashboard on the car and all the way to far distance.
Obviously, things have to be right for this lens to be used. Anatomically the eye needs to be suitable, which means the surface of the eye needs to be healthy and so dry eye is a relative contraindication. The lens needs to be placed in a very secure way without tilting, so if there are conditions which would lead to tilting, then this is not a good option.
Similarly the back of the eye, particularly the macula, needs to be healthy. To get the best from a trifocal lens you need the eye to be able to have the potential to see very well. If none of these anatomical conditions can be fulfilled then you are better off without a trifocal lens and opt for the alternative aspheric monofocal lens.
The thing to remember about a trifocal lens is that it does give a very good range of vision, the best chance of true spectacle independence and it keeps both eyes the same, which is always an advantage.
The disadvantage, and there are always pros and cons of all lenses, is that they do give rings or flare around lights at night. This is not evident during daylight or bright light but only at night or at dusk. If the patient was a professional truck driver I would not use a trifocal intraocular lens, because if they were driving at night these rings around lights would become too annoying. It could still be placed but would generally not be considered a good option for that patient’s lifestyle.
Similarly, if a patient is very particular in terms of clearness of vision or not wanting to have any imperfections in night vision, then I would have to think carefully before using a trifocal lens in that type of patient. It might do well anatomically, but they might focus on the annoying features of the lens rather than the good features, and it may not be the lens for them.
I think people who are very demanding of their visual quality are better off with a lens which maximises the quality of the optics such as the aspheric monofocal lens, and just accepting the fact that they will need reading glasses.
All lenses, but particularly trifocal lenses, where you are attempting to get a patient out of glasses completely, are dependent on the accuracy of the lens selection as well as the quality of the surgery. The accuracy of lens selection can be improved by planning this in a methodical way.
Paying attention to the surface of the eye, making sure it is healthy and there are no subtle tear film problems, and performing the testing with modern equipment in the most accurate way possible. It also requires using latest generation formulae, so the surgeon is able to maximise the chance of getting things exactly on target.
Even so, occasionally there will be some remaining optical error, such as some astigmatism or long/short-sightedness after surgery. If this is significant, there should be a plan to deal with it.
Generally it is done with surface laser to refine the refractive result 2-3 months after the original surgery, or occasionally with a secondary intraocular lens, or an intraocular lens exchange. In certain cases, this is more likely than others, such as a very short or very long eye, or in those patients where they may have had LASIK many years ago.
Trifocal intraocular lenses are a great addition to what is possible for patients today. They have been available in Australia for three years now, and there are three different versions from different manufacturers. They are all good and mostly differ in the platform which is used, but also slightly in the range at which the reading and intermediate is best. This requires a discussion as to what would best suit an individual patient. It is great to have these choices available.