Tuesday, September 15, 2015

What type of lens implant should I choose for my cataract surgery?

Taking a quick look through a few eye care forums often turns this up as a commonly asked question, and one that garners quite a number of readers. This is not surprising, since over the years, more and more types of lenses with different pros and cons have become available. To recap, cataract surgery involves removing the hazy natural lens of the eye (called a cataract), and replacing it with a new lens implant.

Some of the currently available lenses: Tecnis Symfony (left), Acrysof  Toric monofocal (middle), and Zeiss Trifocal (right)

With cataract surgery nowadays, it is not so much the phacoemulsification technology or whether laser is used that affects the outcome. Rather, the outcome is determined by how accurately your doctor can calculate the necessary lens power, and what kind of lens is implanted into the eye. The available implants include 'monofocal' lenses (good vision at one distance), monofocal toric lenses (monofocal but with added feature to reduce astigmatism), and multifocal lenses (of which Extended Depth of Focus (EDOF) lenses can be considered a subset of - these provide clear vision at more than one distance).

Important questions to answer:

1. Do I value distance vision without glasses more, or near vision without glasses more?

2. Would I mind wearing glasses of any kind, including reading glasses?

3. Would monovision (one eye set for clear distance vision without glasses, the other for near) be a suitable option? Any prior experience with monovision or any chance of simulating it?

4. Would I mind intermittent visual disturbances such as halos around lights?

Simulated halo around a light, as seen through a multifocal lens

In some clinics, a questionnaire including these questions is filled in by patients prior to their surgery, to help in deciding on the type of lens for them. Of course, there is the final issue of cost, with multifocal and especially multifocal toric lenses commanding a premium.

Let's talk about some case scenarios:

1. You are very used to wearing glasses, and would actually like to wear them after surgery.
If you were shortsighted (myopic) before cataract surgery, and you habitually took your glasses off to read, then you would be good with monofocal lens implants but aiming to leave behind -1.50 to -2.00D of shortsightedness, in both eyes. Conversely, if you were hyperopic, I find that most patients like emmetropia (good distance vision without glasses), and then wear reading glasses for near visual work.

2. You had experience of monovision before, and liked it.
This could have been achieved naturally, or via glasses/contact lenses/LASIK. In this situation, it would be good to replicate it via cataract surgery.

3.You hate wearing glasses of any kind, and are concerned that monovision might not suit you or have tried it before and it does not suit you. 
In this case, you could consider the Extended Depth of Focus (EDOF) lenses, or the trifocal lenses. These lenses work quite predictably but also can cause some visual disturbances such as halos/rings around lights especially in the dark. Of these varieties, the EDOF lenses such as the Tecnis Symfony tend to cause the least disturbance ie least halos and least reduction in contrast.

If the benefit of seeing clearly at most distances with both eyes outweighs the possibility of some halos, then these lenses can be considered.

Generally, I would continue to avoid 'accommodating' lenses such as the Crystalens, and other multifocal designs such as the Oculentis Mplus range of lenses.

Hopefully, this post gives an idea of the thought processes that go into choosing a lens implant for cataract surgery. There is no one 'best lens' for everybody, and hopefully in the future there will be even better technology that can be applicable to more poeple with fewer side effects. Questions? Please feel free to post comments below.