What is it like having premium IOLs that correct for near vision after cataract surgery?

Some time ago I was asked this question on the Quora website:
What is it like having premium IOL's that correct for near vision after cataract surgery?

A very relevant question, given that nowadays there are so many lens options to choose from and also different approaches to avoid reading glasses. Here is my answer:

There are several different types of IOLs that give multifocality and good near vision as well as distance vision. I will base my answer on the most commonly used lenses-the diffractive multifocal lenses like the Alcon Restor, the Tecnis Multifocal and the Zeiss trifocal lenses.

The Alcon Restor lens (above), and the AT LISA tri (below) are examples of bifocal and trifocal lens implants, respectively.

These diffractive multifocal lenses have rings etched onto either their front or back surfaces, which split/diffract incoming light rays into two foci. Some newer ones can even split the light into 3 foci. This fact gives rise to several implications.

1. Vision will be clear mainly at 2 (or sometimes 3) distances. For the older +4 Restor and the Tecnis multifocal, the near focus is at about 1 foot. So reading material has to be held quite close.

If it is held further away (say at 3 feet or so-intermediate distance), then it is not so clear anymore. 

Then things much farther away, say 15-20 feet away, start to become pretty clear again. (See the figure below-only the AT LISA tri is clear at intermediate distance)

Note: This is only the case if the surgeon has been very accurate in calculating the lens power/biometry.

Simulated clarity of images at various distances with different multifocal lens implants. The top 3 are bifocals, and the bottom one is a trifocal. Only the trifocal gives pretty good intermediate vision-but at some cost in terms of contrast when compared with the Alcon SV25T0 and AMO ZKB00. (From IOVS 2015;56:3970)

2. Because of the light splitting, there is a drop in contrast compared with a monofocal lens. Patients with multifocal lenses tend to be more sensitive to low light conditions-ie when it starts to get a little dark, they start to feel the drop in vision faster than patients with monofocal lenses. A person with a monofocal lens and reading glasses could read in dimmer conditions than a person with a multifocal lens.

3. The rings on the IOL give rings of light (halos) around light sources. This can be an issue when driving at night because of the halos around car headlamps. Having said this, many patients get used to the halos and do not notice it as much after a time.

Simulated halos around lights from a mutifocal lens

The above of course does not completely apply to the Crystalens or the Oculentis MPlus. The Crystalens is an accommodative lens, which gives somewhat unpredictable results-some patients don't get any near effect at all. 

The MPlus (available in Europe/Asia) has a wedged shaped section on the lens to focus for near. Point 1 above applies to this lens as well. However, although this lens does not give rings around lights, it can still cause 'halos' of a different shape-it is more like a smearing effect in one direction. Occasionally if a patient's pupil is small and not aligned with the lens, the patient may only have a far focus or a near focus and not both.

Last but not least, there is the Symfony lens which I covered in my last post. As mentioned, this is an 'in between' lens, ie in between a monofocal and a multifocal. It has no intermediate vision problems, and less halos than the usual multifocals, but does not give quite as good very near vision.

Currently, I offer patients a choice between a monofocal, an in between lens like the Symfony, and a full fledged trifocal like the AT LISA tri. I believe there is little to no benefit to be gained from using older bifocals such as the Restor and Tecnis Multifocal currently. Exactly which of those 3 choices gets implanted comes after a careful discussion with my patient regarding the pros and cons of each option. (So that we get big smiles all round afterwards!)

My experience implanting the Symfony lens this past year

What's a Symfony? Or Symphony? A symphony is actually an extended musical composition written for a variety of musical instruments, usually in an orchestra. Google Symfony and you get results pointing you to free software for a 'web application framework'.

But of course, I'll be talking about a lens implant for cataract surgery. The Symfony lens is a type of lens to allow for a greater range of clear vision after cataract surgery. Normal lens implants (monofocal) allow good vision at 1 particular distance, either near, or far, but not both. Multifocal lens implants can give good vision at 2 or 3 distances, but have not been very popular due to certain side effects like halos.

The Symfony is kind of an in-between lens-ie in between monofocal lenses and conventional multifocal lenses.

Time really flies-it's almost a year now since I started using this lens for patients. So, how's it like? In general, I would say it lives up to expectations.

In this past year, I have implanted the Symfony in different sorts of situations-including for people who already have had cataract surgery with a normal monofocal lens in the other eye.

Distance vision
With correctly done biometry, aiming for close to emmetropia (close to 0 spectacle power), the Symfony gives very good distance vision and patients were universally happy with this. 94% of my patients saw 6/6 or 6/7.5 without glasses after surgery.

The remainder had small amounts of spectacle power and in one patient whose best corrected was 6/12p, she had prior retinal detachment surgery.

What about near vision?
All Symfony lens patients could see N8 type comfortably without glasses, which is this small, and 92% could see N6 comfortably without glasses, which is this small. 

Although perhaps this near vision is 'less good' than the traditional bifocal or trifocal multifocal lenses, I would say this is adequate for most people most of the time...

What about halos?
Some patients, when asked, did describe mild halos around lights at night (such as car headlamps or traffic lights) but were not troubled by these halos. One patient even called it pretty!

The distinguishing feature of Symfony related halos (mentioned by 18% of my patients) seemed to be that they were quite mild/light, and patients were able to see through the halos.

Personal thoughts
There is still no perfect solution for presbyopia as yet. However, I think for myself, the Tecnis Symfony is one of the best compromises out there at the moment.

1. Minimal halos

2. Minimal drop in contrast-patients with a monofocal in one eye and a Symfony in the other are not troubled by the difference in contrast

3. Optical behaviour and patient experience mimics an early stage of presbyopia-there is no sudden fall off in intermediate vision, and vision slowly gets more blurry when things are brought closer. The effect of the Symfony has been likened to vision of somebody in their early forties.

With some of the other multifocals, there is really no equivalent in real life-the feeling could be somewhat unnatural and it could take some time to get used to.

But the Symfony is not perfect.

The chief one is as above-it is like early presbyopia. So, for people who don't mind more halos and who also don't mind a greater drop in contrast, but who would like clearer vision very close up, then a trifocal lens implant like the AT LISA tri or Finevision IOL would be good options. At the end of the day, the adage 'there is no free lunch' still holds true!

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.

Cataract and Cataract Surgery FAQs

In my line of work, I get asked lots of questions about cataracts, quite simply because they are one of the most common causes of blurred vision as one gets older.

Here goes:

1. What are cataracts? Are they a growth in the eye?

Cataracts are not growths.  One of the parts of the eye, called the lens, undergoes ageing processes over the years. A lens, like a camera or spectacle lens, needs to transmit and focus light and therefore needs to be transparent. Unfortunately age causes many lenses to become hazy and this blocks vision, much like trying to look through a dirty window.

2. How do I know if I have cataracts?

The main problem with cataracts is blurred vision. Of course, there are many other causes of blurred vision, such as shortsightedness or astigmatism. Therefore, if vision is blurry, try wearing spectacles first and see if the vision is cleared up.

If so, the problem is probably just spectacle power, or perhaps the cataracts are very mild. Significant cataracts will cause blurred vision even if spectacles are worn. Generally speaking, if vision cannot be made clear with glasses, one should visit the eye doctor to make sure there are no serious eye problems.

3. How does it feel like to have cataracts?

This is related to the prior question. Although we may think that cataracts are just a hazy lens and are the same, in fact there are a few types of cataracts that affect vision in slightly different ways. For example, vision can be clearer under certain conditions, or sometimes patients get double or triple vision.

A yellow nuclear sclerotic cataract

One type of cataract causes the lens to become yellowish (above). This is called 'nuclear sclerosis', and the eye also becomes more and more shortsighted. Patients with this type of cataract may need to increase their shortsighted spectacle power several times a year. On the other hand, long sighted people may find their spectacle power getting less and less, and near vision getting better and better! This is sometimes called second sight.

Another type of cataract causes glare. This means that a person can see reasonably well in the dark, but when there is a bright light shining from in front, vision undergoes a 'white out', ie everything turns bright white and vision suddenly becomes very blurry. This happens with a cataract called a 'posterior subcapsular' cataract.

A very dense, white cataract

If cataracts are neglected for a long time, they can turn white (regardless of which type they originally were). White cataracts are more dangerous than other types, because they sometimes absorb water and swell. A swollen lens can physically block the drainage angle of the eye, or leak proteins which also block the drainage angle. This causes a sharp spike of eye pressure, leading to a type of glaucoma and eye pain. This is the only situation where cataracts are associated with eye pain.

4. What causes cataracts?

As mentioned, most cataracts are due to age related changes in the eye. Proteins break down, clump together, sometimes water is even absorbed into the lens causing to swell.

Besides age, there are other less common causes of cataracts. Certain medicines such as steroid eyedrops or tablets, if taken in high doses for too long a time, can cause cataracts to develop. Diabetes, which results in too much sugar in the blood, also cause cataracts to develop earlier, especially if the blood sugar levels are not controlled properly and become very high for a lot of the time. Cigarette smoking is well known to be associated with earlier cataract development as well. Finally, bad injuries to the eye, such as a direct punch or a hit in the eye can also cause a cataract to develop.

5. How can I prevent cataracts, or can I slow down their progression?

Firstly, any risk factors such as diabetes or cigarette smoking should be addressed. Modifying these risk factors will have the biggest impact on slowing cataract progression.

Secondly, eat a healthy diet full of antioxidants. In general, it is better to get these naturally from green leafy vegetables and colourful fruits, rather than supplements. However, certain nutrients may only be obtainable in large quantities in supplements.

Studies of big groups of people suggest that eating more fruits and vegetables can delay cataract development, but nothing conclusive so far can be said for individual nutrient supplements such as vitamin C.

6. How are cataracts treated?

Cataracts are treated with surgery to remove them, and at the same operation they are replaced by lens implants made of a special acrylic material.

Cataract surgery is carried out under local anaesthesia, and is painless. The hazy lens material is broken up with ultrasound, and then removed through a very small incision about 2mm long. The lens implant can then be folded and injected into the eye through this very small opening.

Recovery is very quick, with most patients seeing very well even on the day after surgery.

Sometimes patients ask me if they should wait until after their holiday to have surgery. I tell them that if time permits, to do it before, as they will enjoy the view so much more!

7. What are the latest advances in cataract surgery?

The most important developments in cataract surgery have to do with how spectacles can be avoided after surgery. Yes, no matter how high the spectacle power before surgery, most of the time spectacle wear can be avoided after surgery. How is that possible?

Focusing of light in the eye depends on the cornea, the lens, and how long the eyeball is. The shape of the cornea can be changed (in LASIK), and the lens power can be changed (in cataract surgery) to reduce or eliminate spectacle power.

A normal spherical Tecnis (AMO) lens

A Toric Tecnis (AMO) lens. Note the dots arranged in a line at the sides of the lens. This allow the surgeon to place the lens in exactly the right position to reduce or eliminate astigmatism after surgery

The Tecnis Symfony (AMO) lens. This is a multifocal lens that is also available in a toric version (right) so it can be used in most patients

Nowadays, lens implants also come in 'toric' versions to correct astigmatism, and there are also 'multifocal' lenses that give good near and far vision to avoid reading glasses after cataract surgery. 

For patients who would like clear far and near vision without glasses, and have astigmatism, there are even multifocal+toric lens implants.

Multifocal lens implants can give halos around lights at night, however, this has been minimised with newer extended depth of focus (EDOF) implants like the Tecnis Symfony (above).

Laser cataract surgery

Some surgeons are now using a type of laser to help to do certain steps of the surgery. They call this bladeless cataract surgery, much like how LASIK became 'bladeless' LASIK.

Unfortunately, using this laser to help with surgery makes the surgery much more expensive and also can result in problems that probably would not have happened if the surgery had been done with conventional phacoemulsification surgery. In the article above, 1/3 of patients had conjunctival haemorrhage, and 1/5 had anterior capsular tags. In 1/3 of patients, the pupil became smaller, making the surgery more difficult for the surgeon and increasing the risk of other complications.

Although this technology may become better with time, and surgeons will become more experienced with using it, currently this is an example of how a 'latest advance' is not necessarily better and in fact has become a kind of marketing tool.

Below is an exchange in the local newspapers in 2013, where the Singapore Academy of Medicine published a response in the Straits Times to counter certain unfounded claims put forth by proponents of the laser cataract surgery procedure:
http://ams.edu.sg/view-pdf.aspx?file=media%5C499_fi_807.pdf&ofile=STForum20130516+-+Traditional+cataract+surgery+remains+%27gold+standard%27.pdf

The story of the Symfony lens

About 2 months ago I was chatting with my parents on Facetime. I had helped my father with his cataract surgery in February/March earlier this year (fortunately everything went fine!) and naturally they were still quite in tune with things happening in this area of medicine.

My mum goes, 'Have you heard of the Symfony lens?'

I went,'Umm, sorry, you mean the Synchrony lens? I've never heard of the Symfony lens.'

Then she went on to point me to the Daily Mail webpage on the Symfony lens:

I was a little taken aback, because there had been no heads up from the company producing the lens implant. (And I was the supposed eye expert in the family too!)

The aforementioned company had previously  bought over the rights to a lens called the Synchrony accommodating lens implant, however, this had been delayed and then from the looks of things, shelved. (after paying a lot of money...)

In any case, this lens didn't look much different from the currently available diffractive multifocal lenses such as the Tecnis multifocal lens. So my mum asks me: 'wah, so this lens can see far and near without having any halos...'. And I went, 'but it has rings, so the patient will have halos...'. And my mum says, 'but that's not what it says in the article!' And so I capitulated. 'I'll just check with the representative tomorrow'. I felt a bit bad, partly because I wasn't able to answer their query but also I wasn't sure if I had inadvertently left them crestfallen after their high hopes about the new lens.

A week later I had the same query from a patient, and so it was that I was a bit more prepared to discuss the lens. Thank god for my mum who surfs the net!

When I asked the company representative about the lens, unfortunately there was not much information to be had. It was only last week that I found out a bit more about the lens. I understand that this is a new lens, but it achieved the CE mark in June and I think companies in this day and age should do more to coordinate the availability of their products, and also the dissemination of information about their products around the world. The thing is, the world has never been a smaller place...

Update 22 October 2014
2 months down, the Symfony lens has finally arrived in Singapore! It is currently in an evaluation phase with limited lens powers available, however, suitable patients can be considered for this lens. I feel that this is a lens which is likely to be better accepted among patients, and also doctors, as it uses a proven platform which should make IOL power more predictable as well.

Update 5 March 2015
My first cataract patients who opted for this lens implant have been very happy, and reported no problems with halos or driving at night. Near vision has also been good, with the ability to read newspapers without glasses.

The Symfony lens is now generally available in Singapore, and is also available in a toric version so that patients with significant corneal astigmatism will also stand to beenfit from this lens. As there are no significant side effects with this lens, I routinely offer it to my cataract patients nowadays, who have no other eye conditions and who desire spectacle freedom after surgery.

Presbyopia treatments: Love them or hate them...multifocal lens implants for cataract patients

The last frontier with regard to presbyopia correction really has to be lens replacement surgery a.k.a. cataract surgery with lens implantation. 'New lenses for old...' to paraphrase something from Aladdin :) Here we are talking about dealing with the problem at its source.

As covered in my post about presbyopia, the underlying problem is the inability of the aging lens to focus, which boils down to its increasing stiffness with age.

For those people young enough not to know how it feels like, the next few lines might give you an idea. Basically, it creeps up on you. You thought you could always do it, you know, things like holding reading material up close to your nose, cutting your nails up close, and for the ladies-doing the mascara and eyeliner to perfection. Then one fine day you realise, it doesn't work up close anymore...it's just too hazy or you get a headache trying to focus it up close! For those in an older age group, even things like the food in front of you are not so clear anymore...

So it is easy to understand why people go to such great lengths to find a way to improve their near vision. Anyway, I digress. If the lens is the problem, let's replace the lens then!

Cataract surgery is pretty much routine nowadays with great outcomes, and a variety of lens implants are available to replace the hazy lens. If we want to provide a patient with both clear distant as well as clear, near vision without glasses after cataract surgery, there are 2 main options: monovision and multifocal lenses. Monovision refers to using a lens to make one eye have clear distance vision, and the other eye using a lens implant that makes it mildly shortsighted. That way, with one eye seeing far and one eye seeing near, both far as well as near objects are in focus. One downside is that since both eyes are not exactly seeing clearly together at a particular distance, 3-D depth perception is somewhat affected and some patients with monovision will get a pair of glasses for certain tasks such as driving.

For each eye to see well in the distance and near, multifocal lenses are a reasonable option. If both eyes are implanted with the same lens, then depth perception is not affected. One thing which needs to cleared up right from the beginning is that these lenses are not the same as progressive or bifocal spectacle lenses-ie with these lens implants, the patient does not look up to see in the distance and down to see near. Instead, the lens splits the incoming light into two focus points all the time, so there is always one in-focus image and one out-of-focus image.

The original multifocal lenses were zonal refractive lenses like the Array, which has been redesigned and renamed as the ReZoom (above). Interesting names... Zonal refractive lenses have alternating ring shaped zones, which focus light alternately for distant objects and near objects. The problem with these lenses is that they are probably the most likely of multifocal lens to cause troublesome halos and visual disturbances. They are also not that good at providing good close up vision.

The other class of multifocal lenses are the diffractive lenses. These lenses use diffraction as a way to split the incoming light into 2 or more focus distances. Diffractive lenses have a series of sharp edged rings cut into the lens surface, and when light rays hit these edges, they will tend to spread out and form 2 different focus distances. By varying the height of these rings, the focus distance can be altered and some of these lenses have 3 focus points.

Another type of multifocal lens uses a near segment, and looks like a bifocal spectacle lens. I was quite interested in this lens but became less so when I realised it was only available as a plate haptic lens.

There is actually a 3rd option available for patients who want good near and distance vision after cataract surgery. These are the 'accommodating' lenses (which are not multifocal), and in one way or another can change their shape or the position of the lens optic in the eye. I put the word 'accommodating' in quotes, because it is unlikely that in the long run they provide much accommodation as the capsule in which they sit scars up and becomes stiffer. Even in the early period after surgery, some patients do not have as good near vision as they would like.

The option I prefer for my patients at this time is the diffractive multifocal lens. These very predictably give good near vision. And the diffractive multifocal lens I favour at this time? The Tecnis multifocal and Tecnis multifocal toric. 

(NB I do not receive any compensation from any of the lens implant manufacturers)

BUT, and this is a big but, I do not implant many multifocal lenses by any means. Most of my patients do well with monovision if they prefer not to have to use reading glasses. Clearly, there are several downsides with multifocal lenses, even if you ignore their cost.

Multifocal lenses degrade vision to some extent. Because there is always one in-focus and one out-of-focus image in the eye, the patient generally notices halos or ghosting of images to some extent. And because not all light from an object is in focus at any one time, contrast is not as good as with a normal monofocal lens. In the 2 pictures below, I've tried to give a simulation of the halos around lights caused by multifocal lenses. The first picture shows a small light source (called a 'muscle light'), and in the picture below that, I have overlayed a drawing from one of my multifocal lens patients of what he sees when I show him the muscle light. This patient has a Tecnis Toric Multifocal and has 6/4.5 unaided distance vision as well as N5 unaided near vision and is very happy. He tells me he sees 2 definite light rings around the main light, and then much fainter rings outside that. But regardless, he was expecting this, and he feels that it is a small price to pay for being able to read up close without glasses again.

Due to the fact that images are innately degraded by the multifocal nature of the lenses, I make absolutely sure that there is nothing else that can degrade the vision further. ie the patient cannot have any other eye disease like glaucoma or macular degeneration, and I will use the toric version of the multifocal lens as necessary to minimise post operative astigmatism as much as possible. All patients also get a pre-operative corneal topography, so that I can screen out the patients with irregular corneas (which are fairly common in the older age group).

Then I usually wait for a patient to request such a lens. And I make sure I tell them about the possible halos, and reduced contrast. Generally I will also use these lenses for patients who have denser cataracts, and who are long-sighted rather than short-sighted before surgery. My approach is extremely conservative, but I do this because the side effects are very real and patients sometimes have unrealistic expectations about what is achievable.

Why the Tecnis lenses, you might ask?

As I covered in an earlier post, I prefer lenses with flexible C loops. I also prefer the diffractive over the refractive designs as there tends to be fewer visual disturbances from halos. And that really leaves me with 2 options: The Tecnis and the Restor. The Achilles heel of the Acrysof Restor really is the problem with glistenings. This is what David Apple said:

'In summary, four clinical issues occur in eyes with glistenings. Most commonly there are subjective
complaints of poor vision in spite of a satisfactory, even normal Snellen visual acuity.

Secondly, subjective poor quality vision develops in patients who also have decreased Snellen visual acuity and/or contrast sensitivity, 

Thirdly, there is decrease or loss of the lenses special function. In such cases there is impairment of the lens’s ability to provide the ‘‘premium’’ result intended. In other words, glistenings can cause not only visual disturbances, but also may impede the designated function of a given lens. In such cases the lens may not only be affected with visual degradation, but also may be unable to provide multifocality. 

Finally, there is iatrogenic decrease in vision secondary to the additional surgical trauma of the explantation/exchange procedure.'

Apple et al. Modern Cataract Surgery: Unfinished Business and Unanswered Questions. SURVEY OF OPHTHALMOLOGY VOLUME 56 SUPPLEMENT 1 NOVEMBER–DECEMBER 2011.

David Apple was a very respected eye pathologist who specialized in lens implants. He maintained a collection of thousands of these lenses, which had been taken out from patients' eyes when they developed problems. As such, he was considered one of the foremost experts on lens implant problems. Sadly, he passed away in 2011.

Finally, multifocal lenses can result in very happy patients...or very unhappy patients. It all boils down to making sure that the patient knows what to expect, and whether they feel that the good near vision outweighs the side effects. Of course, surgery has to be as perfect as possible too...and that is up to the surgeon.

So, that's that with presbyopia options in this day and age. If there is anything I have not covered that you would like to know more about, please let me know. Incidentally I noticed that in the 'Mind Your Body' section of The Straits Times last week, there was another article about presbyopia treatments. This time it was about the Raindrop corneal inlay that I covered in my last post, and apparently there is a private practice eye centre in Singapore that is conducting a trial on it. Hmmm, having so many different inlays (the Icolens was featured in this same section of The Straits Times in January this year only) reminds me of the early days of cataract implants, when there were myriad different designs as well. If there was one design which worked really well, you wouldn't need so many different types...food for thought...

Anybody with comments about these presbyopia treatments?

Update (25 November 2014)
A new generation of lenses is just about coming online, which address presbyopia but with a different twist. Where previous lenses would split light into two focus distances, these newer lenses are called 'extended depth of field' or 'EDOF' lenses and avoid some of the problems with traditional multifocal lenses. Typically, EDOF lenses do not cause significant halos, and provide a longer continuous range of focus distances without any 'gap' in between, like intermediate distance. The first of these is the Symfony lens from AMO, but I hear HOYA has come out with one, I see a patent from Alcon about an EDOF lens, and even from Staar, which are testing an EDOF ICL!

An overview of cataract surgery lens implants

Cataract surgery involves removing the cloudy crystalline lens of the eye and replacing it with a perfectly clear one. Nowadays, these lenses are usually made of flexible clear plastic materials which can be folded and injected through very small incisions of 1.8-2.75mm in width. Most people are not aware that there are various brands competing in the ophthalmic market, and let the doctor make the decision as to which lens to implant in their eye. All well and good, but have you ever wondered what the factors are, that are taken into consideration when selecting a lens? Were you curious to know why your doctor chose the particular lens that was implanted in your eye?

Let's take a step back, and list the important properties of a lens that is meant to stay in the eye for the rest of a person's life.

1) It must stay transparent

2) It must be optically optimal (in harmony with corneal optics)

3) It must have a low association with posterior capsule opacification

4) It must resist the healing/contraction forces of the capsular membrane in which it sits

5) It must not cause any reaction or inflammation

Simple enough?

Let's take point 1. Current materials in use such as silicone and acrylic polymers do stay transparent for many years. In the past some hydrophilic acrylic materials became opaque after developing calcium deposits in the lens optic and had to be exchanged. Among the current lenses, the concern is increasingly with the development of so called 'glistenings' in hydrophobic acrylic lenses. These are tiny water vacuoles that develop in the lens material and have been shown to cause increased forward light scatter, which can reduce contrast. (Notice the minute white dots in the picture below) Although any hydrophobic acrylic material can have this problem, it has been reported especially in lenses made by Alcon, and these include all Alcon Acrysof lenses that are currently being used including the SN60WF (IQ lens), SN6ATT (toric lens), SN6AD1-3 (multifocal lens) and SND1TT/SV25TT (multifocal toric lens).

To be fair, not all Acrysof lenses get such significant glistenings, but it is disturbing that firstly, we cannot predict which particular Alcon lens will get a more severe problem with glistenings, and secondly, among those who develop the problem the glistenings tend to get worse with time.

Vacuoles/glistenings in a diffractive multifocal lens

Miyata A. Water accumulation in polymers [Japanese]. IOL and RS.2007;21:59-62

The only FDA approved and certified glistening free lens currently is the Envista lens by Bausch and Lomb, which is also made of a hydrophobic acrylic material. Almost all other lenses have some degree of glistening formation after some time in the eye, but none to the same degree as what is seen with the Alcon Acrysof lenses.

What about point 2? For the photographers out there, the term 'aspheric' would ring some bells. It turns out that on average, our cornea has +0.27 microns of positive spherical aberration (at 6mm diameter), so if a lens implant has -0.27 microns of negative spherical aberration, the two would cancel out nicely leaving no spherical aberration and improved contrast sensitivity. This has been borne out in some studies, and the effect is more noticeable in dim light when the pupils are more widely dilated.

The lens implants currently in use today with such a degree of negative spherical aberration belong to the AMO Tecnis range of

lenses. Should everybody switch over to these lenses then? Well,

remember that here we are talking about an average figure, so patients with lower degrees of corneal spherical aberration, or those whose lenses might be expected to centre poorly due to pre-existing factors like weak zonules should have an aberration free lens like the Envista lens instead. The problem is that an off centre lens with any built in aberration (like negative spherical aberration in the Tecnis lens) will cause even more aberrations and blurry vision.

Most lens implants in use today are meant to be implanted in the 'capsular bag'. This is like the 'skin' of the cataract that is left behind, and it is in this thin membranous capsule that the new lens sits, right in the same position as the original cataractous lens. Sometimes the original lens cells grow and form a layer behind the new lens implant, blurring vision again. Although this can be very simply treated with a 5 minute YAG laser posterior capsulotomy, it's much better to avoid it in the first place. To this end, most lenses nowadays have a 90 degree sharp peripheral edge, so that when the capsule shrink wraps itself around the lens implant there is a 90 degree bend in the capsule which stops the migrating cells dead in their tracks.

A lens should also sit in the capsule and conform to the size of the capsule as much as possible. It is known that capsular diameters vary among different people and can be larger in people who are highly shortsighted. Flexible loop haptics (like in the lens shown above) allow the lens to be made with haptics of slightly larger diameter, since their flexibility allows them to be compressed for smaller capsules. Plate haptics (like in the lens shown below), however, are rigid and do not allow this kind of ability to adjust for different capsular sizes. They will unduly stretch smaller capsules, and if they are put into larger capsules they either decentre or may move around inside the capsular bag. Woe also to the capsule that contracts and fibroses with time-they will compress and vault a plate haptic lens, causing a refractive shift, usually in a hyperopic direction.

The last point is important but has usually been taken care of in very preliminary studies, and currently lens materials are very biocompatible. Silicone is currently less commonly used, not because it causes reactions or inflammation, but because if a patient has retinal surgery and injection of silicone oil, this oil will stick to the silicone lens andspoil it.

So, to cut a long story short, which lens would I want in my own eye? (or my dad or mum's eye?)

I would have a look at the 6mm corneal spherical aberration first. If it is highly positive, or there is a large amount of corneal astigmatism, the Tecnis lens would be ideal. If the spherical aberration was low, with little corneal astigmatism, I would go for the Envista lens and be guaranteed of no glistenings. Notice that these lenses are both flexible modified C loop designs. I would avoid plate haptic designs or those with rigid 3 or 4 haptic designs. **Would I have a multifocal lens in my own eye? I think not. Presbyopia is not a nice thing to have, but for me personally I think it would be worse to have to put up with constant halos and poor contrast which is only correctable with another surgery to replace the lens!

**Update 16th February 2015
I found myself having to clarify this last part, which I wrote in 2013, because lately I find that my patients who have had the Symfony lens are turning out to be very happy indeed. The Symfony lens is not a conventional multifocal like the Restor or Tecnis multifocal. Instead, it is called an extended depth of focus lens, where the zone of focus is increased to provide good distance and near vision. The best part of it is that there are very few or no side effects like halos. It may not give the sharpest vision when viewing things very close up, but for many people, the benefits of no side effects far outweighs this slight blurring when looking at very near things. So I think this could be my new lens of choice...