Making progressive lenses work for you

Having reached THAT AGE myself has led me to reconsider my own presbyopia options. Many of my peers are also experiencing this rite of passage and my wife has started wearing progressive lenses. Here's a little ditty in case some of you need pointers regarding progressive lenses, and are finding them hard to get used to.

Progressive lens spectacles are in fact a boon for many people. By combining both far and near focus points in a single lens, they allow an older (presbyopic) person to see clearly at both far and near distances, with the same pair of glasses. And besides which, nobody can see the dividing line, thereby making it much better cosmetically than the normal bifocal lenses.

However, they are by no means a panacea for presbyopia. Many people try them for a while, then give up because they cannot find a way to get used to them.

The thing is to know what to expect, and to obtain some tips which will allow one to overcome their deficiencies.

How progressive lenses work

These lenses have a central vertical zone, which changes in power from top to bottom. The top part of this zone is for distance, the middle part for intermediate vision, and the bottom part for near. At the sides there are regions which try to blend the powers together but cause a degree of distortion depending on how high the spectacle power is, especially if it is a high longsighted (hyperopic) power.

Some problems with progressive addition glasses

1. Different focus points depending on where you are looking

It can take a while to get used to the fact that with progressive lenses, rolling your eyes in different directions (especially up and down) gives you clarity at different distances. This can be a problem for some people eg if they roll their eyes downwards to look at steps. Doing so can make the steps go blurry, since the person would be looking through the near part of the lens, which is actually for reading distance.

2. Some degree of distortion when rolling the eyes sideways and looking out the sides of the glasses

3. Sensitivity to slight distortions/bending of the glasses frames

Some tips for progressive lens spectacle wearers

1. Start with progressive lenses that have a lower power reading portion. This also means that it is actually a good idea to start wearing them at an earlier stage (and age). With a lower power reading portion, the shape changes across the lens are more gradual, and less pronounced. As such, any distortions that occur in off centre directions of gaze are also going to be milder.

2. Learn to turn your head to look in different directions more. Eye rolling movements are still fine, but especially in a vertical direction, eye rolling will be used more for changing the effective power of the spectacle, with the changing of object being looked at a secondary/less important effect.

3. In conjunction with the above, many wearers learn to tilt their heads slightly in different directions to help the eyes look through the appropriate portion of the lens. For example, when looking at near objects, the chin may be tilted slightly upwards to help the eyes roll downwards. These head movements are generally minimal, especially since reading materials are usually held in a lower position.

4 .Take good care of them, because it is very critical how these glasses sit on your eyes. If they are accidentally bent because someone sat on them, there is a good chance that wearing them could cause headaches. Imagine this-the slanted glasses (higher on one side and lower on the other) will cause one eye to look through the distance portion, while the other eye looks through the near portion!

5. Some people who do a lot of intermediate and near work (eg, computer distance at about 1 meter and also reading at 1 foot while working at the office) may find the intermediate part of a normal progressive lens too narrow. They may consider special progressives that have a top part for intermediate distance, and a bottom part for near vision. These glasses would only be used while working at the desk, with the computers and reading material.

All you wanted to know: LASIK FAQs

1. What is LASIK?

LASIK is an operation on the front of the eye, the cornea, to correct spectacle power like shortsightedness and astigmatism.

During this surgery, a thin layer of the cornea (the flap) is partly separated and then an excimer laser is used to reshape the front surface of the eye (the cornea). The flap is then replaced in its original position on the eye.

LASIK Part 1: Creating the LASIK flap with a femtosecond laser

LASIK Part 2: Lifting the flap and performing corneal reshaping with the excimer laser

2. Why go for LASIK?

Glasses and contact lenses actually work very well. But, they sometimes get in the wearer's way. Hmm, going swimming? Better get those contact lenses out first, or gingerly get into the pool and make sure the goggles are fitting well with no leaks.

Fogging of glasses can be annoying...

Spectacles can fog up when going from a colder to a warmer place, or when having a hot drink/meal. Plus, the field of view is limited to the spectacle frame, and strong spectacle lenses can cause distortions at the edge of the lenses. That is why a lot of people with high spectacle powers prefer contact lenses.

Having LASIK done is somewhat like having contact lenses built into the eye, so that one does not have to worry about the daily routine of lens wear, the cost of the lenses, or the dryness and allergies that lenses can cause.

For many patients, the best things after LASIK are waking up in the morning to immediate clear vision on opening the eyes, or going to sleep without having to bother about taking out the contact lenses!

3. What is wavefront LASIK?

Although our corneas and eyes look round and smooth, in fact there are little irregularities that cause us to see starbursts around stars. We call these irregularities aberrations.

Wavefront guided LASIK aims to reduce or correct these aberrations ie to improve the focusing of the eye. The benefits of wavefront guided LASIK are more obvious

1. In people whose eyes already have more aberrations before LASIK
2. When seeing things in the dark/at night after LASIK surgery

Some clinics use the term 'wavefront' loosely, to include wavefront optimized treatments and so on. In fact, wavefront optimized is a kind of standard LASIK that does not take a person's own corneal irregularities into account.

True customized treatments are either (ocular) wavefront guided or corneal wavefront/topography guided. Do clarify with your doctor whether your treatment is 'wavefront optimized' or 'wavefront guided', as the former is a kind of standard treatment and the latter is true customised treatment.

To be fair, not everybody needs wavefront guided treatments. People who are lucky enough to be born with few ocular/corneal aberrations would do just fine with wavefront optimized treatments. Also, wavefront guided treatments usually take more corneal tissue, so sometimes for people with thinner corneas, wavefront optimized treatments may also be more appropriate.

4. What is the difference between epiLASIK and LASIK?

epiLASIK involves surgery that uses a special blade to peel the surface layer of cells off the cornea, then the corneal surface is treated with the laser. In epiLASIK, no corneal flap is made. In LASIK, a corneal flap is made with a special laser called the femtosecond laser.

With epiLASIK, only the layer of epithelial cells is scraped off before laser reshaping. As the cells die and are thrown away, the patient has to wait for them to slowly grow back. 

With LASIK, there is a thicker corneal flap that is replaced at the end of surgery. Repositioning the flap means that there is immediately a healthy layer of cells at the end of surgery, so recovery is much faster than epiLASIK or PRK.

Disadvantages of epiLASIK:

1. Without a flap, epiLASIK patients take much longer to recover than LASIK patients as they have to wait for the surface cells to grow over the cornea. The recovery is like PRK, and vision may take several months to get to its clearest level. In comparison, for LASIK vision is very good the next day and often reaches its best level within 2-3 weeks.
2. Also, with epiLASIK there is a risk that the blade may cut deeper than it is supposed to, resulting in an uneven cornea and permanent blurry vision.

That is why I do not perform epiLASIK. If a patient engages in rough contact sports and prefers not to have a LASIK flap, then I would recommend alcohol-assisted PRK (LASEK) or Transepithelial PRK (TPRK).

5. How do I take care of my eyes after LASIK?

Immediately after LASIK, the eyes may feel mildly irritated and vision is misty.

Remember to put the eyedrops prescribed and use a shield to protect the eyes while sleeping. Sunglasses are useful when going outdoors.

One must not rub the eye at all, and avoid splashing water into the eyes. Swimming is to be avoided in the first month. Other sporting activities can be commenced earlier, for example, going to the gym should be fine after 2 weeks.

6. Is it true that the eye never heals after LASIK?

Although the corneal flap does not stick down and heal to 100% of its original strength, it does heal and after 1 month the flap does not shift even if the eye is accidentally rubbed. In fact the flap is extremely stable after the normal recovery period.

The safety of LASIK is attested to in many ways, for example, athletes like Lebron James in the NBA had LASIK done, and NASA allows people who have had PRK or LASIK to become astronauts:
http://astronauts.nasa.gov/content/faq.htm

There is actually an advantage in this feature of LASIK. If at any point some spectacle power creeps back, the LASIK flap can be lifted, and a minor adjustment/enhancement procedure performed. This can be done provided that the underlying cornea is thick enough.

7. What are the upper limits of spectacle power that LASIK can treat?

Depending on the thickness and original curvature of the cornea,

• the maximum shortsightedness that can be treated is about -11 to -12D (1100 to 1200 degrees), 
• astigmatism -5D (500 degrees), and 
• longsightedness about +5D (500 degrees). 

In exceptional cases, higher powers have been treated, but the risks are of a small optical zone causing halos and other visual disturbances, or of regression ie some of the spectacle power comes back.

8. (Update) Is there a lower limit of spectacle power that LASIK treats?

Generally speaking, the lowest spectacle power that I treat with LASIK is in the region of +/-0.50D. With a lower power than that, most patients are not that bothered by the slight blurring of vision.

In special situations, I may treat lesser spectacle powers than that. This applies to patients with irregular corneas, such as after prior refractive surgery or corneal scars, where the measured spectacle power may be low but the visual quality is poor due to what are called 'higher order aberrations'. These patients need special topography guided LASIK/PRK.

9. Who is suitable to have LASIK?

1. People who are between the ages of 20 and 60 are candidates for LASIK if the spectacle power has been stable (no change of 0.5D/50 degrees or more) for a year or more.

2. Younger ladies who are pregnant or breast feeding should wait until the baby is delivered, or until they stop breastfeeding before having LASIK as the hormonal changes may affect their spectacle power and the long term accuracy of the LASIK correction.

3. Patients going for LASIK should not have other eye conditions such as cataracts or glaucoma.

Above 60 years of age, the issue is the possibility of cataract developing in the next few years after LASIK. Cataract surgery is another way to correct their spectacle power, so the effect of the LASIK procedure may have been only for a few years. Occasionally I do perform LASIK for these patients, but only if the lenses in their eyes look very clear on examination.

With glaucoma, the issue is that LASIK thins the cornea, and this can affect the measurement of the pressure of the eye, which is important in glaucoma. After LASIK, the measurements may show a lower pressure than the actual pressure in the eye, however, as long as the eye doctor is aware that prior LASIK has been done, he can make suitable adjustments and the glaucoma can still be treated.

10. What are the side effects of LASIK?

After LASIK, most eyes become temporarily drier during the healing process. This is helped greatly with artificial tear drops and sometimes with plugging of the draining tear channels. Usually the dryness goes away as the eye heals. By 3 months, about 90% of eyes are no longer dry, and by 6 months >95% of eyes are back to normal.

Halos are common in the early period after LASIK. This is due to slight roughness of the corneal surface (and interface) as it heals. Most of this early halo effect will disappear within a month after surgery. Some halos persist after one month, and these are commonly due to other problems, such as an optical zone that is too small, decentered optical zone, or other aberrations and irregularities. If these are persistent, corneal mapping (topography) should be done to see if specialized topography guided treatment might help.

11. Can LASIK treat presbyopia (Lao Hua)?

LASIK cannot actually treat presbyopia. However, there is the option of 'monovision', which means one eye is fully corrected to see distance clearly, while the other eye is made slightly shortsighted so that it can see clearly at near.

Having 2 eyes with slightly different spectacle powers is something most people get used to, and they do not need glasses for most things. Occasionally they may wear distance glasses for certain activities such as driving at night or reading glasses for really close up viewing.

There are some laser centers and machines that offer 'PresbyLASIK'. There are many other names for this kind of treatment such as PresbyMax or SupraCor. This works by trying to give the cornea a multifocal shape. However, most doctors prefer monovision compared with PresbyLASIK, because

1. The multifocal shape can cause poorer distance vision and side effects such as increased halos
2. The multifocal shape often does not last due to the healing process of the cornea
3. The effect is often modest and many patients still need to wear reading glasses in the end

12. Do LASIK doctors go and have LASIK done themselves?

Doctors (including eye doctors) are just like any other group of people). Some of them wear glasses, others wear contact lenses, and some of them have also had LASIK done. One well known LASIK surgeon who had LASIK done himself is Dr Arthur Cummings, and you can read his account of it here.

http://bmctoday.net/crstodayeurope/2014/02/article.asp?f=why-i-chose-to-have-lasik

13. What is the best age for LASIK?

Please see my previous blog post here.

14. Why did the Taiwanese doctor stop doing LASIK?

In February 2012, Dr Ray Tsai announced that he would stop doing LASIK, because some patients developed poor vision many years after their surgery. While the exact problem was not mentioned, he was probably referring to a problem called 'ectasia'. In the past, doctors were not as aware about the signs of corneal weakness, and with older equipment there was a higher chance of making the cornea too weak. In some patients whose corneas became too weak, the normal pressure in the eye caused the weak cornea to bulge outwards. This causes distorted vision and irregular astigmatism.

A large study conducted by SNEC found that the problem in Singapore was rare, occurring in about 8 out of 30000 cases. The risk is probably even lower nowadays, because:

1. Doctors are more aware of the features that are shown by a weak cornea, and these cases rightly are told they are not suitable and do not get LASIK

2. With newer machines like the femtosecond laser to create LASIK flaps of very precise thickness, the risk of corneas getting too thin is minimized

3. There is now 'LASIK Xtra', a way to strengthen the cornea with vitamin B2 and ultraviolet light at the end of LASIK. LASIK Xtra may also reduce the risk of regression (power coming back) in patients with high spectacle power or those with longsightedness

Even if a patient develops ectasia, the process can be halted or stabilized with cross linking treatment, which is like LASIK Xtra but takes a slightly longer time. The important thing is to catch it early. Therefore, if any patient notices that his/her vision is getting blurry after their LASIK, they should get their eyes checked again by their doctor soon.

The best age to have LASIK

So, young, middle, or old? What's the best age?

Is there a best age to have LASIK? I get asked this question quite often when patients enquire about this surgery and the short answer is yes, with some caveats.

I suppose when we decide to have something done (eg surgery), or even when we buy something, we want to get the best that we can get for what we pay. In other words, value. Even more importantly for surgery of course, we want to get a good outcome, and we want to ensure quality and safety, but value is a common factor that pervades many aspects of our lives.

LASIK is somewhat different from other types of surgery, because what you get out of it is influenced by the age when it is done. Let's take a few scenarios.

A typical patient in their 20s comes for LASIK. In such a situation, both eyes are corrected for distance, so everything is clear after surgery, whether it is something far away or something close up that is being looked at. However, when this patient gets to his/her early forties, they are just like any other patient who does not wear glasses for distance, ie near vision for reading slowly starts to get blurry, and they find they have to start holding things further away. This condition is called presbyopia. At some point, reading glasses are needed for comfortable close work like reading.

When a patient comes for LASIK and they are already in their forties or older, presbyopia is an issue that needs to be considered straight off, at the time of the pre-LASIK consultation. This is because LASIK cannot 'cure' presbyopia as such. The usual option offered to patients who desire spectacle independence is monovision, with its attendant compromises. PresbyLASIK is unfortunately unpredictable in its effects, and so far corneal inlays have also shown problems relatively commonly.

Having said this, many presbyopes are very happy with monovision LASIK. The important thing is to allow a trial period of monovison adaptation to see if patients can tolerate it. This simulation is best done with contact lenses. If a patient does not tolerate monovision with contact lenses, then if LASIK is done both eyes should be corrected for distance and then reading glasses worn for near. Therefore it can be seen that LASIK after the age of 40 or so does not provide as much clarity of vision for all distances compared with when it is done earlier, and also involves some compromises, whether it be monovision or reading glasses for near work.

The next group of patients to consider are those 60 and above. Generally speaking, age is associated with an increased incidence of cataracts, especially with those above 60 years of age. The issue with cataract development is that once a patient has cataracts, then they are no longer suitable for LASIK, since the cataract will blur vision even if LASIK is performed. Furthermore, doing cataract surgery is also a way to correct spectacle power, giving an effect like LASIK. In some ways, you could consider cataract surgery as having the ability to reset the power of the eye, therefore, this is the point where the effects of the LASIK surgery are 'lost'.

To cut a long story short, the best age to have LASIK in my opinion is the early twenties, once spectacle power has stabilized and remains unchanged for more than a year. Patients above 40 will still benefit from LASIK, but one might want to consider certain compromises to avoid reading glasses. Generally, patients above 40 who do get LASIK done avoid progressive/bifocal spectacles, which many people find difficult to get used to. Glasses, if needed, tend to be reading glasses, or occasionally distance glasses for monovision patients who drive a lot at night.

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!

Presbyopia treatments: So, you want to be a spring chicken again?? (Part 1)

To follow on from the last post, so if your lens has now matured nicely in its eyeball and is no longer focusing as well as it used to, what can you do?

As with most things in life, it depends...(unfortunately, 'it depends', because there is no one size fits all, cure-all solution and all methods currently involve compromises in one fashion or other)

The simplest, time proven method is the spectacle. Spectacles are great-besides being a fashion statement, people like me gain an air of authority at work and they are also eminently adjustable and flexible. Your eye power changed by 50 degrees? No problemo, your friendly neighbourhood optometrist just needs to change the spectacle lens and Voila! everything is nice and clear again.

But...spectacles fog up, they can collect droplets of rain/sweat/etc, and if they are only used for reading they are often lost or they are not handy just when you needed them. Progressives give you a narrower field of vision and require slight adjustments of head position to work well. With contact lenses, monovision can be used (one eye corrected for far, the other corrected for near),or multifocal contact lenses can be worn to reduce the need for near reading glasses, but they are not perfect too and also there is the hassle of wearing them.

So, many clever people have thought up ideas to get around this problem while avoiding the need to wear glasses or contact lenses. Primarily the procedures can be divided into corneal operations and lens operations.

In terms of corneal operations, the most recently promoted procedures (fads? time will tell...) are corneal inlays, which are tiny pieces of special plastic implanted inside the cornea* itself.

*This is the transparent part covering the front of the eyeball.

The first of these inlays that comes to mind is the Kamra, which had been undergoing trials in Singapore some years ago. This is a very thin circular membrane with a central opening that is like a very tiny doughnut, and acts like a pinhole to sharpen images which would normally be out of focus.

The black polyvinyl pyrrolidone disc is 5 microns (0.005mm) thick and has a central 1.6mm diameter hole. Surrounding this hole is a rim which is perforated with thousands of microscopic openings that allow nutrients to pass through. This disc is implanted under a LASIK type corneal flap or into a pocket dissected within the cornea.

Most of us with some degree of long/shortsightedness or astigmatism know that if we squint or close our eyelids partially, vision can get a little sharper. This is because doing so creates a kind of ‘pinhole’ effect. Light rays entering dead centre of the cornea and eye do not have to be accurately focused to create a relatively sharp image. Similarly photographers know that if you step down the aperture to eg f11, you can increase the depth of field of the picture so that more things in the fore and backgrounds appear in focus. In fact, published articles report that many patients experienced better near vision after having had this implant.

However, photographers also know that if you step down the aperture excessively, image quality suffers. This is a result of diffraction, a physical phenomenon where light spreads out from a small point source. The smaller the light source, the greater it spreads out (in relative terms) and the blurrer an image gets. Among other factors, this is one source of the halos that patients with the Kamra inlay experience.

There are other sources of dissatisfaction as well. Excessive dryness from a thick flap, and the increased perception of floaters and other media opacities in the visual axis. Some patients developed refractive shifts (developed increasing long or shortsightedness) with the implant. It is not surprising that where such surgery is being done, there will be anecdotes of patients wanting the inlay to be removed-definitely not something either the surgeon or patient wants done after very expensive surgery! You can find a comprehensive summary from the UK National Institute of Clinical Excellence here http://guidance.nice.org.uk/IPG455/DraftGuidance and a pdf is downloadable from here http://www.nice.org.uk/nicemedia/live/13701/62162/62162.pdf

The Icolens

This is a small, 3mm diameter disc shaped implant with a 0.15mm channel in its centre to allow for the diffusion of nutrients within the cornea. The periphery of this implant has extra reading power to help with near focusing, while the centre of the implant has no power to allow for good distance vision. It is also placed under a LASIK type flap like the Kamra inlay above.

While this sounds like it could work in theory, in practice it is not so simple. Devices like this are dependent on pupil size, and if a patient’s pupil size happens to be bigger than usual then the effect is less than expected or the patient may experience significant halos from light scattering at the edge of the implant/multifocality. There is also some concern that the central channel could get blocked up in the long term from deposits that were seen to develop with other, earlier types of corneal  implants.

The Raindrop implant

This implant is so called because it looks like a droplet when implanted in the cornea (like the 2 other inlays above, also under a LASIK type corneal flap). It works by increasing the curvature of the central 2mm of the cornea, with the increased curvature helping the eye to focus for near. However, in a similar way to the Icolens, the patient's pupil size will affect the usefulness of the device and there is a very real risk of halos and distortions due to the multifocality induced by the implant. The increased central curvature on the cornea also makes that eye more shortsighted, and you can actually get this effect from plain monovision in the first place!

The only positive thing about any of these corneal inlays is that they can be removed and the procedure reversed. But personally if there was even a 2 or 3 percent chance that a patient would not like an implant and request its removal, I don't think it's worth the effort and financial cost involved, plus the blurred vision and side effects that necessitate reversal of the procedure.

PresbyLASIK
PresbyLASIK is basically LASIK, but in this case using the excimer laser to sculpt the cornea into a shape to give the effect of either the Icolens (centre-far presbyLASIK) or the Raindrop implant (centre-near presbyLASIK). Suffice to say this has not really caught on either, due to a high chance of poor quality vision/halos as above, and also the high chance of not getting the desired effect of good near vision. If anything, presbyLASIK gives less predictable outcomes than corneal inlays, and that is because the body tends to smooth out the newly sculpted shape, leading to a regression of effect.

If all of the above doesn't sound all that promising...it's mainly because it's somewhat difficult and unnatural to try and treat a lens problem on the cornea. Creating a multifocal cornea will also inevitably lead to lowered visual quality due to the aberrations (Imagine trying to take photographs with a multifocal camera lens...especially one where the effect varies as you change the aperture settings...)

It's probably too early to write off the above technologies at this time, but still it concerns me how they are being presented to the public sometimes. Goodness knows there have been so many dead ends in the last decade or so. (Remember Conductive Keratoplasty? or Intracor?)

In the second part of this series I will be giving my take on something just a little more promising-lens implants for improving near vision.

**If any reader has had corneal inlay surgery done and would like to share their experience, I would be most grateful if you could add your comments below!

Presbyopia: A sign you’re not a spring chicken anymore…..

Imagine you had a camera and it stopped focusing. It might take clear pictures in the distance, but up close everything becomes a hazy mess. Well, back goes the camera to the service centre or perhaps it's time to get the next iteration of your favourite DSC or DSLR (or autofocus lens...)

If only we could do the same with our eyes, for this is exactly what happens when the big 4-0 arrives. The lens in our eyes becomes stiffer, and this prevents it from focusing well for both far and near. In short, the eye becomes a fixed focus camera.

In actual fact, the process is a gradual one, and the lens loses its elasticity from as young as the twenties. However, it is in the early 40s when the loss of elasticity reaches such a level that focusing at reading distances becomes a pain. By the time one reaches the mid-fifties to sixties, there is virtually no focusing ability left.

The proper term for this is ‘Presbyopia’, but people may call it ‘old sight’, ‘longsightedness’, Lao Hua in Chinese, or Rabun Tua in Malay.

How it affects different people

How the condition affects you depends on what your existing spectacle power is, and what you normally use to obtain clear vision.

Let’s talk about the simplest situation, that of people who see well in the distance and do not need to wear glasses. (This includes people who have had refractive surgery like LASIK). These people continue to see well in the distance, but find that they have to hold reading material further and further away to keep it in focus. Eventually, it just becomes too tiring to read at arms length and also having to squint forcefully causes significant brow ache. That’s when reading glasses become one’s indispensable companion.

The second situation is of people who are shortsighted, ie they need glasses to see clearly in the distance. Without glasses, these people’s eyes are like cameras with extension tubes fitted. They lose infinity focus but on the other hand can focus at macro distances. Therefore, if they take off their glasses, they can see remarkably well for near even when they reach the presbyopic age group. If they wear glasses or contact lenses for distance, though, they are no different from the people in the ‘normal’ group, ie their eyes have had their extension tubes removed and with the glasses everything nearby becomes blurry too. So for looking at near things, shortsighted people either remove their glasses, or they may get glasses with a reduced distance correction.

The final situation is of people who have real longsightedness. To give a camera analogy, these people’s eyes are like cameras where the lens has been mounted too close to the film or sensor plane. To make an object at any distance clear, some degree of focusing effort needs to be put in. Even for an object at infinity, the lens needs to be focused for closer than infinity for clarity. Because these people have to put in more effort at focusing, they will notice the problem with reading earlier than others. At some point, when they are unable to focus even for distant objects, everything becomes blurry. Distant objects are blurred, and near objects even more so. Many of these people end up wearing bifocal or progressive glasses, because they always need something to clear their vision, whether for far or near objects.

Common myths

I’m shortsighted, so ‘longsightedness’ after the age of 40 will cancel out my shortsightedness

Since shortsightedness is a focusing error related to the length of the eyeball, while ‘old sight’ is a problem related to the focusing ability of the lens, they cannot cancel each other out. A shortsighted person will remain shortsighted no matter how old he or she gets. However, they have the option once presbyopic, of seeing things close up by taking off their glasses/contact lenses.

Once I start to wear reading glasses, my presbyopia/old sight/lao hua/rabun tua will get much worse very quickly. So I’m not going to wear them!

Without wearing reading glasses, many older people manage to get by, by squinting, by reading in very bright light, and by holding things as far away as physically possible. It takes a lot of effort. Once they have the reading glasses, everything gets clearer without having to put in all this effort. They may forget that they used to have to strain very hard to see, so that now, without the extra effort and without the reading glasses everything appears blurry. They may blame it on the glasses, when it was actually due to their overcompensating in the past! In actual fact, the condition slowly progresses, with or without reading glasses. Therefore, I advise my patients to wear the reading glasses if they have to and if they feel easily tired otherwise.

(PS: If the camera analogies don't quite ring a bell, feel free to clarify with me. Unfortunately I'm going through a 'gearhead' phase...)