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.

Eyelid cysts a.k.a. chalazia or styes

Most of the time, cysts of the eyelids or ‘bak chiam’ (in Hokkien) are caused by blockages of the oil glands inside the eyelids. When the openings of these glands are blocked, the oil produced by the gland cannot be released, and it builds up to form a lump in the eyelid.

The white dots are blocked oil gland openings

Oil collects inside the blocked gland, causing a lump to form

Commonly, it feels like a little pea, which can be painful if it gets infected. These cysts are also called ‘chalazion’, and they are very common. They can be associated with inflammation of the eyelids called ‘blepharitis’. Normally, most chalazia are not serious and many do go away on their own with time. Big ones near the middle of the upper eyelid can cause blurring of vision by pressing on the cornea/window of the eyeball.

Problems with these cysts arise especially when they do not go away after a long time, or if they keep coming back. Big cysts that do not resolve on their own are easily treated with a 5 minute office procedure to drain the oil from the blocked oil gland.

Cysts usually happen individually, and then disappear for long periods of time. On the other hand, a smaller proportion of people get cysts that go away and then come back, often in another eyelid or even on the other side. Recurrent cysts are usually associated with ongoing eyelid inflammation. For many people, hot compresses at night followed by eyelid cleaning (perhaps with products such as Lid Care/Blephagel) are helpful in reducing the chances of recurrence.

Very stubborn cases may be related to changes in the eyelid oil to a very thicky waxy material which blocks the channels of the glands. It is thought that these changes are related to the type of bacteria living on the skin of that person, which can also change the normal oil to other irritating substances.

Treating chalazia

The simplest measure recommended is hot compresses, with which we hope to make the oil more liquid and to flow out better.

It has been found that long courses of certain antibiotics from 1 month to several months help to resolve many of these blepharitis cases. Besides their antibacterial action, antibiotics in the tetracycline class also have anti-inflammatory properties. Besides antibiotics, taking Omega 3 oils in the diet or via supplements also helps to reduce the thickness of the eyelid oils and to reduce inflammation in the body.

Oil in some of the glands has turned into a thick material like toothpaste. In some other glands, the oil remains liquid and comes out as little droplets.

Recently, it has also been reported that some people have an overgrowth of skin mites in the eyelids. An article in the American Journal of Ophthalmology (Am J Ophthalmol. 2014 Feb;157(2):342-348) found that more patients with chalazia had these mites, and that patients found to have these mites had a higher chance of cyst recurrence. I routinely check for the presence of these mites in patients with inflammatory eyelid problems, and start treatment against them if necessary.

Pulling gently on the eyelashes causes the white tails of the mites to poke out. They can be teased out onto the eyelid surface and then scooped up with forceps.

One mite having a stroll across the microscope slide...

If despite simple measures the cysts persist, then a simple incision and drainage procedure can be performed in clinic. This usually take 5 minutes or less, after which the eye is padded for 2-3 hours.

Can these cysts be anything more dangerous? Very rarely, yes. There is a rare oil gland tumour that can present like a cyst. If a cyst keeps recurring in the same place, and especially if it is gradually getting bigger or associated with adjacent loss of eyelashes, the doctor should consider taking a specimen and sending it to the laboratory for further examination. But this is a rare condition and is unlikely if the recurrent cysts are happening in different places.

To summarise, do consult an eye specialist, as sometimes prescription medicines like antibiotics or other treatments may help. Dietary changes like taking more Omega 3 oils also would be good, and in the meantime continue with hot compresses and keeping the eyelids clean.

Keratoconus-a conical corneal conundrum

Keratoconus is a condition where the collagen of the cornea is weaker than normal, resulting in its stretching and deformation by forces such as pressure inside the eyeball, which may increase with actions like eye rubbing.

The eye is rather like a balloon or car tyre, and has a pressure to keep its shape. But if there is a weakness somewhere, the pressure can 'blow' out that weak area and cause it to protrude.

Protruding corneal apex in a keratoconic eye

Although a lot is still unknown about the condition, there is a strong genetic component with the condition being more common in certain ethnic groups. Some families also have several members with this condition, or a milder latent variant called 'Forme Fruste Keratoconus'. Around the world, prevalence rates range from 0.0003% to as high as 2.3% in one study from central India.*

*Jonas JB, Nangia V, Matin A, Kulkarni M, Bhojwani K. Prevalence and associations of keratoconus in rural Maharashtra in central India: The central India Eye Medical Study. Am J Ophthalmol. 2009;148:760–5

Patients with keratoconus usually are diagnosed in their teenage years or in their twenties. For many, the first sign of an eye problem is when blurry vision cannot be fully corrected with glasses.

The treatment of keratoconus

Traditionally, the treatment of keratoconus was optical (making vision clearer with glasses or rigid gas permeable contact lenses), until the  condition became very serious, in which case corneal transplantation would be needed. Besides causing very blurred vision, advanced keratoconus can cause corneal scarring, and occasionally the stretched Descemet's membrane tears resulting in a condition called hydrops where the cornea suddenly swells and becomes very hazy.

A rigid gas permeable contact lens

A keratoconic cornea with hydrops, which caused the central cornea to go a hazy white in colour

Since keratoconus is associated with a weakness of the cornea, a logical remedy would involve strengthening the cornea. A way to do this only became available relatively recently, and this treatment is called 'corneal collagen crosslinking'.

What is crosslinking?

Many things around us are made of long chains of atoms, such as rubber, leather, and even our own hair. Our corneas are made of many layers of collagen stacked one above the other.

The process of crosslinking is used all the time, from vulcanizing rubber to make into car tyres, to tanning leather, to perming our hair. Our corneas can also be crosslinked to make them stiffer.

From: Wollensak et al, Am J Ophthalmol 2003;135:620-627

How is corneal crosslinking done?

Crosslinking can be achieved in many ways, but one reason it took so long to discover a way to crosslink the cornea was that most of the methods are toxic and damaging to living tissue. Take formaldehyde for example. This chemical crosslinks tissue in the process of embalming/preservation of dead tissue, but would severely damage live tissue.

Finally, in the late 90s and early 2000s, Wollensak and Seiler described a way to crosslink the cornea using vitamin B2 (riboflavin) and ultraviolet light. The cornea was soaked with riboflavin for 30 minutes, and then ultraviolet light was shone onto the cornea for another 30 minutes. This process successfully stiffened the cornea by about 4 times, and provided the cornea was carefully screened to ensure enough thickness, proved to be a very safe procedure. Recent data suggests it is effective, with a 10 year study showing that only 2 of 34 eyes required repeat crosslinking at 5 and 10 years after the original procedure.
J Cataract Refract Surg. 2015 Jan;41(1):41-6. doi: 10.1016/j.jcrs.2014.09.033.

The majority of eyes in fact showed mild corneal flattening after the corneal crosslinking treatment. However, the main aim of this procedure is to stabilise the condition, and for most patients there is no significant change in the spectacle power.

Nowadays, 'accelerated crosslinking' using higher ultraviolet light energies is available, and this improves patient comfort by making the procedure shorter. Accelerated crosslinking generally soaks the cornea for 10 minutes, followed by ultraviolet light for 4 minutes.

The treatment of advanced keratoconus

Unfortunately, some cases of keratoconus continue to be diagnosed at a late stage. The condition can be difficult to pick up in the early stages, because there are no obvious corneal signs and vision may be correctable with normal spectacles. The diagnostic equipment of choice, a corneal topographer, is also not universally available in every eye clinic.

In advanced cases, the cornea is often too thin to allow safe crosslinking, and also too distorted to allow comfortable wearing of contact lenses. Some cases have scarring resulting from a very advanced cone or from previous hydrops. In such cases, the treatment of choice is a corneal transplant.

A perfectly clear corneal graft

Although a relatively big operation for the eye, corneal transplants traditionally do very well in keratoconic eyes. These eyes are uninflamed, not vascularized, and the grafts can survive for decades. Nowadays, partial thickness corneal transplants (deep anterior lamellar keratoplasty-DALK) are performed wherever possible, thus avoiding serious endothelial rejection episodes. Such grafts could well survive indefinitely (while the patient lives).

Other methods

There is actually a method of trying to regularize the corneal shape by implanting curved ring segments of a special plastic called PMMA into the cornea (IntraCorneal Ring Segments). This method works by flattening the middle part of the cornea, and was originally used to treat shortsightedness. However, once LASIK and other excimer laser procedures came into being, this procedure was abandoned for shortsightedness. 

Partly it was due to the reduced accuracy of treatments when compared with LASIK, but partly it was also because many patients who had these implants developed deposits of a whitish material within the cornea after some years. I haven't found a good reason for using this method of treatment at this time, but will continue to monitor studies on this.

Usually those patients having less severe keratoconus can be fitted with either RGP contact lenses or semiscleral lenses, and the more advanced cases would benefit from a corneal graft.

So, keratoconus-an old condition, but patients are getting better options to improve their vision, and finally (!), an option to actually address the condition at its root cause.

PS. This is an old review article I wrote back in 2007 on the treatment options for conditions like keratoconus:

Current treatment options for corneal ectasia.Tan DT, Por YM.

Curr Opin Ophthalmol. 2007 Jul;18(4):284-9. Review.

The early steps I took...to become an eye doctor

Plenty of people around me wear glasses. Both my parents are myopic, as are all my siblings. (Interestingly, none of my 4 grandparents were myopic, but this is a topic for another day) I'm not sure, but perhaps this constant reminder of our bodily imperfections was the beginning of an interest in the eye and vision.

My paternal grandmother had cataract surgery back in the 60s, and in those days the norm was large incision ICCE followed by thick aphakic glasses. I was always amazed that she could see through those glasses, which looked pretty much like the magnifying glasses we played with to focus light and make small burns with sunlight. Sadly, in her later years, her vision dimmed as her corneas became swollen from aphakic bullous keratopathy.

However, I hadn't exactly set my mind on ophthalmology at the time I set off to Melbourne for medical school. My eventual career goal was actually quite fuzzy at the time, and medicine was relatively reassuring as a stable career which I was familiar with through my father's occupation. I knew it could be a very satisfying job as well.

Where I stayed-49, Haines Street, North Melbourne. It was a 15 minute walk to the medical faculty at Melbourne University

As a medical student, I initially found it quite discouraging to study ophthalmology. We had all of 2 weeks attached to an eye unit. When the doctors looked at the eye, we could not usually see what they were looking at. And they were not very interested to show us how to use the instruments.

How does the doctor focus the slit lamp microscope??-One of the many mysteries I faced while watching eye doctors at work as a medical student...

John Colvin, Ophthalmology teacher extraordinaire

In my clinical years I heard about John Colvin's lectures on Saturday mornings, and started attending them, if only to ensure that I had a basic competency in ophthalmology when I graduated. I was grateful for his handouts, and for making a pretty mysterious subject understandable. I was also fascinated by his aviation anecdotes, and he kept us awake by the use of the bugle and gong. It was a highlight of my medical school years.

By my final year of medical school I started to seriously entertain thoughts of specialising in ophthalmology as a career. My father was pretty encouraging in this respect as well. Studying for and winning the RANZCO Ophthalmology prize for Victoria in my final year of medical school more or less sealed my decision to embark on this as a career.

Most people would prefer staying in one place for their career, however, I became a bit of a nomad after graduating from Melbourne University in 1997. Medical school was followed by House Officer posts in Stoke-on-Trent and Glasgow, the United Kingdom. While in Glasgow, I started applying for and going to interviews for Senior House Officer (SHO) posts in ophthalmology. I got an offer from Northampton, which resulted in an overnight drive from Glasgow to Northampton at the end of February 1998. Along the way, I dropped my wife off at St Mary's Hospital in Manchester, where she had obtained a job in obstetrics and gynaecology. Yes, we made our minds up pretty quickly about our areas of specialization!

It was one long night's driving for me, with the sum total of our possessions packed in the car boot

At Northampton, I was introduced to Mr Pierre Hein, who took me through my first ECCEs (extracapsular cataract extractions-punctuated by cigar and coffee breaks in between cases, when sagely advice would be given), and Mr Ian Fearnley, who introduced me to phacoemulsification cataract surgery. Mr Atkinson had a 'photo clinic', where cases with prominent clinical features were present and we, the junior doctors were given grillings...

There were moments of excitement unrelated to ophthalmology too-Michael Schumacher broke both his legs at Silverstone that year (1999) when his F1 car speared into the barriers. He was airlifted to where else but...Northampton General Hospital! Sadly, I was not able to penetrate the barriers to have a good chat with him-it was one of the rare occasions where I thought of doing orthopaedic surgery instead...

The nomadic lifestyle continued, with interesting sojourns to Windsor (watching Concorde fly overhead was a truly earsplitting experience), followed by the major part of my Basic Specialist Training at Manchester Royal Eye Hospital.

But finally, with the impending birth of our eldest daughter, we sought to return to Singapore, where we had my in-laws to help take care of the baby, and easier access to domestic help.

Cuts of the eye and first aid tips

Corneal lacerations-cuts to the eyeball

Mr L, a trainee carpenter, was trying to remove a nail from a piece of wood. He was thinking of getting off early that day, because of a date that evening to celebrate his girlfriend's birthday. As he levered the nail with the claw of the hammer, he suddenly felt it give and the nail flew off, straight into his eye.

The cornea is the clear window at the front of the eye. It is also the part of the eye closest to the object being looked at. 

Being constantly exposed to the environment, corneal injuries are a fairly common problem. They range from foreign bodies such as metallic particles from drilling or welding work, to abrasions/scratches, lacerations and chemical injuries.

Corneal lacerations occur when a sharp object cuts or pokes the cornea. They may be partial thickness, or they may go through the full thickness of the cornea and affect the inner parts of the eyeball.

Apart from direct damage to the eye, corneal lacerations are serious injuries which may also damage the eye by causing an infection, or impair vision because of corneal scarring after the eye heals.

Causes of lacerations

Common causes include flying objects, which may happen, for example with a nail as above or while cutting grass with an uncovered mower and while drilling and hammering. Broken glass from road traffic accidents are also a notorious cause of lacerations.

At the time of injury, a severe sharp pain will be felt as the cornea is one of the most sensitive parts of the body. There is almost always a clear history of a foreign object cutting or flying into the eye.

After the injury, vison is commonly blurred, especially if the laceration is deep and close to the centre of the cornea. There may be increased sensitivity to light, tearing, and it may be difficult to open the eye.

What the doctor will do to examine the eye

The doctor will usually instil some local anaesthetic eyedrops first to numb the eye and allow comfortable examination. Usually a careful examination on a slit lamp microscope then follows, with the doctor determining whether there are any remaining foreign bodies, and also very importantly, the depth of the laceration. If the cornea suffered a full thickness cut, fluid may leak from inside the eye, or internal parts of the eye such as the iris may protrude outwards.

A full thickness laceration has occurred in the centre of Mr L's eye. The nail penetrated the cornea, and also the lens of the eye, which has become a trauma induced cataract. Fine black nylon stitches were used to close the laceration.

Treatment of corneal lacerations

First aid for suspected corneal lacerations

• ·         Do not attempt to remove any foreign bodies or what appear to be foreign bodies/dirt (protruding parts of the eye may look like foreign bodies or dirt)
• ·         Do not wash or press on the eye
• ·         If possible, obtain an eye shield or fashion one from a plastic cup. This is easily done by cutting the cup around the rim about 1-2cm from the bottom, so that the cup now only has a shallow rim. (see below)
• ·         This can be taped so that the rim rests on the bony edges of the eyebrow and cheek.
• ·         Send the patient straight to a specialist eye clinic or the emergency department.

Cuts of the cornea require different types of treatment, depending on how long or large they are, and even more importantly, whether the eye is penetrated.

If the cut is small and only affects a partial thickness of the cornea, it is treated like a corneal scratch or abrasion. Usually, this type of injury heals well with some antibiotic eyedrops to prevent infection, and the removal of any remaining foreign bodies. A bandage contact lens is sometimes used to protect a long shelving laceration.

For a corneal laceration that cuts through the full thickness of the cornea, the situation is more complicated. Usually, the first step, which is performed by the eye surgeon in an operating theatre, is to clean the wound and to stitch up the cornea so that there is no longer any fluid leakage from the eye. If there is internal tissue protruding from the eye, this is carefully repositioned into the eye when possible. Where there is more extensive damage such as lens damage causing a cataract, this may be dealt with at a second stage when tests are done to allow selection of the most suitable lens implant for the patient.

Mr L had his corneal laceration stitched up, followed by a cataract removal operation and lens implant. He now has good vision in that eye, however, due to the cataract surgery now has 'presbyopia' in that eye because the lens implant cannot autofocus like his original lens could before.

Prevention of corneal lacerations

·      These injuries can be prevented by wearing protective eyewear when engaging in activities such as grass cutting, hammering or drilling.

Corneal lacerations are potentially very serious injuries of the eye. Besides possible internal eye injuries, infections can also occur and lead to impaired vision. Do take care and use safety eyewear when engaging in hazardous activities, as the old adage ‘prevention is better than the cure’ certainly holds true here.

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.