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.

What is the Bates method and does it work for shortsightedness?

William Bates was an American eye doctor who proposed and developed a method for improving eyesight in the late 19th century. This was based on the theory that poor vision such as that from shortsightedness was related to eye strain, and that this could be cured by a series of eye exercises.

What does 'eye strain' mean?

Generally most of us would characterise eye strain to be an ache or discomfort around the eyes after using them for too long trying to read things like fine print at near. This ache can be due to fatigue of the ciliary muscle of the eye, or of the facial/eyelid muscles if the person has been squinting excessively. There is little doubt that these muscles, or any muscles of the body can be stressed or fatigued after prolonged work.

In the eye, near focus can be achieved in young people by the ciliary muscles contracting, this action causing the crystalline lens of the eye to bunch up into a rounder and thicker shape. There are many ways to prove this, but the most obvious is when a patient gets dilating drops at the eye doctor's clinic, and then find that they cannot read up close for a few hours due to the drops relaxing the ciliary muscles as well.

Dr Bates, however, had a very different explanation for eye strain. We all have muscles that attach on the outside the eye, and these muscles are used to turn the eye in different directions, so that we can look in these directions without having to turn our heads all the time. Dr Bates thought that it was these muscles that became strained when someone developed poor vision from refractive error, and so he thought that by relaxing or exercising these muscles, vision could be improved.

Extraocular muscles (Pic from Wikimedia commons): These muscles only work to turn the eyeball to look in different directions, but Dr Bates thought they were used to focus light

Methods

The methods advocated by Dr Bates to improve vision included:

Palming

Sunning

The swing
There are various swings, one of the main ones practiced being the long swing. The person holds a pointer (a long stick) vertically, and holds it out at arm's length. While fixing gaze at the tip of the pointer, the person swings from one side to the other, trying to appreciate the movement of the background.

The sway
While swaying from side to side, the person looks at a distant object and tries to observe surrounding, nearer objects. They may be noticed to move in opposite directions to the sway.

Colour days
For a particular day, the person spends time looking out for and being aware of a particular colour of his/her choice.

Why do we become shortsighted?

Shortsightedness occurs because the eyeball becomes too long for the focusing apparatus of the eye (the cornea and the crystalline lens). Sometimes in older people, the development of a kind of cataract can also cause shortsightedness to develop and get worse, since the cataract increases the refractive index of the lens and causes it to bend light more.

The exact cause of eyeball elongation is still debatable, but important factors appear to be the amount of daylight one is exposed to, as well as the amount of near work being done at a young age. Atropine eyedrops have been found to help to stabilise the size of the eye.

Once the eyeball has grown to a certain length and size, it does not shrink or shorten unless something disastrous happens in the eye. When the eye is terminally damaged, it stops secreting aqueous fluid, the eyeball becomes soft, and it starts to shrink like a flat car tyre.

There is no obvious reason why a series of exercises would be able to shorten the eyeball to reduce a person's shortsightedness.

How can something like the Bates method seem to work (while being based on no scientific foundation and on the wrong assumptions)?

Blur adaptation

A recent study found that shortsighted people are less affected by blurring of images when it comes to being able to recognise letters. Shortsighted eyes seem to be less affected by defocused images at the retina when compared to people who are not shortsighted.

If vision is purposely blurred by lenses for a long time of 60 minutes, then improvements in vision can be measured after this time even through the blurring lenses.

This suggests that there is a natural adaptation process happening among the nerve cells in the brain that are responsible for vision. This process can make vision a little better compared to before the adaptation occurred, but it cannot make vision perfectly clear (especially when spectacle power is high) as happens when the images are completely in focus.

However, although blur adaptation is well recognised, there is no evidence that it is improved through performing the exercises of the Bates method.

Placebo effect

A placebo is a 'fake' treatment that consists of nothing which will treat a medical problem. It can take several forms, such as 'sugar pills' and even occasionally 'sham surgery'. It is known that in some cases, a perceived or actual improvement in a patient's condition can occur merely by suggestion and the use of inert 'sugar pills'. This is called the 'placebo effect', and that is why when studies are done to test the effectiveness of new medicines or surgeries, the studies are often done in 2 groups of patients with one group receiving the new medicine or surgery and the other receiving the placebo or sham surgery.

Not everyone responds to a placebo, and the responsiveness may also depend on the condition that the patient has. For example, the responsiveness would be 0 in patients with blood poisoning (sepsis), and it could range up to 30% or more for pain effects or depression.

The placebo effect is related to the expectations and perception of the patient. It is intriguing that sugar pills of different sizes and colours can have different effects, with red hot coloured ones doing better as stimulants! Motivation also plays a role in the effectiveness of placebos.

Here is what seems to be an example of suggestion by a proponent of the Bate's method, Aldous Huxley, who wrote that "Vision is not won by making an effort to get it: it comes to those who have learned to put their minds and eyes into a state of alert passivity, of dynamic relaxation." It is a play on the patient's perception and an attempt to influence that perception with words.

While I hesitate to claim that the Bates method is a placebo, it does seem to me that the absence of a scientific explanation for the method, with its lack of effectiveness in many people, and its methods which require suggestion and much motivation, suggest some aspects of the placebo effect is taking place among people who seem to benefit from it.

Finally

The long and short of it is that there is no real explanation as to how eye exercises could help to improve vision or shortsightness. On the other hand, the method does not cause physical harm, except for the original description of sunning, which is extremely dangerous and can cause blindness.

Those who would like to palm, or swing and sway, could carry on doing so but should not ignore conventional medical treatments which have withstood great scrutiny and the tests of time.

References:

Ophthalmic Physiol Optics 2013;33:130-137
Mon-Williams M, Tresilian JR, Strang NC, Kochhar P & Wann JP. Improving vision: neural compensation for optical defocus. Proc Biol Sci 1998; 265: 71–77.

Secrets in the war to stop shortsightedness from increasing

Trying to stop myopia progression is like deciding to go on a diet. Seriously. I'll get to that eventually but before we get too philosophical, let's take a step back.

Currently, more than 50% of twelve year olds in Singapore need to wear glasses because of myopia. And by the time the boys enter the army at 18 years of age, it will have increased to 80%. Unfortunately, myopia is a problem that continues to worsen as children grow up, usually stabilizing by the late teenage years. By this time, it is not uncommon to see patients with myopia of -6D and above. High myopia of course, can give rise to other problems such as an increased risk of retinal detachments and an earlier onset of cataracts.

Myopia or shortsightedness arises because of an imbalance between the focusing power of the cornea and lens of the eye, versus the length of the eyeball. In the type of myopia that arises in children, it is mainly a problem of the eyeball growing too long, ie axial myopia.

For many decades now, research has been ongoing both to find a cause of this abnormal eyeball growth, as well as to find ways to stop it or at least to slow it down. Because the actual cause and mechanism are not known, methods that have been tried are all based on theories or empirical data. Let's take a look at the things that have been tried.

Things that have been tried and failed

1. Timolol eyedrops to lower eye pressure.
Since eye pressure may potentially stretch an eyeball and make it bigger and longer, people tried to see if lowering the eye pressure could stop the eyeball from enlarging. Unfortunately Timolol eyedrops did not work. However, it remains to be seen whether more powerful pressure lowering medications like bimatoprost may have an effect.

Things that may work (either the evidence or effect is weak)
1. Glasses which reduce peripheral hyperopic defocus (Myovision by Zeiss)
These glasses appeared to have an effect in younger children who had myopic parents. Why it would only work in this subgroup of people is unknown but could reflect a weak effect or a chance finding.
Sankaridurg P, Donovan L, Varnas S, et al. Spectacle lenses designed to reduce progression of myopia: 12-month results. Optom Vis Sci 2010; 87: 631–41. 

2. Rigid gas permeable (RGP, or semi hard) contact lenses
At the age of about 11 I was introduced to 'hard' or RGP contact lenses in the hope that it could slow down the rate of increase of my myopia. In fact in my case, it wasn't that successful in this regard. A well conducted trial showed that RGP lenses do not slow down the growth of the eyeball, but may have an effect by reducing the steepening of the cornea.# This may be only a temporary effect from the pressure of the lens on the eyeball.
#Walline et al. A randomized trial of the effects of rigid contact lenses on myopia progression. Arch Ophthalmol. 2004 Dec;122(12):1760-6.

3.Orthokeratology
Orthokeratology (OK or Corneal Refractive Therapy/CRT) takes the concept of corneal flattening using pressure from a lens one step further. In this method, RGP lenses of a special shape are worn to sleep. The lenses press on the patient's cornea during sleep, so that during the day the lens can be removed, and the cornea retains the ideal shape which corrects the long/shortsightedness and astigmatism. After a few days of not wearing the lens to sleep, this effect is lost, so the power lowering effect is temporary.

But does it stop myopia from increasing?

Walline JJ, Jones LA, Sinnott LT. Corneal reshaping and myopia progression. Br J Ophthalmol. 2009 Sep;93(9):1181-5.

The above study showed that yes, it seemed that orthokeratology can slow down the growth of the eyeball compared with soft contact lenses. This effect is not as strong as 1% atropine eyedrops (0.25mm elongation with OK versus -0.02+/-0.35 mm with atropine at 2 years).

In other words, OK lenses had an effect somewhere between soft contact lenses and 1% atropine, but without the side effects of the atropine. Do consider though, that wearing contact lenses to sleep is generally felt to increase the risk of eye infections.

Things that work (with strong evidence and strong effect)

1. Atropine
The idea of using atropine came about because of its well known ability to relax the ciliary muscles in the eye (which are used for near focusing). Since as the theory goes, too much near work is related to shortsightedness, and near work results in prolonged contraction of this muscle, would relaxing the muscle have an effect on myopia progression? The results of well conducted studies show that yes, indeed atropine has a powerful effect on slowing or stopping the worsening of myopia.

There are two concentrations in common usage: 1% (stronger) and 0.01% (weaker). The 1% concentration is very effective but has side effects of causing sensitivity to bright lights and temporary inability to focus for near. These are reduced by using special progressive glasses that turn dark in bright light. With the 0.01% concentration, there are no side effects but the effects of slowing down myopia are not as pronounced. Which specific medicine is used depends on the degree of shortsightedness, how fast it is progressing and the child's tolerance to the side effects of the stronger concentration. Read more about this at my other post on atropine and myopia.

2. Outdoor time
2 generations ago, it was much less common to see a shortsighted person in Singapore, despite people having essentially the same set of genes. Other things have changed, notably our environment and activities.

Increasingly, evidence points to the importance of outdoor activities in reducing the rates of myopia and its progression.# What is it about being outdoors that slows myopia? Many people think it is because we get to see things far away when we step outdoors, but this effect of distance versus near visual work has been shown to be only a weak one.*
#Rose KA, Morgan IG, Ip J, et al. Outdoor activity reduces the prevalence of myopia in children. Ophthalmology 2008; 115: 1279–85.
*Mutti DO, Mitchell GL, Moeschberger ML, Jones LA, Zadnik K. Parental myopia, near work, school achievement, and children’s refractive error. Invest Ophthalmol Vis Sci 2002; 43: 3633–40.

In fact, it is likely to be due to the difference in amount of light being seen by the eye, when comparing being indoors versus outdoors.

When we step outdoors, even at 5 or 6pm in the evening, we are typically being exposed to much more light than we get even with the brightest lamps indoors. It has been shown that bright light leads to the release of more retinal dopamine, a chemical which may play a role in controlling eye growth. It is intriguing that using a chemical to block dopamine in animals can also block the protective effect of bright light.#
#Ashby RS, Schaeff el F. The eff ect of bright light on lens compensation in chicks. Invest Ophthalmol Vis Sci 2010; 51: 5247–53.

SO.....
It is said that in losing weight, '..., you must accept that this is your new lifestyle of eating healthy and being physically active...' http://www.webmd.com/diet/features/10-diet-secrets-lasting-weight-loss-success

And equally, in trying to control myopia, the patient must accept a new lifestyle of regular outdoor activity (in sunlight) and being more active. At least 1-2 hours everyday. As a follow on from that, it's also important to ensure that when indoors/doing near work, that the child has a brightly illuminated environment. It does not matter what type of light it is (eg sunlight by the window, fluorescent, LED etc), as long as it is bright. Failing which, the most effective treatment so far is atropine eyedrops.

No, wait..... Actually it's easier to control myopia than to go on diet. If only our waistlines would stabilise after a certain age (like myopia), so that we don't have to worry about it any more after that!

References:
Lancet 2012; 379: 1739–48
Ophthalmology 2002;109:415–427

Understanding your spectacle prescription

Have you ever looked at the seemingly random numbers scribbled on a piece of paper that you sometimes get at the optometrists? If you are more familiar talking in terms of hundreds of degrees of short or longsightedness, how come there are all these + and - signs and then all the decimals?

And then there is the funny fraction at the end, which may say 6/6 in most parts of the world (or 20/20 in the US) for good vision. Singapore parents with school going children may remember seeing the note below, as all primary school children undergo vision screening once a year and if vision is less than adequate will be referred to refraction clinics or optometrists.

Oh no! Vision not great on the screening test and it's time to go to the optometrist's again!

Let's take a step back, and look at what your optometrist is trying to do. Basically, the aim is to get the best vision possible using spectacle lenses which bend/focus light.

A slightly blurry Snellen chart, vision ~6/9

A clear ETDRS chart, vision ~6/6

How good is your vision?

Optometrists will first ask the patient to read one of the charts above, to find out what are the smallest letters that can be read without glasses. For most people with normal vision, letters of 6/6 size are visible/distinguishable at 6 meters. So in a way, one could say that 6/6 means being able to see letters at 6 meters that a normally sighted person would be able to see at the same distance. 20/20 is the equivalent notation in feet.

For those interested in mathematical notations, a 6/6 letter on the whole subtends an angle of 5 minutes of arc at the nodal point of the eye. This means that each element of the letter, such as the thickness of the vertical line on a 'D', subtends an angle of 1 minute of arc at the nodal point of the eye. The nodal point refers to the point in the eyeball where the center of an imaginary lens combining all the focusing power of the eye is located.

Sometimes, vision is poorer than 6/6, which means that the person could not read the 6/6 line on the chart at 6 meters. In that case, the smallest letters that could be read would be recorded, such as 6/9 or 6/12.  6/9 means that the patient can see at 6 meters, what a person with 'normal vision' would be able to see at 9 meters, and so on for 6/12 and 6/18. The optometrist will then try different lenses to make the patient's vision (with the lenses) 6/6.

Generally 6/12 and above vision is considered good vision, and this is the threshold which is considered good enough for driving. Generally speaking, vision worse than 6/12 due to a focusing problem (long/shortsightedness/astigmatism) is an indication that glasses are needed. For most people though, the aim is to achieve 6/6 vision.

Spectacle power notation

Having got all of that out of the way, now let's talk about how spectacle power is written down.

Pure long sight or short sight is corrected by lenses called 'spheres', or spherical lenses. Longsightedness is corrected by convex lenses, which we will give a plus ('+') sign to, while shortsightedness is corrected by concave lenses, which we will give a minus ('-') sign to.

An eye with astigmatism has focusing areas (cornea/lens) which are more curved in one direction than the other (see above). This is like the cylinder (below), which is curved in one direction and completely flat in the other direction. In order to correct astigmatism, a lens which is more curved in one direction than the other (called also a cylinder) is placed so that its curved direction is in the same position as the eyes' flat direction (and vice versa), so the lens' astigmatism cancels out the eyes' astigmatism!

Astigmatism is corrected by lenses called 'cylinders', or cylindrical lenses. This can be denoted with either plus or minus cylinders depending on where in the world you are. In places like Singapore, the cylinders tend to go with a minus sign.

For example    Sph       Cyl         Axis
                       -4.00     -1.50     180
or otherwise also written as -4.00/-1.50x180

means 4 dioptres of shortsightedness with -1.50 dioptres of cylinder at an axis of 180 degrees (the long axis of the spectacle cylinder is placed horizontally).

Colloquially, 1 dioptre of spectacle power is called 100 degrees in Singapore and some other parts of the world. So the above example would mean a patient with 400 degrees of shortsightedness and 150 degrees of astigmatism.

Putting it all together

Let's say if you asked somebody to read the chart, and they could only read to the 6/18 line. As a rough rule of thumb, if he/she is shortsighted, then this person is likely to have about 100 degrees of shortsightedness. The 6/36 line corresponds with about 200 degrees of shortsightedness. And anything above that means vision is limited to only the largest letter (6/60) or just counting fingers.

I mentioned earlier that 6/12 and better vision is generally considered good vision. Following from this, most people with unaided (without spectacles) vision of worse than 6/12 (ie~6/18) would benefit from glasses. And as a rough rule of thumb that would be somebody who is about 100 degrees shortsighted. That is my general threshold for starting a child with childhood myopia on glasses. Of course, the decision whether to start wearing glasses also depends on how the child's activities are being affected by their vision, so if for example, the myopia is only 50 degrees but the child is sitting at the back of the classroom and cannot see the teacher's writing on the white board, then glasses may already be necessary even for this small amount of shortsightedness.

Take home points

1. 6/XX indicates the ability to read different size letters at 6 meters (checked with and without glasses)
2. People with 6/12, 6/9, 6/7.5 and 6/6 vision are generally considered to have good vision.
3. Spectacle power can be of the plus sign or minus sign for long and short sight respectively.
4. The numbers for spectacle power indicate the power of the lens required for good vision, ie the higher the number, the higher the degree (the worse) of the long / short sight or astigmatism.
5. For shortsightedness, a general rule for children is to consider starting glasses wear when the spectacle power is 100 degrees and above.

In a future post I will review the methods people have tried to either prevent or delay the onset of shortsightedness, which is a problem of epidemic proportions in many cities around the world.

Atropine eyedrops for the control of shortsightedness

Shortsightedness is a huge problem in Singapore and many big cities around the world. More than half of Singapore schoolchildren are already wearing glasses for shortsightedness by the age of 12 years. What is worrying is that the earlier one starts out becoming shortsighted, the higher the final spectacle degree tends to be. Very highly shortsighted people are at increased risk of eye problems like cataract and retinal problems at a younger than average age.

It is important therefore that we try to slow down the increase of shortsightedness as much as possible. Ensure that a child spends 1-2 hours outdoors in sunlight each day. Take regular breaks from near work when reading or with computer use. Apart from these, using Atropine eyedrops is the only method proven in big studies (randomised controlled trials) to slow down the rate at which shortsightedness increases.

What is Atropine?

This is a chemical obtained from plants in the same family as the nightshade plant. Owing to the presence of extremely high levels of atropine and other chemicals, the berries and leaves of the plant are poisonous. 

Interestingly, the nightshade plant is also called ‘belladonna’ (meaning beautiful woman in Italian) as people in the past used atropine to dilate the eyes for a cosmetic effect! It achieves its effects in the body by blocking a special receptor molecule that among other things controls the action of muscles as well as the growth of the eyeball.

Atropine is available in many forms, but for eye conditions it is used as an eyedrop. Various concentrations have been tried but the commonly available concentrations are 1%, 0.125% and 0.01%.

Traditional treatment (Atropine 1%)

Traditionally, to reduce the rate at which shortsightedness increases, 1% Atropine eyedrops were used once a day or even once a week. In a study at the Singapore National Eye Centre, 1% eyedrops used once a day reduced the progression of shortsightedness from an average of 100 degrees a year to less than 25 degrees a year. Our experience suggests that using it even once a week has a very similar effect.

Side effects of traditional Atropine treatment

Atropine 1% dilates the pupil and relaxes the muscle used for near focusing inside the eye. As a result patients feel very sensitive to bright lights and with normal glasses on have difficulty with close up work such as reading. If this concentration is used, special glasses which turn dark outdoors (‘Transitions’ lenses) and which have progressive lenses (having a near section below for near focus) are required. All of these side effects are temporary and disappear when the patient stops using the drops.

Newer treatments (Atropine 0.125% and 0.01%)

In an effort to do away with the side effects of Atropine, lower concentrations of Atropine were tried. When used once every day, 61% of those using 0.1% and only 6% of those using 0.01% Atropine felt a need for special ‘Transitions’ and progressive lenses. Therefore, normal glasses or contact lenses can usually be worn while the 0.01% Atropine concentration is used.

However, the lower concentrations are not as effective as the 1% concentration at slowing progression of shortsightedness. On average, the myopia progression over 2 years for 1% Atropine was 28 degrees, for 0.1% 38 degrees, and for 0.01% 49 degrees. This was still better than the 120 degree increase seen in those who were not using the Atropine eyedrops.

General pointers about using Atropine for shortsightedness

Whether 1% or 0.01% Atropine is used, the eyedrops must be used for a long period of time. Although the shortsightedness increases at a slower rate while Atropine is used, the rate increases again when it is stopped. The idea is therefore to use the Atropine during the period of time when the shortsightedness is increasing fastest. Usually by about 18 years of age, the rate of increase of shortsightedness would have already slowed down naturally.

This means that on average, most children who use the eyedrops would be using them for several years. The longer the eyedrop is used, the bigger its potential effect. For example, if a child had shortsightedness that was increasing by 100 degrees every year, using the 1% eyedrop for 3 years would reduce the final power by 300 degrees. This might mean that instead of having 500 degrees of shortsightedness as an adult, he/she would only have 200 degrees of shortsightedness finally.

In trying to slow the progression of shortsightedness, a number of decisions have to be made. Should Atropine be used or not? Should the 1%, 0.125% or 0.01% concentration be used? How long should the child continue with the eyedrops?

These decisions should be made after a discussion of the pros and cons of each decision with your eye doctor. For example, if the shortsightedness is increasing very fast and is already of a high degree, one would favour using the 1% eyedrop despite the side effects. On the other hand, if the side effects cannot be tolerated and one is willing to give up some of the stabilizing effect of the 1% eyedrop, then the 0.01% concentration is a good option.

EDIT 7 MAY 2018
Please note that I do not run an online pharmacy, and these are illegal in many parts of the world. Do not request Atropine from myself, or any other doctor, unless you or your child have seen the particular doctor and it has been determined after a proper consultation that Atropine is necessary. Requests for Atropine will be deleted in the future to avoid cluttering up the comments section in this post.

P/S.
Have you ever seen pinhole glasses? I heard that they are available at Watsons. Do NOT waste your money on these gimmicks. They do nothing to help the eyes or vision. Have a look at this link: Case Watch report on settlement of charges of misleading claims

Contact lens FAQs

Problems such as shortsightedness have become so common in Singapore that by 12 years of age, about 60% of children are already wearing glasses. Although spectacle wearing is effective and safe, they are not always the most convenient of things to use.

At my clinic, we often come across patients who are either keen to start wearing contact lenses or are already wearing them but have some nagging questions about them that they just thought of. Hopefully this post, which is in a Q+A format, will help to answer those queries.

1. Can my contact lenses get lost in my eyes?

Contact lenses cannot be lost in the eyes, because there are natural pockets at the side of the eyes which prevent the lenses from going further backwards. However, they may sometimes slip off the cornea onto the white part of the eye. If this is noticed, you may reposition it yourself, or see an eye care professional for help.

2. If I’m playing soccer and the ball hits me near or on my eye, will my lenses break or tear in my eyes?

Direct impact by the soccer ball onto the eyeball will cause injury of varying severity depending on the force of the trauma. A soft contact lens will not generally break or tear due to its flexibility. A hard contact lens could theoretically break although that is also very unlikely due to the softness of the surrounding tissues. What happens more commonly is the lens is knocked or rubbed off the eye. Surface abrasions of the cornea may be caused as a result.

4. I want to wear coloured lenses to look different sometimes... Will these lenses damage my eyes?

Coloured or tinted lenses are available from major manufacturers such as Cibavision. These are generally safe to use but like all contact lenses should be dispensed only after fitting by an eye care professional. Buying these lenses from internet sources, or from manufacturers with an unknown reputation risks severe damage to the eye from problems such as infection, irritation from chemicals in the soaking solution, or poorly fitting lenses.

5. I heard that I could catch Acanthamoeba infection by swimming without removing my contact lenses. This parasite can burrow into my eyes and make me blind. Is this true?

Acanthamoeba is a one-celled protozoan parasite that is found in many places in our environment, including tap water. If contaminated water from the swimming pool enters the eye, Acanthamoeba can stick to the contact lens and establish an infection on the surface of the eye. If not treated, a severe corneal ulcer can develop causing blindness. In general contact lenses should be removed before swimming and they should not be cleaned with tap water or home made saline to avoid this infection.

6. I have no access to saline solution and even tap water. There is a problem with one of my lenses (the edge has curled inwards slightly and is causing me pain). What can I do? Can I remove the affected lens and re-wet it with saliva?

The best thing to do is to remove the contact lens and discard it. Saliva should not be used because the mouth is filled with bacteria and using saliva is going to contaminate the lens, thereby making it very likely for a corneal infection to occur.

7. I fell asleep overnight with my lenses on. Will they get stuck to my eyes?

Sleeping with contact lenses on for any length of time raises the risk of infection and should not be done for any length of time. Even without an infection, lens adherence or sticking to the eye is very common after sleeping with them on and is due to a combination of dryness and the pressure of the eyelids. This sticking is not permanent, and if it happens, the wearer should wet the eyes with re-wetting solution or artificial tears, and then attempt to remove the lens after a few minutes. If this cannot be done, then an eye care professional should be consulted for removal of the lens.

8. I use daily disposables. However, I’ve been wearing them continuously for a week (I don’t remove them). How long can I overuse disposable lenses?

It is very dangerous to wear daily disposable lenses in such a fashion. The lenses become coated with deposits and sooner or later an infection develops or the eye becomes red and irritated from the lack of oxygen and deposits. Disposable contact lenses should be changed strictly according to the schedule recommended by the manufacturer.

9. I was travelling overseas when I ran out of saline solution. I used tap water to rinse my lenses instead. After a few days, I started noticing coloured spots on my lenses. What is happening to my lenses?

It is not possible to say with certainty what these spots are but they could be mineral deposits if the tap water was hard (with a high concentration of dissolved substances). Worse, they could even be fungus growing on the contact lens. These lenses should be discarded immediately.

11. Do the new “HD” soft lenses work for people with astigmatism? Can people with severe astigmatism wear such “HD” lenses? Are RGP lenses still preferred for people with astigmatism?

“HD” refers to optimized optics which include aspheric designs but it does not necessarily mean that the lens will have a toric component to correct astigmatism. A person with severe astigmatism needs either a toric soft lens or a rigid gas permeable (RGP, otherwise known as hard) lens. RGP lenses correct astigmatism very well and possibly provide the sharpest vision among the types of contact lenses. However this must also be balanced with comfort issues.

12. I have lazy eyes. Will contact lenses help my condition? What types of contact lenses are best suited for my condition?

Lazy eyes (amblyopia) develop during childhood because a disturbance of vision prevents normal development of the nerve pathways between the eye and brain. Later on in life, vision remains blurred in the lazy eye even when glasses or contact lenses are worn, because the problem has to do with the nerves and brain, and is not related only to spectacle power. If lazy eyes are detected in childhood, the better eye is patched and the child is forced to use the lazy eye to see, with the use of glasses or contact lenses as appropriate. Beyond the age of about 10 years, patching is no longer useful. Older children and adults with lazy eye are now treatable with a revolutionary computer based training program called Neurovision (see http://www.neurovision.com.sg/). This presents customised images to the patient and over a period of several months improves nerve connections and vision even in adults with lazy eye. As such, lazy eyes are not treated by particular contact lenses per se, but the contact lenses or glasses will help with any long/short-sightedness or astigmatism that is present.