Friday, August 29, 2014

What are 'lazy' eyes?

Many of you may have come across the term 'lazy eye'. What exactly does it mean?

In truth, there is the term that is understood medically, and then there are the other interpretations or myths-which sometimes makes it difficult to know what people mean when they use this term.

Lazy eye medically speaking, refers to the condition called amblyopia. In this situation, the amblyopic eye is unable to see well, even though the eyeball itself is structurally normal. An amblyopic eye develops because connections between the nerves of the eye and the brain are not fully developed at birth. This process requires well focused images on the retina of the eye together with good signals reaching the brain, and continues for several years after birth. The system generally matures around the age of about 8-9 years of age, after which a lazy eye will not develop even if that particular eye develops a disease which prevents it from seeing well.

So, a lazy eye develops because something prevents a well focused image from reaching the retina of the eye and the brain. These possible causes include high longsightedness or astigmatism, a constant (present all the time) squint (eg crossed eyes, which cause double image, resulting in the brain blocking the image), or even more rarely things like corneal scars or cataract.

Do you think the above is a lazy eye?
Answer: Maybe...

The above left eye has drifted outwards, and some would call this a squint. If a squint happens only some of the time, it is very unlikely to have amblyopia, or be 'lazy'. In other words, the eye would be able to see well at whatever it was looking at.

However, if the squint is present all the time, the child would have double vision-so the brain automatically blocks the image from the squinting eye. This blockage, or 'suppression', can cause the eye to become amblyopic, so that this particular 'lazy' eye would be unable to see clearly even if any long/shortsightedness/astigmatism was corrected.

Many children with 'lazy' eyes do not display any outward sign of the poor vision in that eye. This is the case especially when the 'lazy' eye is caused by different and high degrees of spectacle power/astigmatism. That is why screening the vision of young children of 5-6 years of age is so important. In Singapore, schools and kindergartens routinely screen student's eyes once a year.

What 'lazy' eyes are not...

So just to recap, lazy eyes are not squints (although constant squints can cause lazy eyes), and lazy eyes do not mean an eye with very high spectacle power (although an eye with high spectacle power/astigmatism can be lazy). As long as an eye can see well (with or without glasses), then it is not considered 'lazy'. It follows from the explanation above that lazy eyes can only develop in childhood, and that if it is detected much later-eg in adulthood when the visual system is mature, there are no effective cures.

Lazy eye treatments

When 'lazy' eye or amblyopia is detected at a young age less than 7 years of age, treatment is generally straightforward and involves patching the good eye to force the child to see with the poorer, amblyopic eye. The younger the child, the shorter the time needed for patching.

There are several different methods, but in my practice the child patches the good eye one hour /day/year of life (age). So a 3 year old may patch for 3 hours a day, while a 6 year old patches for 6 hours a day. Once the child gets older than 7 years of age, the eye is less responsive to patching, and in some cases even whole day patching may be required for a period of time. For somebody above 12-13 years of age, patching essentially does not work anymore. There exists an FDA approved treatment for amblyopia for those older children and adults, consisting of eye exercises (called Neurovision), however, my personal experience with it is disappointing.

Saturday, August 23, 2014

The story of the Symfony lens

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

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

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

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

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

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

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

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

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

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

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

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

Sunday, August 17, 2014

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
Timolol eyedrops

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.  2004 Dec;122(12):1760-6.

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)
Atropine eyedrops

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.

Outdoor activities against myopia
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.

It is said that in losing weight, '..., you must accept that this is your new lifestyle of eating healthy and being physically active...'

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!

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

Monday, August 11, 2014

Conjunctivitis: What you should do if you get pink/red eye...

Have you ever had one eye inexpicably and rapidly turn red, swollen and sticky in a day or so, and then horror of horrors, the same thing starts to happen in your other eye?

This condition, medically termed conjunctivitis, is also known as 'red eye' or 'pink eye'. It is an eye infection, affecting the outer 'skin' covering the eyeball called the conjunctiva (hence conjunctiv-itis). There are many different germs that can cause this infection. Most cases are caused by viruses, while occasionally we see cases that are caused by bacteria. Among the viruses that cause this condition, the more common ones include adenoviruses and coronaviruses.

Occasionally this condition is mild, and the eye gets better within a few days. However, many cases of viral conjunctivitis can take much longer to recover fully from. In my experience, the eyes can be red, swollen and sticky for up to 2 weeks before improving.

When things go well, usually the stickiness starts to get less, and the swelling improves. The eyes then become less red, and finally everything including vision goes back to normal.

Complications of conjunctivitis

Sometimes though, complications occur. Some patients get a layer of mucus and dead cells stuck to the inner surface of the eyelids. This is called a 'pseudomembrane' (below), and can make the patient feel very uncomfortable as the pseudomembrane, if located at the upper eyelid, rubs the cornea with each blink.
Pseudomembrane in conjunctivitis

Another complication is unusual in that it actually occurs as the redness is going away and the eye is starting to feel better. This condition is called 'nummular' (coin shaped) keratitis, and consists of little white spots appearing on the cornea of the eye. This condition can cause vision to become hazy/smoky, and can cause glare in bright lights.
Nummular keratitis after adenoviral conjunctivitis

How we treat conjunctivitis

The vast majority of cases have a viral cause, and these are typical in having copious discharge that is watery/mildly sticky and whitish to slightly yellowish in colour. The eyes can be very swollen and red, and on the inner surface of the eyelids there can be small bumps called follicles. These cases are typically treated with combined antibiotic and steroid eyedrops. The steroids help to avoid excessive inflammation and reduce the risk of pseudomembranes. Although the antibiotics do not actually kill the virus, they are a commonly prescribed when steroids are used and may help to reduce the risk of secondary infection by bacteria. There is unfortunately not a lot of evidence to support treatment this way, but patients do seem to feel more comfortable using these medications.

If a patient gets nummular keratitis and little white spots that block vision, then steroids are needed to eliminate the white spots. Unfortunately, once the steroids are stopped, the spots can recur sometimes. Occasionally patients with this complication end up needing a little steroids (eg once a day) for many months to avoid blurry vision. Fortunately most patients recover without experiencing this issue.

The other extremely important issue in managing these infections is to break the transmission cycle ie to avoid spreading it. I advise my patients to observe the following:

1. Wash their hands frequently, and especially every time after touching their affected eye eg when they are instilling eyedrops or cleaning the eye
2. Avoid touching the unaffected eye, and 
3. To tell their family members/close contacts not to touch their eye unless they wash their hands first
4. To tell their family members/close contacts not to apply any eyedrops in the hope of 'preventing' an infection. In fact by instilling eyedrops (especially if contaminated) there is the risk of transmitting the infection to that eye!

Sometimes the virus causing conjunctivitis gets into the throat and causes sore throat/flu like symptoms, in which case that is treated as usual with lozenges, paracetamol (panadol/tylenol), and good old rest.

Monday, August 4, 2014

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.

School health service vision screening report
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.

Snellen Eye Chart
A slightly blurry Snellen chart, vision ~6/9

ETDRS Eye Chart
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.

Friday, August 1, 2014

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.