When deciding whether or not to have an OCT scan, people sometimes say to me "See if you find anything during the eye examination that requires a scan."
But if I've found a problem just from looking in the eye, I usually don't need a scan to confirm it. The point about the OCT is that it enables us to see beneath the surface, to give information that I don't already know; to see what I haven't already seen.
This is particularly useful for glaucoma and macular degeneration, which I talk about separately. But it also shows up diabetic changes in the eye; it helps to distinguish between benign and malignant pigment spots; and it's even been used to diagnose a child at risk of getting colon cancer.
Using the Topcon OCT, we also get a photograph of the retina, which is really useful for seeing the changes to blood vessels that occur with raised blood pressure or high cholesterol levels. When you can combine the surface view and the view underneath, you get the complete picture. I recently saw a lady who had quite poor vision, especially in one eye, and cataracts. The OCT revealed a hole in the macula in one eye. But it also showed that a cataract operation in the other eye would restore her vision to normal.
In the 18 months since we've had the OCT, we've done thousands of scans. Most of them have shown normal, healthy eyes. But some have shown problems at a much earlier stage than we would otherwise have detected them. This has meant earlier and therefore more effective treatment, and much sight has been saved. I'm often thankful that we now have this technology.
David Donner
Wednesday, 10 November 2010
OCT and Macular Degeneration
What is Macular Degeneration?
Macular degeneration is a condition in which the centre of the retina (known as the macula) becomes damaged. You may have seen the term "AMD", which stands for age-related macular degeneration. Macular degeneration is rare in younger people, but around 30% of people over 75 have early signs of AMD, and about 7% of those over 75 have more advanced AMD. This is why it's the most common cause of visual impairment in the UK.
Two types
There are two types of AMD; wet and dry. The dry type is more common and develops slowly. In the wet type, blood vessels beneath the macula leak fluid, which can damage the macula relatively quickly. Both types only affect central vision, which means that they don't cause complete blindness. Tasks like reading, however, can be very difficult when there's a blurred patch in the centre. An early symptom of wet AMD is when straight lines suddenly develop a kink in them.
Treatment
Wet AMD can now be treated with injections of new (anti-VEGF) drugs. The key to their success is early detection and treatment.
There's no real treatment for dry AMD at the moment. There's evidence, however, that progression from an intermediate to an advanced stage can be inhibited by taking a supplement of antioxidants and zinc.
OCT
Most of what happens in AMD, at least in the early stages, happens beneath the surface. Often, therefore, the standard eye examination with an ophthalmoscope yields only limited information.
But because the OCT shows a cross-section of the retina, we can see what's going on beneath the surface. This makes it possible to distinguish between wet and dry AMD. When wet AMD is detected, there's a fast track referral system in Surrey to ensure treatment starts quickly.
The OCT can also show other macular problems, such as an epimacular membrane. This is a collagen membrane that damages the surface of the macula and that sometimes requires surgery. Macular oedema is also clearly shown up in an OCT scan, and this is particularly useful when examining diabetics, in whom it's a major cause of loss of vision.
Quite often, people with AMD have cataracts as well. The OCT can give really useful information about whether the vision will be clear or still blurred after cataract surgery.
David Donner
Macular degeneration is a condition in which the centre of the retina (known as the macula) becomes damaged. You may have seen the term "AMD", which stands for age-related macular degeneration. Macular degeneration is rare in younger people, but around 30% of people over 75 have early signs of AMD, and about 7% of those over 75 have more advanced AMD. This is why it's the most common cause of visual impairment in the UK.
Two types
There are two types of AMD; wet and dry. The dry type is more common and develops slowly. In the wet type, blood vessels beneath the macula leak fluid, which can damage the macula relatively quickly. Both types only affect central vision, which means that they don't cause complete blindness. Tasks like reading, however, can be very difficult when there's a blurred patch in the centre. An early symptom of wet AMD is when straight lines suddenly develop a kink in them.
Treatment
Wet AMD can now be treated with injections of new (anti-VEGF) drugs. The key to their success is early detection and treatment.
There's no real treatment for dry AMD at the moment. There's evidence, however, that progression from an intermediate to an advanced stage can be inhibited by taking a supplement of antioxidants and zinc.
OCT
Most of what happens in AMD, at least in the early stages, happens beneath the surface. Often, therefore, the standard eye examination with an ophthalmoscope yields only limited information.
But because the OCT shows a cross-section of the retina, we can see what's going on beneath the surface. This makes it possible to distinguish between wet and dry AMD. When wet AMD is detected, there's a fast track referral system in Surrey to ensure treatment starts quickly.
The OCT can also show other macular problems, such as an epimacular membrane. This is a collagen membrane that damages the surface of the macula and that sometimes requires surgery. Macular oedema is also clearly shown up in an OCT scan, and this is particularly useful when examining diabetics, in whom it's a major cause of loss of vision.
Quite often, people with AMD have cataracts as well. The OCT can give really useful information about whether the vision will be clear or still blurred after cataract surgery.
David Donner
Saturday, 6 November 2010
Practice Makes Expert
I’ve recently finished Matthew Syed’s excellent book “Bounce”. Much of it is based on the well known idea that to become an expert requires 10,000 hours of practice, but it’s fleshed out with plenty of good examples, including his own story of how he became a top table tennis player.
There are a couple of important points that I think should have been included. Firstly, how participating in several different sports can reduce the amount of sport-specific practice well below 10,000 hours. Also, the importance of deliberate play in establishing expertise in team sports was not mentioned.
Syed does make the excellent point that the practice must be challenging. He gives the example of someone who’s been driving for years without becoming a better driver, and even possibly becoming a worse driver through the accumulation of bad habits. This is because we’re not practising to improve our skill each time; we’re just trying to get somewhere.
His Chinese coach, Chen Xinhua, increased the intensity of his practice by firing lots of balls at him from different angles, with different spins and speeds. He even widened the table at Syed’s end to make him work harder. Syed’s world ranking rocketed.
Practising an individual (but not usually team) sport for hours on end is not actually inherently enjoyable. Individuals can be motivated to do it when they feel that their performance is improving. But they actually need to have been participating in the activity, and motivated to improve, before embarking on deliberate practice.
The role of parents in this early stage is often crucial. They will notice the child playing, having early attempts at the sport, and feel that there are signs of promise. Whether that feeling is justified or not doesn’t seem to matter much (Bloom 1985). What’s important is that they facilitate further practice and, possibly with the help of teachers or coaches, point out the improvement that they are making as a result of their practice. After a while, the child can monitor the effects of practice for themselves, whilst competitions can provide further motivation for practice. Eventually, practice becomes an integral part both of becoming an expert and of daily life (Ericsson et al 1993). But if the desire to compete at the highest level is lost, the motivation to maintain practice also goes. Kaminsky et al (1984) found that many elite adolescents who decided to stop competing remained active in the sport, but virtually stopped engaging in practice.
Elite performers generally start practising at an earlier age than lesser performers, and spend a large amount of time practising even at a young age: 20 hours a week for 13-year old tennis players (Monsaas 1985) and 24-30 hours a week for swimmers around the age of 11. Kaminsky et al (1984) found that national level swimmers, ice skaters and gymnasts aged 15-16 practised about 16 hours a week, 3 hours longer than those below national level. Sack (1975) found that male national level runners aged 17-18 trained on average 4.9 times a week; runners at regional and local levels trained on average 4.2 and 3.2 times a week respectively.
There is a limit, however, to how much practice is sensible. Studies have shown essentially no benefit from practising for more than 4 hours a day, and reduced benefit after 2 hours a day (Welford 1968). The actual desirable amount is limited by the individual’s ability to recover mentally and physically. If the individual can’t recover each day from a given level of practice, sustaining that level will lead to exhaustion and mental fatigue. In athletics, for instance, this results in injuries such as “runner’s knee”, shin splints and Achilles tendonitis.
An inability to recover mentally from practice leads to staleness and burnout, as well as the physical problems of fatigue and soreness. The individual may start to become unenthusiastic about practice, and may drop out of the sport altogether. This can be the fate of those who started practising at a later age than the best of their peers, and who try to catch up by suddenly increasing their hours of deliberate practice. But those who started earlier, and built up their practice hours more gradually, are able to sustain maximal levels without suffering from exhaustion. In contrast, those trying to catch up quickly by practising at the level or even above the level of the best performers are likely to encounter injuries and exhaustion.
Finally, the demands on parents, both financially and in terms of their spare time, can be very high at elite levels of sport. Back in 1988 in the US, Chambliss estimated the parents’ costs for a national level swimmer to be over $5,000 a year.
So, whilst an understanding of sports vision can improve performance, don’t expect it to turn you into a world beater overnight.
David Donner
www.donneroptometrists.co.uk
There are a couple of important points that I think should have been included. Firstly, how participating in several different sports can reduce the amount of sport-specific practice well below 10,000 hours. Also, the importance of deliberate play in establishing expertise in team sports was not mentioned.
Syed does make the excellent point that the practice must be challenging. He gives the example of someone who’s been driving for years without becoming a better driver, and even possibly becoming a worse driver through the accumulation of bad habits. This is because we’re not practising to improve our skill each time; we’re just trying to get somewhere.
His Chinese coach, Chen Xinhua, increased the intensity of his practice by firing lots of balls at him from different angles, with different spins and speeds. He even widened the table at Syed’s end to make him work harder. Syed’s world ranking rocketed.
Practising an individual (but not usually team) sport for hours on end is not actually inherently enjoyable. Individuals can be motivated to do it when they feel that their performance is improving. But they actually need to have been participating in the activity, and motivated to improve, before embarking on deliberate practice.
The role of parents in this early stage is often crucial. They will notice the child playing, having early attempts at the sport, and feel that there are signs of promise. Whether that feeling is justified or not doesn’t seem to matter much (Bloom 1985). What’s important is that they facilitate further practice and, possibly with the help of teachers or coaches, point out the improvement that they are making as a result of their practice. After a while, the child can monitor the effects of practice for themselves, whilst competitions can provide further motivation for practice. Eventually, practice becomes an integral part both of becoming an expert and of daily life (Ericsson et al 1993). But if the desire to compete at the highest level is lost, the motivation to maintain practice also goes. Kaminsky et al (1984) found that many elite adolescents who decided to stop competing remained active in the sport, but virtually stopped engaging in practice.
Elite performers generally start practising at an earlier age than lesser performers, and spend a large amount of time practising even at a young age: 20 hours a week for 13-year old tennis players (Monsaas 1985) and 24-30 hours a week for swimmers around the age of 11. Kaminsky et al (1984) found that national level swimmers, ice skaters and gymnasts aged 15-16 practised about 16 hours a week, 3 hours longer than those below national level. Sack (1975) found that male national level runners aged 17-18 trained on average 4.9 times a week; runners at regional and local levels trained on average 4.2 and 3.2 times a week respectively.
There is a limit, however, to how much practice is sensible. Studies have shown essentially no benefit from practising for more than 4 hours a day, and reduced benefit after 2 hours a day (Welford 1968). The actual desirable amount is limited by the individual’s ability to recover mentally and physically. If the individual can’t recover each day from a given level of practice, sustaining that level will lead to exhaustion and mental fatigue. In athletics, for instance, this results in injuries such as “runner’s knee”, shin splints and Achilles tendonitis.
An inability to recover mentally from practice leads to staleness and burnout, as well as the physical problems of fatigue and soreness. The individual may start to become unenthusiastic about practice, and may drop out of the sport altogether. This can be the fate of those who started practising at a later age than the best of their peers, and who try to catch up by suddenly increasing their hours of deliberate practice. But those who started earlier, and built up their practice hours more gradually, are able to sustain maximal levels without suffering from exhaustion. In contrast, those trying to catch up quickly by practising at the level or even above the level of the best performers are likely to encounter injuries and exhaustion.
Finally, the demands on parents, both financially and in terms of their spare time, can be very high at elite levels of sport. Back in 1988 in the US, Chambliss estimated the parents’ costs for a national level swimmer to be over $5,000 a year.
So, whilst an understanding of sports vision can improve performance, don’t expect it to turn you into a world beater overnight.
David Donner
www.donneroptometrists.co.uk
Monday, 1 November 2010
Glaucoma and OCT
What is glaucoma?
That’s not as easy question to answer as you might think. One study, looking at a group of patients aged over 80, found that the prevalence of glaucoma amongst them varied between 0.5% and 6% depending on which definition of glaucoma they used.
Because glaucoma is generally a slowly progressive disease, it’s often difficult to tell whether it’s started or not unless you have accurate measurements from before.
Glaucoma is not the same as high pressures.
There’s a circulating fluid within the eye that has its own pressure, known as the intraocular pressure. Many people will be familiar with the measurement of this pressure, which is often by an instrument that blows air into the eye. Frequently, when I do this test, I hear the comment “this is the glaucoma test, isn’t it?”
Well, actually it isn’t. Raised intraocular pressure is just a risk factor for glaucoma. So glaucoma is now described as a group of diseases that cause progressive damage to the nerves at the back of the eye, with or without raised pressures. The most common of these is Primary Open Angle Glaucoma (POAG).
Half of all cases of glaucoma are undiagnosed
This refers to cases of POAG, according to surveys across several industrialised countries. In one study in East Anglia, 90% of those with undiagnosed glaucoma were found to have normal pressures.
If that isn’t bad enough, the figures in other parts of the world are far worse. The percentage of glaucomas that are undiagnosed was found to be 75% in Bangkok, 93% in India, and 100% in Mongolia (i.e. every case they found was undiagnosed). No wonder glaucoma is the leading cause of irreversible blindness in the world.
So how can you tell if someone has glaucoma or not?
Visual fields
As nerve fibres get damaged, there comes a point when vision starts getting lost. But it won’t appear as a big splodge in the centre of your vision; it’s the more peripheral areas that get affected first. The reason people don’t notice this is because the brain fills in the gaps from neighbouring images. By the time it is noticed (for instance when the car wing mirror keeps getting knocked) quite a lot of vision has already been lost.
We routinely test the field of vision, but analysis isn’t always straightforward. Factors affecting the visual field include pupil size, high prescriptions, other eye conditions, and normal aging. The best field tests are able to take these factors into account by examining in more detail those areas most likely to be affected by glaucoma, but these can be quite long and demanding. And, by the time some field is lost, quite a bit of nerve damage has already taken place.
The optic nerve
When we look into the eye, we can see where the optic nerve comes into the retina. As nerve damage occurs, it’s possible to see changes occurring to this part of the nerve. There’s a paler part in the centre, known as the cup, and this gets larger when the nerve gets damaged. The overall size of the nerve doesn’t change, so if the cup gets abnormally large in comparison, glaucoma is indicated. The difficulty is in deciding what’s normal and what’s abnormal, because some people (especially if they are short-sighted) have larger optic nerves than others, and this also affects the size of the cup.
Imagine you have two sets of equal numbers of cut flowers. One set goes in a narrow vase, and the other goes in a wide vase. In the narrow vase, the flowers will be bunched up with no space in the middle. But in the wide vase, the flowers will be arranged towards the outside, and the space in the middle will be the equivalent of the cup in the optic nerve. As the flowers die, the “cup” increases in size.
In the optic nerve, you can’t be sure that nerves have died (at least not in the early stages) unless you knew how many were there before. And this is where the OCT comes in.
OCT and Glaucoma
The OCT can measure the thickness of the nerve fibre layer, which indicates how many nerves are coming into the main optic nerve from all over the retina. This helps in the diagnosis of glaucoma in two ways.
Firstly, it compares the measurement against an average of people of the same age, sex and ethnicity, so it shows the likelihood of glaucoma by virtue of being out of step with average. The, secondly, it stores those measurements. Then, if they are repeated some time later, any deterioration can be picked up.
In one study (Paul 2010) OCT technology was shown to predict field defects that developed on average four years later.
Treatment
People often ask me if anything can be done about glaucoma once it’s been detected. The answer is “Yes, very much so”. The usual treatment is drops, to bring the pressures down, even if they aren’t especially high. But it needs to be detected early, because any vision that’s been lost can’t be regained. Also, once some nerve fibres died, the remaining ones seem to be especially sensitive to even normal pressure.
Closed angle glaucoma
In about 10% of all cases of glaucoma, the iris gets in the way of the drainage system. This is known as closed angle glaucoma because the angle between the drainage system and the iris gets very narrow and can even close completely. When this happens, the pressure builds up very rapidly in an acute attack. The eye becomes red and painful, and vision loss can occur rapidly without treatment. Unfortunately, two-thirds of those with closed angle glaucoma develop it slowly without any symptoms prior to an attack.
Another use of the OCT is that we can use it to see whether the angle is open or close, so we can detect those at risk of an acute glaucoma attack. Often, all that’s required is a little laser treatment to allow fluid to get through and prevent an attack.
Conclusion
OCT is now playing a vital part not only in the early detection of glaucoma, but also in monitoring the effectiveness of glaucoma treatment.
Contact me for more information on Glaucoma and OCT
David Donner
That’s not as easy question to answer as you might think. One study, looking at a group of patients aged over 80, found that the prevalence of glaucoma amongst them varied between 0.5% and 6% depending on which definition of glaucoma they used.
Because glaucoma is generally a slowly progressive disease, it’s often difficult to tell whether it’s started or not unless you have accurate measurements from before.
Glaucoma is not the same as high pressures.
There’s a circulating fluid within the eye that has its own pressure, known as the intraocular pressure. Many people will be familiar with the measurement of this pressure, which is often by an instrument that blows air into the eye. Frequently, when I do this test, I hear the comment “this is the glaucoma test, isn’t it?”
Well, actually it isn’t. Raised intraocular pressure is just a risk factor for glaucoma. So glaucoma is now described as a group of diseases that cause progressive damage to the nerves at the back of the eye, with or without raised pressures. The most common of these is Primary Open Angle Glaucoma (POAG).
Half of all cases of glaucoma are undiagnosed
This refers to cases of POAG, according to surveys across several industrialised countries. In one study in East Anglia, 90% of those with undiagnosed glaucoma were found to have normal pressures.
If that isn’t bad enough, the figures in other parts of the world are far worse. The percentage of glaucomas that are undiagnosed was found to be 75% in Bangkok, 93% in India, and 100% in Mongolia (i.e. every case they found was undiagnosed). No wonder glaucoma is the leading cause of irreversible blindness in the world.
So how can you tell if someone has glaucoma or not?
Visual fields
As nerve fibres get damaged, there comes a point when vision starts getting lost. But it won’t appear as a big splodge in the centre of your vision; it’s the more peripheral areas that get affected first. The reason people don’t notice this is because the brain fills in the gaps from neighbouring images. By the time it is noticed (for instance when the car wing mirror keeps getting knocked) quite a lot of vision has already been lost.
We routinely test the field of vision, but analysis isn’t always straightforward. Factors affecting the visual field include pupil size, high prescriptions, other eye conditions, and normal aging. The best field tests are able to take these factors into account by examining in more detail those areas most likely to be affected by glaucoma, but these can be quite long and demanding. And, by the time some field is lost, quite a bit of nerve damage has already taken place.
The optic nerve
When we look into the eye, we can see where the optic nerve comes into the retina. As nerve damage occurs, it’s possible to see changes occurring to this part of the nerve. There’s a paler part in the centre, known as the cup, and this gets larger when the nerve gets damaged. The overall size of the nerve doesn’t change, so if the cup gets abnormally large in comparison, glaucoma is indicated. The difficulty is in deciding what’s normal and what’s abnormal, because some people (especially if they are short-sighted) have larger optic nerves than others, and this also affects the size of the cup.
Imagine you have two sets of equal numbers of cut flowers. One set goes in a narrow vase, and the other goes in a wide vase. In the narrow vase, the flowers will be bunched up with no space in the middle. But in the wide vase, the flowers will be arranged towards the outside, and the space in the middle will be the equivalent of the cup in the optic nerve. As the flowers die, the “cup” increases in size.
In the optic nerve, you can’t be sure that nerves have died (at least not in the early stages) unless you knew how many were there before. And this is where the OCT comes in.
OCT and Glaucoma
The OCT can measure the thickness of the nerve fibre layer, which indicates how many nerves are coming into the main optic nerve from all over the retina. This helps in the diagnosis of glaucoma in two ways.
Firstly, it compares the measurement against an average of people of the same age, sex and ethnicity, so it shows the likelihood of glaucoma by virtue of being out of step with average. The, secondly, it stores those measurements. Then, if they are repeated some time later, any deterioration can be picked up.
In one study (Paul 2010) OCT technology was shown to predict field defects that developed on average four years later.
Treatment
People often ask me if anything can be done about glaucoma once it’s been detected. The answer is “Yes, very much so”. The usual treatment is drops, to bring the pressures down, even if they aren’t especially high. But it needs to be detected early, because any vision that’s been lost can’t be regained. Also, once some nerve fibres died, the remaining ones seem to be especially sensitive to even normal pressure.
Closed angle glaucoma
In about 10% of all cases of glaucoma, the iris gets in the way of the drainage system. This is known as closed angle glaucoma because the angle between the drainage system and the iris gets very narrow and can even close completely. When this happens, the pressure builds up very rapidly in an acute attack. The eye becomes red and painful, and vision loss can occur rapidly without treatment. Unfortunately, two-thirds of those with closed angle glaucoma develop it slowly without any symptoms prior to an attack.
Another use of the OCT is that we can use it to see whether the angle is open or close, so we can detect those at risk of an acute glaucoma attack. Often, all that’s required is a little laser treatment to allow fluid to get through and prevent an attack.
Conclusion
OCT is now playing a vital part not only in the early detection of glaucoma, but also in monitoring the effectiveness of glaucoma treatment.
Contact me for more information on Glaucoma and OCT
David Donner
Wednesday, 13 October 2010
Reading, Dyslexia and the Eyes
One of my patients told me recently that her son had been referred to have some tests on his eye movements because he sometimes makes spelling mistakes. He can read perfectly well, and actually does OK in spelling tests, but just makes mistakes when writing. It struck me that if you referred every child who made spelling mistakes for special tests, you’d probably need to refer 98% of them. So how do these ideas come about, and what’s the story of eyes, reading and dyslexia?
Why reading – especially English – is difficult
Reading is a complicated task that requires the involvement of several different parts of the brain. The image of words falls on the retina and is transferred to the visual cortex of the brain. Here, the image that we see is formed. As part of the processing of that image, shapes are recognised. This information has to link up with the language centres, which recognise sound and meaning.
The written word is, in evolutionary terms, a relatively modern invention. Our brains are really set up to learn language through sound, as we nearly all manage to do easily when we learn to understand and speak our native language at a young age. So when we read, we still have to link the words with how they sound. Even expert readers will say the words in their head when they read.
English is a particularly difficult language to learn to read because there are so many words like “eye” or “cough” whose pronunciation isn’t obvious from the way they’re spelt. These words are generally learned through their meaning, and efficient readers go straight to the meaning when they read, so they don’t have to piece words together from the sounds. Because Italian is a much more phonetic language than English, there are only half as many diagnosed dyslexics in Italy than in England. It seems likely, however, that there are many more Italians whose dyslexia is too mild to be significant.
Reading and the brain
Cutting & Rimrodt (2010) found used a form of MRI scanning called Diffusion Tensor Imaging to study part of a branch of nerves that runs from the visual cortex to the areas at the front of the brain that are responsible for articulation and speech. They found that some of these nerve fibres were less well organised in dyslexics than in controls.
There have been many reports of differences in nerve structure in dyslexics, but these have not been consistent. Differences have been found in the temporal or parietal or occipital parts of the brain, as well as in the cerebellum. It may be that a well organised nerve structure is a sign of proficiency in that particular task, and that, for a mixture of genetic and environmental reasons, this is achieved more easily in some than in others. Italian dyslexics have been found to show the same kind of nerve activation when reading as English and French dyslexics (Paulesu et al 2001). They also had the same difficulty in tests that looked at their ability to recognise the sounds of words. It’s just that in Italian, there’s only one way to represent a sound, whereas in English there are lots, such as “their” or “there”.
Dyslexia and eye movements
Because anomalies have sometimes been found in the nerve pathways that control eye movements, and because dyslexics often have irregular eye movements when reading, it’s been suggested that poor control of eye movements is a cause of dyslexia.
Hutzler et al (2006) investigated this idea by showing dyslexics and controls groups of consonants, such as DSB, LQWB, ZBB and VPLL. The subjects had to say whether each group of consonants had a double letter in them or not. This meant that the subjects had to look at each “word” in a similar manner to reading, but no higher order skills of language and sound recognition were required. No difference in the eye movement patterns between dyslexics and non-dyslexics were found.
The researchers then changed things, so that the subjects had to try and pronounce “words” such as ZIB, VULL and CRUF. Now, the dyslexic subjects showed the same irregular eye movement patterns as had been found in previous research. Patients with diseases such as Parkinson’s and Huntingdon’s often have trouble with reading because of poor control of eye movements. However, they have a lot of other problems for the same reason, and this would not appear to be the case for the vast majority of dyslexics.
Dyslexia and the cerebellum
Similarly, because scans have sometimes shown anomalies in the cerebellum of dyslexics, it’s been suggested that the cerebellum holds the key to dyslexia. The cerebellum is in control of the things we do without thinking, such as brushing our teeth, and it also plays a crucial role in maintaining our balance. And it’s certainly true that dyspraxia (a disability affecting movement and coordination) and attention deficit hyperactivity disorder (ADHD) are more frequently found in dyslexics than non-dyslexics. On this basis, it’s suggested that specific exercises aimed at improving balance and coordination will improve reading.
One of the many problems with his idea is that there are plenty of elite sportsmen and sportswomen, who would appear to have excellent balance and coordination, but who have suffered from dyslexia. Another problem, and one shared with several other “miracle cures”, is that the statistics used to promote it are unreliable. One of the main reasons for this is a statistical phenomenon called “regression to the mean”.
Imagine 100 people took a multiple choice test in a subject about which they knew absolutely nothing, so had to guess every time. If each question had 2 choices, you’d expect the overall mark to be around 50%. Some people, however, would do rather better, and some worse. If you got the top 10% do another similar guessing test, their mean score would be about 50%, so on average, will have done worse on the second test than on the first. Similarly, a repeat test on the bottom 10% would see their average score improve. This is regression to the mean, and it’s why it’s easy to show that people who weren’t very good at something when you first tested them, can show a dramatic improvement when you test them again after their “treatment” compared with those who did well first time round. The only way round this is to have a genuine control group, who are as similar as possible to the treated group, and who have the same tests at the same time. So you would need to compare dyslexics of the same level of disability, with and without the treatment, to make a valid comparison. This seems to be rarely done.
Dyslexia and eye dominance
I recently read the claim by an optometrist offering diplomas in “Schoolvision” that the “predominant visual skill in reading is aiming”, and that this can be undermined by unstable eye dominance. The role of aiming in reading has been largely neglected up until now (for good reason, you might think), although the importance of eye dominance in aiming sports is widely accepted, including by myself.
But the idea that eye dominance is relevant to dyslexia is not a new one. Stein & Fowler (1982) claimed that more than half of the dyslexic population had an unfixed reference eye on a binocular vision test, compared with 1% of controls. The test used was the Dunlop Test, in which the eyes diverge until double vision occurs, and the child has to say in which direction an object has moved. The test is repeated ten times, and if they give inconsistent answers they’re said to have an unstable response. This doesn’t seem to bear much relation to reading, and, anyway, others (Newman et al 1985; Bishop et al 1979) found that excellent readers did just as badly as poor readers on this test.
Stein & Fowler went on to suggest that some dyslexic children might be helped by the occlusion of one eye. But when Bishop (1989) re-analysed the data, she found no evidence that occluding one eye improved reading scores, and described the original findings as “methodologically flawed”. And whilst some have claimed that cross-dominance (e.g. right eye dominant + left handedness) is especially prevalent in dyslexia, many studies of large numbers of dyslexics have failed to find this link.
What’s the answer?
Most dyslexics clearly don’t have something fundamentally wrong with them, otherwise they’d have a lot more problems than being slower than others in learning to read. Also, we wouldn’t see the differences between languages if vision were really at the heart of dyslexia.
Having said that, there are quite a lot of children who have difficulty when reading because of their vision, and some of them will be dyslexic. Their difficulty often arises because they have either a weakness of accommodation (ability to focus on near objects) or convergence (ability to bring the eyes together for near objects), or both. After a while, they find words go blurred and/or double.
These children generally respond very well to simple exercises, and rarely need glasses. So if your child is having reading difficulties, it’s worth getting their eyes examined to rule out this kind of problem.
Whatever the cause of dyslexia, the answer seems to be one-to-one tuition in reading. Whether this should be phonics or something else, I leave to others to debate.
David Donner
Why reading – especially English – is difficult
Reading is a complicated task that requires the involvement of several different parts of the brain. The image of words falls on the retina and is transferred to the visual cortex of the brain. Here, the image that we see is formed. As part of the processing of that image, shapes are recognised. This information has to link up with the language centres, which recognise sound and meaning.
The written word is, in evolutionary terms, a relatively modern invention. Our brains are really set up to learn language through sound, as we nearly all manage to do easily when we learn to understand and speak our native language at a young age. So when we read, we still have to link the words with how they sound. Even expert readers will say the words in their head when they read.
English is a particularly difficult language to learn to read because there are so many words like “eye” or “cough” whose pronunciation isn’t obvious from the way they’re spelt. These words are generally learned through their meaning, and efficient readers go straight to the meaning when they read, so they don’t have to piece words together from the sounds. Because Italian is a much more phonetic language than English, there are only half as many diagnosed dyslexics in Italy than in England. It seems likely, however, that there are many more Italians whose dyslexia is too mild to be significant.
Reading and the brain
Cutting & Rimrodt (2010) found used a form of MRI scanning called Diffusion Tensor Imaging to study part of a branch of nerves that runs from the visual cortex to the areas at the front of the brain that are responsible for articulation and speech. They found that some of these nerve fibres were less well organised in dyslexics than in controls.
There have been many reports of differences in nerve structure in dyslexics, but these have not been consistent. Differences have been found in the temporal or parietal or occipital parts of the brain, as well as in the cerebellum. It may be that a well organised nerve structure is a sign of proficiency in that particular task, and that, for a mixture of genetic and environmental reasons, this is achieved more easily in some than in others. Italian dyslexics have been found to show the same kind of nerve activation when reading as English and French dyslexics (Paulesu et al 2001). They also had the same difficulty in tests that looked at their ability to recognise the sounds of words. It’s just that in Italian, there’s only one way to represent a sound, whereas in English there are lots, such as “their” or “there”.
Dyslexia and eye movements
Because anomalies have sometimes been found in the nerve pathways that control eye movements, and because dyslexics often have irregular eye movements when reading, it’s been suggested that poor control of eye movements is a cause of dyslexia.
Hutzler et al (2006) investigated this idea by showing dyslexics and controls groups of consonants, such as DSB, LQWB, ZBB and VPLL. The subjects had to say whether each group of consonants had a double letter in them or not. This meant that the subjects had to look at each “word” in a similar manner to reading, but no higher order skills of language and sound recognition were required. No difference in the eye movement patterns between dyslexics and non-dyslexics were found.
The researchers then changed things, so that the subjects had to try and pronounce “words” such as ZIB, VULL and CRUF. Now, the dyslexic subjects showed the same irregular eye movement patterns as had been found in previous research. Patients with diseases such as Parkinson’s and Huntingdon’s often have trouble with reading because of poor control of eye movements. However, they have a lot of other problems for the same reason, and this would not appear to be the case for the vast majority of dyslexics.
Dyslexia and the cerebellum
Similarly, because scans have sometimes shown anomalies in the cerebellum of dyslexics, it’s been suggested that the cerebellum holds the key to dyslexia. The cerebellum is in control of the things we do without thinking, such as brushing our teeth, and it also plays a crucial role in maintaining our balance. And it’s certainly true that dyspraxia (a disability affecting movement and coordination) and attention deficit hyperactivity disorder (ADHD) are more frequently found in dyslexics than non-dyslexics. On this basis, it’s suggested that specific exercises aimed at improving balance and coordination will improve reading.
One of the many problems with his idea is that there are plenty of elite sportsmen and sportswomen, who would appear to have excellent balance and coordination, but who have suffered from dyslexia. Another problem, and one shared with several other “miracle cures”, is that the statistics used to promote it are unreliable. One of the main reasons for this is a statistical phenomenon called “regression to the mean”.
Imagine 100 people took a multiple choice test in a subject about which they knew absolutely nothing, so had to guess every time. If each question had 2 choices, you’d expect the overall mark to be around 50%. Some people, however, would do rather better, and some worse. If you got the top 10% do another similar guessing test, their mean score would be about 50%, so on average, will have done worse on the second test than on the first. Similarly, a repeat test on the bottom 10% would see their average score improve. This is regression to the mean, and it’s why it’s easy to show that people who weren’t very good at something when you first tested them, can show a dramatic improvement when you test them again after their “treatment” compared with those who did well first time round. The only way round this is to have a genuine control group, who are as similar as possible to the treated group, and who have the same tests at the same time. So you would need to compare dyslexics of the same level of disability, with and without the treatment, to make a valid comparison. This seems to be rarely done.
Dyslexia and eye dominance
I recently read the claim by an optometrist offering diplomas in “Schoolvision” that the “predominant visual skill in reading is aiming”, and that this can be undermined by unstable eye dominance. The role of aiming in reading has been largely neglected up until now (for good reason, you might think), although the importance of eye dominance in aiming sports is widely accepted, including by myself.
But the idea that eye dominance is relevant to dyslexia is not a new one. Stein & Fowler (1982) claimed that more than half of the dyslexic population had an unfixed reference eye on a binocular vision test, compared with 1% of controls. The test used was the Dunlop Test, in which the eyes diverge until double vision occurs, and the child has to say in which direction an object has moved. The test is repeated ten times, and if they give inconsistent answers they’re said to have an unstable response. This doesn’t seem to bear much relation to reading, and, anyway, others (Newman et al 1985; Bishop et al 1979) found that excellent readers did just as badly as poor readers on this test.
Stein & Fowler went on to suggest that some dyslexic children might be helped by the occlusion of one eye. But when Bishop (1989) re-analysed the data, she found no evidence that occluding one eye improved reading scores, and described the original findings as “methodologically flawed”. And whilst some have claimed that cross-dominance (e.g. right eye dominant + left handedness) is especially prevalent in dyslexia, many studies of large numbers of dyslexics have failed to find this link.
What’s the answer?
Most dyslexics clearly don’t have something fundamentally wrong with them, otherwise they’d have a lot more problems than being slower than others in learning to read. Also, we wouldn’t see the differences between languages if vision were really at the heart of dyslexia.
Having said that, there are quite a lot of children who have difficulty when reading because of their vision, and some of them will be dyslexic. Their difficulty often arises because they have either a weakness of accommodation (ability to focus on near objects) or convergence (ability to bring the eyes together for near objects), or both. After a while, they find words go blurred and/or double.
These children generally respond very well to simple exercises, and rarely need glasses. So if your child is having reading difficulties, it’s worth getting their eyes examined to rule out this kind of problem.
Whatever the cause of dyslexia, the answer seems to be one-to-one tuition in reading. Whether this should be phonics or something else, I leave to others to debate.
David Donner
Tuesday, 31 August 2010
A Look At Shooting
If you’re shooting inaccurately, it could be due to poor alignment with the target, or it could be due to body movement or hand/arm tremors as you fire. There are now pistols equipped with lasers to help distinguish between these errors. The laser isn’t turned on until the shooter has aimed. If the laser centres on the target, then the problem is with body movement and not with aiming.
Because of the distance between the gun’s sight and the target, both cannot be seen clearly. So should one focus on the sight or the target? The general consensus is that you should focus on the sight. This makes sense, as it intuitively seems easier to put a clear object in the centre of a blurred ring, than trying to put a clear ring equidistant around a blurred object. It also explains why some short-sighted people have been excellent marksmen. But it does cause problems for older shooters.
Unless one is short-sighted, one’s ability to focus close objects, such as a gun sight, goes down as one gets older. It’s possible, however, to have a correcting lens for this, and there are special shooting spectacles which can be adjusted to ensure that the lens is perfectly positioned.
Ripoll et al (1985) compared the gaze strategies of international elite pistol shooters with national near-elite shooters. They found that the near-elite looked at their hand and weapon as they brought it up towards the target, whereas the elite shooters fixated the target, and then brought the pistol into line with their gaze before aiming and pulling the trigger. Compared with the near-elite, the elite shooters were quick to bring the pistol into line, but then took longer to aim and complete the shot.
Although this might appear to contradict the advice to focus on the sight, and not the target, it’s likely that the elite shooters did their final aiming adjustment fixated on the sight, but because the sight and target were in alignment, no difference in gaze would be found by the cameras monitoring them.
The gaze strategy of elite shooters goes beyond sport. For some, it’s been a matter of life and death.
Joan Vickers (of “Quiet Eye” fame) and Bill Lewinski (Force Science Research Centre) studied members of Britain’s Emergency Response Team. 11 were highly experienced, and 13 were younger rookies who’d just completed their training.
They set up a scenario in which the subjects were to provide security at an Embassy. A man gets into an argument with the receptionist, and at some point turns around, taking an object from his coat pocket, which is either a gun or a mobile phone.
In more than 60% of trials, the trainees fired when the assailant brandished a mobile phone, compared with only 18% of elite trials. When the assailant pulled out a gun, elite officers shot first 92.5% of the time, compared with 42% for the trainees. The elite officers were also more accurate in their shooting, with the trainees more likely to miss the target completely.
In the last half-second before aiming, in 82% of their tests the trainees took their eyes off the assailant and attempted to look at their own gun, trying to find or confirm the sight alignment as they aimed. Although 30% of the elite also looked at their gun, these fixations were before they aimed (and fired).
When most officers learn to shoot a handgun, they are taught to focus first on the rear sight, then on the front sight, and finally on the target, aligning all three before pulling the trigger. It seems that through experience, the elite officers had learned to keep most of their attention on the assailant’s weapon. Like Ripoll’s elite shooters, they kept their gaze on the assailant’s weapon and brought their gun up into their line of sight.
This research by Vickers & Lewinski is likely to result in changes to the way that officers learn to shoot. If this had been done before, might Jean Charles de Menezes still be alive today? DD
If you’re shooting inaccurately, it could be due to poor alignment with the target, or it could be due to body movement or hand/arm tremors as you fire. There are now pistols equipped with lasers to help distinguish between these errors. The laser isn’t turned on until the shooter has aimed. If the laser centres on the target, then the problem is with body movement and not with aiming.
Because of the distance between the gun’s sight and the target, both cannot be seen clearly. So should one focus on the sight or the target? The general consensus is that you should focus on the sight. This makes sense, as it intuitively seems easier to put a clear object in the centre of a blurred ring, than trying to put a clear ring equidistant around a blurred object. It also explains why some short-sighted people have been excellent marksmen. But it does cause problems for older shooters.
Unless one is short-sighted, one’s ability to focus close objects, such as a gun sight, goes down as one gets older. It’s possible, however, to have a correcting lens for this, and there are special shooting spectacles which can be adjusted to ensure that the lens is perfectly positioned.
Ripoll et al (1985) compared the gaze strategies of international elite pistol shooters with national near-elite shooters. They found that the near-elite looked at their hand and weapon as they brought it up towards the target, whereas the elite shooters fixated the target, and then brought the pistol into line with their gaze before aiming and pulling the trigger. Compared with the near-elite, the elite shooters were quick to bring the pistol into line, but then took longer to aim and complete the shot.
Although this might appear to contradict the advice to focus on the sight, and not the target, it’s likely that the elite shooters did their final aiming adjustment fixated on the sight, but because the sight and target were in alignment, no difference in gaze would be found by the cameras monitoring them.
The gaze strategy of elite shooters goes beyond sport. For some, it’s been a matter of life and death.
Joan Vickers (of “Quiet Eye” fame) and Bill Lewinski (Force Science Research Centre) studied members of Britain’s Emergency Response Team. 11 were highly experienced, and 13 were younger rookies who’d just completed their training.
They set up a scenario in which the subjects were to provide security at an Embassy. A man gets into an argument with the receptionist, and at some point turns around, taking an object from his coat pocket, which is either a gun or a mobile phone.
In more than 60% of trials, the trainees fired when the assailant brandished a mobile phone, compared with only 18% of elite trials. When the assailant pulled out a gun, elite officers shot first 92.5% of the time, compared with 42% for the trainees. The elite officers were also more accurate in their shooting, with the trainees more likely to miss the target completely.
In the last half-second before aiming, in 82% of their tests the trainees took their eyes off the assailant and attempted to look at their own gun, trying to find or confirm the sight alignment as they aimed. Although 30% of the elite also looked at their gun, these fixations were before they aimed (and fired).
When most officers learn to shoot a handgun, they are taught to focus first on the rear sight, then on the front sight, and finally on the target, aligning all three before pulling the trigger. It seems that through experience, the elite officers had learned to keep most of their attention on the assailant’s weapon. Like Ripoll’s elite shooters, they kept their gaze on the assailant’s weapon and brought their gun up into their line of sight.
This research by Vickers & Lewinski is likely to result in changes to the way that officers learn to shoot. If this had been done before, might Jean Charles de Menezes still be alive today?
"http://www.donneroptometrists.co.uk/sports-vision.htm"
Wednesday, 11 August 2010
Brain Waves
Does the study of brain waves help us distinguish experts from novices, and can brain waves be altered to improve performance?
Four types of brain wave have been identified. Alpha waves (8 – 14 Hz) are seen when we are relaxed, daydreaming or visualising. Increases in alpha waves are often associated with reduced overall activity of the brain. Beta waves (15 – 38 Hz) are associated with conscious thought, with higher frequency beta being associated with anxiety or stress. Gamma and delta waves are mostly seen in different stages of sleep.
Neurofeedback, also known as EEG biofeedback, is a strategy to enable people to alter their own brainwaves. It has been used in the treatment of ADHD (Attention-deficit hyperactivity disorder). Often the patient is using a videogame that’s linked to their EEG, and the aim is usually to increase beta waves and reduce theta waves. When the desired effect is taking place, they get some kind of encouragement in the game, such as beep or a character moving in the desired direction.
Neurofeedback has also been used to improve the balance of patients who have suffered brain injury or stroke. Significant improvements have been found after just 8 – 10 sessions, whereas ADHD treatments usually take 40 – 50 sessions.
Before trying neurofeedback to improve sporting ability, one would need to know if experts demonstrate different brainwave activity compared with lesser players. And there is actually some evidence for that. It’s hard to play rugby or football when attached to the electrodes of EEG equipment, so most of the evidence comes from aiming sports, such as archery, shooting and golf putting.
Haufler et al (2000) found that during aiming, when marksmen were compared with novice shooters, marksmen exhibited less activation (increased alpha with less beta and gamma activity) at all electrode sites on the head, but especially in the left hemisphere. Kerick et al (2001) looked at skilled marksmen during shooting. Over an 8-second period preceding the pull of the trigger, they exhibited greater alpha activity in the left temporal area compared with when they were doing a control activity. Hatfield et al (1984) also found a progressive increase in alpha power in the left temporal area during the last 7.5 seconds of aiming, with no change in the right temporal area.
These results could fit in with the idea that the left hemisphere dominates in language, and that a lot of verbal thoughts could inhibit efficient sporting performance.
Landers et al (1991) used neurofeedback to try and improve the performance of pre-elite archers. On the basis that reduced cortical activity in the left hemisphere (associated with increased alpha waves and reduced beta waves) would increase accuracy, the archers were randomly assigned to one of three groups. One group was given “correct” feedback (reduced left hemisphere activity), another “incorrect” feedback (reduced right hemisphere activity), and a control with no feedback.
They found that those trained to have reduced left temporal activity showed a significant improvement in performance, whilst those trained to have reduced right temporal activity showed a significantly worse performance. The control group showed no change.
However, there’s a problem. Examination of the participants’ EEG spectra failed to show a clear pattern of change after the test compared with beforehand. It’s as if the feedback changed something, but not what it was supposed to.
Also, the link between brain waves and sport performance turns out not to be as simple as first thought. For instance, Del Percio et al (2007) found a correlation between a reduction in alpha output in part of the right hemisphere and skilled karate performance. In contrast, Collins et al (1990) found that skilled karate performance was linked to a bilateral increase in alpha output.
Crews & Landers (1994) found that in the last second before a golf putt, increased alpha waves in the right hemisphere were associated with increased putting accuracy. This is in contrast with the increase in the left hemisphere that had been found in shooting and archery. Looking at putting novices, however, Shelley-Trembley et al (2006) found that lower beta levels in the right hemisphere correlated with accuracy.
So it seems that we need to understand brain waves rather better before we can be sure that trying to change them will improve performance. Oh well, back to practise then.
David
www.donneroptometrists.co.uk
Four types of brain wave have been identified. Alpha waves (8 – 14 Hz) are seen when we are relaxed, daydreaming or visualising. Increases in alpha waves are often associated with reduced overall activity of the brain. Beta waves (15 – 38 Hz) are associated with conscious thought, with higher frequency beta being associated with anxiety or stress. Gamma and delta waves are mostly seen in different stages of sleep.
Neurofeedback, also known as EEG biofeedback, is a strategy to enable people to alter their own brainwaves. It has been used in the treatment of ADHD (Attention-deficit hyperactivity disorder). Often the patient is using a videogame that’s linked to their EEG, and the aim is usually to increase beta waves and reduce theta waves. When the desired effect is taking place, they get some kind of encouragement in the game, such as beep or a character moving in the desired direction.
Neurofeedback has also been used to improve the balance of patients who have suffered brain injury or stroke. Significant improvements have been found after just 8 – 10 sessions, whereas ADHD treatments usually take 40 – 50 sessions.
Before trying neurofeedback to improve sporting ability, one would need to know if experts demonstrate different brainwave activity compared with lesser players. And there is actually some evidence for that. It’s hard to play rugby or football when attached to the electrodes of EEG equipment, so most of the evidence comes from aiming sports, such as archery, shooting and golf putting.
Haufler et al (2000) found that during aiming, when marksmen were compared with novice shooters, marksmen exhibited less activation (increased alpha with less beta and gamma activity) at all electrode sites on the head, but especially in the left hemisphere. Kerick et al (2001) looked at skilled marksmen during shooting. Over an 8-second period preceding the pull of the trigger, they exhibited greater alpha activity in the left temporal area compared with when they were doing a control activity. Hatfield et al (1984) also found a progressive increase in alpha power in the left temporal area during the last 7.5 seconds of aiming, with no change in the right temporal area.
These results could fit in with the idea that the left hemisphere dominates in language, and that a lot of verbal thoughts could inhibit efficient sporting performance.
Landers et al (1991) used neurofeedback to try and improve the performance of pre-elite archers. On the basis that reduced cortical activity in the left hemisphere (associated with increased alpha waves and reduced beta waves) would increase accuracy, the archers were randomly assigned to one of three groups. One group was given “correct” feedback (reduced left hemisphere activity), another “incorrect” feedback (reduced right hemisphere activity), and a control with no feedback.
They found that those trained to have reduced left temporal activity showed a significant improvement in performance, whilst those trained to have reduced right temporal activity showed a significantly worse performance. The control group showed no change.
However, there’s a problem. Examination of the participants’ EEG spectra failed to show a clear pattern of change after the test compared with beforehand. It’s as if the feedback changed something, but not what it was supposed to.
Also, the link between brain waves and sport performance turns out not to be as simple as first thought. For instance, Del Percio et al (2007) found a correlation between a reduction in alpha output in part of the right hemisphere and skilled karate performance. In contrast, Collins et al (1990) found that skilled karate performance was linked to a bilateral increase in alpha output.
Crews & Landers (1994) found that in the last second before a golf putt, increased alpha waves in the right hemisphere were associated with increased putting accuracy. This is in contrast with the increase in the left hemisphere that had been found in shooting and archery. Looking at putting novices, however, Shelley-Trembley et al (2006) found that lower beta levels in the right hemisphere correlated with accuracy.
So it seems that we need to understand brain waves rather better before we can be sure that trying to change them will improve performance. Oh well, back to practise then.
David
www.donneroptometrists.co.uk
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