Congratulations to Roger Federer and his ATP Tennis final win this weekend in London but it got me thinking and researching from a Sports Vision point of view...
Linesmen are more likely to call a ball "out" when it was "in", rather than the other way. Why?
After an image is focused on the retina, there's a time delay of about 100 milliseconds before it is recreated in the brain. This is the image that we see, not the one on the retina.
Therefore, our perception of things lags fractionally behind reality. For moving objects, the visual system gets round this problem by shifting the image forward. This means that a tennis player can get their racket in the right place at the right time, and not fractionally late.
In theory then, when a ball bounces there's a likelihood that it will be perceived to have bounced further on (in the direction of travel) than it actually did.
To test the theory, Whitney et al (2008) reviewed more than 4,000 randomly selected Wimbledon points. They found 83 incorrect calls, of which 70 were of the type predicted.
The researchers suggest that players are therefore more likely to be successful challenging calls of "out" than calls of "in".
David Donner
Monday 29 November 2010
Wednesday 24 November 2010
Rugby Line Out
The importance of an accurate line-out throw was highlighted when Dylan Hartley’s overthrow led to an Australian try in the recent international.
One of the best ways of practising the line-out throw is to suspend a ball from the crossbar at the required height. This gives the hooker a target to aim for, and the catchers have to catch the thrown-in, as opposed to the suspended ball. When line-outs are contested, the hooker has to learn to give the ball the correct flight to beat the front jumpers. When the suspended ball is removed, the hooker has to imagine that there’s a ball there to aim at.
The importance of holding the ball in a consistent fashion has been demonstrated in research on basketball free throws.
Aglioti et al (2008) tested 10 elite professional players, 5 sports journalists, 5 sports coaches and 10 students who were complete novices. They were shown video clips of different lengths of a professional player taking free throws, and had to predict whether or not the throws were successful. They found that the professional players were able to predict significantly more successfully when the clips were stopped at the point when the ball left the hand. The other groups needed to see the trajectory of the ball after release before they could make accurate predictions.
Researchers then used transcranial magnetic stimulation (TMS) to assess activity in the brain when the participants were watching the video clips. They found that both expert players and watchers had increased activity in the parts of their brain concerned with movement when they watched video clips of free throws, as opposed to when they watched static pictures or videos of footballers taking a penalty. Novices did not show this higher level of brain activity.
The really interesting bit was when the researchers studied the brain activity of elite players when they watched a “miss”. At the moment the ball was released from the hand, there was a spike in activity in the area of the brain that controls a muscle in the little finger called the abductor digiti minimi. This muscle pulls the little finger away from the body’s midline.
The researchers also looked at the angles formed by the little finger, wrist and knee joints during free throws. At the point when the ball was released, when the elite players watching got their vital information, the only difference between shots that were accurate and those that missed was the little finger angle.
So, hookers note: if your little finger is in the wrong position at the moment the ball is released, your throw is likely to be off target.
David Donner
One of the best ways of practising the line-out throw is to suspend a ball from the crossbar at the required height. This gives the hooker a target to aim for, and the catchers have to catch the thrown-in, as opposed to the suspended ball. When line-outs are contested, the hooker has to learn to give the ball the correct flight to beat the front jumpers. When the suspended ball is removed, the hooker has to imagine that there’s a ball there to aim at.
The importance of holding the ball in a consistent fashion has been demonstrated in research on basketball free throws.
Aglioti et al (2008) tested 10 elite professional players, 5 sports journalists, 5 sports coaches and 10 students who were complete novices. They were shown video clips of different lengths of a professional player taking free throws, and had to predict whether or not the throws were successful. They found that the professional players were able to predict significantly more successfully when the clips were stopped at the point when the ball left the hand. The other groups needed to see the trajectory of the ball after release before they could make accurate predictions.
Researchers then used transcranial magnetic stimulation (TMS) to assess activity in the brain when the participants were watching the video clips. They found that both expert players and watchers had increased activity in the parts of their brain concerned with movement when they watched video clips of free throws, as opposed to when they watched static pictures or videos of footballers taking a penalty. Novices did not show this higher level of brain activity.
The really interesting bit was when the researchers studied the brain activity of elite players when they watched a “miss”. At the moment the ball was released from the hand, there was a spike in activity in the area of the brain that controls a muscle in the little finger called the abductor digiti minimi. This muscle pulls the little finger away from the body’s midline.
The researchers also looked at the angles formed by the little finger, wrist and knee joints during free throws. At the point when the ball was released, when the elite players watching got their vital information, the only difference between shots that were accurate and those that missed was the little finger angle.
So, hookers note: if your little finger is in the wrong position at the moment the ball is released, your throw is likely to be off target.
David Donner
Rugby Place Kicking
Place kicking is an area where visualisation and ritual can play a huge part in success. They are necessary because these are the occasions when the player has time to think about what he’s doing, which makes it more difficult to act instinctively.
When an action is so grooved that it becomes routine, it indicates that the subconscious brain, and the cerebellum in particular, has taken control. If, however, the conscious brain takes over, which is especially likely to happen on important kicks, performance is likely to deteriorate. Rituals, such as crouching, or tapping the feet, keep conscious thoughts at bay, and allow the player to follow a pre-set routine.
Many successful kickers visualise the whole process before executing it. The same patterns of the brain are stimulated when visualisation is used as when the actual activity is performed. So visualisation seems to prime neural circuits, and this also helps to exclude the conscious, analytical parts of the brain from the execution.
When Johnny Wilkinson was taking kicks for England, he’d imagine that there was a lady called Doris whom he could see through the posts sitting in the crowd. I think at one time he imagined she was reading a newspaper. Then he imagined she was holding a drink which he would try and knock out of her hand. He would then have an imaginary line, like an imaginary wire, the ball would follow on its way through the posts to Doris.
I’ve always assumed that the best kickers would focus on a particular part of the ball with which they would aim to make contact, rather than just focusing generally on the ball. I’d not seen any evidence for this, until I read a recent quote from Dave Alder, the Wasps fly half: “I was once practising with a set of six (balls) and something didn’t feel right about one of them. It was only after I’d been kicking for a while that I realised the logo on the ball had been printed upside down”.
If you could get a ball marked up with lots of different sectors, it would help those learning to kick to discover which parts of the ball they should be focusing on in order to execute the desired type of kick.
David Donner
When an action is so grooved that it becomes routine, it indicates that the subconscious brain, and the cerebellum in particular, has taken control. If, however, the conscious brain takes over, which is especially likely to happen on important kicks, performance is likely to deteriorate. Rituals, such as crouching, or tapping the feet, keep conscious thoughts at bay, and allow the player to follow a pre-set routine.
Many successful kickers visualise the whole process before executing it. The same patterns of the brain are stimulated when visualisation is used as when the actual activity is performed. So visualisation seems to prime neural circuits, and this also helps to exclude the conscious, analytical parts of the brain from the execution.
When Johnny Wilkinson was taking kicks for England, he’d imagine that there was a lady called Doris whom he could see through the posts sitting in the crowd. I think at one time he imagined she was reading a newspaper. Then he imagined she was holding a drink which he would try and knock out of her hand. He would then have an imaginary line, like an imaginary wire, the ball would follow on its way through the posts to Doris.
I’ve always assumed that the best kickers would focus on a particular part of the ball with which they would aim to make contact, rather than just focusing generally on the ball. I’d not seen any evidence for this, until I read a recent quote from Dave Alder, the Wasps fly half: “I was once practising with a set of six (balls) and something didn’t feel right about one of them. It was only after I’d been kicking for a while that I realised the logo on the ball had been printed upside down”.
If you could get a ball marked up with lots of different sectors, it would help those learning to kick to discover which parts of the ball they should be focusing on in order to execute the desired type of kick.
David Donner
Rugby and Sports Vision
Few sports demonstrate the interaction between vision and action better than rugby. And rarely has this been better highlighted than in England’s second try against Australia at Twickenham recently.
When Ben Youngs had the opportunity to clear the ball into touch from his own try line, he realised that Quade Cooper had over-committed himself. Instead of passing the ball immediately, Courtney Lawes drew the tackler first. Chris Ashton initially thought of going outside Drew Mitchell, but realised that the Australian was backing off, so cut infield to score under the posts.
These were split-second decisions made on analysis of the defender’s body position, as well as awareness of the positions of support attackers. There’s no time to think, which means that these decisions have to be made instinctively. And the only way to achieve that is through hours and hours of relevant practice.
Yet so much rugby coaching concentrates on teaching the skills in isolation. How much time is spent learning to pass the ball without any opposition? How many second-row forwards are given the opportunity to learn the skill of timing a pass from reading the defender’s body position, as opposed to always running with their head down? It’s perhaps no coincidence that Lawes, like Simon Shaw, came late to rugby. Both of them learned their ball-handling and spatial awareness skills though basketball and other sports they played as youngsters.
These skills can be, and probably need to be, learned from a young age. Playground games of tag, and other park or street games are an ideal start. They’re fun, largely unstructured, and have most of the required elements. Small-sided rugby games do a similar job.
When Courtney Lawes was young he used to accompany his dad to martial arts training, and judo, in particular is really useful for learning how to tackle, and be tackled, without being injured. A prime example is Thierry Dusautoir, yet another forward who didn’t take up rugby until in his teens, yet had been doing judo since the age of 4. When France defeated New Zealand in the World Cup quarter-final in 2007, Dusautoir made 38 tackles. That was more than the entire All Blacks team.
There are two areas where the visual requirement is largely an aiming skill: line-outs and place-kicking. So these shall have blogs of their own.
David Donner
When Ben Youngs had the opportunity to clear the ball into touch from his own try line, he realised that Quade Cooper had over-committed himself. Instead of passing the ball immediately, Courtney Lawes drew the tackler first. Chris Ashton initially thought of going outside Drew Mitchell, but realised that the Australian was backing off, so cut infield to score under the posts.
These were split-second decisions made on analysis of the defender’s body position, as well as awareness of the positions of support attackers. There’s no time to think, which means that these decisions have to be made instinctively. And the only way to achieve that is through hours and hours of relevant practice.
Yet so much rugby coaching concentrates on teaching the skills in isolation. How much time is spent learning to pass the ball without any opposition? How many second-row forwards are given the opportunity to learn the skill of timing a pass from reading the defender’s body position, as opposed to always running with their head down? It’s perhaps no coincidence that Lawes, like Simon Shaw, came late to rugby. Both of them learned their ball-handling and spatial awareness skills though basketball and other sports they played as youngsters.
These skills can be, and probably need to be, learned from a young age. Playground games of tag, and other park or street games are an ideal start. They’re fun, largely unstructured, and have most of the required elements. Small-sided rugby games do a similar job.
When Courtney Lawes was young he used to accompany his dad to martial arts training, and judo, in particular is really useful for learning how to tackle, and be tackled, without being injured. A prime example is Thierry Dusautoir, yet another forward who didn’t take up rugby until in his teens, yet had been doing judo since the age of 4. When France defeated New Zealand in the World Cup quarter-final in 2007, Dusautoir made 38 tackles. That was more than the entire All Blacks team.
There are two areas where the visual requirement is largely an aiming skill: line-outs and place-kicking. So these shall have blogs of their own.
David Donner
Wednesday 10 November 2010
OCT Scanning
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
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
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
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