How did you become involved in the field of visual stress?
Professor Bruce Evans (BE): When I first qualified in 1980, I was working in a new town. This involved seeing lots of children, including those with dyslexia, and I became aware that some of these children had unexplained symptoms including blurring and moving text when reading.
I did all the optometric tests to investigate, and often did not resolve their problems. This spurred me on to research dyslexia and vision, and, in particular, the claims that coloured filters helped.
These claims did not make much sense to me, but I then came across the work of Professor Wilkins. I think he was the first scientist who took these claims seriously in the UK. He approached the topic with an open mind, and asked whether there was something in the claims.
We collaborated in the 1990s in the first randomised trial of tinted lenses, and we have been working together intermittently on various projects ever since.
"When you place two colours side by side very fine differences in colour are just noticeable. We have never claimed that judgements in the colorimeter are as fine as that"
Professor Arnold Wilkins (AW): In 1973, I was asked to see a patient who had seizures whenever she looked at striped lines, and I became fascinated. I realised that it was not as rare as we thought and was a component of a lot of photosensitive epilepsy.
I learned that the factors that promote seizures were very similar to the things that cause headaches, and that led to a discovery that text was a stimulus.
Over the years there had been isolated cases of pattern-sensitive epilepsy being treated by coloured filters. When Helen Irlen made her claim that some reading difficulties could be treated using her colour filters, known as the Irlen Method, I thought it was worth investigating. And although they are not a panacea for dyslexia at all, they do have the ability to treat visual disturbance for some with reading difficulties.
With this knowledge in mind, I developed the colorimeter, as a means to finding a tint, because a lot of people could not afford the Irlen Method.
Through the development phase, we needed apparatus that allowed people to compare different chromaticities. We discovered that, for many people, the tint needed to be reasonably precise, and that meant that we needed a set of filters that could reproduce a wide range of colours.
Visual stress and the Intuitive Colorimeter have attracted some controversy recently. Why is that?
AW: The recent controversy seems to have been orchestrated by one or two individuals, and there has been a paper in Ophthalmic and Physiological Optics (OPO) arguing that colorimetry is unreliable.
If it were true it would be a knock-down argument – but it is not true. The reason they think it is unreliable is that they are using the wrong measure, which is just noticeable difference.
When you place two colours side by side very fine differences in colour are just noticeable. We have never claimed that judgements in the colorimeter are as fine as that. What we have shown in a follow-up to that study is that the u’ v’ chromaticity has to be within 0.02 – which is slightly better than when a healthy individual is trying to remember the colour.
BE: I think you can explain the controversy in a number of ways. The first relates to who we treat with coloured lenses. My response is that we treat people with visual stress, and the latest evidence is that it is one in five people with dyslexia. Other people have said that this is a treatment for dyslexia, but this is not the case. Apart from a few extreme people, those of us in this field have never argued that. If you look at coloured lenses as a treatment of dyslexia, they do not work – 80% of dyslexic people do not have visual stress.
It is also important to consider when people first experience the problem. My belief is that usually it is only when children get to a certain age, when they are looking at more text, and if they are looking at it for long periods. If you get them to look at text for a short period, you will not get the effect.
Third, we need to consider what helps patients. As we have heard from Arnold, in some cases, they need to be precisely defined, although not in every case. If you use a system that does not cater for that precision, then you will underestimate the benefit from coloured filters.
The fourth reason for controversy relates to our understanding of the mechanism for visual stress. This is where Professor Wilkins’ work has been ground-breaking, uncovering the mechanisms of cortical hyperexcitability.
Academic papers can paint a confusing picture at first glance. The recent review by Peter Allen and I concentrated on studies of people with visual stress, using methods allowing precision, and appropriate outcome measures, and found that nearly all this literature supported the use of coloured filters.
Another review looked at whether colour filters treat reading difficulties. It included research with participants who did not have visual stress who were studied with inappropriate methods and which came up with a negative view. In my opinion, this is not surprising. We need to think about whether the review is asking intelligent and appropriate questions.
Where there is agreement between supporters and detractors of colour filters is that these are not a treatment for dyslexia. This is true of all optometric interventions: optometrists do not diagnose or treat dyslexia and claims that they do are ultimately counter-productive to the more modest role that optometrists can play.
When you talk to clinicians that work in this field, they have come across many children for whom coloured lenses do help. We do need to factor in referral bias; I think visual stress is not as common as those who receive referrals of people with visual stress symptoms think it is, but it does exist. And is more common than the ultra-sceptics argue, who say that it does not exist.
There is I think a reasoned position between the two extremes. There is not good evidence to suggest that we can treat dyslexia, but equally it is unreasonable to argue that vision is irrelevant to reading or that visual stress cannot impact on comfortable reading.
Can you tell us about the newly launched Intuitive Colorimeter Curve?
AW: The new product is the brainchild of a knowledge transfer partnership between Cerium and the University of Essex. I designed the original requirements, a colleague at Essex designed the electronics, and another partner built the software. It is a collaborative effort – I guided it through.
The Curve is based on LED technology. Most of the lighting we have in the world will be LEDs by the end of the decade, and we wanted to make sure that the type of light used in the machine was the same as that being used in the general environment.
We have created a digital machine that is controlled by a tablet. The tablet takes the optometrist through the process of colorimetry assessment, gauges how reliable the patient’s response is and specifies what trial lenses are needed. It makes the process more efficient.
What is your view on professional bodies’ guidance on precision tints? What impact has it had on the perception of this intervention in the profession?
BE: I think the guidance produced recently by the professional bodies is useful, and it is helpful for optometrists to have that guidance.
As you would expect, the emphasis is slightly different: the College of Optometrists (CoO) takes a more cautious, academic view; the AOP’s advice is more clinician- and user-friendly.
Both guidelines make important points, including that precision tints are not a treatment for dyslexia, and that practitioners need to rule-out conventional optometric problems first before using precision tints. This can’t be stressed enough. If you see a child that is reporting issues, first we must look for routine factors like refractive error and binocular vision problems. We should only look at colour as a potential treatment once we have ruled out these factors.
In the CoO advice, it highlights the need to make it clear to the patients and their family that the evidence for precision tints is not strong. In reality, this is something that optometrists need to do with most things – it is not specific to this area of practice.
I would argue that many things that optometrists do, don’t have strong evidence for them. In a 2018 Optometry in Practice paper, 10 commonplace optometric activities are highlighted. If you ask the question, ‘how many of these activities has strong evidence?, it is only two or three. That’s understandable in that the risk of optometrists’ practice is lower than the risk of drugs and surgery. But it does mean that we need to convey uncertainty to patients and explain what is controversial, and to explain evidence-based practice.
Do you think that the message about dyslexia and visual stress misconceptions is getting through?
AW: There is always more that can be done. There is a whole range of disorders that involve the visual cortex that are neurological in origin, where tints might offer some help, although tints won’t help all of those with the disorder.
There is something called visual stress that is co-morbid with a lot of neurological conditions that might affect vision. Until we can better identify visual stress as an entity, we are not going to be able to identify the right people and treat them.
"I would like to get back to researching visual stress. We recently applied for a grant to carry out a randomised control trial of coloured lenses for visual stress. This was unsuccessful, but we are working up another application. We really need a big, multicentred randomised trial"
What projects and research ambitions do you have currently?
AW: I am looking at text from the point of view of its being an uncomfortable stimulus. The mathematics of text shows it is an unnatural stimulus that is difficult for the brain to process. Before long, we should be able to produce, mathematically, text that is easier on the eye.
BE: At the Institute of Optometry (IoO) we offer the professional doctorate – and we have had a bumper year of six optometrists awarded their Dr Optometry in the last year, which has kept me very busy as the director of research.
However, I would like to get back to researching visual stress. We recently applied for a grant to carry out a randomised control trial of coloured lenses for visual stress. This was unsuccessful, but we are working up another application. We really need a big, multicentred randomised trial.
About the interviewees
Professor Arnold Wilkins (AW) is professor emeritus in the department of psychology at the University of Essex. He designed the Intuitive Colorimeter, which was launched in 1993, and was a co-lead on the new Intuitive Colorimeter Curve. Professors Arnold Wilkins, Bruce Evans and Peter Allen are co-authors of the book, Vision and reading difficulties.
Professor Bruce Evans (BE) is a community optometrist in Essex, director of research at the Institute of Optometry, and visiting professor to City, University of London and London South Bank University