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One of the most important and unique instruments to be designed for optometry during the past twenty years is the Intuitive Colorimeter. Now used world-wide and in the UK by over 600 community optometrists, some hospital and university clinics as well as every university school of optometry,  the Colorimeter is able to predict the precision tinted lenses to alleviate Visual Stress in reading and in other neurological conditions.

Visual Stress (a condition related to light sensitivity) is an underlying cause of some people’s inability to read or read well when they often perceive visual distortions in the printed text. They may also develop headaches whilst attempting to read.

The Intuitive Colorimeter, distributed by Cerium Visual Technologies under license to the British Medical Research Council was designed by Professor Arnold Wilkins in the early nineties following substantial published research, at the British Medical Research Council.

The symptoms of the condition that can be treated by precision tinted lenses are often confused with those of dyslexia.  The precision lenses do not treat dyslexia or any other specific learning problems. They do treat Visual Stress and the two conditions must be treated separately.

There is a propensity amongst the dyslexic population however, to also suffer from Visual Stress and where the conditions run concurrently the optimum tinted lenses can be beneficial in helping towards dealing with the more complex specific learning problems.

Thousands of UK schools use coloured overlays in the classroom to help poor readers. With the selection of the optimum coloured overlay both reading speeds and accuracy can improve, sometimes dramatically. The overlays are non-invasive, cheap to provide, durable and can be used continually.  They cannot be used effectively however when copying from the board or from another book.  In these instances precision tinted lenses are more convenient.

The Wilkins Rate of Reading Test, created in the early nineties by Professor Arnold Wilkins and Manchester University School of Education’s Professor Peter Pumphrey, is used widely to determine the degree of improvement in reading speed and accuracy and before considering precision tinted lenses. The protocol within optometry for testing with overlays and prescribing precision tinted lenses from the Intuitive Colorimeter was validated by the College of Optometrists at the launch of the Colorimeter.

Claims bya New Zealand and US educationalists in the late nineteen eighties that coloured sheets of plastic and in some cases coloured lenses, helped reduce visual distortions, were met with scepticism on both sides of the Atlantic by vision and education professionals alike.  Professor Arnold Wilkins noted press reports from individuals claiming that movement in printed text had been remedied by the use of coloured overlays and lenses and cited symptoms that Wilkins recognised, from his previous research of photosensitive epilepsy in Canada, as being similar to those reported by visually induced epileptic sufferers. 

In  1990, with British government and private funding, Professor Wilkins undertook a double blind study that lead to the design of the Intuitive Colorimeter. His published work confirmed an underlying photosensitive condition that could affect reading. His research also showed the need for a wide range of colours to achieve an optimum precision tint for many. The then British government’s chief Medical Office, for simplicity, chose to entitle the condition as ‘Visual Stress’. This is the term largely accepted to describe the condition.

The Intuitive Colorimeter allows for swift selection of colour space particular to the needs of the individual. It also allows for fine tuning of hue and saturation until the optimum colour is arrived at. Presenting over 10,000 permutations of colour in strict scientific sequential order, the normal time required to arrive at the optimum colour in practice is usually 20 – 30 minutes, thereby ensuring patients are unlikely to tire before finalising their selection.

In 2011 professor Wilkins collaborated with Michigan State University in a study that induced migraine in a number of patients. Using a selection of control and other lenses to subjugate the migraine attacks, the research concluded that only the pre-selected precision lenses, chosen prior to the attacks from the Intuitive colorimeter, were capable of subjugating the activity in the brain.

Precision tinted lenses are also used to help remedy some neurological conditions such as MS, Autism and closed head injury – following stroke or heart attack (including TBI-acquired traumatic brain injury)

It is necessary that any system designed to prescribe precision tints to achieve the optimum useful colour or combination of colours must offer a wide gamut of colours. The need for this has been clearly shown by Wilkins in a recent study. He explains:

‘Children from a previous study who had used coloured overlays were asked to observe text illuminated in the Intuitive Colorimeter and again chose a colour that best improved the comfort and clarity of the text. They were then asked to change the setting of hue from optimal until distortions and discomfort began to return. The colour of the settings for the optimal benefit and the colour of the setting at which the distortions just returned were colours that were separated by an average distance of xx in the CIE diagram (xx). This distance corresponds to 6 just noticeable difference of colour (based on MacAdams elipses). This is six times the difference in colour that can just be detected when two coloured surfaces are presented side by side. When tints were presented in succession, as in this study, the colours could not be distinguished, partly because people tend to remember colours in terms of their verbal label, which was usually similar for the active and control colours.

These behavioural studies have now been corroborated by two imaging studies in which patients with migraine chose an optimal tint in the Intuitive colorimeter, and another tint, differing in colour by 6 just noticeable differences, was randomly selected as a control by computer. The patients showed an abnormal cortical haemodynamic response to gratings with mid spatial frequency, and this response was normalised with the optimal tint. The control tints had no beneficial effect, notwithstanding the small difference in colour.

Precision is possible with coloured lenses. Perhaps in consequence lenses are usually more effective than coloured overlays. Precision is not practical with coloured overlays. Nevertheless overlays are suitable in assessing whether assessment for coloured lenses is likely to be useful.

The Intuitive Colorimeter provides a large range (gamut) of chromaticities with the same spectral distribution as that obtained when the trial lenses are worn under typical artificial lighting. The lenses sample chromaticity systematically and densely, using only two dyes. Given widely reviewed literature other systems that offer less than 20 lenses are unlikely to provide an optimal tint”.

Although thousands of overlays are used in schools through the UK each year and thousands of pairs of precision tinted lenses are manufactured by Cerium Visual Technologies in their special purpose laboratory in Tenterden, Kent, and despite the Colorimeter having been in service now for over twenty years, some research academics still view the process as controversial.

Numerous small studies have been undertaken over the years, in the main by worthy professionals who have little experience of prescribing overlays in the classroom or lenses within practice.  Many of these studies have been criticised for their poor design or small number of participants.

Recently, a Review of such ‘scientific’ literature has concluded, in the opinion of its authors, that the beneficial effect of coloured lenses is due to placebo, The Review included papers that were not peer reviewed. It has also been criticised because it used the Cochrane Risk of Bias tool, which is now known to be suspect. Another recent Review has however concluded that the beneficial effect of overlays is not simply due to the effects of belief. 

The use of coloured overlays and precision tinted lenses is not going to disappear, that is clear. People have realised that sometimes they are of a great help and that consensus is sufficient to support the continuing use within education and optometry of overlays and precision tinted lenses.


The Intuitive Colorimeter, by Cerium Visual Technologies