Intuitive Colorimeter: Technique for the 21st century?

The intuitive colorimeter is a device that is said by its proponents to provide the best means of prescribing colour to alleviate visual stress. Kriss and Evans for example state that ‘people almost invariably report more benefit from precision tinted lens than from coloured overlays because precision tinted lenses are easier to use (eg with white boards and when writing) and because colour can be prescribed with more precision’(1)

In a lecture hand-out, Bruce Evans has argued that the Intuitive Colorimeter Mark III is the 21st-century method for assessing visual stress. So I thought it would be worth assessing the evidence for this device.

Random letters (why?) illuminated in the Intuitive Colorimeter

The intuitive colorimeter is, in essence, an illuminated box with an aperture for viewing text. The hue and saturation of the light in the box can be changed. The light source is a halophosphate fluorescent tube. Rotating the dial alters the filter condition to change the illumination of the text which consists of random letters (why?) The colorimeter setting can then be assessed against a set of trial lenses which are then be prescribed in the form of glasses - so called precision tinted lenses.

So what is the evidence for lenses prescribed with the intuitive colorimeter?
I have been able to identify a hand-full of trials(2)(3)(4) (5)(6) which address this issue. Taken together or individually they do not amount to a compelling case for the use of the intuitive colorimeter.

The trial by Wilkins and Colleagues published in 1994 in the Ophthalmic and Physiological Optics in 1994 is often cited in support of precision tinted lenses even though it is a negative or at best inconclusive study. 68 poor readers with visual stress, diagnosed according to the criterion of voluntary sustained use of overlays, were enrolled. All subjects were tested with the intuitive colorimeter and their preferred tint identified. They were also prescribed a closely related tint which did not ameliorate their perceptual distortions.

The study had a crossover design and subjects were randomised to use experimental tint or placebo tint first.
Unfortunately, the dropout rate from the study was so high that it is not possible to draw meaningful conclusions. For the 45/68 for whom reading data was available, there was no difference in reading speed accuracy or comprehension comparing preferred lens with placebo lens. Interpretation of the symptom diaries is even more problematic because data was only available for 36/68 subjects. Using experimental lens 71% of days were symptom-free and with the placebo lens 66%. An unimpressive set of results when you remember that nearly 50% of the data is missing 

Perhaps the most striking result is that 31 preferred the first lens and 17 the second; a difference that is highly significant and suggestive of novelty or Hawthorne-effects.

The trial by Mitchell and colleagues published in 2008 was a parallel groups study with a control group of 17 who received no lens, a placebo lens group of 15 and an experimental lens group of 17 who received their chosen tint as determined with the Intuitive Colorimeter.

The subjects were individuals with reading difficulties who complained of visual distortions so the diagnosis of visual stress was purely symptom based.

The outcome measures were symptom scores from the Irlen Differential Perceptual Scale and the Neale analysis of reading Test. There was no difference between the experimental lens or placebo lens groups for any of the measures although there were differences with the no treatment control group which is suggestive of a strong placebo effect.

Singleton and Trotter 2005 Like many studies in this area, this study starts with a small group which is divided into even smaller groups. As a result, the statistical power of the study is limited.

There was a total of ten students with dyslexia of whom 5 had visual stress and there were ten normal readers of whom 5 had visual stress diagnosed according to the Visual Processing Problems Inventory VPPI. There was no placebo control group. The study was a crossover design that compared lenses prescribed with the intuitive colorimeter against no lens. The outcome measure was the Wilkins Rate of Reading Test.

The only group to show some improvement were the five patients with dyslexia and visual stress  However there are a number of serious problems with this study which include. Small sample size and no placebo control group.

The external validity of this study is poor because subjects were recruited via the disabilities service of the University and included subjects who may have been aware of the potential benefits of colour. Finally, because the WRRT is a non-standardised reading test and it is not clear if the results can be generalised to naturalistic text.

Machlachlan  Yale and Wilkins 1993 wasn’t a controlled trial at all. Fifty-five subjects were recruited. Twenty-three of the cases were volunteers responding to an article in 'Living magazine' and the remainder were referrals from educationalists, psychiatrists and neurologists. As a result, external validity is likely to be low.

The criteria for diagnosing visual stress was awareness of visual distortions, sustained use of overlays and having chosen a colour with the Intuitive Colorimeter.

The outcome measure was what percentage continued wearing glasses over 10 months. 82% reported that they were still using the glasses 10 months later. 

Unfortunately, this based on self-report and is unreliable. The external validity of this study is questionable because of the way the subjects were recruited and finally.. so what?

Simmers et al 2001. This study comes from a reputable psychophysical laboratory at Imperial College. It has been reviewed in a previous post. Instead of using text it looks at the kind of geometric patterns that are said to be most aversive in visual stress. The authors found no difference between subjects with visual stress and controls. In those cases with visual stress no difference in aversive symptoms when using precision tinted lenses.

So -Intuitive ColorimeterTM method for the 21st century? If you believe that you will believe anything.

1.         Kriss I, Evans BJW. The relationship between dyslexia and Meares-Irlen Syndrome. J Res Read. 2005 Aug;28(3):350–64.

2.         Wilkins AJ, Evans BJ, Brown JA, Busby AE, Wingfield AE, Jeanes RJ, et al. Double-masked placebo-controlled trial of precision spectral filters in children who use coloured overlays. Ophthalmic Physiol Opt J Br Coll Ophthalmic Opt Optom. 1994 Oct;14(4):365–70.

3.         Mitchell C, Mansfield D, Rautenbach S. Coloured filters and reading accuracy, comprehension and rate: a placebo-controlled study. Percept Mot Skills. 2008 Apr;106(2):517–32.

4.         Singleton C, Trotter S. Visual stress in adults with and without dyslexia. J Res Read. 2005 Aug;28(3):365–78.

5.         MacLachlan A., Yale S., Wilkins A. Open trial of subjective precision tinting: A follow-up of 55 patients. Ophthalmic Physiol Opt. 1993;13(2):175–8.

6.         Simmers AJ, Bex PJ, Smith FK, Wilkins AJ. Spatiotemporal visual function in tinted lens wearers. Invest Ophthalmol Vis Sci. 2001 Mar;42(3):879–84.