Pritam Dutta, M.Optom, FAAO

Instructor Neuro-Optometry, Vision Science Academy

Background

Meares–Irlen (MI) syndrome or visual stress syndrome is a perceptual processing difficulty characterized by difficulties with reading and symptoms of eye strain and headaches. It is accompanied with visual perceptual distortions such as blurring, double patterns and movement of print on the page. Meares–Irlen syndrome (previously known as scotopic Sensitivity syndrome) is more likely prevalent in dyslexics.⁽¹⁾ However the symptoms would also include lack of concentration while reading along with page text appearing too bright, pattern distraction from space between the lines and the words, slow in reading fluency after a prolonged exposure, headaches on viewing text with pattern or flickering lights, visual fatigue with prolonged exposure to reading, colours and shapes pattern appearing on the reading page. ⁽²⁾ Changes in the visual cortex as deficits in the magnocellular system (responsible for reading and coordinating the visual cortex information on movements) are the underlying pathophysiology of MI syndrome. ⁽³⁾

Role of coloured lenses in Meares-Irlen syndrome

Existing literature suggest that the symptoms mitigate with usage of coloured filters of a specific tint (Table 1). Filters and coloured lenses are generally recommended for transforming the light spectrum and reducing the intensity between light and dark to aid visual and retinal photoreceptor adaptation. Moreover, since coloured lenses were one of the recognition methods proposed to evaluate MI syndrome, it was indeed a confusing factor.

Table 1: Recent research on Meares–Irlen syndrome and coloured lenses using variable mode of intervention

It is hypothesized that the pyramidal neurons share inhibitory interneurons and a strong stimulation to it might lead to local depletion, resulting a spread of excitation.⁽⁹⁾ This spread of excitation leads to inappropriate firing of cortical neurons causing perception of illusions and distortions. Therefore, by means of topographic encoding of chromaticity in the cortical areas, the colours reorganize excitation with large deviation in spectral sensitivity of cortical neurons. Thus, colours that are comfortable reduce the excitation in hyper-excitable areas. ⁽¹⁰⁾ Moreover, apart from colours, few modifications in the working environment can also be made to enhance their daily activities (Table 2).  

Colour selection using Intuitive colorimeter

The colour of the lens could be selected using an instrument called Intuitive colorimeter (Figure 1) that illuminates the text page with coloured light permitting the saturation, hue and luminance to vary self-sufficiently.^(11,12) The optimum amount of tint required can be matched using the trial-coloured lenses. These lenses do have a property of smoothly varying spectral transmission, minimizing metamerism under various lighting condition. ⁽¹³⁾ However, the detailed steps of examining with intuitive colorimeter are as follows: ⁽¹³⁾

(i) The optimal chromaticity is selected using the Intuitive Colorimeter. At first, 12 different hues are compared. The saturation of the hues that enhance vision is optimized, and the results are compared. Although hue and saturation are alternately changed by small amounts to find the best chromaticity, the eyes remain colour adapted.

(ii) A computer programme is used to determine the best tinted trial lens combination.

(iii) The patient is given the trial lenses and the combination is changed if desired.

(iv) The (calculated) colour prescription is comprised of a series of lenses that is sent to a dyeing company.

(v) To attain the ideal spectral transmission, spectacle lenses are submerged in two dyes.

(vi) A Spectroradiometer and computer software monitors the transmission and then provides the prescribing practitioner and patient with customized details.

(vii) The practitioner visually inspects the colour of the supplied spectacle lenses using trial lenses.

Figure 1: The Intuitive colorimeter

(courtesy: https://ceriumvistech.com/colorimetry-protocol/)

Table 2: Methods of adapting modifications in school environment for MI individuals

References:

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2. Evans, B. J. W. Dyslexia and Vision. Whurr, London. 2001
3. Pieh CH, Lagréze WA. A critical view of alternative methods for treating visual complaints. Ophthalmologe.2008;105(3):281-4
4. Chang M, Kim SH, Kim JY, Cho YA. Specific visual symptoms and signs of Meares-Irlen syndrome in Korean. Korean J Ophthalmol. 2014; 28(2):159-63.
5. Kim JH, Seo HJ, Ha SG, Kim SH. Functional magnetic resonance imaging findings in Meares-Irlen syndrome: a pilot sudy. Korean J Ophthalmol. 2015;29(2):121-5.
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10. Xiao, Y., Wang, Y., Felleman, D.J. A spatially organized representation of colour in macaque cortical area V2. Nature 421 (6922). 2003. 535–539.
11. Wilkins, A., Nimmo-Smith, M.I., Jansons, J. A colorimeter for the intuitive manipulation of hue and saturation and its application in the study of perceptual distortion. Ophthalmic Physiol. Opt 12. 1992; 381–385.
12. Wilkins, A., Sihra, N., Nimmo-Smith, I. How precise do precision tints have to be and how many are necessary? Ophthalmic Physiol. Opt 25. 2005; 269–276.
13. Wilkins, A.J.Reading Through Colour. John Wiley and Sons, Chichester. 2003