What does the colour of your tinted overlay or reading ruler mean?
The link between coloured overlays and vision for learning.
Research has shown1, 2 that coloured overlay preference is related to the overlay users’ visual development; the difficulty the eyes have in focusing and working together. It is possible to estimate the degree of a reading difficulty by the choice of colour. When the distraction of light is reduced and managed by the coloured overlay reading does get easier, it is important to remember that the tinted overlay is treating the symptom (light sensitivity) and not the cause (binocular imbalance and/or reduced contrast sensitivity). Optometry intervention will treat the cause and will reward the patient with a higher learning potential.
In summary, coloured overlays work in two ways: they will either:
- reduce the levels of reflected light off a white page (light sensitivity – choosing blue, green, purple or grey tints) and/or
- increase the contrast of black letters against the background of colour (contrast sensitivity – choosing yellow, brown, pink or orange tints).
Colour preference is influenced by light sensitivity. In general, light sensitive individuals will choose grey, green or blue and reject yellow and orange. This is likely to be because yellow, pink and orange are at, or near, the peak spectral sensitivity of the eye, but even green can sometimes be too bright for some people. Many youngsters have reading difficulties just because of light sensitivity and glare from a white page in bright indoor light. If for instance, the two eyes are not perfectly aligned, have a tendency to turn out for example, it requires a lot of energy to keep them working together to stop double vision. If bright light is then shone into their eyes it really is the straw that broke the camel’s back. Eyes that are struggling to see suddenly can’t cope with the extra distraction (bright light) and binocular vision begins to break down. This translates to an aversion to bright light. Loving blue and hating yellow is diagnostic of clinically significant light sensitivity (blue tint absorbs the fierce yellow light).
Contrary to what may be expected, loss of contrast sensitivity can have an effect on colour preference even in someone who is naturally light sensitive. The light sensitive individual may still choose a yellow overlay with all its brightness because the gain of increased contrast outweighs the gain of reducing light sensitivity – this individual is crying out for visual help.
Poor vision can be caused by a binocular vision problem or a focusing problem, or a combination of both. In some people this can be so difficult that it prevents the eye from developing normal sensitivity to details around them (amblyopia). This can be measured as a loss of contrast sensitivity. People experiencing loss of contrast sensitivity would likely pick an overlay from the colour range towards the top of the table shown below (yellow, pink, orange and green to a lesser degree) to enhance contrast. A bright contrast is achieved by absorbing blue and ultraviolet (UV) light. A great example of contrast is in tennis; the yellow tint in a tennis ball transmits the colour yellow and absorbs the colour green in grass increasing the contrast between the object and the background. Contrast sensitivity is related to visual development. If vision is impeded during the formative years it prevents the eyes developing really sharp vision. People with good contrast sensitivity can see well in poor light when the contrast between the print and its background is reduced. Amblyopia is the word, which is often used to mean poor contrast sensitivity.
The brighter the light the better the contrast. The visual system is very sensitive to edges that are defined by the contrast between the edge and its background. Sharpness of vision or contrast sensitivity develops in infancy. The cells in the visual cortex and the number of their connections to other cells is directly dependent on the quality of visual information coming from the rods and cones (photo receptors) in the retina. It is also dependent on the combined information from the two eyes. This gives us even higher levels of visual performance including depth perception and positional sense. Any lessening in the quality of visual information contributes to loss of contrast sensitivity.
The cause of light sensitivity is a binocular deficiency. Binocular vision controls eye tracking skills, eye teaming skills, visual-motor integration (eye hand coordination) and visual perception (visual memory, visual form perception and visualisation). The need for a coloured overlay is a very important indication of deeper visual problems.
What does your overlay or reading ruler colour mean? Why did you choose that colour?
The further down the table of colours (wavelengths) the greater the degree of text/page contrast reduction, conversely the higher up the table you go the greater the user will enjoy a higher level of contrast.
Tints chosen from higher up the table are less suitable for light-sensitive individuals compared to the tints in the bottom section of the table.
An individual may require high levels of contrast and be light sensitive – what happens then? One visual need overrides another until your visual performance is improved by correcting the binocular or focusing problem. In our son’s case, although he was extremely light sensitive (requiring the lights in the testing room to be turned off) he chose yellow in his desperation to gain more contrast on the page. With the use of tinted prism lenses and magnification (a secondary effect of positive lenses used to help focusing) his light sensitivity reduced significantly and he is now in the final eye development stage and wears the neutral wavelength grey tint just to take a little of the brightness out of his world. Oli’s tint progression is a classic illustration of how colour preference changes as visual performance improves. He now reads faster, spells more accurately, can understand and remember more of what he reads and all his senses are functioning at a far higher level, he can even hear better.
The need for and use of a coloured overlay (especially when a tinted reading ruler is needed to follow the sentence) is diagnostic of a binocular vision and/or a visual development anomaly (abnormality). The coloured overlay or reading ruler user should seek help and assessment from a Schoolvision practitioner who is experienced in the use of the Eye Bright colour preference test. Unfortunately this type of testing is not yet included in the N.H.S. eye test. A Schoolvision optometrist will test: binocular vision at near point, Eye Bright colour preference, reading speed and contrast assessment. None of these tests are performed in the standard NHS eye test resulting in critical eye abnormalities being missed that are proven to cause learning difficulties.
This article was compiled using a great deal of technical knowledge, research and statements written by Geraint Griffiths MSc Optom, MCOptom (Managing Director of Schoolvision and practise owner of Optical 3 in Leicester). http://www.sportvision.co.uk/school/
The article was inspired by our family’s personal experience: Our son was struggling in most areas of his little life and was given a 20/20 perfect NHS vision eye test result from a high street optician. Unhappy with the outcome I felt there was something unanswered in my son’s visual system. It turned out that there were huge problems with his vision that were directly affecting his ability to learn. These visual difficulties were identified by the Schoolvision optometry assessment. The outcome of the assessment had immediate positive results: improvements socially, academically, physically, in speech, hearing and processing. It is unfortunate that the series of tests performed by Schoolvision are not part of the NHS eye test – the learning outcomes of so many children are being cut short by an NHS eye test that spends precious little attention on the way the eyes work at the near point. If your child is using coloured overlays or reading rulers I would urge you to book in with the Schoolvision team, you may be surprised at what has been missed in your child’s previous NHS eye tests.
Contrast: Contrast is the difference in the reflected light or colour from an object clear enough to be recognised, compared with its background. Contrast sensitivity refers to the ability to detect differences between light and dark areas; therefore, if you have low contrast sensitivity increasing the contrast between an object and its background will generally make the object more visible. Black objects or print against a white or yellow background usually provide the strongest colour contrast.
Light sensitive: some people have problems with certain levels of light, with some being more light sensitive than others. Many eye conditions can make people more sensitive to light. We need light to see around us and to tell us what colour things are. Light bounces off of things around us and different objects reflect different amounts of light. There are times when the amount or quality of light can affect our ability to see and read. Too much light can cause problems with glare.
Binocular vision: ‘bi’ means ‘two’, ‘Ocular’ means ‘eye’ – this is vision with two eyes. Most people use two eyes all the time so it is not sufficient to measure one eye then the other. It is the way that the two eyes work together that causes most of the problems. This process is highly complex in neurological terms and it is surprising that most people do not regard binocular vision as a potential source of problems. Prism is used to balance the way the two eyes work together. If one eye has a tendency to turn out a prism is placed in front of it (with the thick edge near the nose, incorporated invisibly in the glasses) to bend the light in. In this way the two eyes can work comfortably together. This does not require eye exercises, the spectacles just support the weakness the eye was born with. In truth, none of us were born with the ability to spend all our time looking at books or computers or worse still smart phones (even smaller, brighter and nearer). This is purely a modern IT era problem. Binocular vision controls eye tracking skills, eye teaming skills, visual-motor integration (eye hand coordination) and visual perception (visual memory, visual form perception and visualisation).
1G.W Griffiths 2001. Colour preference – a comparative study. Optometry Today vol. 41:20
2G.W Griffiths 2003. Prescribing tints – measuring colour preference in practise. Optometry Today Vol. 43:19
Article copyright of authors Lisa Bochenek and Geraint Griffiths. February 2018. This article may not be reproduced without written permission from the authors.