Questions about visual stress

What is visual stress?

Visual stress refers to discomfort and perceptual distortions that occur when looking at certain patterns and text. Visual stress can affect reading and occur in other contexts as a form of photophobia.

Visual stress has been given many names. These include Meares-Irlen syndrome, pattern-related visual stress or simply visual stress. The Irlen Centers have used the terms Scotopic Sensitivity Syndrome (SSS) and Irlen syndrome. 

The methods used to recognize visual stress vary. Optometrists in the U.K. use the findings of a scientific study to guide their diagnosis: Evans, B.J.W., Allen, P.M. and Wilkins, A.J. (2017). A Delphi study to develop practical diagnostic guidelines for visual stress (visual stress) Journal of Optometry 10(3), 161-168.  There is an emphasis on avoiding misdiagnoses and over-identification. 

Guidelines from the U.K. College of Optometrists stress the dangers of making claims about the impacts of tinted lenses that are unsupported by research.

Visual stress is not the same as "visual dyslexia".


What causes visual stress?

Visual stress is probably of cerebral origin, most likely due to a hyperexcitability of the visual cortex of the brain.  The tints alter the relative activation of retinal photoreceptors and may change the distribution of activity in visual areas of the brain, avoiding local areas of hyperexcitability.


What are the signs and symptoms of visual stress?


       Fidgeting when reading

       Frequent change of reading position

       Halting effortful reading

       Watering/sore eyes

       Evident discomfort/headache




       Tiredness after reading

       Blurring, fading or movement of print

       Letters changing size

       Illusions of colour on the page


Any of the signs and symptoms of visual stress may be caused by other conditions.  It is therefore important to have a thorough eye examination.


What helps with visual stress?

A variety of measures can be used to reduce visual stress when reading:

1.             Redesign of text

       large typeface

       large spacing of lines

       fonts with low spatial periodicity such as Open Sans, Verdana, Tahoma

2.             Screens without flicker e.g. Amazon Kindle

3.             Coloured filters of various kinds, including coloured overlays and coloured spectacles


What are coloured overlays? What do they do?

Coloured overlays are sheets of translucent or transparent coloured plastic that can be placed over a page of a book so as to colour the text beneath without interfering with its clarity. They can be obtained from ioosales, Cerium Visual Technologies, Crossbow.

Coloured overlays reduce the perceptual distortions of text that people sometimes describe. They enable some people to read text more fluently and with less discomfort and fewer headaches. Each individual needs a different colour, so it is important to assess the effects of a wide range of colours.


What are precision tinted lenses?

Precision tints are spectacles with coloured lenses prescribed by optometrists who use the Intuitive Colorimeter.


Which eye care professionals provide this service?  

There are now about 600 optometrists in the UK who offer precision tinted lenses. They are listed on the Cerium site. Some are members of the Society for Coloured Lens Prescribers and are signatories to a code of conduct. They may be contacted via the Society’s site.


Could any other issues cause the same signs and symptoms of visual stress?


There are no signs and symptoms that are caused by visual stress and not by other disorders. It is therefore important that your examiner is familiar with all the disorders which can lead to symptoms similar to those of visual stress. The three eye-care professions with the relevant skills are optometrists, ophthalmologists and orthoptists.


How do registered eye care professionals assess for visual stress? 

Visual stress can be diagnosed only after problems with eyes and eyesight have been ruled out with a thorough assessment of refraction, focusing, eye-coordination and other issues. 

A person needs to have at least 3 of the following 6 typical symptoms before they can be diagnosed with visual stress. 

1.  Words move 

2.  Words merge 

3.  Patterns or shadows in text e.g. rivers 

4.  Text seems to stand out in 3D above the page 

5.  Words or letters fade and darken 

6.  Discomfort with certain artificial lights and flicker 

AND before they prescribe coloured lenses vision professionals also need to see at least two of the following three signs of visual stress from special investigations: 

1.  Voluntary, unprompted use of a coloured overlay for 3 months or more 

2.  Overlay improves performance on a specific test of reading speed (Wilkins Rate of Reading Test, WRRT) by at least 15%. This test uses small, crowded text including 10 of the most commonly occurring words in the English language. It is designed to look particularly at the influence of visual and oculomotor factors on reading rate. 

3.  Pattern Glare Test (scores above 3). This test looks at symptoms of distortion and discomfort when looking at uncoloured striped patterns.

If it is decided that a person has difficulties due to visual stress, the use of precision-coloured lenses may be considered. There is a strict protocol for colour identification and combination with Intuitive Colorimetry,


Can you see in double if you have visual stress?

Visual stress is not usually responsible for double vision, although many people do describe doubling of words on the page.


Is light sensitivity/photophobia common? 

     Light sensitivity of various kinds occurs in many ophthalmic and neurological conditions, the most common of which is probably migraine.


Do you get headaches with visual stress? 

Headaches are a common symptom but there can be many other causes for headaches.

Children may get stomach ache instead of headache as a manifestation of migraine.


What training do eyecare professionals receive to assess and treat visual stress using Intuitive Colorimetry?

Eyecare professionals are familiar with the signs and symptoms of a wide variety of eye problems and are skilled at separating visual stress from other eye disorders that have similar symptoms.

They have received individual training in the use of the Intuitive Colorimeter.

Most will have attended the courses run by the Institute of Optometry such as these


Do eye care professionals have guidelines for working with patients with visual stress?

Yes. There are clear professional guidelines and advice from the College of Optometrists. 


At what age do signs of visual stress become evident? So what is the youngest age it could be assessed?

The signs often begin when a child starts to have to read small closely spaced text.

Children aged 8 are usually old enough for assessment with the Intuitive Colorimeter, although assessment with overlays can be carried out with children who are younger.


Does visual stress affect adults?

Yes, particularly those who are required to do a lot of reading such as university students. 


Do the symptoms of visual stress only affect reading? Would they only be apparent if a person has been reading for several minutes?

The symptoms do not necessarily occur only when reading, although reading is a common precipitant.

Text often appears clear when first looked at. The symptoms can appear gradually the longer the person reads.


Is visual stress a type of dyslexia?

No. Visual stress occurs in a minority of individuals with dyslexia. The exact proportion cannot currently be estimated with precision.


Is visual stress a symptom of dyslexia?

No. It occurs in individuals who do not have dyslexia. It may be slightly more common in individuals with dyslexia than in the general population but there is currently insufficient evidence.


Is visual stress hereditary?

It can run in families and often there is a family history of migraine. The hereditary nature of visual stress has not been explored in depth.


Is there any evidence that puberty and hormonal changes affect visual stress?

It is likely that puberty and hormonal changes affect visual stress but there have been no formal studies. 


Can symptoms of visual stress disappear?

Yes. People can develop resilience to visual stress, and often choose work environments where close attention to text is unnecessary. 


Would visual stress be missed in a standard NHS sight test? 

There are no tests for visual stress in the standard NHS sight test, but most eye-care practitioners will be aware of visual stress.  There is a list of those who specialize in visual stress at the Society for Coloured Lens Prescribers and on the Cerium website.


How can visual stress be first spotted in children?

Visual perceptual distortion should be suspected in children who have trouble learning to read, particularly if they report headaches and eye-strain from prolonged exposure to the page. If the child reports any illusory movement of the letters or words, or glare from the white paper, then treatment with coloured overlays should be considered.


What questions can you ask a child to find out whether visual stress may be an issue?

One possible question to ask is: "After you have been reading for a while, do the words or letters do anything different?".  

If no distortions are reported, try more direct questions.

Ask your child to look at a page of text and ask the following questions:

       Do the letters stay still or do they move?

       Are they clear or are they fuzzy?

       Is the page too bright, not bright enough or just about right?

       Are the words too close together or far enough apart?

       Does it hurt your eyes to look at the text or is it OK?


Any instability of the text or glare from the page suggests it is worth consulting an eye-care practitioner who specializes in visual stress.


What information should you give an eye care professional if you think you or your child are showing signs of visual stress? 

You should mention the difficulty with reading and perceptual instability.


Do people who have visual stress also have light sensitivity? Do you need different treatments for these issues?

Visual stress is a form of light sensitivity.  Any sensitivity to bright light will probably be reduced by precision tints determined within a careful protocol.  The potential cause/s of any light sensitivity should be carefully assessed by an eye care professional (see below).


Is an assessment for visual stress specific to reading?

It is not specific to reading, although text is one of the provocative patterns that is used for assessment.


Is flicker from lighting a problem? 

Flicker from lighting (usually at frequencies that are too high to be visible) is a common cause of headache and eye-strain.  Take a video of the lighting using the slo-mo setting on your smart phone.   This will make most flicker visible, and having found out which lighting flickers, you can take steps to avoid exposure to this lighting. 


How would a person with visual stress cope in a standard NHS eye test? Are adjustments needed?

Adjustments are not usually necessary.

Sometimes visual stress will reduce performance on tests of binocular vision.

These tests can be repeated when wearing appropriately coloured filters to check whether the visual stress or binocular instability is the main problem.


If visual stress is a neurological issue, why should people be seen by eye care professionals?

Most eyecare professionals are familiar with visual stress and other visual-perceptual issues. They are skilled at separating visual stress from other disorders, and this needs to be done before visual stress can be diagnosed.  There is a list of optometrists who specialize in visual stress at the Society for Coloured Lens Prescribers and on the Cerium website.


Can funny visual effects from patterns be experienced by people who don’t have visual stress?

Some large strongly contrasted patterns (such as the metal tread of an escalator) can produce visual distortions in most people.


Are assessments and treatments for visual stress free? Can you be referred to a hospital or university clinic where it would be free?

There are a few orthoptic departments where assessment can be undertaken. The lenses are not generally available on the NHS


What would an eye care professional be looking for in a standard NHS eye test?

Are the eyes healthy?

What are the smallest letters that can be seen?

Are the eyes focusing correctly? 

Do the two eyes move together appropriately?


Can a person have have "perfect eye sight" and still experience distortion?

An optometrist reports "perfect eye sight" when someone can see a letter chart without needing refractive correction (glasses), and when there are no (orthoptic) problems of coordination between the eyes. The perceptual distortions may occur quite independently of any refractive error, although they are often, but not always, associated with a mild binocular vision difficulty (i.e. a difficulty in moving the eyes together, keeping the direction of gaze appropriately co-ordinated). In most cases the binocular difficulties do not appear to be the basis for the distortions.


If there are signs a person has issues with the two eyes working together, should this be treated before looking at treating issues with visual stress?

Yes. This is recommended. Visual perceptual distortions can sometimes be caused solely by binocular vision problems, so it is sensible to have these corrected first. If the distortions remain then coloured filters need to be tried.





Questions about Coloured overlays


What is the best method for combining overlays?

The best method is that which most efficiently covers the largest number of possible colours.

The Intuitive Overlays were scientifically developed so that similar colours can be combined two at a time in a simple yet thorough way. If these overlays are used and all suggested combinations are tried, a wide range of colours will have been efficiently and systematically sampled.


When are you actually diagnosed with visual stress? Is it after a coloured overlay has been trialed?

Use of a coloured overlay is one of the criteria used in the diagnosis of visual stress.

The use of a coloured overlay may not be necessary when coloured filters are used to treat adults who experience migraine with aura.


Which texts show a benefit from colour?

Overlays can increase the speed of reading, although with conventional text the improvement may only be apparent after ten minutes continuous reading when the person would begin to tire were an overlay not used. If the text is closely spaced, the benefit is more immediate. Books with large text are less of a problem, and may not need an overlay.


Does it matter if you still see areas of white page around the overlay?

No, but the conditions of the test should resemble those under which the overlay will be used. 


If you get benefit from an overlay do you need to have coloured glasses? 

No, not necessarily, although precision tints in spectacles are useful for board work and for writing.

Precision tints usually give better correction.


Do glasses need to be a specific tint for each individual?

Yes, the colour will be specific to each individual.  Other colours may work, but probably not as well.


What is the purpose of the Wilkins Rate of Reading Test? Why have easy-to-read words been chosen? Is there research to show it is a valid and reliable measure of improvement to reading speed? 

The purpose is to measure reading in a short test that is sensitive to the effects of perceptual distortions on reading performance.

The test vocabulary is familiar to children whose reading is poor.

The test is both reliable and valid (see Gilchrist, J.M., Allen, P.M., Monger, L., Srinivasan, K.,

Wilkins A. (2021) Precision, Reliability and Application of the Wilkins Rate of Reading

Test. Ophthalmic and Physiological Optics. 41(6), 1198-1208.) 

If an overlay increases reading speed by more than 15% it is likely to be used.

The effects of practice are small, and the test can be repeated.


How do you control for personal preferences and tester questioning to make sure visual stress isn’t overidentified and unnecessary products purchased?

Over-prescribing is reduced by the requirement for unprompted use of an overlay prior to the provision of precision tints and the use of the Rate of Reading Test.


Should tests to assess visual stress always involve reading horizontal text? Would a test of reading of words in vertical format show impacts of coloured lenses?

They might, particularly if the letter strokes were evenly spaced, as in the font Times New Roman, but the effects would probably be smaller than with horizontal text because of the pattern produced.


Why does an overlay have to be trialed for several weeks? Why can’t you be assessed for precision-tinted glasses when you are tested with overlays?

A trial is a way of assessing the need and ensuring that coloured lenses are not prescribed unnecessarily. It is a way of reducing placebo effects and any gender bias in the choice of colour.     





Questions about Colorimetry


How does the Intuitive Colorimeter work?

The Intuitive Colorimeter enables clients to observe text illuminated by coloured light, and permits the colour, strength of colour (saturation) and light level (luminance) to be varied separately, so that the effects of these three variables can be assessed independently. It allows the examiner to rapidly identify colours that improve perception and those that do not, and to do so while the eyes are adapted to the shade of colour.

The colorimeter specifies precisely which combinations of trial lenses are good candidates for assessment.  This colour is then replicated using combinations of tinted trial lenses. The trial lenses are designed so that any colour obtained in the colorimeter can be closely replicated. If necessary, stronger colours are also available and a selection of grey lenses can be added.

The combination of trial lenses specifies the colour and enables spectacle lenses to be dyed precisely that colour.


How are colours tested systematically with Intuitive Colorimetry? Why is this important?

The testing occurs in three stages.

In the first stage, 12 different colours are compared with white, each colour being increased in strength (saturation) and then decreased.

In the second stage, the helpful colours are refined and the best chosen.

In the third stage, the effects of light level are explored so as to check for residual glare and to see whether the chosen colour will be too dark when offered in lenses.

This procedure avoids prolonged exposure to uncomfortable visual stimulation.  


Does the Intuitive Colorimetry machine use fluorescent lighting? Would it be hard for anybody with light sensitivity to use this method?

The following publication compares the spectral power distribution in the instrument with that from lenses. Wilkins, A.J. and Sihra, N. (2000). A colorizer for use in determining an optimal ophthalmic tint. Color Research and Application, 26(3), 246-253. The decisions are quicker than those using lenses partly because small adjustments can be made while the eyes are colour-adapted.

Fluorescent lighting has a bad reputation because in the past it has flickered at twice the frequency of the AC electrical supply.  This flicker is invisible but causes headaches. Wilkins, A.J., Nimmo-Smith, I.M., Slater, A. and Bedocs, L. (1989) Fluorescent lighting, headaches and eye-strain. Lighting Research and Technology, 21(1), 11-18. Nowadays fluorescent lighting is usually controlled by electronic ballast and does not flicker in this way.  

The Intuitive Colorimeter is lit with lighting that is in common use. The lighting does not flicker or flash. The early machines used a small flicker-free fluorescent lamp (with electronic high frequency ballast). More recent machines use LED lighting.  The lamps are filtered by the same filters that are used in lenses. As a result, the spectral power distribution is closely similar to that when wearing lenses under typical lighting. The text can be varied to suit the individual. The Intuitive Colorimeter result can be ratified under natural viewing using coloured trial lenses with the same spectral transmission as those that will be prescribed.


Do Intuitive Colorimetry lenses in glasses colour everything that colour?  

Whether the lenses colour what you see depends on their saturation (strength of colour).

If the saturation is low enough so as not to interfere with the perception of colours in the world this is generally preferable. Whether this is possible depends on the extent of any reduction in symptoms by colour, and is therefore dependent on choices made by the examiner and their patient.

It is better to tint so that the patient sees no cast of colour when looking through the lenses – coloured surfaces can, and ideally should, appear quite normal. The brain then discounts the effect of the lens colour.  This is not always possible in severe cases when a strong (highly saturated) colour is necessary to remove symptoms.


Do the eyes always get used to seeing through colour? 

Usually what you see will not be coloured, and you will be able to see surface colours as normal. If the world appears coloured you can try a weaker saturation, but this may not be as effective at reducing your symptoms.


Will the colour of lenses be the same as the chosen overlay? 

The colour of your lenses is unlikely to be the same as the colour of the overlay. The lenses tint most of the visual field and the brain processes this colour differently from the colour of surfaces. The brain takes account of the colour of the lighting that illuminates surfaces so that the colour of the surfaces appears constant. These mechanisms of "colour constancy" apply when coloured glasses are worn.


Are precision tinted lenses an overlay in glasses form?

No. Overlays are a surface colour. Precision tinted lenses function as if they were a lighting colour and the brain then makes allowance for their colour so that coloured surfaces can appear quite normal.  


Will you only ever have one colour in your glasses? Why don’t you need multiple colours? 

Your lenses will appear one shade of colour, but this is made from two or sometimes three dyes. These have been chosen to maximise the light transmission while combining to make the appropriate colour.

Your lenses will reduce transmission over a range of wavelengths. 


Would you ever need different colour lenses in each eye?

This is rare and is avoided where possible.


Do children need coloured overlays or coloured glasses permanently?

It seems that children benefit most from colour if it is offered as soon as any reading difficulty is suspected, before the cycle of failure has begun. Many 7-year-olds appear to use coloured overlays for a year or two and then discard them as unnecessary. This may be because the acquired familiarity with text then makes the distortions less distracting.


Do you get prescribed a dark lens because the test takes place in a dark room?

Although the initial testing takes place in a dark room, this is to remove the effect of surrounding colours. The light in the Intuitive Colorimeter is as bright as text usually is in a well-lit room. The patient is given the opportunity of trying your lenses in several well-lit environments with different lighting.


How many colour possibilities are available?

The Intuitive Colorimeter comes with a set of tinted trial lenses that can be combined in a stack to create a wide range of colours. There are at least 5 trial lenses of seven colours.

The colours lie on a hue circle: rose-orange-yellow-green-turquoise-blue-purple-rose etc.  Neighbouring pairs of colours on this circle can be combined to create shades of colour – for example yellow and green can be combined to give various shades of yellowy green; green and turquoise can be combined to give various shades of greeny turquoise; rose and purple can be combined to give various shades of red.  

All the 25 =32 different combinations of one colour are available to be added to the 25 combinations of a neighbouring colour. Discounting the combination that constitutes 0 lenses of both colours, this makes 32*321=1023 shades available for each pair of colours.

There are seven pairs of colours in the hue circle so the total number of shades of colour theoretically possible is 1023*7=7161 shades. Rose and Purple have 6 trial lenses rather than five, and if the most saturated lenses of these colours are added, the total possible number of different shades of colour is considerably greater. Combinations using more than three lenses of any colour are rare so the combination of trial lenses does not get too dark.


Is there a protocol for combining colours in Intuitive Colorimetry?

Yes. Coloured trial lenses are combined to ensure they achieve the optimal colour. Only similar colours can be combined and this prevents the lens being too dark. If lenses of complementary colour (such as yellow and blue, or rose and green) were combined, for example, the lens would appear grey: there would be little relationship between the chosen colour and the colour of the combination.


There is a detailed scientific rationale for the manner in which tinted lenses are combined during Intuitive Colorimetry (Wilkins, A.J. (1996).

A system for precision ophthalmic tinting and its role in the treatment of visual stress. In:

C.M. Dickinson, I. J. Murray, and D. Garden (Eds), John Dalton's Colour Vision Legacy. London; Taylor and Francis, pp. 695-708.)


Is it correct that Intuitive Colorimetry lenses should just be worn when needed and, if so, why?

Precision tinted lenses can be worn whenever it is necessary to reduce symptoms, except in circumstances, such as driving or cycling, if the colour might interfere with the recognition of traffic signals. There is evidence that long-term wear changes the perception of colours slightly, but no other effects have been reported thus far.  Some patients find it comfortable to wear their lenses all the time. 


If you wear precision tinted lenses all the time will any benefits wear off more quickly than if you just wear them when you really need them?

It is best to wear the tints only when they reduce symptoms.


How quickly would you feel an impact from precision tinted lenses? Is it immediate or does it take time?

The impact is usually immediate.


Do eye care professionals who offer a specialist service to diagnose and treat visual stress produce any report for school/workplace detailing recommendations? Is a report needed?

A report for schools may be requested.  There is guidance for teachers on the classroom use of overlays and other adjustments.


Can a prescription for long-sightedness, short-sightedness etc be precision-tinted?

Yes, the coloured lenses will incorporate any necessary refractive correction.


How are colours chosen in Intuitive Colorimetry? Do you have to restrict the number of colours that are combined? Do several colours get combined in glasses to deal with different symptoms?

Two dyes (from a selection of seven) are all that is necessary to provide any colour. The combination provides the colour in the lightest lenses.  

Occasionally a grey dye is added to the combination in patients who are very light sensitive.


How do you know that the colour you choose is the actual colour you get in the glasses you receive?

They are checked with a spectroradiometer and computer program before they are issued.


How is the colour of a precision tint put on a lens?

The lens is dipped successively into two dyes (chosen from a selection of seven), each for a few minutes.


Why don’t all people with visual stress need precision-tinted glasses?

Coloured overlays are sufficient if symptoms are not severe. Some prefer coloured overlays because of the reduction in text contrast that these can provide.  


When the colorimetry assessment is taking place, do all the tests require reading?

No. None of the tests require reading.  They simply require a subjective assessment of the clarity and comfort of a page of text. The entire exploration of colour takes about 20 minutes.  


How can you be sure the Colorimetry assessment has been accurate? Are trial lenses made up and tested under different lighting conditions?

Patients are given the opportunity to try out the trial lenses under different lighting conditions, and lighting levels, including daylight.


Do you get any sorts of warnings about wearing tinted lenses? 

The lenses are issued with warnings if they are likely to affect the perception of traffic signals.

Precision tints are not sunglasses and may be unsuitable for strong sunlight.


Are colorimetry lenses CE approved? Are they patented specifically for visual stress?

The lenses are CE approved. The Intuitive Colorimeter is patented.


How long should you see a benefit from tinted lenses? Why might you need another colour?

Children should be re-assessed on a yearly basis, or sooner if symptoms return. If they return, a different tint can sometimes help. In adults the symptoms only rarely recur and tint only rarely needs changing.


Would tinted lenses act as sunglasses?

Precision tints are not a substitute for sunglasses. Discuss the options for additional tinting with your optometrist.


Would sunglasses improve visual stress if it is a type of light-sensitivity? Or glasses with grey lenses?

These may help a little but are not usually sufficient, and they interfere with vision when indoors.


Where would I find research that Intuitive Colorimetry lenses are effective for both discomfort and reading? 

The book “Vision, Reading Difficulties and Visual Stress” by A J Wilkins and B J W Evans published by Springer 3rd Edition 2024 discusses the research and the controversy. Wilkins’ publications are available here. Evans’ publications are available here.  


Can you have precision tinted contact lenses instead of glasses?

Yes, but they are expensive and suitable only for continuous wear.


Would the optometric treatment for ‘light sensitivity’ issues (unrelated to any serious visual or medical issue) be coloured lenses or would a different option be used? 

There are so many different conditions that can cause light sensitivity and it all depends on the cause. The question rules out pathological causes such as ulcers. Other causes include a problem with the eye coordination (in which case glasses or eye exercises may be helpful) or visual stress. Most optometrists these days will recognise visual stress. Some people are just naturally light sensitive, perhaps because they have large pupils, light colour irides, are prone to migraines, or just have a natural predisposition to be light sensitive. 

The conventional approach for such people is to use photochromic spectacles, or tinted spectacles that are worn when required. Typically, either a grey (neutral) tint is used, or the patient chooses a tint by looking through samples with dispensing opticians, or often based on previous preference. These are often called cosmetic tints and typically the range available will be very limited compared to precision tints. Interestingly, recent research indicates that precision tints may help people with light sensitivity due to migraine, especially the more severe form of migraine that is associated with aura. 

When people or patients say they are light sensitive they may mean different things. A high proportion of older people report light sensitivity driving at night. By this, some people mean that the glare from car headlights causes them more problems than when they were younger. One reason for this is that the lenses in the eye become less transparent (more cloudy) throughout life, so that light from the headlight is scattered in the eye causing flare or coronas (a starburst effect around lights).

Other people mean that after they have been dazzled by a car headlight, they have more problem seeing along a stretch of unlit road. This can be because our dark adaptation deteriorates throughout life, usually very slowly but rarely more rapidly due to eye diseases. Tints with a significant depth of tint should not be used in this case because, although they may reduce the dazzle from a car headlight, they will also reduce the person’s ability to see on the dark road after the car has passed. This could cause them to fail to see, for example, a pedestrian or unlit cyclist.


Would it be inappropriate for a person without medical and optical training to diagnose and treat light-sensitivity?

Overlays are non-invasive and can be trialled before an optometric assessment. If they are found to be helpful an optometric examination is essential. Training is necessary to distinguish visual stress from the other disorders of vision that have similar symptoms. 


Would the optometric treatment for ‘light sensitivity’ issues (unrelated to any serious visual or medical issue) be coloured lenses or would a different option be used? 

Precision tinted lenses have been used in many neurological conditions that affect the visual system, including photosensitive epilepsy, migraine (with aura), autism, visual snow, multiple sclerosis, head injury and possibly cluster headache. There are preliminary studies suggesting that precision spectral filters can provide symptom relief in these conditions. 


Other questions


Would increasing the size of font and spacing between letters, words and lines remove any symptoms of visual stress?

Yes, it might well do so.  And so would a change of font to a non-periodic font such as Google Open Sans, Verdana or Tahoma.


Does visual perceptual distortion cause writing to deteriorate?

The visual perceptual distortions that people experience can affect all aspects of visual function, but they are more likely when the visual material has many similar contours (letters). Text is unlike natural scenes in that it is composed of many identical elements. These are at their most confusing in small closely spaced printed text, but they also occur in handwritten work.


Is there any science or research behind the benefits of using coloured paper for any reason?  

Often fluorescent dyes are added to white paper. The dyes absorb ultraviolet radiation and emit visible light, making the paper “whiter than white”.  These dyes are not used in cream or buff paper.  Coloured paper (with a colour that suits the individual reader) presumably has an effect similar to that of coloured overlays, but can be used for writing tasks. It is likely to be more effective than cream or buff paper. There have been no scientific studies of the effects of coloured paper.


In terms of physics, how would coloured paper help with writing? 

Coloured paper will not have the fluorescent brighteners that are often added to white paper making it whiter than white (just like some washing powders).  Coloured paper can help individuals who find it difficult to read what they have written.


If a student uses precision tinted lenses would there be any need to use coloured paper as a ‘top-up’?

Just occasionally both lenses and surface colours can be used together, but this is rarely necessary.


In terms of impact on reading, is there a difference in the physics behind the impact of a coloured overlay as opposed to coloured paper?

A coloured overlay will slightly reduce the contrast of the black ink, which coloured paper will not do.