Follow us on

Visual Stress & Colorimetry

Coloured overlays
Tinted glasses with different colour
Woman looking into the colorimeter

What is visual stress?

Visual stress, a light sensitive condition that contributes to visual perceptual problems, impairs reading and can also be the cause of headaches, feelings of nausea or tiredness when reading.

Visual stress is also known as Meares-Irlen Syndrome.

People who suffer from this condition often find it difficult to focus on closely designed patterns, such as stripes or multi-patterns for instance. They may also suffer from problems of glare and feel uncomfortable in bright daylight or sunlight or under fluorescent lighting conditions.

Although present in 20 percent of the population to some extent, visual stress may not be recognised as a serious hindrance until it comes to coping with small repetitive black print on a white background, or with a volume of reading.

Many children who suffer from visual stress are often unaware that they see the page differently from others, until someone applies an appropriate coloured overlay (colorimetry) or prescribes precision tinted lenses. Then they often exclaim how words stop moving and how the page appears clear and still. Particularly with children, they don’t know what they see isn’t normal.

Some people do not recognise the severity of the problem, until it comes to a volume of reading at exam times for instance, when the inability to focus for a long period of time without becoming tired or suffering perceptual difficulties, suddenly arises.

The underlying photosensitive syndrome is also frequently involved in various neurological disorders that affect the visual cortex of the brain such as migraine, photosensitive epilepsy, autism, multiple sclerosis, head injury and stroke.

What is colorimetry?

Colorimetry is used to explore colour to find the optimal tint which provides relief of visual stress.


Joanna Williams is our Senior Optometrist and an expert in colorimetry and visual stress. She has many years’ experience using a colorimeter and regularly visits children in schools to screen for the condition.

What tests do we offer?

We have two tests available.

Optometrist Joanna with coloured overlays
Joanna visiting a school with the coloured overlays

The first is an assessment using coloured overlays, which is usually carried out on children as a screening test. This can be done by Joanna at Sudbury, Halstead or Haverhill and costs £20 or free when booked with an eye test.

The second uses the Intuitive Colorimeter and provides a specific tint for spectacles if required. This can only be done at the Sudbury practice. The cost for this is £50. Should you require tinted spectacles, you will require an up-to-date eye examination prescription.

The cost of single vision Precision Tinted lenses is £189, less the value of any voucher that you are entitled to, plus a frame.

What happens during a colorimetry assessment?

An overlay assessment lasts about 30 minutes and is carried out by Joanna. A variety of coloured overlays are shown to identify the colour which reduces the symptoms of visual stress the most. A Wilkins Rate of Reading Test is then carried out to assess if the coloured overlay improves the reading ability. If there is an improvement, this chosen overlay colour is prescribed to be used for reading over the next four to six weeks.

If using the overlay significantly improves reading, the next test we recommend is an Intuitive Colorimetry Assessment. This allows precision tinted lenses to be prescribed in glasses.

At this appointment, Joanna will find the exact hue (colour) and saturation (darkness of colour) that helps relieve the visual stress symptoms. This piece of equipment can prescribe from up to 100,000 colour combinations. Spectacle lenses are then tinted in this exact colour and can be used for reading as well as looking at computer screens and whiteboards.

The optimal colour which will benefit each individual can change over time, especially with children. It is therefore important that the patient visits regularly for re-evaluations.

For more information, see our printable information sheet about Colorimetry.

The Science of Colorimetry

Watch Optometrist Joanna Williams explain the Science of Colorimetry below. Joanna is an expert in visual stress and offers coloured overlay assessments at Sudbury (Suffolk), Halstead (Essex) and Haverhill (Suffolk); and colorimetry only at the Sudbury practice of Wardale Williams, the only opticians in the local area who offers this – call to make an appointment.

Sudbury 01787 372 492
Halstead 01787 472 209
Haverhill 01440 761 922

Frequently Asked Questions (FAQs) about colorimetry and visual stress

All or some of the following symptoms may be present:

  • Words moving, blurring or going double
  • Letters changing size or shape
  • Patterns or halos of colour in text
  • Red, sore, watery eyes
  • Headaches when reading

Signs to look out for that may indicate visual stress:

  • Misreading text or reading words in the wrong order
  • Missing out words or whole lines of text
  • Losing the place on a page when reading
  • Tiring quickly when reading
  • Moving closer to or further away from the book
  • Moving the book around on the desk or fidgeting continuously
  • Using a finger as a marker on the page
  • Rubbing eyes or blinking frequently when reading
  • Poor comprehension of reading content

Some people may have all these symptoms but often people only suffer with one or two. It’s also harder for children to describe their symptoms or for them to know that what they’re seeing isn’t normal.

No. Dyslexia is a specific learning difficulty which causes the person with the condition to have problems with reading, writing, spelling as well as other things. People with dyslexia often suffer from visual stress and can benefit from overlays or tinted lenses. However, you can have visual stress but not be dyslexic.

We can diagnose and treat visual stress but not dyslexia. If a patient is diagnosed with visual stress and is struggling in other areas than just reading, we would advise a referral to a:


  • Psychologist specialising in specific learning difficulties (SpLD) registered with the Health Care Practitioners Council (HCPC). These are usually called Educational Psychologists.
  • Specialist teacher/assessor with AMBDA and/or an Assessment Practising Certificate (APC).


More information can be found on the British Dyslexia Association’s website.

The degree of improvement for each person differs. Some people experience improvements in reading age of one to two years very quickly. In others, the lenses may make it easier to read, but the improvement may be less dramatic because of other difficulties.

We have had some great success stories. You can read the story of Ethan here.