Welcome. Jeffery and Associates are an established independent opticians that specialise in personalised eyecare and designer eyewear for both you and your family.

Dyslexia & Visual Stress


Overlay and Colorimetry Assessments

Visual stress (also known as Meares Irlen Syndrome) is the discomfort some people feel that contributes to reading difficulties, headaches when reading, and eye strain.

It can cause nausea or tiredness when reading or studing for prolonged periods or times. People who suffer from this condition often also find it difficult to focus on closely designed patterns such as stripes, or on certain font types on a computer, and may feel unconfortable in bright daylight or sunlight, or under flourescent lighting conditions.

Signs include:

  • moving closer to or further away from the page when reading
  • skipping words and lines, or re-reading the same line
  • rubbing eyes and blinking excessively
  • restlessness when reading

Symptoms include:

  • Movement of print on the page
  • Print appears to be blurred
  • Letters change shape, size or colour on the page
  • Patterns appear in the print sometimes described as ‘rivers’ or ‘worms’

The cause of theese symptoms is unknown.

Visual stress can only be diagnosed after an eye examination, once other abnormalities, such as binocular vision problems, have been excluded.

Visual stress is prevelant in 12% to 14% of normal readers, but in 46% of readers with dyslexia. Many people who suffer from visual stress are often unaware that they see the page differently from others, until someone applies an appropriate overlay of prescribed precision tinted lenses, and they notice how words stop moving, and the page appears clear and still. Visual Stress and migraine – migraine attacks have many triggers, including stress, particualr foods and hormones.

About 40% of migraine attacks may be visually induced by flickering light, patterns or reading. These attacks may be helped by precision tinted lenses.

What is dyslexia?

Dyslexia varies from mild to servere and affects between 5% and 10% of the population. The current British Dyslexia Association (BDA) definition states that “Dyslexia is a learning difficulty that primarily affects the skills involved in accurate and fluent reading and spelling. Characteristic features of dyslexia are difficulties in phonological awareness, verbal memory and verbal processing speed.”

Dyslexia occurs across the range of intellectual abilities.

Coloured Overlays

A coloured overlay is a transparent sheet of plastic that can be laid over the text. It is used to decide which individuals will benefit from the colour. 12 colours, including grey, are used singley or together to produce a range of hues and saturations, and the patients is asked to report the affect each one has on the page. The colour is patent specific andt he overlays are only sample areas of colour, so if a positive response to overlay screening is noted, the next step would be ‘Colourimetry Assessment.’


This is an assessment to establish a much more precise tint, which would have to be made up to wear in spectacles.

Colourimetry Assessment

The optician uses an instrument called an intuitive colourimeter, to find the optimal precision tint that releaves the patients visual symptoms.

The patient sits in a darkened room and looks at random text through the viewing window. The patient is the asked about the distortions they are experiencing with the text. The colour saturation is slowly increased, then reduced again, together with the hue, and each time the practicioner asks the patient about the effects on the text.

There are approximately 10,000 colour combinations that can be found and the colour requirements differ significantly between individuals. Any deviation from the optimum colour may prevent achievement of the optimum improvements in both reading speed and accuracy.

Reseach has established that it is very unlikely that the ultimate optimum lenses will be that of the chosen overlay.

Since its launch in the early 1990s, over 150,000 pairs of lenses have been prescribed by vision practioners throughout the UK and worldwide.


Continuing Care

For patients who are prescribed Precision Tinted lenses, we recommend that we repeat the Colourimetry Assessment at yearly intervals, because the colour of the tint required can, like any other optical prescription, change over time.