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What are Irlen overlays?

Irlen overlays are colored filters used to improve reading efficiency and comfort for those with Irlen Syndrome, also known as Scotopic Sensitivity Syndrome. This condition causes visual stress and perceptual distortions when reading black text on white paper, which can lead to reading and learning difficulties. Irlen overlays work by changing the color spectrum of text to one that is easier for the reader to process.

What is Irlen Syndrome?

Irlen Syndrome is a visual processing disorder characterized by sensitivity to certain wavelengths of light. It is estimated to affect 12-14% of the population and can cause the following symptoms when reading:

  • Letters appearing to move or vibrate
  • Blurring of print
  • Loss of place, rereading lines
  • Eye strain, fatigue, headaches
  • Light sensitivity

These symptoms are caused by an inability of the brain to correctly process visual stimuli received through the eyes. The incoming signals become scrambled, leading to visual distortions and instability of text. This in turn impacts reading fluency, comprehension, attention and concentration.

How Do Irlen Overlays Work?

Irlen overlays are colored transparent plastic sheets that are placed over reading material to improve visual processing. Each overlay filters out offensive wavelengths of light that trigger symptoms, while allowing comfortable wavelengths to pass through.

This effectively creates a more stable visual environment for the reader. The color of the overlay is specifically selected to match the individual’s reading preference. The most common colors used are rose, mint, purple, aqua and yellow.

Research shows that Irlen overlays work by:

  • Reducing glare and brightness that cause visual stress
  • Increasing contrast sensitivity
  • Enhancing edge detection of text
  • Stabilizing erratic eye movements
  • Decreasing perceptual distortions

The net result is improved reading fluency, comfort, comprehension and endurance.

Who Benefits From Irlen Overlays?

Irlen overlays can benefit a variety of individuals with reading difficulties and light sensitivity issues:

  • Those diagnosed with Irlen Syndrome/Scotopic Sensitivity
  • People with dyslexia, ADHD, sensory processing disorders
  • Individuals with head injury, stroke or neurological dysfunction
  • Patients with photosensitive epilepsy, migraines or eye strain
  • Autism spectrum disorders
  • Learning disabilities like dyslexia

The overlays have been shown to help both children and adults gain control over reading, resulting in improved skills, efficiency and enjoyment of learning.

How to Get Tested for Irlen Syndrome

Determining if you have Irlen Syndrome and selecting an optimal colored overlay is done through a screening and assessment process. Here are the steps involved:

  1. Screening Test: This 5-10 minute test uses colored overlays to quickly identify if you experience improvements in reading comfort, accuracy or fluency. If positive results are shown, you move to a full assessment.
  2. Irlen Assessment: This diagnostic process tests reading performance under Irlen Spectral Filters of different colors, intensities and combinations. It pinpoints your ideal filter color to maximize reading speed, accuracy, fluency and comfort.
  3. Reading Evaluation: Standardized reading tests and questionnaires evaluate current reading abilities and difficulties. This identifies specific problem areas that need improvement.
  4. Specification of Overlays: Your personalized colored overlays are determined based on testing data and ordered. Overlays are tailored to individual needs and may use single colors, combinations or gradients.

The testing provides objective data verifying your symptoms, reading skills and the precise colored filters that offer optimal visual processing for your eyes and brain.

Types of Irlen Colored Overlays

There are two main types of Irlen overlays used to treat Scotopic Sensitivity Syndrome:

Full Sheet Overlays

These are full page plastic sheets that are placed directly over reading material. They are available in a range of single colors and color combinations including rose, purple, aqua, mint, yellow, blue and green. Full sheet overlays provide maximum filtering of offensive light wavelengths.

Precision Tinted Lenses

These are glasses with precision tinted lenses made after formal Irlen testing. They are useful for people who need full-time use of the colored filters. Tints and gradients are customized to match the overlay color selected during assessment. This allows for seamless use of overlays and glasses.

How to Use Irlen Overlays

Using Irlen overlays or tinted lenses is simple. Follow these tips for optimal results:

  • Place the colored overlay directly over reading material to filter text
  • Angle overlay to minimize glare and reflections
  • Use under regular lighting or fluorescent lights
  • Use a clip to keep overlay securely in place
  • Position yourself correctly; don’t slouch over the overlay
  • Use for all visually intensive activities like reading, homework, computer work, etc.
  • Be patient adjusting to the new colored environment

With consistent use, the overlays and lenses help recalibrate the visual system for improved processing of text and images. Symptoms are reduced and reading skills enhanced.

Studies on Effectiveness of Irlen Overlays

There has been extensive research validating the benefits of Irlen colored overlays for individuals with Scotopic Sensitivity Syndrome. Here are findings from a few key studies:

Study Results
Robinson, G.L., & Miles, J. (1987) 94% of subjects had immediate increases in reading speed with overlays. Accuracy also improved.
Robinson, G.L., Foreman, P.J. (1999) Colored overlays increased reading speed by 26% and accuracy by 16% on average.
Kruk, R., Sumbler, K., Willows, D. (2008) Children with reading disabilities showed gains in word decoding and reading comprehension using overlays.

Additional studies have confirmed overlays help increase reading fluency, attention, concentration and comfort for both Irlen Syndrome sufferers as well as broader learning disabled populations.

Criticisms and Controversy Over Irlen Syndrome

While many studies support the benefits of Irlen colored overlays, there are critics of Irlen Syndrome’s existence as a medical condition. Some of the controversy stems from the following:

  • It is not recognized in any major diagnostic manuals like the DSM-5 or ICD-10
  • Symptoms are considered subjective and self-reported
  • No conclusive physiological cause has been determined
  • Diagnosis relies heavily on proprietary testing materials
  • Research tends to be published by the Irlen institute; few large independent studies validate it

Additional high quality research by independent bodies is still needed to validate Irlen Syndrome and overlays. However, the evidence indicates they currently help many struggling readers.

Alternatives to Irlen Overlays

Those experiencing reading difficulties similar to Irlen Syndrome symptoms do have other options besides colored overlays to help improve text visibility and processing:

  • Colored Lenses: Rose-tinted or chromaGen lenses to increase contrast.
  • E-readers: Allow font, spacing, brightness and background color manipulations.
  • Colored Paper: Yellow, blue, pink or mint paper reduces glare.
  • Modified Fonts: Fonts like OpenDyslexic optimized for readers with visual stress.
  • Low Vision Aids: Glasses to magnify text and reduce aberrations.

However, Irlen overlays remain the most targeted intervention to specifically address Scotopic Sensitivity Syndrome.


Irlen overlays are colored transparencies placed over text to reduce visual distortions and instability associated with Irlen Syndrome. They work by filtering out light wavelengths that cause visual stress, while allowing comfortable wavelengths to pass through. This stabilizes the text, reducing symptoms like light sensitivity, eyestrain, headaches and reading difficulties. Irlen overlays have been shown to benefit diverse individuals with reading problems and light sensitivity issues. While more research is still needed, for many they currently provide an effective intervention for improving reading fluency, endurance and enjoyment.