An representation of how black-on-white text appears for some people with Irlen syndrome

Visual stress, often called Irlen syndrome, describes a pattern of discomfort and distortion that shows up when a person is exposed to certain types of light, contrast or visual environments. It is far more than simply finding reading hard. Clients often describe words as moving or blurring, colours around the edges of print shimmering on the page, glare that feels overwhelming and a sense that the print is just too intense to look at for long. Many also experience headaches, nausea, eye strain, difficulty concentrating, reduced comprehension, depth-perception challenges and even anxiety because of how uncomfortable visual tasks can feel.

Although visual stress can coexist with dyslexia, the two conditions are not the same. Dyslexia is a phonological language-based difficulty. Visual stress is about how the brain processes sensory information. When both are present, each needs its own intervention. Reducing visual stress often helps clients feel more physically comfortable so they can engage more confidently in reading and learning, but it doesn’t replace literacy support.

Two main approaches are often talked about in relation to coloured filters. Colourimetry and the Irlen Method both aim to reduce visual discomfort but they are built on different clinical philosophies and are used in different environments.

Colourimetry is carried out using a machine under controlled lighting. This approach is very structured and focuses on sampling colour in a standardised way. It is designed for consistency and reproducibility, which is valuable for research and for prescribing within a tightly controlled clinical framework.

Contrastingly, the Irlen Method works in real-life lighting and with real tasks. Clients are assessed while reading and interacting with their environment under the same lighting that usually triggers their symptoms. This includes LED or fluorescent lighting, bright screens, glossy pages and changes in natural light. Because visual stress is so dependent on context, many people report that colours chosen in a natural environment feel more accurate and effective in daily life. This makes sense when we consider how different modern lighting sources are in their spectral output and why symptoms often show up only in specific settings.

There is also a growing scientific basis behind what clients describe. Research points to cortical hyper-responsiveness in some people when they are exposed to certain spatial frequencies and patterns. Neuroimaging studies, including fMRI, have shown measurable differences in visual cortical activation in individuals with visual stress. When they use their optimal filters, activation patterns shift toward a more typical response. This reinforces that Irlen syndrome is not an optical issue but a sensory processing one.

Clinically, the first step is always to rule out refractive, binocular or pathological causes. When those are managed and symptoms remain, incorporating screening for visual stress can make a real difference. Some people respond well to overlays while others need precision-tinted lenses for consistent comfort across different environments.

Visual stress is real and it affects daily function. Eyecare professionals are in a unique position to recognise it, support clients and contribute to a more informed and evidence-aware conversation across our profession.

Further reading

• Evans BJW, Allen PM. (2016). A systematic review of controlled trials on visual stress using Intuitive Overlays or the Intuitive Colorimeter. Journal of Optometry.
• Wilkins AJ. (2022). Visual Stress and Coloured Filters: A Review of Mechanisms and Evidence.
• Chouinard BD et al. (2012). A functional neuroimaging case study of Meares–Irlen syndrome visual stress. Brain Topography.
• Monger LJ et al. (2015). Pattern glare and the effects of contrast and colour on visual discomfort.
• Allen PM, Gilchrist JM, Hollis J. (2008). Use of visual stress assessment and overlays in educational and clinical settings.
• Irlen H. (1991–2020). Clinical case series and practitioner reports on colour filter use in visual stress.

Samantha Fleming, who has Irlen syndrome, is a Irlen diagnostician in Northland and a qualified dispensing optician. She set up The Eye Lady, a clinic for Irlen syndrome, works with local schools and allied health professionals, to educate more people about the condition.