Visual stress is a common condition of the visual cortex which is often experienced by people with dyslexia, but is a separate and distinct condition. Apparent movement and distortion of text, headaches and sore eyes are common symptoms of visual stress. Coloured overlays can improve reading experience for about 20% of the population. For a recent (2014) summary of research into the condition, see the Frontiers in Psychology review article here. Visual stress has some common misnomers, particularly "Scotopic sensitivity" (which suggests that it is a condition of the retina and not the visual cortex), and "visual dyslexia", which confuses the cognitive processing (dylexia) with visual processing (visual stress). Visual stress will create extra difficulties for a dyslexic person by making words hard to decipher, but once a reading ruler or overlay has made them visually clearer they still need to be decoded, and that is where dyslexia causes its problems..
The Crossbow Visual Stress range was named SEN Product of the year at BESA's UK Educational Resources Awards in 2014.
The Eye Level Reading Ruler is a finalist for Global SEN Product of the Year at the GESS awards in March 2017.