Irlen Syndrome (also referred to at times as Meares-Irlen Syndrome, Scotopic Sensitivity Syndrome, and Visual Stress) is a perceptual processing disorder. It is not an optical problem. It is a problem with the brain's ability to process visual information. While it is primarily in 10 - 15% of the population, by some accounts 50% of people will experience this at some time in their lives (for example when fatigued, etc.). A weird thing is that people rarely realize what they are seeing is not what everyone else is seeing. There can also be connections to headaches, sensitivity to light, etc. Here is a link to a ~1 min. youtube video showing how things can look when this syndrome is active: This has real implications for traders using charts.