Irlen syndrome, occasionally referred to as scotopic sensitivity syndrome (SSS) or Meares-Irlen syndrome, very rarely as asfedia, and recently also as visual stress, is a proposed disorder of vision.

The Irlen Method uses coloured overlays and tinted lenses in the form of glass or contact lenses. The method is intended to reduce or eliminate perceptual processing errors; it is claimed the resultant retiming of visual signals in the brain improves the reading difficulties associated with scotopic sensitivity syndrome.