Stein suggests that retinal magnocellular ganglion cells receive 45% from red light receptors (cones); 45% from green; and 10% inhibition from blue cones. Deep yellow filters eliminate the inhibitory blue cone input and hence yellow filters enhance magnocellular sensitivity. As many as 33% of dyslexics benefit from wearing yellow filters for 3 months; their eye control improves and their reading progress can increase four fold. Perhaps 10% of dyslexics seem to have too weak blue input to magnocells. These children often complain of glare and letters moving around. Blue filters can improve their reading dramatically.

Occlusion (eye patching): this theory based on the work of Stein dates back to the 1980s and suggests that some dyslexic children have problems because their eyes do not work well together. This is known as 'unstable fixation'. Children's quotes reveal their unstable vision - oscillopsia: "The letters go all blurry"; "The letters move over each other, so I can't tell which is which"; "The letters seem to float all over the page"; "The letters move in and out of the page"; "The letters split and go double"; "The c moved over the r, so it looked like another c"; "I keep on losing my place".

Stein has measured binocular stability on the Dunlop test which presents 2 slides of a house and a post, viewed through an instrument called a synoptophore. When the eyepiece tubes are moved away from each other, one of the posts seems to move towards the door of the house just before fusion breaks. Stable fixation is shown when children respond with the same eye each time. This demonstrates that they have a dominant eye. However there are problems with this test which Stein (1989) acknowledges. When children show that they have unstable vergence, they may complain that the words move around on the page. It is therefore more difficult for them to learn to read. For children under the age of 10, Stein suggests that they patch one eye. This forces the visual system to switch to using the uncovered eye.