Dr Northway's Research


I have researched  visual processing skills of dyslexic readers who find coloured lenses beneficial. My thesis entitled Psychophysical and Ocular Motor Aspects of Visual Processing in Dyslexics with Meares-Irlen syndrome was completed in 2004. A summary of my research and findings can be found below.


It has been widely documented that dyslexics have a deficit of magnocellular processing ( the where system in vision) resulting in abnormal contrast sensitivity, poor fusional vergences and poor motion detection. In addition there have been studies highlighting poor saccadic control in dyslexics. There have however been few investigations looking specifically at visually symptomatic dyslexics or at how a treatment may be affecting visual processing in such individuals. Many dyslexics find using precision tinted lenses allow them to read more comfortably and more quickly however this mechanism is poorly understood.

There have been several papers that have shown that the effect of colour is not purely a placebo effect and that each individual requires an individual precision tint in order to maximise visual comfort. There were however several questions which personally intrigued me. Were the dyslexics with MIS the ones with a magnocellular dysfunction or oculomotor difficulties? How did coloured lenses increase reading speed? Was there some objective method to differentiate the dyslexics with MIS from those without?

A variety of investigations were carried out to satisfy two questions.

Is there a magnocellular deficit or saccadic abnormality in dyslexics with MIS?

And do precision tinted lenses alter visual performance in dyslexics with MIS who show an increase in reading speed when wearing precision tinted lenses?

The investigations

All the studies involved three groups of patients - dyslexics with MIS, dyslexics without MIS and non-dyslexic subjects. The subjects carried out the investigation under normal conditions e.g. no lenses, using their own tint and using a luminance matched neutral density filter.

I investigated contrast sensitivity function, letter recognition in central and peripheral retina, internal noise and sampling efficiency using psychophysical methods. I also investigated saccadic and smooth pursuit eye movements using eye trackers, and looked at clinical methods of investigating the effect of colour on school children.


What I found

Dyslexics with MIS have normal contrast sensitivity function and normal smooth pursuit and saccadic eye movements. They did have poorer recognition of letters in the central foveal area. They also showed reduced sampling efficiency (this is how well we use the information we see) and the coloured lenses improved sampling efficiency in the MIS sufferers only.


The dyslexics with MIS did not show any evidence of a magnocellular deficit. They were however the only group of subjects to show any change in saccadic performance when wearing colour thus providing objective evidence of an effect of colour on visual processing which was not seen in the other groups or with grey filters. I also found that the developmental eye movement test was more sensitive in predicting the continued use of coloured overlays in school children than the rate of reading test.


Current Investigations


I am currently looking at eye movement control and visual perceptual skills in dyslexic readers but also in children with developmental coordination disorder (DCD) (dyspraxia). I have to date reviewed over one hundred patients with DCD and there would appear to be a high incidence of poor binocular vision, tracking and visual perception.


Published Papers


Predicting the continued use of overlays in school children – a comparison of the Developmental Eye Movement test and the Rate of Reading test Author: Northway N.1 Link: click here

Source: Ophthalmic and Physiological Optics, September 2003, vol. 23, no. 5, pp. 457-464(8)