The Colorimeter is a logical and sequential means of exploring colour space to find the optimal Precision Tint for the relief of perceptual distortion in dyslexia, migraine and photosensitive epilepsy. The Intuitive Colorimeter is a new optometric instrument allowing specific prescribing of tinted lenses for beneficial purposes. With the Intuitive Colorimeter the effect of colour on visual discomfort can be measured under controlled conditions in an efficient way, thorough manner and while eyes are colour adapted. The hue, saturation and brightness can be varied independently and variations of colour can be made sufficiently small to give the appearance of continuous change. Cerium Precision Tinted Lenses enable the prescribed colour to be reproduced as a tinted lens. The Precision Tinted Lenses are dyed to a degree of accuracy beyond that normally found in ophthalmic tinting and are issued with a certificate of authenticity to verify this. With this new system an almost infinite number of different tints are available. Other applications where the Colorimeter has been used are migraine, headache, photosensitive epilepsy and cases of retinopathy. This technology is now in use by optometrists throughout the United Kingdom and many other countries giving satisfaction to both practitioner and patient. The Dyslexia Institute recogninses the importance of this new technology and has co-operated closely in its development. Research has shown that the colour of the lenses is likely to differ from the colour chosen as a overlay.* "Practitioners should be warned that t is not acceptable practice to offer lenses tinted to the colour of a selected overlay. Lenses tinted this way may offer relatively little benefit.