Originally Posted by
jarralad2
They are basically a good idea - BUT - they are not a panacea and are essentially a way of making colour vision different - but it will give the impression of "curing" the problem. We can get someone through the Ishihara easily enough in most cases (again this does not make a colour defective become cured) but it can achieve significant improvements. We place Ishihara on lectern and modify LMS ratios using additive colour instrument. In most cases there is a colour space position in which the Ishihara becomes completely readable and it appears that colour vision is normal. We then work out the mathematics to enable this absolute colour position to be converted to a lens for a given environment - or if possible - all normal ambient lighting. The lens allows the Ishihara to be seen normally
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