The Nagel anomaloscope can be incorporated in the diagnosis of eye diseases. Three parameters are relevant: 1. The measure of the absolute matching range (scale units) 2. The preferred direction of the widened matching range (to red or to green) 3. The luminance matches with the yellow (decreasing matches indicating a pathologic scotopisation). - Six pathologic anomaloscope findings can be differentiated: 1. Pseudoprotanomaly (retinal diseases; type III acquired blue-yellow defects) 2. Symmetrically widened absolute matching range (reduced hue discrimination without reference to its etiopathology) 3. Absolute matching range asymmetrically widened to red with scotopisation (retinal diseases; type III acquired blue-yellow defects or type I acquired red-green defects) or without scotopisation (retinal diseases or optic nerve diseases; type III acquired blue-yellow defects) 4. Absolute matching range asymmetrically widened to green (mostly optic nerve diseases; type II acquired red-green defects) 5. Acceptance of both end matches ("0" up to "73") with scotopisation (retinal diseases) or without scotopisation (optic nerve diseases) 6. Achromatic matches (selective cone diseases, such as Stargardt's dystrophy or progressive cone dystrophy). Indications for anomaloscope examinations and clinical application of the method are discussed in ten cases. The utility of the Rayleigh-equation consists in diagnosing pathologic scotopisation (differential diagnosis between retinal diseases and optic nerve diseases) and in making a quantitative evaluation of the acquired color vision defect (follow-up examination).