Abstract: To determine a cataract or the degree of cataractogenesis in an eye of a patient, the patient views two lights juxtaposed, wherein each light comprises a mixture of two different wavelength lights. One of the lights is a fixed reference mixture, while the mixture of the other non-fixed light is varied until the patient observes less distinction between the two light mixtures in terms of brightness, hue or saturation. The luminance levels of the light components of both light mixtures for providing comparison and the ratio levels of the components are predetermined. Once a transition range is established from the comparison, the predetermined ratios are then related to respective ratios of a standardized group. Deviations between the ratios of the patient and the standardized group indicate the existence of a cataract and/or the degree of a cataract precursor formation.