Definition: 1. Photo-tone: a dysfunctional or pathological condition of the photoreceptor cells that produces defective phototopic sensitivity. 2. Photozonus: a disorder in which the phototopic sensitivity is affected. (Source: Wiley Medical Dictionary, 10th ed.)<0x0A><0x0A>2. The condition caused by photo-tone, characterized by dysfunctional or pathological phototopic sensitivity. This phenomenon results in defective phototopic sensitivity.
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