What condition describes a form of partial color blindness where the eye has only one type of cone photopigment?

The condition that describes a form of partial color blindness where the eye has only one type of cone photopigment is monochromatism. Individuals with monochromatism possess only one type of cone cell, which significantly limits their ability to perceive colors because they cannot discriminate between different wavelengths of light effectively. Their vision is primarily based on the intensity of light, resulting in a very limited color spectrum, often perceived in shades of gray.

In contrast, options like trichromatism refer to the typical color vision found in most individuals who have three types of cone photopigments enabling the perception of a broad range of colors. Dichromatism involves having two types of cone photopigments, allowing for some color discrimination but still not as extensive as trichromatism. Anomalous trichromatism, while also involving three types of cone photopigments, refers to a variation where one type of cone operates differently, leading to some color perception deficits but not as severe as in monochromatism. Thus, monochromatism specifically points to the condition where only a single type of cone is present, resulting in the defined state of partial color blindness.