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How do rods and cones differ in their responses to light?
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Photoreception
The mammalian eye has a cornea and a lens and functions as a dioptric system, in which light rays are refracted to focus on the retina.
Rods and cones are the two primary types of photoreceptor cells in the vertebrate retina, and they differ significantly in their sensitivity, function, and distribution:
- Sensitivity and Illumination: Rod cells are much more sensitive to light than cone cells, making them essential for vision in low-light (scotopic) conditions. Cones are less sensitive to low illumination and are primarily responsible for vision in brighter (photopic) conditions.12
- Visual Perception: Rods are responsible for perceiving the size, shape, and brightness of images but do not perceive color or fine detail. Cones are associated with colour vision and the perception of fine detail.12
- Mechanism: Both cell types use photopigments consisting of an opsin protein and a chromophore (retinal). Rods contain one type of opsin, while humans have three types of cone opsins, each sensitive to different wavelengths (blue, green, and red), which allows for color discrimination.32
- Distribution: Cones are highly concentrated in the central retina (the fovea), where rods are absent. Conversely, rods are more numerous and are found in higher densities toward the outer edges of the retina.14