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Why does rhodopsin bleaching reduce the sensitivity of rod cells?

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details of the mammalian eye — 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.

Rhodopsin bleaching reduces the sensitivity of rod cells by limiting the degree to which they are stimulated in bright environments.1

When light enters the eye, it triggers a change in the configuration of the rhodopsin molecule, causing the protein opsin to dissociate from its pigmented component, retinal. This process, known as bleaching, effectively breaks down the rhodopsin molecules. By reducing the concentration of available rhodopsin, the rod cells become less sensitive to light, which prevents them from being overstimulated in bright conditions. This mechanism allows cone cells to take over and mediate vision in brighter environments.12

Conversely, in dim light, there is minimal bleaching, and the resulting high concentration of rhodopsin enables the rod cells to function at their peak sensitivity, which is essential for vision in low-light conditions.12