Britannica Sources used in this answer

How does absorption of a photon change 11-cis-retinal?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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.

When a photon is absorbed by 11-cis-retinal, the molecule undergoes a process known as photoisomerization. Specifically, the double bond between the 11th and 12th carbon atoms flips, which causes the retinal molecule to reconfigure from its folded 11-cis shape into a straighter all-trans form.12

This change in shape is the fundamental event that triggers the visual transduction cascade. The alteration of the retinal molecule creates instability in the attached opsin protein, causing it to change its own configuration and expose previously shielded chemical groupings. This structural shift ultimately leads to the closure of sodium channels and the hyperpolarization of the photoreceptor cell, which generates the electrical signals sent to the brain.12