When you look at a brightly lit object, your eye responds quickly to the change in light level. It converts the light energy into nerve impulses, which are transmitted through your brain to the visual cortex, a part of the brain that allows you to recognize objects.

The eye has a transparent medium called the cornea, which allows light to enter and focus on the retina (the layer of tissue in the back of the eye that contains photoreceptor cells). When you move your eyes from near to distant objects, your cornea and lens adjust so that the rays of light entering your eye are curved towards the object and strike the retina at an angle. This is known as accommodation.

Rods and cones are the two types of photoreceptors in the eye that detect light. They are specialized sensory neurons that contain membrane disks organized in stacks inside modified sensory cilia.

Transduction occurs when the photoreceptor molecule rhodopamine is activated by light. This triggers a series of chemical reactions that bind the molecule to and activate a trimeric G protein called transducin. The G protein then binds to a specific protein receptor on the cytoplasm of the rod or cone.

In a rod, the protein receptor is the trimeric G protein transducin (T); in a cone, the receptor is the trimeric G protein cGMP phosphodiesterase (PDE). Conclusion: These reactions alter the membrane potential of the rhodopsin and the PDE, allowing them to send nerve signals through the retina and the visual cortex.