In ocular physiology, adaptation is the ability of the eye to adjust to various levels of darkness and light. This article or section is missing references or citation of sources. ...

The human eye can function from very dark to very bright levels of light - its sensing capabilities reach across nine decades. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly one thousand million apart. However, in any given moment of time, the eye can only sense a contrast ratio of one thousand. What enables the wider reach is that the eye adapts its definition of what is black. The light level that is interpreted as "black" can be shifted across six decades - a factor of one million. Contrast has several meanings: // Visual perception Left side of the image has low contrast, the right has higher contrast. ...

The eye takes approximately 30 minutes to fully adapt from bright sunlight to complete darkness - one million times more sensitive than at full daylight. In this process, the eye's perception of color changes as well.

In ocular physiology, adaptation is the ability of the eye to adjust to various levels of darkness and light. The human eye can function from very dark to very bright levels of light - its sensing capabilities reach across nine decades. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly one thousand million apart. However, in any given moment of time, the eye can only sense a contrast ratio of one thousand. What enables the wider reach is that the eye adapts its definition of what is black. The light level that is interpreted as "black" can be shifted across six decades - a factor of one million. The eye takes approximately 30 minutes to fully adapt from bright sunlight to complete darkness - one million times more sensitive than at full daylight. In this process, the eye's perception of color changes as well.

Photoreceptors send out glutamine signals in the dark and have -40mV as their resting potential. The addition of light causes the gating molecule cGMP to be degraded such that membrane gates close, there is no more inward flux of positive sodium and calcium ions, and the cell polerizes to -70mV where it stops signaling. When we walk from darkness to light, we are temporarily blinded because our photoreceptors have stopped sending signals. Our cells recognize this, however, and are able to depolerize the photoreceptors back to -40 mV so that we may perceive signals in the light. Two factors allow this adaptation to happen. First, the transducing molecule, which degrades cGMP, self-destructs after a short period of time so that membrane channels open again and the cell can depolerize. Second, at -70mV the cell is not receiving influxes of calcium. Calcium is an inhibitor of guanilyl cyclase which is responsible for cGMP production. At lower calcium levels, therefore, more cGMP is produced and membrane channels are opened.

See also

• Neural adaptation
• Photopic vision
• Purkinje effect
• Scotopic vision