Light and Eyeballs
Be able to describe the different stages of dark adaptation (time duration, luminance levels, etc.).
Know the differences between our scotopic and photopic vision.
Dark adaptation refers to the ability of both rod (scotopic) and cone (photopic) mechanisms to recover sensitivity in the dark following exposure to bright lights. The first rapid recovery is attributed to the cones and the later recovery to the rods.
Let’s Break It Down: A Timeline
- First Few Minutes: The rods and cones both become more sensitive during the first few minutes. However, after 5-10 minutes, the cones reach their maximum sensitivity. This is known as the rod-cone break because it’s the point where rods become more sensitive than cones.
- 5-10 Minutes: The rods will continue to become more sensitive over the next few hours as they regenerate a receptor protein called rhodopsin. After 7 or 8 minutes, the rod photopigments have replenished enough that the rods become the most sensitive cells in the retina, and sensitivity continues to improve for another 13-22 minutes (20-30 total) while the rod visual pigment finishes replenishing.
- 30 Minutes: At this point, the rhodopsin has mostly been replenished, so you should be about 90% dark-adapted.
Rhodopsin, a photopigment, plays a large role in dark adaptation because it’s so sensitive. However, light causes it to deteriorate rapidly, in a process called photobleaching. Photobleaching occurs when the pigment epithelium cannot regenerate 11-cis retinal as fast as it is converted to all-trans retinal. During daylight viewing, rods are essentially completely photobleached, and cones are partially photobleached.
So if you’re trying to get dark-adapted, it’s crucial to avoid light—it can undo hours of dark adaptation in seconds. All the rhodopsin you have built up over the previous 30+ minutes disappears, and it will take time for your retina to replenish it.
Cheryl Olman PSY 3031 Detailed Outline
Provided by: University of Minnesota
Download for free at http://vision.psych.umn.edu/users/caolman/courses/PSY3031/
License of original source: CC Attribution 4.0
Adapted by: Savannah WhisenhuntWebvision: The Organization of the Retina and Visual System, Light and Dark Adaption by Michael Kalloniatis and Charles Luuz
License: CC BY-NC
Adapted by: Savannah Whisenhunt