Adaptation to light and dark
Light adaptation
Dark adaptation
Light adaptation
- Adaptation to light > adaptation to dark
- Recovers normal vision in less than a minute
- Pupil constriction à restrict amount of light entering eye
- Bleaching of photopigments
- In bright light:
- Sensory cells contain little uncleaved photopigment
- Low light sensitivity
- sensory cells are light adapted
Dark adaptation
Figure 1: Dark adaptation curves. Purple: rod adaptation curve. Green: cone adaptation curve. Red: two-stage dark adaptation curve of both rods and cones. The initial time delay between "light-adapted sensibility" and beginning of the curves is due to delay between time the lights are switched off and when measurement of curves start.
Source: Goldstein E.B. (2014) Sensation and Perception, 9th edn., Wadsworth: Cengage Learning.
- Photopic (light-adapted) state to scotopic (dark-adapted) state
- Maximal light sensitivity
- Cones adapt more quickly to darkness than rods
- Cones: 5 minutes
- Rods: 20-30 minutes
- Species dependent
- Dependent on pre-existing light level
- Brighter pre-existing light, lower rhodopsin stores à longer to reach maximal light sensitivity
- Increase light sensitivity by
- Dilation of pupil
- Synaptic adaptation of retinal neurons
- Increase rhodopsin available in rod outer segments à regeneration of rod photopigments
References
- Akers R.M. and Denbow D.M. (2013) Anatomy and physiology of domestic animals, 2nd edn., Iowa: John Wiley & Sons, Inc.
- Goldstein E.B. (2014) Sensation and Perception, 9th edn., Wadsworth: Cengage Learning.
- Maggs D.J., Miller P.E. and Ofri R. (2013) Slatter's fundamentals of veterinary ophthalmology, 5th edn., Missouri: Elsevier.
- Sjaastad O.V., Sand O. and Hove K. (2010) Physiology of domestic animals, 2nd edn., Oslo: Scandinavian Veterinary Press.
