Dark adaptation Flashcards
This is known as the process by which the visual system adjusts to the prevailing light level.
Visual adaption
What are the 4 mechanisms to visual adaptation?
- 2 different PRs
- Change in pupil size
- Conc. + level of bleached photopigment
- Change in neural responsiveness
What are the 3 characteristics of rods?
- High gain system
- High sensitivity
- Low resolution
What are the 3 characteristics of cones?
- Low gain system
- Low sensitivity
- High resolution
The pupil size can change from __ to ___ in less than 1 second
2 to 8 mm
The change in pupil size alters retinal illuminance by __ log units
1.2 log units
~16x
This is used to measure light reflected from the fundus of the eye
Retinal Densitometry (tells us the amount of photo pigment that has been bleached)
The time course for dark adaptation and rhodopsin regeneration are ____
the same/equal
bleaching rhodopsin by 1% decreases sensitivity by___
by 10 (or increases sensitivity threshold by 10)
Bleaching 50% of cones raises threshold only be __ log units.
- 5 log units
- bleaching of cones has a very small effect on threshold when compared to rods
T/F: Rod sensitivity is not based on changes at the receptor level alone.
True
This is known as the process that increases threshold luminance in response to an increased level of illumination
Light adaptation
This is known as the process that decreases threshold luminance as a function of time in the dark; happens slowly.
Dark adaptation
Cones recover in __ mins. Rods recover in __ mins.
1.5 mins
5 mins
This represents the rapid reduction in threshold up to about 10 mins where the curve plateaus; called the cone plateau
The cone or photopic threshold:
First section of dark adaptation curve
This represents the curve with a slow reduction in threshold to about 35 mins where the rod plateau occurs
Rod, scotopic threshold: Second section of dark adaptation curve
What changes to the pupils occur at time zero?
- get larger
- allow in more light
- more retinal stimulation
What % of cones become dark adapted within 5-10 mins ?
99.21%
When do cones fully dark adapt?
10 mins
This is known as the abupt change in shape (slope) of the curve
the rod-cone break
This is known as the dividing point from where the cones were detecting the flash to where the rods are detecting the flash
Kohlrausch bend
When do rods fully dark adapt?
35mins
This is known as the difference in sensitivity between the cone plateau and the rod plateau
Phtochromatic interval - separation between the cone and rod plateau
What 4 ways can the shape and time course of the DA curve be affected?
- If both rods and cones are present
- Changes in adapting light
- Changes in flash stimulus
- Task required of patient
What are the 3 ways the adapting light can be changed?
- Luminance
- Duration
- Wavelength
At a luminance that is too dark, which PRs will be affected?
rods only
A short duration of the adapting light will cause what?
Only rods will be bleached
- need at least 5 mins for full bleaching
A 400nm wavelength light will only cause __?
rapid cone adaptation (cones aren’t bleached)
A 650nm wavelength will only cause what?
prolonged cone adaption (rods arent bleached
Flashing testlight in the foveal area will only cause which PR response?
cone response
- theres no rods in fovea
If we use a central test flash, what PR will be stimulated?
Cones
If we use a very narrow grading..
we know the rods don’t have good detection ability (will see cone branch only)
This is known as a rapid decrease in test flash detection threshold after the first offset of the adapting light (time 0)
Early adaptation
This occurs within the first second after the adapting light is turned off
Early adaptation
An adapting light of one minute will result in?
Rods only, no cone portion
A wide flash stimulus during dark adaptation will result in?
Normal dark adaptation
