Rods- consist rhodopsin
Impotent for retinal sensitivity (dim light, see in the drak) scotopic vision, most of
them located in the peripheral parts of the retina.
Cones- consist photopsin, important for visual acuity (see if square or circle etc... And
for color vision (photopic vision), most of them located in the fova centralis (in the
mecula lutea)
• More rods Tham cons.
Dark to light adaptaion:
1. The pupils constrict
2. Bleaching photo pigments
3. Rhodopsin (11 cis retinal+ opsin) hit with light and converted to all trans retinal and
opsin released
4. Photopsin also broken down
5. Opsin actives protein transducin
6. Transducing activities PDE (phosphodiesterase)
7. Brakes CGMP
8. Sodium and calcium can't enter to the rods
9. Rods come off
10. Retinal sensitivity decrease
11. Cons turn on
12. Visual acuity increase
Can take 5-10 minutes to completely adjust.
When we have to much brake the transducin leave the outer segment and enter the
inner segment in the rods, the rods stop to function and the retinal sensitivity
decrease.
The cones start to help by constrict to focus light centrally on the macula lutea
Light to dark adapation:
1. The pupil dilate-allow more light to reach the periphery of the retina where most of
the rods are.
2. Rhodopsin accumulating- retinal sensitivity increases, rods trun on
3. Cons turn off- dark light is low wave length and the cons don't activated by this
type of wave length. Visual acuity and color vision decrease.
Can take 20-30 minutes
Color blindness: X linked recessive disorder
More common to men
Lack of certain type of photopsins (the most common is not responding to red and
green wave lengths of light)
Nyctalopia/ night blindness:
Decrease production/ intake of vitamin A.
Less retinol production
Decrease in photo pigments