Duplex Retina Flashcards
What makes it possible for the human eye to see something very bright and very feeble in the night sky?
Pupil changing diameter in response to light
Consider a white page with luminance of 100 nits. Compute the reitnal luminance for a 9mm diameter pupil. (Now what about a pupil with 2 diameter pupil)
Pir^2
(3.14)(4.5)^2=63.62
td= (100)(63.62)= 6,362 td
(3.14)(1^2)= 3.14mm^2 td= (100)(3.14)= 314 td
Pupillary diameter account for about 10% of light adaptation, what does the rest?
Rods and cones
Scotopic vision distinctions:
REPN scotopic vision: RODS Exquisite sensitivity to very dim lights Poor VA (20/200 vision) NO color discrimination
Photopic vision
PECC (imPECCable) VA with photopic Poor sensitivity to dim lights Excellent VA Color discrimination CONES
The existence of 2 classes of photoreceptors, each operating under diff lighting conditions is known as:
Duplex Retina
The photopigment ________ is contained within the discs of the rod’s outer segment.
Rhodopsin
captures light and contributes to our sensitivity to dim lighting
Quanta of ____nm have the highest probability of absorption.
507nm
Once a quantum of light is absorbed, all info regarding its wavelength is lost, this is referred to as:
Univariance
A molecule of rhodopsin becomes ______ when it absorbs light.
bleached
The absorption of _____________ of light is required to bleach a molecule of rhodopsin.
one quantum
The half life of rhodopsin regeneration is _________..
5 minutes (50% of bleached rhodopsin molecules will recover in 5 minutes)
3 cone photopigment colors and nm for each
Blue: 426nm
Green: 530nm
Red: 557nm
Which cones make little contribution to spectral sensitivity?
s-cones
The difference in sensitivity between scotopic and photopic systems, for a given wavelength, is referred to as the:
photochromatic interval.
The scotopic is more sensitive than the photopic system in all wavelengths except what?
red region
T/F: Photochromatic intervals increase with retinal eccentricity
True
As lighting conditions change from scotopic to photopic, the wavelength to which we are most sensitive increases from ___ to ___.
507 to 555nm
The relative increase in the brightness of longer wavelength stimuli as lighting conditions change from scotopic to photopic.
Purkinje shift
Human retina contains approx _____ rods and ______ cones
120 million rods
6 million cones
After _____ minutes in the dark the eye is ________ times more light sensitive.
35 min
100,000 times
T/F: Rods recover faster than cones
False, cones recover faster than rods
The lower the threshold the _______ the sensitivity.
higher
threshold is inverse of sensitivity
____________ is the difference between the cone plateau (min photopic threshold) and the rod plateau (min scotopic threshold)
Photochromatic interval (is ~3 log units)
True/False: Rods are not more sensitive than cones for long wavelengths.
True
Weber fraction for scotopic vision is what?.
~0.14
Wener fraction for photopic vision is what?
~0.015
T/F: Photopic system is more sensitive to contrast than scotopic, its absolute sensitivity is less.
True
