Flashcards in Duplex Retina Deck (28):
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)
td= (100)*(63.62)= 6,362 td
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:
Exquisite sensitivity to very dim lights
Poor VA (20/200 vision)
NO color discrimination
PECC (imPECCable) VA with photopic
Poor sensitivity to dim lights
The existence of 2 classes of photoreceptors, each operating under diff lighting conditions is known as:
The photopigment ________ is contained within the discs of the rod's outer segment.
(captures light and contributes to our sensitivity to dim lighting)
Quanta of ____nm have the highest probability of absorption.
Once a quantum of light is absorbed, all info regarding its wavelength is lost, this is referred to as:
A molecule of rhodopsin becomes ______ when it absorbs light.
The absorption of _____________ of light is required to bleach a molecule of rhodopsin.
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
Which cones make little contribution to spectral sensitivity?
The difference in sensitivity between scotopic and photopic systems, for a given wavelength, is referred to as the:
The scotopic is more sensitive than the photopic system in all wavelengths except what?
T/F: Photochromatic intervals increase with retinal eccentricity
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.
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.
T/F: Rods recover faster than cones
False, cones recover faster than rods
The lower the threshold the _______ the sensitivity.
(threshold is inverse of sensitivity)
____________ is the difference between the cone plateau (min photopic threshold) and the rod plateau (min scotopic threshold)
(is ~3 log units)
True/False: Rods are not more sensitive than cones for long wavelengths.
Weber fraction for scotopic vision is what?.
Wener fraction for photopic vision is what?