Eye and Vision
"everything there [Emerald City] is of a green color -- just
as everything in this Country of the Gillikins is of a purple color."
"ls everything here purple?" asked Jack.
"Of course it is. Can't you see?" returned the boy.
"I believe I must be color-blind" said the Pumpkinhead, after
staring about him.
--L Frank Baum, The Land of Oz, 1904
Purves et al Chapter 11 covers optics, the eye and the retina, also some
pictures from chapter 12
More on color vision and visual transduction can be found in my signalling
course where the text figures refer to Alberts et al., Molecular Biology
of the Cell, 3rd edition, New York, Garland:
Transduction (how do we get from energy to nerve response?) first and best
understood for light.
Centures old literature on light (e.g. Newton) and color vision
"Medically," vision is very important to the quality of life
"the eye is the window to the brain" -- (NEI phrase) physician
can actually look at CNS.
For instance, increased crainial pressure (like from tumor) shows up as
Funding for research and private foundations.
Vision is fundamental to the nature of human experience.
Fig. 11.9A p. 241
Rhodopsin is the visual pigment
Protein plus chromophore (11-cis retinal) makes visual pigment
George Wald 1967 Nobel
Fig. 11.9B p.241
isomerization of retinal
(A rod can see one quantum, see below)
Energy of one photon = Planck's constant (h) x the frequency (nu)
Frequency = speed (c) / wavelength (lambda)
frequency = for 500 nm (blue-green), 3 x 10 to the 8 m/s divided by 0.5
x 10 to the -6 m = 6 x 10 to the 14 sec to the -1
E = 6 x 10 to the 14 per sec x 6.63 x 10 to the -27 erg-sec = 3.96 x 10
to the -12 erg
Demonstration: A Mercury arc lamp feeds into a monochromator to make monochromatic
lights of the spectrum. In your text, the spectrum is described in Fig.
10-12. We have a monochromator which generates a spectrum using a grating
(the obvious alternative being a prism). On the front of the monochromator
is a slit that picks off a small section of the spectrum. Using another
monochromator, where I could look inside, I obtained this
picture to show how the slit selects a portion of the spectrum. The slit
picks off 6.4 nm/mm, i.e. if it is 1 mm open, it lets through 6.4 nm of
the spectrum. With the slit set at 1 mm, we project the beam onto a screen.
Cranking the monochromator, we go through ROYGBIV (red orange yellow green
blue indigo violet). We note that it is brighter at some wavelengths than
others.I scanned this graph of the spectral output of various light sources
to demonstrate that there are "lines"
in the mercury arc (HBO) spectrum at 580, 550, 438, 405 and 365 nm. At a
setting of about 579 nm, light looks uniquely yellow (Just 5 nm higher looks
orangish, while just 5 nm lower looks greenish). At 365 nm (we need an additional
filter), the screen looks dark but an index card looks blue. That is fluorescence.
A short wavelength excites electron orbitals, then there is some radiationless
deexcitation, so, when the electron falls to its ground state, there is
less energy and a longer wavelength. Neutral density filters are used to
attenuate light. The values are in log to the base 10. A 0.3 log unit filter
would cut the light in half (you do the arithmetic) [it doesn't seem that
much, does it?] and 0.6 would cut it to 1/4. A 0.3 plus a 0.6 is the same
as the 0.9.
Fig 11.14 p. 245
"Light" is a portion of the electromagnetic spectrum - 400-700
400 is violet, 700 is red
For over a century, it has been known that insects see "near"
ultraviolet (UV) (300-400 nm)
My research contributions in the 1970's concerned UV sensitivity in Drosophila:
Starting in the early 1980's, researchers showed that various vertebrates,
fish, birds, eventually mice, see UV.
Snakes "see" infrared (IR) (heat of warm blooded prey) with pit
organs - pinhole eye, (reference: RIGamow and JFHarris, The infrared receptors
of snakes, Scientific American, May 1973, 94-100)
The eye with
The eye with
orbital fat removed clearly showing optic nerve
Here is a sheep
eye showing the exit of the optic nerve
Retina is white
film, black is pigment epithelium
Tapetum gives eye
glow, reflecting light back through retina increases sensitivity for nocturnal
An albino eye
cut around the orbit is better for showing ciliary muscle
Here is the lens
of the eye
Fig. 11.1 p. 230
the eye picture of an ophthalmologist's office
cornea, iris, pupil, conjunctiva, sclera, extraocular muscles
Fig box 11B p. 234
lens, aqueous, vitreous, retina, fovea, optic n.
there is a blind spot
where the optic nerve exits
Fig. Box A p. 231
diopters - reciprocal of focal distance in m
cornea is 0.024 m, 42 diopters
Hyperopia-far-sighted, need convex lens,
Myopia-near-sighted, need concave lens, involves abnormal elongation of
visual angle, acuity - Snellen eye chart - 20/20 is seeing letter 5 min
1980's radial keratotomy (RK)
Both change shape of cornea
Fig. 11.2 p. 230
TRANSPARENCY Fig from another book,
(1) ciliary muscle relaxed, suspensory ligaments taut, lens thin for distance
(2) ciliary muscle contracted, suspensory ligaments relaxed, lens thick
for near vision
loss of accomodation with age explains Presbyopia
Benjamin Franklin developed bifocals
pressure is too high because aqueous humor does not drain well, ganglion
cells die, treated with drops or surgery, canal of Schlemm
in vitreous especially in people with myopia
blood vessels overgrow, leak, blast holes in retina with laser decreases
lens becomes opaque, remove and often replace with intraocular lens, made
of polymethyl methacrylate, known to be tolerated since pieces from airplane
visors would lodge in pilots under fire (and since about 1988, these have
been doped with UV blockers)
Humans see UV, but only if the lens is removed (aphakia), one of my
Retinopathy of prematurity
High O2 in incubator causes overgrowth of blood vessels
"Little" Stevie Wonder
Fig. 11.3 p 233
ophthalmologists view of eye
optic disk = papilla (where optic nerve exits and site of blood supply)
fovea, site of high acuity (cone vision) - point of fixation
Macula lutea pigment
better shows a yellow pigment that absorbs blue light
Box B (Chapter 11)
demonstrates the blind spot
Fig Box D Chapter 11 p. 237
Retinitis pigmentosa is tragic, people can see when young, lose rod vision
(tunnel vision [ring scotoma] because rods are in mid-periphery).
Rods go first and eventually cones which is strange if rod molecules are
There are autosomal and X-linked types, dominant and recessive.
There are other genetic degenerations and stationary (not progressive) blindnesses
are in molecules of transduction cascade as well as in other rod and cone
There is a web site where information relevant to the retina, especially
genetic causes of blindness, accumulates (site)
Box C Chapter 11 C p 235
Age-related (it used to be called "senile") macular degeneration
People about 80 yrs old lose high acuity vision (cannot read)
"Wet" (10%) is a sudden and treatable (laser surgery) medical
emergency from blood vessel leaking
"Dry" complicated but may have an genetic basis too, worse in
More on genetic blindnesses can be found in my signalling course:
and age related macular degeneration
Rods and Cones
Fig. 11.5C p. 236
Photoreceptors- 125 million receptors 20/1 rods to cones
(converge on 1 million ganglion cells)
Fig. 11.13A p 244
Rod and cone number as a function of visual angle [angle is the way to express
it] (note blind spot)
Rod, peripheral vision, dim black and white, sensitive - "scotopic"
[Explains ring scotoma (loss of vision in mid periphery) in RP]
Very sensitive - 1 photon
People can see light of 6-14 quanta over a 500 rod area (SHecht, SSchlaer
and MHPirenne, Energy, quanta and vision, J. Gen. Physiol., 25, 819-840,
Cone, fovea, color, acuity - "photopic"
Shown in rats, rods are supported by retinal
Fig. 11.6 p. 239
RPE: (1) melanin that blocks light reflection
(2) metabolism to provide 11-cis retinal (chromophore ofvisual pigment,
(3) phagocytosis and recycling of shed rod tips
Cells are postmitotic and the indigestible residue of the phagolysosomal
system is lipofuscin,
a fluorescent aging pigment, a topic on which I've done research.
Fig. 11.13B p. 244
fovea is pit without rods and with cells and blood vessels out of the way
PKKaiser The Joy of perception, a web book
Follow leads, table of contents, 3-fun things in vision, afterimages
Fig. 11.14A p. 245
spectral sensitivity of rods and 3 cone types
confirms Young -Helmholtz trichromatic theory
3 kinds of cone 420 530 560
3 kinds of cone opsins which are evolutionarily related in humans and OW
Fig. 11.16 p. 248
green and yellow (middle and long wavelength) cone opsins are near each
other on X
(blue cone opsin is on human chromosome 7, rod on chromosome 3)
Fig. 11-14B p. 245
technique to see cones
bottleneck hypothesis color vision re-evolves after nocturnal life (where
adaptive pressure for cone vision is relaxed) early in mammalian evolution
Red or green color blindness - on X, thus preferentially in males.
Blindnesses were thought to be from altered genes, but numbr of copies in
human population is variable, and cross-over accidents can even make chimeric
Female "carriers" should actually be mosaics of color blind vs
normal retina because of Mary Lyon X-inactivation hypothesis
See recent evolution in superfamily of G-protein-coupled receptors (7 transmembrane
Gerald H. Jacobs and Jeremy Nathans, The evolution of primate color vision,
Scientific American, April 2009, 56-63
I was in graduate school when a seminar speaker (also in a paper) argued
that the separation of disks from the plasmalemma meant that there must
be an intracellular signal that diffuses across the cytoplasm; at that time,
they thought it was Ca2+
Fig 11.7 p. 239
response is hyperpolarization
response is slow (this is cone, rod is even slower)
"You can walk through the forest with nothing but starlight, but you
Fig. 11.9 9. 241
details of transduction cascade
Stacks of disks. Lumen is like outside cell
vitamin A is the chromophore
Transducin activates cGMP PDE, less cGMP (ligand) and channel closes so...
Fig. 11.8A p. 240
Fig. 11.8B p. 240
...since sodium channel closes.
Fig. 11.21A p. 255
center surround (excitation vs inhibition or vice versa) receptive fields
This kind of processing emphasizes contrast detection.
Feature detection - introduction and summary
Lateral inhibition H. K. Hartline - 1967 - Nobel
"primary physiological and chemical visual processes"
Limulus horseshoe crab
Mach (Ernst) bands - see edges (bright-dark contrast) especially well
(from Classic paper W.H.Miller, F. Ratliff & HK Hartline, How
cells receive stimuli, Scientific American, September 1961, 222-238)
at a light-dark boundary the response "boundary" from the array
of corresponding nerves is exxagerated
(from Classic paper F. Ratliff, Contour and contrast, Scientific
American, June 1972, 90-101) The moon seems bright because it is next to
a dark edge, relative to the nearby sky which is next to a shallow gradient
Personal reflection. When I applied to graduate school, Rockefeller
invited me down for an all day interview (since I was already in Manhatten
at Columbia College "the gem of the ocean"). Lunch (and a lab
tour) was with Floyd Ratliff. Unfortunately for me (I was rejected by Rockefeller),
I thought he was mispronouncing "stimulus" when he kept saying
"Limulus." I learned about Limulus the very next week in physiological
psychology. (You never know when the knowledge you are armed with will come
in handy.) Oh well. I went to Wisconsin (go Badgers!) and loved it so much
that I gave them my first born.
Purves home page interactive Demos,
Blobs in Hermann grid (Michael Bach, follow leads Optical
illusions and visual phenomena, 6 down 2 over - Hermann grid) explained
by more inhibition at corners
Sensory processing (in lots of sensory systems) uses lateral inhibition
to give feature detection, which for vision is color, contour and contrast
and movement. In other words, the brain does not keep track of a point by
point stimulation of each rod and cone, but rather reduces that information
into evolutionarily (depending on the species) relevant fetures. The retina
does this by lateral connections, and the input to the nervous system, like
at the thalamus and cortex, processes further.
Lower animals, like frogs (with less brain power) have more retinal processing
(since there is less that can be done in the brain). The process of lateral
inhibition gives feature detection, for features such as contrast and movement.
Some ganglion cells in frog retina fire preferentially to small dark spots
moving rapidly through receptive field ("bug detectors"). The
idea is that there are ganglion cells which fire only with quickly moving
small dots, stimuli resembling flies which frogs must detect expeditiously
in order to catch them on their sticky tongues.
Classic Paper J.Y.Lettvin, H.R.Maturana, W.S.McCullock & W.H.Pitts,
What the frog's eye tells the frog's brain, Proceedings of the institute
of radio engineers, 1959, 47, 1940-1951.
Primate ganglion cells -
Magnocellular (large) 10% - movement
Parvocellular (small) 90% - form and detail
cat ganglion cells -
morphology and function WXY
color opponent cells
Fig. 11.18A p. 252
glutamate is "excitatory" transmitter (usually would give an EPSP)
released in dark - but less glutamate in light on
off bipolars respond (depolarize) to increased glutamate (dark) with EPSP
off thus hyperpolarize to light and decrease firing of off ganglion cell
on bipolar hyperpolarize to glutamate (dark) probably through metabotropic
thus on depolarize in light and increase firing of on ganglion cell
Fig. 11.17AB p. 249
all this comes in center surround organization mediated by horizontal connections
(not well covered in book)
If red in center of visual field excites ganglion cell filing, then red
in periphery inhibits.
In this same cell, green in periphery excites and green in center inhibits.
Also there are cells that are the opposite.
In the LGN, there are center - surround cells and color processing
My interests center around vision, so a visit to the
research interests of my home page will offer various topics about vitamin
A, ultraviolet light, and Drosophila mutants. Dr.
Kisselev is in SLU's Ophthalmology Department and Dr.
Ariel in SLU's Pharmacology - Physiology Department are some of my fellow
wizards in visual science.
Exam questions from 2005 - 2012 relating to this outline
In what way is Planck's constant relevant to calculations concerning light?
used to calculate energy of one photon
Say something about why vision, as we know it, would not work for wavelengths
far below or above "visible wavelengths."
too short is ionizing (also cut off by ozone layer), just right excites
electrons, too long vibrates molecules (heat is waste)
"The cornea is the strongest lens in the eye." Explain this in
terms of relative indices of refraction.
the air to cornea interface is the only large difference in index of refraction,
so the corneal curve has a profound effect
For what visual disorder is angiogenesis an underlying cause?
"Foveal cones are protected from blue light" (by what?).
macular pigments (zeaxanthin and lutein)
A paper published in 1942 demonstrated that a rod can respond to a single
photon of light. Say something about the methodology in this study.
human subject answered if he could see carefully calibrated 500 nm light;
6-14 quanta were absorbed by a 500 rod area (psychophysics)
Histological autoradiography demonstrated that a radioactive amino acid
was incorporated into those disks of the outer segment nearest to the inner
segment. What eventually happened to this band of radioactivity?
over a few weeks, it moved up the outer segment until those disks were shed
and phagocytosed by the RPE
Say something about how there came to be genes for two of the cone rhodopsins
on the X chromosome in people.
in reevolution of mammalian colover fision after it was lost in an evolutionary
bottleneck, unequal crossing over in meiosis happened along the line, a
difference from old to new world monkeys
It might be better to say that "Light stops photoreceptor depolarization"
than to say "Light causes photoreceptors to hyperpolarize." Justify.
in the dark, cGMP keeps sodium-calcium channels open
Why is there lots of cGMP in a rod in the dark?
PDE is not activated
How was the horseshoe crab Limulus used to show how contrast detection was
enhanced by feature detection?
neural input from ommatidia at a light-dark boundry show a more accentuated
gradient of activity
"Light briefly loosens up the bonding orbitals of this chromophore."
Answer either (1) What is the chemical that makes this visual pigment a
pigment? Or (2) What is the word for the whole molecule, the prototypical
member of the G protein coupled receptor superfamily?
vitamin A, specifically 11-cis retinal, rhodopsin
A person who had had emmetropia (normal vision) developed hyperopia. Another
person who had had emmetropia developed presbyopia. Answer either (1) What
kind of corrective lens would help in both situations? Or (2) What is the
difference in these two disorders?
convex lens, hyperopia is far sightedness person would always wear glasses,
presbyopia is loss of accomodation, person would need reading glasses
The aqueous humor does not drain sufficiently. Answer either (1) What is
this disorder called? Or (2) What cells die, causing blindness?
glaucoma, ganglion cells
In what disorder does angiogenesis contribute to blindness?
diabetic retinopathy, also wet age related macular dystrophy
"Mutations of proteins of the visual transduction cascade cause retinitis
pigmentosa." I never listed specific molecules, but you should know
enough to tell me one.
rhodopsin, transducin, PDE, channel
A radioactive amino acid allowed the rod outer segment disks closest to
the inner segment to be labeled. On the basis of this methodology, what
fundamental finding ensued?
that new outer segment is continuously made, the outer segment turns over,
old outer segment is phagocytosed by the retinal pigment epithelium
Presumably, New World monkeys have one rhodopsin coded for on the X chromosome
while Old World monkeys (and apes and humans) have two (or more). How did
unequal crossing over
In terms of cGMP levels, explain why the rod hyperpolarizes in response
With the cation channel continuously gated by cGMP in the dark, the cell
is depolarized, and when PDE is activated in phototransduction, the channel
closes because cGMP has been turned into 5' GMP
Dark spots moving against a light background cause some ganglion cells in
the frog retina to fire. Explain why this was considered an important finding.
it shows feature detection of a biologically relevant stimulus, bug detectors
The conjugated double bond system of 11-cis retinal loosens up and the chromophore
relaxes to the all-trans configuration. What causes that loosening?
excitation by light
Zonule fibers ("ligaments") answer either: (1) connect the lens
to (what?), or (2) to mediate (what?).
ciliary muscle, accomodation
Say something about vision in either (1) the ultraviolet; or (2) the infrared.
UV - insects have, people usually do not b/c lens absorbs UV; IR - snakes
have pit "eyes" to detect warm blooded prey
Why would you go blind with poorly controlled diabetes?
What was the Nobel Prize - winning finding of Hartline in Limulus relating
to Mach bands and lateral inhibition?
neural firing pattern accentuates light-dark boundary
Explain why blindness in retinitis pigmentosa is witnessed by a ring scotoma
rods go first and rods are localized in the mid-peripheral retina
Labeled amino acids are incorporated into rod outer segment proteins. What
is the significance of the movement of the band of label over the next two
new disks are made and old ones are shed and phagocytosed (by the RPE)
This question relates to the evolution of protein families, for example
the G protein linked receptor. At one point on an evolutionary time scale,
there is one gene, later two, example those coding for the long and middle
wavelength rhodopsins. How do they think one gave rise to two?
unequal crossing over
Why would there be a current along the outside of a rod from the inner segment
to the outer segment in the dark?
ion pumps and the ATP that powers them are in the inner segment while channels
for those ions are in the outer segment
Why would the release of the neurotransmitter glutamate be decreased when
the rod is stimulated with light?
because the rod is hyperpolarized
How does the G protein coupled receptor known as rhodopsin come to be bound
to all-trans retinal?
after light stimulated the 11-cis
Regarding the energy of a photon, answer either (1) What is the equation?
Or (2) What are the units energy for the answer (3.96 x 10-12 [for 500 nm
E = hv (that v is a nu), ergs
In addition to refractive correction for myopia (glasses or contact lenses)
name one of the two treatments used to correct myopia in the last 20 years.
Everybody should get tested for glaucoma regularly. Answer either (1) What
is being measured? Or (2) Why, if left untreated, would glaucoma lead to
pressure of the eyeball, ganglion cells die
When the zonule fibers (suspensory ligaments) are relaxed, answer either
(1) What is the state of the ciliary muscle? Or (2) For what type of vision
is the lens accommodated?
How come a young person with autosomal dominant retinitis pigmentosa (a
rhodopsin missense mutation) still has rod-mediated vision?
the recessive allele still mediates transcription of a functional rhodopsin
People with retinitis pigmentosa develop "tunnel vision." Answer
either (1) What does this mean? Of (2) Why is that the visual impairment
of this disorder?
they are blind in a ring around the center (ring scotoma), loss of rods
For age-related macular degeneration, answer either (1) What specific aspect
of vision is lost? Or (2) When does it usually occur?
cone vision, around age 80
Concerning the extraordinary sensitivity of rods, answer either (1) Why
can you conclude that a rod can "see" one photon if it takes 6-14
photons absorbed by rods to see? Or (2) How did Hecht, Schlaar and Pirenne
do this landmark study?
those fall on 500 rods so one rod virtually never gets more than one, psychophysics
In addition to housing the melanin that keeps light from reflecting around
the inside of the eye, name one of the functions of the retinal pigment
epithelium (RPE) in maintaining the health or function of the rod outer
phagocytose shed rod tips, provide ii-cis retinal
The mechanism by which one gene (for long wavelength cones in New World
monkeys) became the yellow-green cone rhodopsin pair (in Old World monkeys)
is the general mechanism for the origin of the G protein coupled receptor
superfamily. How did one gene become two?
unequal crossing over in meiosis
By their very nature, fluorescent lights go on and off with alternating
current. Why don't you notice this?
above flicker fusion frequency (visual receptors are slow
For the phosphodiesterase in visual transduction, answer either (1) What
is directly upstream? Of (2) What is directly downstream?
transducin, channel (cGMP)
For the extracellular space outside the rod, answer either (1) Why is there
a current from inner to outer segment? Or (2) When is there a current from
inner to outer segment?
ions are pumped from the inner segment while channels are in the outer segment,
in the dark
Hartline won a Nobel Prize for showing that lateral inhibition contributes
to detection of what feature in Limulus?
contour and contrast
What is the specific defect in AMD (age-related macular degeneration)?
cone vision in fovea
If stimulation in the center of the receptive field of an on-center ganglion
cell increases firing a lot, how would stimulation of the whole receptive
field with the same intensity affect
Out of the "corner of your eye," you see a dim star. You do not
see it when you look right at it. Why can you see it when you look away
rods are more sensitive and they are off fovea
When would you use Planck's constant in calculations concerning sensory
to calculate the energy of a photon of light
How does PDE (phosphodiesterase) affect the membrane potential in the rod?
decreases cGMP, channel closes, cell hyperpolarizes
Why is there a "ring scotoma" (dougnnut-shaped blind area) in
people afflicted with retinitis pigmentosa?
rods go first, that is where they are prevalent
"There are bug detectors in the frog retina." State this in a
less casual way.
Movement of a small dark spot in the receptive field preferrentially increases
firing in some ganglion cells.
"Three nuclear layers and two plexiform layers" describe the histology
of what sensory structure?
What is the status of cation channels of rods in the dark?
Unless something is wrong with them, the proteins in the cornea and lens
transmit light quite well. How come, by contrast, the G protein-coupled
receptor (rhodopsin) absorbs light?
is has a chromophore, a pigmented portion, 11-cis retinal
Capillaries are in the choroid, a pigmented layer behind the retinal pigment
epithelium. Why is it that an ophthalmologist can see the other blood supply?
those pass on the vitreal side of the retina
Scotopic sensitivity would be highest at about 15o off fovea. Why?
that is where rod concentration is highest
The age pigment, lipofuscin, is the indigestible residue of the phagolysosomal
system. How does this apply to the rods and retinal pigment epithelium?
rods shed their tips and the RPE phagocytoses them
What is the cause of blindness in diabetes, and how does laser photocoagulation
of the retina slow the progression of diabetic retinopathy?
angiogenesis, formation of new blood vessels that leak, burning out part
of retina, though it causes some vision loss, inhibits angiogenesis
How come surgical manipulations of the cornea such as LASIK and RK can be
so effective in correcting myopia?
because the curved cornea-air interface, with its huge difference in index
of refraction, is a powerful lens and these surgeries change the shape of
What is the name and cause of the disorder that makes people over 40 need
reading glasses or bifocals?
presbyopia is from stiffness of the lens
"You can walk through the forest with nothing but starlight, but you
cannot run." Why not?
phototransduction is slow especially in rods
Pick a person, any person. How many copies of middle- and long-wavelength
(green- and yellow-) coding genes would you find on one X chromosome?
cannot say. could be one, 2 or even more
You are recording intracellularly from a rod. What would happen if the cGMP
it would hyperpolarize
What is the term for the enhancement of contour-contrast information in
which the gradient of neural responses across the retina is more exaggerated
than the intensity gradient?
hyperpolarization, feature detection, Mach bands
"Magnocellular" and "parvocellular" are terms applied
to retinal ganglion cells based on size and processing (movement vs contrast
respectively). What is the difference in projection to the brain?
they project to different layers in the LGN. M-> 1 & 2, P -> 3-6
Long before they could record intracellularly from single rods or cones,
they knew that a rod could see a single photon of light. How?
testing whether subjects could see carefully calibrated lights (psychophysics)
Under what circumstances would a person be able to see ultraviolet light?
if the lens is missing
"The blue cone opsin is on human chromosome 7 while rod rhodopsin is
on 3." Where are the genes for yellow- and green-absorbing opsins?
There is a huge amount of phagocytosis that retinal pigment epithelium (RPE)
cells must do. Phagocytosis of what?
the tips of rod outer segments are shed daily
"The blind spot is at about 15o on the nasal retina at the horizontal
plane." Why is there a blind spot?
there can be no receptors where the optic nerve exits
Abnormal elongation of the eyeball is associated with what refractive error?
Cones would be preferentially damaged in what debilitating disorder affecting
age related macular degeneration (AMD)
A woman has lots of sons, half red-blind (protanopic) and half with normal
color vision. How would her retina be with respect to red color vision?
Specifically, what gates the channels in the rod plasmalemma?
Hartline found that there is increased firing from brightly lit facets (of
a crab's eye) near a dark area than a brightly lit area near only brightly
lit areas. Why?
Rhodopsins (such as the 4 of rods and cones) are sometimes called visual
pigments, yet proteins usually do not absorb visible wavelengths of light.
What makes rhodopsin a pigment?
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