Vision
Dr. Janet Fitzakerley
jfitzake@d.umn.edu
http://www.d.umn.edu/~jfitzake/Lectures/Teaching.html
OPTICS
RETINA PHYSIOLOGY
Which of the following is MOST LIKELY to occur in
Parkinson disease?
One best answer
1. Decreased corneal reflex due to death
of neurons in the trigeminal ganglion
2. Decreased corneal reflex due to
macular degeneration
3. Decreased blinking due to loss of
dopaminergic input to premotor
brainstem structures
4. Decreased sympathetic drive from the
superior cervical ganglion
5. Increased acetylcholine release from
facial and oculomotor neurons
innervating OO and LPS
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20%
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Blink Circuits
REFRACTION
The cornea and lens focus light on the retina; the cornea has
greater refractive power but the focusing power of the lens can
be adjusted to allow near vision (accommodation). Refractive
errors include cataracts, hyperopia, myopia, presbyopia and
astigmatism.
Which of the following involves the image being
focused inappropriately in front of the retina?
More than one “correct” answer – but one best answer!
1.
2.
3.
4.
5.
6.
Astigmatism
Cataracts
Emmetropia
Hyperopia
Myopia
Presbyopia
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17%
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6
How would you correct the problem
in the previous question?
One best answer!
1. Contact lenses that correct refraction in
one meridian
2. Glasses with positive diopters
3. Refractive surgery to flatten the cornea
4. Replacement of lens
5. Reading glasses
6. No need to do anything
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HYPEROPIA
AXIAL
REFRACTIVE
CORRECTION
MYOPIA
PUPILLARY LIGHT REFLEX
Light intensity is regulated by the PUPILLARY LIGHT REFLEX,
which causes MIOSIS as a result of parasympathetic
stimulation of the sphincter pupillae muscles (muscarinic
receptors). MYDRIASIS results from sympathetic stimulation
(α1 receptors) that activates the dilator pupillae muscles.
Where is the damage if you shine a bright light
into a person’s left eye,
and the right pupil DOES NOT constrict?
More than one “correct” answer
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Photoreceptors in the left eye
Photoreceptors in the right eye
Left optic nerve
Right optic nerve
Left optic tract
Right optic tract
Left visual cortex
Right visual cortex
Left oculomotor nucleus
Right oculomotor nucleus
Left dilator pupillae muscle
Right dilator pupillae muscle
Left sphincter pupillae muscle
Right sphincter pupillae muscle
http://www.youtube.com/watch?v=dotS3BaEH8s
If I told you that the person’s left eye constricts in response
to light in the left eye, would that help you localize the lesion?
Which of the following would result in increased
intraocular pressure?
One “correct” answer
1. Decreased carbonic anhydrase
activity
2. Increased parasympathetic activity
3. Relaxation of the ciliary muscle
4. Stimulation of α1 receptors
5. Stimulation of β2 receptors
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Aqueous Humour Production
Increased intraocular pressure causes loss of vision
(potentially permanent). Open angle glaucoma (the most common
form) results from overproduction of the aqueous humor.
Closed angle glaucoma (typically the most rapidly evolving form)
is caused by blockage of fluid outflow.
OPTICS
RETINA PHYSIOLOGY
Which of the following is
MORE CHARACTERISTIC of rods
compared to cones?
One “correct” answer
1.
2.
3.
4.
5.
6.
Detection of far red wavelengths
Location in the fovea
Only activated by multiple photons
Fast responses
Response to scattered light
Lack of convergence (in terms of
output from retina)
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17%
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17%
17%
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5
17%
6
Astronomers know that the best way to see faint nebulae and
star clusters is to avert their vision (at night, you can see a
dim object better if you look a bit to one side)? Which of the
following BEST explains this phenomenon?
One “correct” answer
1. Rods have better spectral
sensitivity than cones.
2. Rods have better temporal
sensitivity than cones.
3. Rods have better spatial acuity than
cones.
4. Rods undergo dark adaptation
more than cones.
25%
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25%
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Rods are responsible for SCOTOPIC vision (the monochromatic
vision that occurs in low light). The three types of cones (blue,
green and red; or Short, Medium and Long wavelength) have
better temporal and spatial resolution than rods, making
PHOTOPIC VISION better for discrimination of surfaces and
movement under bright light conditions.
The ability to discriminate fine details of the visual scene is
termed VISUAL ACUITY.
Three types are recognized:
SPATIAL, TEMPORAL and SPECTRAL. Visual acuity is primarily a
function of the cone system.
Types of Acuity
How is transduction in olfactory receptor neurons
similar to rod phototransduction? Both systems:
One “correct” answer
1. have multiple receptor proteins in
individual receptor cell.
2. use the same G-protein.
3. activate phosphodiesterase.
4. involve ligand-gated non-selective
cation channels.
5. result in depolarization following
receptor activation.
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Steps in Rod Phototransduction
PHOTOTRANSDUCTION occurs via a 4 step process that uses a
2nd messenger cascade to amplify the signal. In rods, activation
of rhodopsin ultimately results in the closure of cyclic nucleotide
gated Na+ channels, and hyperpolarization of the photoreceptor.
Which of the following occurs
when low intensity light hits the photoreceptors?
One “correct” answer
1. Rhodopsin is cleaved but cone
pigments are not.
2. An opsin and all-trans-retinal are
formed from rhodopsin.
3. The retinal pigment epithelium
takes up rhodopsin.
4. Rods accumulate rhodopsin.
5. Rhodopsin is reformed in the retinal
pigment epithelium from an opsin
and all-trans-retinal.
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The VISUAL CYCLE consists of bleaching and recycling of 11-cisretinol between the photoreceptors and the retinal pigment
epithelium (RPE). It is a key component of dark adaptation in rods
and is disrupted in vitamin A deficiency and macular degeneration.
Visual Cycle