7 Vision Flashcards
A minimum of how many neurons are needed for vision?
3- photoreceptor, bipolar cell, ganglion cell
What type of neurons generate graded potential?
Action potential?
Photoreceptors & Bipolar cell
Ganglion Cell
What phagocytoses the outer segments of photoreceptors and converts all-trans-retinal back to 11-cis retinal?
Retinal pigment epithelium
What leads to increased intraocular pressure?
decreased aqueous humor outflow
Homonymous visual defects suggests lesions where?
behind the optic chiasma
Altitudinal defects suggest lesions where?
in the eye
where is the primary site of injury in diabetic retinopathy and atherosclerotic disease?
retinal vasculature
What is the major site of injury in macular degeneration?
choroidal circulation
T-F – vision is not important to all patients?
False
T-F – eye disorders are very common?
True
T-F – the eye is a window to many physiologic systems?
True
What physiological systems are represented by an eye exam? [4 of them]
CNS (II, III, IV, V, VI and SNA)
Vascular System
Endocrine System
Immune System
What are the 5 components of vision?
Pointing the eye Focusing Adjusting Exposure Converting image to impulses Transmit impulse to brain and interpreting them
Focusing of light is accomplished by the combination of what two structures?
Cornea and lens
Refractive power is provided by what structure?
Cornea (75%)
Lens (25%)
What structure allows one to adjust the focus for accommodation?
Lens
T-f? The degree to which the focal length of the lens can be changed increases with age?
False- it decreases with age
T - F - cornea and lens are vascular?
False
What is the inner surface of cornea and both surfaces of lens bathed in for oxygen/nutrient purposes? Synthesized by what?
aqueous humor- synthesized by non pigmented epithelium on ciliary body. (Superficial layer)
What is the second most common blindness in the world? Caused by what?
glaucoma- trabecular meshwork is impeded, aqueous humor outflow is low, intraocular pressure increases and damages optic nerve
Opacification of lens is called what?
Cataract
paraSNA does what to pupils?
constricts pupillary sphincter and causes constriction
SNA does what to the pupil?
innervates radial dilator muscles to dilate the pupil
What 2 afferent signals cause paraSNA activity to the pupil?
Light falling on the retina
fixating on a near target
What nucleus is stimulated in CNS when para SNA is activated?
edinger westphal nucleus in midbrain
Axons of edinger westphal travel in what CN?
III—> ciliary ganglion—>short ciliary nerves—>
ciliary body for accommodation or
pupillary sphincters
How do you test for a relative afferent pupillary defect or Marcus-Gunn pupil?
Bright light at one eye at a time
T-F — the pupils are different in size in a pure afferent defect?
False– the are always EQUAL
T-F — previous trauma to one iris prevents one from looking for an afferent defect?
False- because you can observe either eye for an efferent response
T-F — the pupil response is largely affected by media opacities such as cataract or blood?
False
T-F– Unilateral efferent defects result in unequal pupils?
True
T-F—uncal herniation results in dialated unresponsive pupil?
True- compresses CNIII as it leaves the midbrain
[HOWEVER, PATIENTS HERNIATING ARE USUALLY COMATOSE, patients with blown up pupils probable have had a pharmaco agent or atropine exposure.]
Where does the sympathetic pupilomotor system begin?
neurons in the hypothalamus
Sympathetic pupilomotor nerves exit what 3 spinal nerves?
T1,2,3,—> ascend and synapse in cervical ganglion
T-F —SNA nerves synapse in the ciliary ganglion?
False–they just pass through and join paraSNA on short ciliary fibers
Injury to the SNA between hypothalamus and orbit will result in what?
Horner’s Syndrome
What is the reason for several steps in photransduction?
amplification
The end result of photo cascade is what?
closure of sodium channels—this is why the water tank analogy can account for it.
What type of receptor is rhodopsin?
G coupled protein and light is the ligand
What must the rhodopsin protein have bound to it to be sensitive to light?
vitamin A derivative- 11-cis retinal—which is isomerized to all trans by photon capture
T-F – the visual cycle or conversion back to 11-cis-retinal occur outside the photoreceptor?
True
What is the G protein in the phototransduction cascade?
transducin
How are Na+ channels kept open in the dark?
cGMP molecules
What is the overall phototransduction pathway?
Light—> activated rhodopsin—> activated transducer—> activated PDE—>hydrolysis of cGMP—>closure of Na+ channels—> hyperpolarization
The photoreceptors synapse on bi polar cells and use what as the neurotransmitter?
glutamate
What do bipolar cells do?
conduct the graded output of photoreceptors to the ganglion cells—-> ganglion cells become first to generate AP
Where does re-isomerization occur of 11-cis-retinal?
retinal pigment epithelium
What is the 2nd major function of retinal pigment epithelium?
phagocytose outer segments of photoreceptors
What is the most common cause of severe visual loss in the developed world?
macular degeration- lipofuscin accumulations within and beneath the RPE
The face of the retina nearest the center of the eye is supplied by what vessel?
central retinal vessels (vessels seen in the opthalmascope)
The face of the retina near the sclera is supplied by what vessel?
choriocapillaris anastamosing network beneath the RPE
What is the choriocapillaris derived from?
posterior ciliary arteries
What is the area bounded by the temporal vascular arcades is known as the ?
Macula
Point of fixation in the center of the macula is known as the?
fovea
What is the structural specialization of the macula?
division of the temporal retinal blood supply into a superior and inferior division
Vascular occlusions of the retinal vessels have what effect on the visual field?
horizontal effect
What is necessary for complex perception of depth?
signals from both eyes need to converge on single cortical area
Where are axons of the retinal ganglions cells are sorted so that the axons carrying info from the temporal field of one eye travel with axons that carry information from the nasal field of the other?
optic chiasma— complex perception of depth
Injury to visual pathways behind the chasm cause visual defects that affect what?
same side of vertical meridian–homonymous visual field defects
Altitude visual defects suggest?
disease inside the eye
unilateral visual defects suggest?
disease anterior to chiasm
bitemporal visual defects suggest?
disease at the chiasm
homonymous field defects suggest disease?
behind the chiasm
