eye physiology from guyton and halls physiology part 3
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Eye physiology from guyton and halls physiology Part 3TRANSCRIPT
BY Muhammad Ramzan Ul Rehman Nishtar Ken 1
BY Muhammad Ramzan Ul Rehman Nishtar Ken
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PHYSIOLOGY OF EYE
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Neurophysiology of Vision
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the visual system/pathway consists of:
the retina
The optic nerve
The optic chiasma
The optic tract
The lateral geniculate body
The optic radiation
The visual cortex
The visual association cortex
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Visual Pathways to the Brain
optic nerve axons of ganglion cells of the retina
optic chiasm At optic chiasma, all fibers from the nasal halves of the
retina cross to the opposite side
crossed fibers join fibers from the opposite temporal retina to form the optic tracts
These fibers synapse in the dorsal lateral geniculate nucleus (LGN)
from LGN to primary visual cortex by way of the optic radiation (geniculocalcarine tract)
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Visual pathways to the brain
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Lesions of the optic pathway
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LESION OF OPTIC RADIATION OR GENICULOCALCARINE TRACT
Homonymous contralateral hemianopia with macular sparing.
Macular sparing occurs because lesion of visual cortex don't destroy all neurons that represent the macula.
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PITUITARY TUMOR MAY COMPRESS ON OPTIC CHIASMA AND CAN CAUSE BITEMPORAL HEMIANOPIA
BITEMPORAL HEMIANOPIA
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BITEMPORAL HEMIANOPIA BINASAL HEMIANOPIA
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Lateral Geniculate NucleusHigh degree of spatial fidilityLayers II, III and V receive temporal fibers
Layers I, IV and VI receive nasal fibers
Layer I & II receive Y neuronsLayerr II & VI receive X cells
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Primary Visual Cortex????
Area 17
located in the occipital lobe in the calcarine fissure region extending to the pole
large representation in visual cortex for the macula (region for highest visual acuity)
receives the primary visual input
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Secondary Visual Areas
visual association cortex (area 18, 19)
responsible for analyzing the visual information
area for 3 dimensional position, gross form, and motion
area for color analysis
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Retinal Projections to Subcortical Regions
suprachiasmatic nucleus of the hypothalamus control of circadian rhythms??
pretectal nuclei pupillary light reflex accommodation of the lens
superior colliculus rapid directional movement of both eyes
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The Autonomic Nerves to the Eyes
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The Autonomic Nerves to the Eyes The eye is innervated by both parasympathetic and sympathetic neurons.
Parasympathetic fibers arise in the Edinger-Westphal nucleus, pass in the 3rd cranial nerve to the ciliary ganglion. Postganglionic fibers excite the ciliary muscle and
sphincter of the iris.
Sympathetic fibers originate in the intermediolateral horn cells of the superior cervical ganglion. Postganglionic fibers spread along the corotid artery and eventually innervate
the radial fibers of the iris.
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Pupillary Light Reflexes If a light is shone directly into one eye, its pupil constricts. This response is
known as the direct pupillary response.
The pupil of the other eye also constricts, and this is known as the consensual response.
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PUPILLARY REFLEXES
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Fig. 16.07
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Pupillary Light Reflex
When the amount of light entering the eyes increases, the pupils constrict.
Functions to help the eye adapt extremely rapidly to changing light conditions.
Direct light reflex: same pupil constricts
indirect (consensual) light reflex: pupil of the opposite eye constricts
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Pathways of direct and indirect light reflexes (v.imp.)
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Control of Pupillary Diameter
miosis: decreasing of pupillary aperture due to stimulation of parasympathetic nerves that excite the pupillary sphincter muscle
mydriasis: dilation of pupillary aperture due to stimulation of sympathetic nerves that excite the radial fibers of the iris
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ARGYLL ROBERTSON PUPIL.
Pupil that fails to respond to light but does respond to accommodation and is very small in size.
It is an important diagnostic sign of CNS disease (syphilis).
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HORNER’S SYNDROME
The sympathetic nerves to the eye are occasionally interrupted . Interruption occurs in cervical sympathetic chain.
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HORNER’S SYNDROME
One pupil remains persistently constricted to a smaller diameter than the pupil of the opposite eye (miosis)
Drooping of Upper eyelid (ptosis)
Blood vessels on the corresponding side of the face & head become persistently dilated (flushing of face)
Sweating can’t occur on the affected side of the face (anhydrosis)
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CONFRONTATION METHOD TO TEST THE FIELD OF VISION
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perimetry
Lister’s perimeter
Perimetry maps and quantifies the visual field, especially at the extreme periphery of the visual field.
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GOLDMAN’S PERIMETRY
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Physiologic blind spot: In all perimetry charts, a blind spot caused by lack of rods and cones in the retina over the optic disc is found about 15 degrees lateral to the central point of vision, as shown in the figure.
Scotoma
A blind spot in any other portion of the visual field
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Fields of Vision nasal field located on the temporal side of the retina
temporal field located on the nasal side of the retina
interruption of the visual pathway at different points leads to very specific visual field defects
“blind spot” located about 15 degrees lateral to the central point of vision
no rods or cones in this area, called the optic disc, exit point for axons of the ganglion cells
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35 Thank You
By Muhammad Ramzan Ul Rehman