Eye physiology from guyton and halls physiology Part 3

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


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


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)


Visual pathways to the brain


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Lesions of the optic pathway



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.




PITUITARY TUMOR MAY COMPRESS ON OPTIC CHIASMA AND CAN CAUSE BITEMPORAL HEMIANOPIA

BITEMPORAL HEMIANOPIA


BITEMPORAL HEMIANOPIA BINASAL HEMIANOPIA


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


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


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


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


The Autonomic Nerves to the Eyes


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.


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.


PUPILLARY REFLEXES


Fig. 16.07


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


Pathways of direct and indirect light reflexes (v.imp.)


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


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).


HORNER’S SYNDROME

The sympathetic nerves to the eye are occasionally interrupted . Interruption occurs in cervical sympathetic chain.


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)


CONFRONTATION METHOD TO TEST THE FIELD OF VISION


perimetry

Lister’s perimeter

Perimetry maps and quantifies the visual field, especially at the extreme periphery of the visual field.


GOLDMAN’S PERIMETRY



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


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


35 Thank You

By Muhammad Ramzan Ul Rehman

Eye physiology from guyton and halls physiology Part 3

Education

postganglionic fibers

fibers synapse

theradial fibers

crossed fibers

parasympathetic fibers

optic chiasma

optic radiation

optic tracts