3rd Lecture on Physiology of Eye by Dr. Roomi

7/28/2019 3rd Lecture on Physiology of Eye by Dr. Roomi

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PHYSIOLOGY OF EYE

BY

DR. MUDASSAR ALI ROOMI (MBBS, M.Phil.)


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Neurophysiology of Vision


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the visual system/pathwayconsists 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 dorsallateral 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 ORGENICULOCALCARINE TRACT

Homonymouscontralateralhemianopia with

macular sparing. Macular sparing

occurs becauselesion of visual cortex

don't destroy allneurons thatrepresent themacula.


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PITUITARY TUMOR MAY COMPRESS ON OPTIC CHIASMAAND CAN CAUSE BITEMPORAL HEMIANOPIA

BITEMPORAL HEMIANOPIA


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BITEMPORAL HEMIANOPIA BINASAL HEMIANOPIA


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Lateral Geniculate Nucleus

High degree of spatial fidility

Layers II, III and V receive temporal fibers

Layers I, IV and VI receive nasal fibers

Layer I & II receive Y neurons

Layerr II & VI receive X cells


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Primary Visual Cortex????

Area 17

located in the occipitallobe in the calcarinefissure region extending tothe pole

large representation invisual cortex for the

macula (region for highestvisual acuity)

receives the primaryvisual input


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Secondary Visual Areas

visual association cortex(area 18, 19)

responsible for analyzingthe visual information

area for 3 dimensionalposition, grossform, andmotion

area for color analysis


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Retinal Projections toSubcortical Regions

suprachiasmatic nucleus of thehypothalamus

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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Pupillary Light Reflexes

If a light is shone directly into oneeye, its pupil constricts. Thisresponse is known as the direct

pupillary response.

The pupil of the other eye alsoconstricts, and this is known as the

consensual response.


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PUPILLARY REFLEXES


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HORNERS SYNDROME

The sympathetic nerves to the eyeare occasionally interrupted .

Interruption occurs in cervicalsympathetic chain.


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HORNERS SYNDROME

One pupil remains persistentlyconstricted to a smaller diameter thanthe pupil of the opposite eye (miosis)

Drooping of Upper eyelid (ptosis)

Blood vessels on the corresponding side

of the face & head become persistentlydilated (flushing of face)

Sweating cant occur on the affectedside of the face (anhydrosis)


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CONFRONTATION METHOD TOTEST THE FIELD OF VISION


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perimetry

Listers perimeter

Perimetry maps andquantifies the visualfield, especially at theextreme periphery of

the visual field.


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GOLDMANS PERIMETRY


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Physiologic blind spot: In allperimetry charts, a blind spotcaused by lack of rods andcones in the retina over theoptic disc is found about 15

degrees lateral to the centralpoint of vision, as shown in thefigure.

Scotoma

A blind spot in any other

portion of the visual field


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3rd Lecture on Physiology of Eye by Dr. Roomi

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