physiology of vision-lecture

8/6/2019 Physiology of Vision-lecture

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LIGHTy DEFINITION Energy to which eye is sensitive

y UNIT FOR MEASURING LIGHT

y ELECTROMAGNETIC RADIATION

y OPTICAL RADIATION

y 7 WAVES BANDS OF OPTICAL RAD

UVC 200 280nm , UVB 280 315nm

UVA 315 400nm, Visible Rad 400 -780nm

IRA 780 -1400nm IRB 1400 -3000nmIRC 3000 - 10000 nm


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LIGHTy Shorter the wave length greater the energy.

y Cornea and sclera absorbs UVC and UVB also IRB and IRC.

y UVA is absorbed by the lens.


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How we see ?y Best understood by comparison with a camera.


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y CAMERA

y uses a shutterwith a

small, central opening toadmit light

y lens focuses the light, tomake a sharp image onfilm

y The "developing process"involves light-sensitive imagepreservation on film which islater on converted intopositive

y HUMANEYE

y Uses pupil to admit

appropriate lighty lens assumes a globular

or flat shape to formimage on retina

y The "developing process"involves light-sensitivereceptor cells on the retina -the rods and cones.


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RETINAy Optic cup differentiate as two layers

Outer layer RPEInner layer Sensory Retinay Retinal Layers1.Retinal Pigment Epithelium2.Rods and Cones

3.External limiting membrane4.Outer nuclear layer5.Outer plexiform layer6.Inner nuclear layer7.Inner plexiform layer

8.Ganglion cell layer9.Nerve fibre layer10.Internal limiting membrane


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RETINA (Contd)RODS AND CONES (PHOTORECEPTORS)

y Are light sensitive element ofretina

y Rods function at low level of illumination (Scotopic vision)

y Cones function at medium and high level of illumination (Photopic vision)

y Cones are mainlyfound in fovea

y Rods are mainlyfound in peripheral retina

y

Outer segment of

photoreceptors are removed diurnally andregenerated by inner segment


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RODS AND CONES (Contd)y Outer segment contain light sensitive pigment i.e. Rhodopsin in

rods and three photopigments in cones

y Axons of Rods and Cones synapse with bipolar cells and

amacrine cells which in turn synapse with ganglion cellsy Axons of ganglion cells form optic nerve which extend to brain

y Sensory retina contain 100 million rods and 6 million cones

y Optic disc has no photoreceptors and is a blind spot in the visualfield


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Image is laterally reversed &

upside down on retina


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y The rodcellscontainrhodopsin, a protein

partially derivedfromvitamin A.

y Rods are sensitive tolight and enable us to see

in dim light.y The conecells, contain

iodopsin, are used forfine details and bright,

color vision.


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y Humans have three types

ofcones, each sensitiveto a different color oflight: red, blue and green

y Center ofthe macula :

foveacontainsmaximum no ofcones


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Rhodopsin Bathorhodopsin

Lumirhodopsin

Metarhodopsin 1

Metarhodopsin 2

Opsin11cisretinal All transretinal

11cisretinol All transretinol


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y Information is passed to the ganglioncellswhichsend their axons to form opticnerves

y

Opti

cC

hi

asm

a

is the portion where opticf

ibersf

romthenasal portion ofeach retina cross.

y OpticTracts. fibers from chiasma join the fibers fromthe temporal portion ofthe retina on the oppositeside.

y Left optic tract = impulses from Right visual field,y Right optic tract = impulses from Left visual field.


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y Optic Tracts. fibers fromchiasma join the fibers fromthe temporal portion of the

retina on the opposite side.

y Left optic tract = impulsesfrom Right visual field,

y Right optic tract = impulses

from Left visual field.


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y Optic tract synapse atthe left/right lateralgeniculatebodies

y From here fiberscontinue as opticradiations to terminate

in the right and leftoccipital lobes.


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we do not see with our eyes but, rather, with

our brains. Our eyes merely are the beginnings

of the visual process.


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y THANK YOU

THANKYOU

physiology of vision-lecture

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