Special Senses

Prof. Abdulrahman Prof. Abdulrahman FahmiFahmi 11

الرحيم الرحمن الله بسمخير على والسالم والصالة

المرسلين


PhysiologyPhysiology

Special SenseSpecial Sense

ByByProf. Dr. Abed-Elrahman FahmiProf. Dr. Abed-Elrahman Fahmi


Objectivs-NS&SSObjectivs-NS&SSLecture 15: physiology of the eyeLecture 15: physiology of the eye

(Anterior chamber accommodation) (Anterior chamber accommodation)

By the end of this lectures you By the end of this lectures you should be able to: should be able to:

Describe the eye as a camera.Describe the eye as a camera. Explain Accommodation allows the Explain Accommodation allows the

eye to focus on near objects eye to focus on near objects List and explain the function, of List and explain the function, of

cornea, lens, and aqueous humourcornea, lens, and aqueous humour


The human eye


Stimulus of the eye = light wavesStimulus of the eye = light wavesLens system of the eye = cornea Lens system of the eye = cornea

+ lens, they focus light from + lens, they focus light from objects as inverted images on the objects as inverted images on the

retinaretina


How objects are How objects are perceivedperceived

Retinal photoreceptors (Rods + Retinal photoreceptors (Rods + Cones) changes light to nerve Cones) changes light to nerve impulses which passes through impulses which passes through optic nerve and visual pathway optic nerve and visual pathway to visual sensory areas to visual sensory areas (Occipital cortex),objects are (Occipital cortex),objects are perceived upright.perceived upright.


Optic diskOptic disk It lies 3 mm medial to posterior pole It lies 3 mm medial to posterior pole

1.5 mm in diameter It is site of optic 1.5 mm in diameter It is site of optic nerve exit, and entry of retinal blood nerve exit, and entry of retinal blood vessels. It is called blind spot as it has vessels. It is called blind spot as it has no visual receptorsno visual receptors

Macula lutea:Yellow spot on temporal side of posterior pole. It has a central depressed area, called fovea centralis .which is the part of retina with maximal visual acuity (contain Cones only).


OPTICS OF THE EYEOPTICS OF THE EYE

Lens system of the eye is Lens system of the eye is composed of :composed of :

AirAir

1- Interface between air and cornea1- Interface between air and cornea2-Interface between aqueous 2-Interface between aqueous

humour and anterior surface of humour and anterior surface of lens.lens.


Refractive index (R.I)Refractive index (R.I):: Ratio of velocity of light in air to that in substance, Ratio of velocity of light in air to that in substance,

e.g. : R.l (of air) = 1. lens = 1.42Cornea, Aqu. e.g. : R.l (of air) = 1. lens = 1.42Cornea, Aqu. hum, or vit.hum. = 1.33hum, or vit.hum. = 1.33

Optical axis of eye: Line connecting anterior and Optical axis of eye: Line connecting anterior and posterior poles of the eye.posterior poles of the eye.

Visual axis:Visual axis: Line between pupil and fovea centralis ,and Line between pupil and fovea centralis ,and

passes through nodal point. passes through nodal point.

Convex lens has:Convex lens has:a- Nodal point (central point): a- Nodal point (central point): Through which light rays, Through which light rays, pass without refractionpass without refraction


b-Focal b-Focal length: Which connects length: Which connects between focus (on retina) andbetween focus (on retina) andnodal point = 17 mm.nodal point = 17 mm.

Refractive power Refractive power of the emmetropic of the emmetropic eye at rest (without accommodation):eye at rest (without accommodation):

11= –––––––––––––––––––= –––––––––––––––––––

Focal length in metersFocal length in meters 11 1000 1000

= ––––– = –––––––– 59 Diopters= ––––– = –––––––– 59 Diopters 0.017 170.017 1743 Diopter for cornea 16 Diopter for lens.43 Diopter for cornea 16 Diopter for lens.


Why cornea has more Why cornea has more refractive power than lens?:refractive power than lens?:

1) Mo re curvature 1) Mo re curvature

2) Difference in refractive indices between 2) Difference in refractive indices between adjacent media.adjacent media.

Air = 1.Air = 1. Aqueous humour = 1.33. Aqueous humour = 1.33.cornea = 1.33 lens = 1.42cornea = 1.33 lens = 1.42

N.B:N.B: Outside the body .power of lens =150 Outside the body .power of lens =150 Diopter, as it faces air. The refractive Diopter, as it faces air. The refractive power of lens can be increased as during power of lens can be increased as during accommodation ,but the refractive power accommodation ,but the refractive power of cornea can not be changed.of cornea can not be changed.


ACCOMMODATION REFLEXACCOMMODATION REFLEX ( Near response) ( Near response)

Stimulus:Stimulus: looking to near object looking to near object Function:Function: To see near object clear ; To see near object clear ; Components: 3 parts:Components: 3 parts:1- Medial convergence of both eyes1- Medial convergence of both eyesCause:Cause: Contraction of medial recti Contraction of medial recti

muscles.muscles. Near objectNear object

EffectEffect: Bring the image of a near object on : Bring the image of a near object on fovea centralis of both retina to see its fovea centralis of both retina to see its details.details.


2- 2- Miosis Miosis = constriction of the pupils= constriction of the pupilsCauseCause: contraction of the constrictor : contraction of the constrictor

Pupillary muscle.Pupillary muscle.EffectEffect::a) Prevention of light rays falling on edges a) Prevention of light rays falling on edges

of the lens to avoid (Spherical & of the lens to avoid (Spherical & chromatic chromatic aberrations) these aberrations ) these aberrations result in a blurred image of a near object. result in a blurred image of a near object. Peripheral parts of lens has less Peripheral parts of lens has less refractive index causing spherical refractive index causing spherical aberration, while peripheral part acts as aberration, while peripheral part acts as prism causing chromatic aberration.prism causing chromatic aberration.

b) Increase the depth of the focus.b) Increase the depth of the focus.


33 - -AccommodationAccommodation

CauseCause:: contraction of cilliary musclecontraction of cilliary muscle

EffectEffect:: Increase convexity of anterior Increase convexity of anterior surface of the lens witch leads to surface of the lens witch leads to increase refractive power of the lens increase refractive power of the lens 10 diopters above normal leading to 10 diopters above normal leading to focusing of the image of a near object focusing of the image of a near object ononretina. retina.

EmmetropicEmmetropic eye see far object, more eye see far object, more than 6 meters without accommodation.than 6 meters without accommodation.

EmmetropicEmmetropic eye see near object eye see near object less than 6 m. with accommodation less than 6 m. with accommodation to be focused on retina to be focused on retina


Mechanism of Mechanism of accommodationaccommodation

Contraction of cilliary muscle changing the Contraction of cilliary muscle changing the shape of the lens from flat to sphericalshape of the lens from flat to spherical..

Rest During AccommodationRest During Accommodation

Cilliary muscle relaxed Cilliary muscle relaxed Cilliary muscle Cilliary muscle contracted contracted

Suspensory ligaments Suspensory ligamentSuspensory ligaments Suspensory ligamentTens = Lens flat.Tens = Lens flat. Relaxed=Lens spherical Relaxed=Lens spherical


Pathway of Pathway of accommodation reflexaccommodation reflex

Pathway of Accommodation to Near objects.

Temporal

Optic nerve

Optic chiasma

Lateral geniculate

Optic Radiation

Area 18

Area 17

Nasal

optic tract

Cillary muscle

Cillary ganglion


Proofs of increased anterior surface Proofs of increased anterior surface convexityconvexity::

1-Decreased antero-posterior1-Decreased antero-posterior diameter of anterior chamber diameter of anterior chamber 2-Purkinje-Samson images:2-Purkinje-Samson images:accommodation:accommodation:

Near visionNear vision Far vision Far vision Second image becomes smaller and Second image becomes smaller and

nearer to first image. nearer to first image.

Near point of vision:Near point of vision: It is the nearest point to the eye at It is the nearest point to the eye at

which objects can be seen clear, which objects can be seen clear, after which they appear blurred after which they appear blurred (focused behind retina)(focused behind retina)


At this point:At this point:1-Curvature of lens is maximum = 1-Curvature of lens is maximum =

no more increase in refractive no more increase in refractive power of lens = Max. power of lens = Max. accommodation.accommodation.

2- Image is focused on the retina.2- Image is focused on the retina.

3-lt is not maximal contraction of 3-lt is not maximal contraction of ciliary muscle.ciliary muscle.

It becomes farer with age: 9 cm It becomes farer with age: 9 cm

at age of 10 years. 25 cm in at age of 10 years. 25 cm in adult age 83 cm at age of 60 adult age 83 cm at age of 60 years.years.


Amplitude of Amplitude of accommodationaccommodation::

Difference between refractive Difference between refractive power of the eye during distant power of the eye during distant vision (rest) and at maximum vision (rest) and at maximum accommodation ( near vision ), it accommodation ( near vision ), it is decreased with aging: 11 is decreased with aging: 11 Diopters in 10 years. Diopters in 10 years. 10 Diopoters in adult age, 1.510 Diopoters in adult age, 1.5

Diopoters in 60 years old. Diopoters in 60 years old.


PresbyopiaPresbyopia:: The reduction in accommodative power of the eye , it occurs in old The reduction in accommodative power of the eye , it occurs in old

age (40-45 years old).age (40-45 years old).

Cause:Cause: Loss of elasticity of lens proteins by continuous loss Loss of elasticity of lens proteins by continuous loss of Hof H22O.;O.;

ComplaintComplaint: Near point more than the comfortable reading: Near point more than the comfortable reading distance (25 cm)distance (25 cm)

CorrectionsCorrections: By Biconvex lens.: By Biconvex lens.

N.B.:N.B.: Effect of atropine: Blocks autonomic and not somatic action. Effect of atropine: Blocks autonomic and not somatic action.

Argyil-Robertson pupil:Argyil-Robertson pupil:

CauseCause: Neuro-Syphilis.: Neuro-Syphilis.

Site of lesion:Site of lesion: Pretectal region of Mid. brain Pretectal region of Mid. brainEffect:Effect:

a- Loss of light R.(both direct and indirect), in both eyes.a- Loss of light R.(both direct and indirect), in both eyes.

b- Intact accommodation R in both eyes.b- Intact accommodation R in both eyes. N.BN.B. Relation with tabes dorsalis. Relation with tabes dorsalis


Cornea

Function.1)Entry of light rays2) Entry of drugs ( eye drops).3)Acts as refractive medium.

To do this function , it must bea)Proper curvature b)Transparent


Cornea

Cause of tranparencya)Parallel lamellae of the same

refractive index.b)Dehydratedc)Avascular.

Vit. B2 deficiency -> corneal vasocularization that leads to -> Corneal opity>


Iris It gives the eye its coloer ( melanin).

Pupil :- Central penning protected by :-Circular muscle ( constrictor

Pupillary muscle )parasympathetic III N.

Radial M. ( Dilator Pupillary M. ) cervical sympathetic M.


Lens:-it is formed of 70% H2O & 30 % Proteins

Cataract

it is opacity of the lens due to denaturation and agglutination of its proteins either :-

a)Mature (Complete).

b)immature (incomplete).


Cataract causes-:

1. Senile cataract2. Diabetic3. High temp. & ultra-violet rays.4. Traumatic.5. Tryptophan & Vit. C defeciency.



Humours Humours of the eyeof the eye

A) Aqueous Humour:A) Aqueous Humour: It is the fluid filling both anterior and posterior It is the fluid filling both anterior and posterior

chambers of the eye.chambers of the eye.

Composition :Composition : HH22O, NaCl, sugar, small amount of protein and O, NaCl, sugar, small amount of protein and

hayluronic acid . hayluronic acid .

Formation & drainage : (not known) Formation & drainage : (not known) It is formed by active process from ciliary processes It is formed by active process from ciliary processes

at a rate of 2 mm/min. in posterior chamber → at a rate of 2 mm/min. in posterior chamber → anterior chamber through pupil → spaces of anterior chamber through pupil → spaces of Fontana → canals of Schlem (in corneo-scleral Fontana → canals of Schlem (in corneo-scleral junction) → episcleral veins .junction) → episcleral veins .

Functions :Functions :1-Refractive medium 1-Refractive medium 2-metabolism of cornea and lens (a vascular)2-metabolism of cornea and lens (a vascular)3-Normal I.O.P. (Intra-occular pressure).3-Normal I.O.P. (Intra-occular pressure).


B) Vitreous HumourB) Vitreous Humour:: It is found in the space from posterior It is found in the space from posterior

surface of eye lens to retina .surface of eye lens to retina .

Functions :Functions :1-Refractive medium 1-Refractive medium 2-Prevent backward displacement of lens2-Prevent backward displacement of lens3-Retinal support (globular shape of eye).3-Retinal support (globular shape of eye).-It is the pressure inside eye chambers (N = -It is the pressure inside eye chambers (N =

20 - 25 mm/Hg).20 - 25 mm/Hg).

Factors affecting it:Factors affecting it:1-Increased venous pressure →1-Increased venous pressure → I.O.P. I.O.P.2-Exposure to light pupillary constriction -» 2-Exposure to light pupillary constriction -»

wide spaces -> 4 I.O.P.wide spaces -> 4 I.O.P.3-Dark → pupillary dilatation →3-Dark → pupillary dilatation → I.O.P. I.O.P.4- 4- formation or formation or drainage of aqueous drainage of aqueous

humour →humour → t I.O.P. t I.O.P.


Glucoma :Glucoma : ( ( I.O.P.) I.O.P.)A) Primary :A) Primary : Obstruction in spaces of Obstruction in spaces of

Fontana → decreased drainage of aqueous Fontana → decreased drainage of aqueous fumour.fumour.

B) Secondary :B) Secondary : Eye infection → oedema and Eye infection → oedema and pus → occlusion of canal of Schlem .pus → occlusion of canal of Schlem .

-Complications : Optic atrophy and blindness .-Complications : Optic atrophy and blindness .-Treatment: by Diamox-Treatment: by Diamox

Strabismus :Strabismus :-Loss of conjugate movements of both eye -Loss of conjugate movements of both eye

balls .balls .

-Effects :-Effects :1-Squint 2-Diplopia (double vision).1-Squint 2-Diplopia (double vision).

-Types :-Types :-Convergent, divergent, vertical or horizontal.-Convergent, divergent, vertical or horizontal.



VISUAL FIELDVISUAL FIELDDefinitionDefinition::It is the maximal part of the outer world It is the maximal part of the outer world

that can be seen by one fixed eye.that can be seen by one fixed eye.

( ) ( )

T N N T

Divisions:It is divided into Nasal & Temporal.Nasal: is divided into Upper quadrant & Lower quadrant Temporal: is divided into Upper quadrant & Lower quadrant.Projection of field of vision on the retina:The temporal half of the visual field is perceived by the nasalhalf of the retina and vice versa. Normal visual field:

In

nasal

50 up

o

o

70-80 downo

90-100out

o o

temporal

60


MeasurementMeasurement::1-1-Confrontation method:Confrontation method: (Bed-side (Bed-side

method); Distance = 60 cm, it is method); Distance = 60 cm, it is practical but not accurate practical but not accurate

2-Perimetry: 2-Perimetry: Done in different meridians, Done in different meridians, it is accurate but not practical.it is accurate but not practical.

Significance:Significance:1- 1- Diagnosis ofDiagnosis of site and may be cause of site and may be cause of

lesion in visual pathway as Bitemporal lesion in visual pathway as Bitemporal hemianopia = lesion in center of optic hemianopia = lesion in center of optic chiasma = pituitary tumor.chiasma = pituitary tumor.

2-Diagnosis of2-Diagnosis of : :a) Blind spot = Physiological optic disk.a) Blind spot = Physiological optic disk.b) Scotomata = Pathological blind spot.b) Scotomata = Pathological blind spot.c) Retinites pigmentosa = causes c) Retinites pigmentosa = causes

scotomata.scotomata.


N.B.:N.B.: Central macular vision is the Central macular vision is the central part of visual field, it has central part of visual field, it has highest visual acuity (More highest visual acuity (More details), as there is no details), as there is no convergence between cones. The convergence between cones. The peripheral retina is more sensitive peripheral retina is more sensitive to weak light than the to weak light than the centercenter (F.C) due to convergence and (F.C) due to convergence and summation between rods and summation between rods and nerve fibers. There is nerve fibers. There is convergence of 140 rods and 6 convergence of 140 rods and 6 cones on each optic fiber. In fovea cones on each optic fiber. In fovea centralis it is one to one centralis it is one to one connection (no convergence).connection (no convergence).


VISUAL-SENSORY AREASVISUAL-SENSORY AREASSite: The occipital lobe :Site: The occipital lobe :

Primary visual areas (area 17-v1) Primary visual areas (area 17-v1) Function: Function: 1-Sensation of light (without 1-Sensation of light (without

understanding)understanding)2-Fusion of images2-Fusion of images3-Colour analysis3-Colour analysis4-Perception of luministy4-Perception of luministy2)Visual association areas (area 18-19 2)Visual association areas (area 18-19

V2-V3) Function:V2-V3) Function:Understanding of the meaning of Understanding of the meaning of

light ,its lesion causes light ,its lesion causes visualagonsia.visualagonsia.


Visual acuity

Def. I is the ability of the eye to Detect

details and boundaries objects. Emmetropic Eye.

Which what can differentiate between 2 points at distance of 6 meters , making visual angle of 1 minute in the nodal point ----retinal distance of 4 μ enough to stimulate 2 cone with one cone in between unstimulated---- Tow separate images in visual cortex .


Maximum Visual acuity( acuity of fovea)

Only cones . No convergence. Wider cortical representation.

Test

Snellen’s letter cards. Fandolt cards ( in EGYPT). Patient sights at distance 6

meters.


What is meant by visual acuity 6/18 of a patient ?

It means What the normal person can see at a distance of 18 meters the patient can only see at a distance 6 meters .

To diagnose Blindness:-1.6/60 . 2.5/60 .3.1/60.4.Finger counting.5.Hand movement.6.Light preceptation.


Factor affecting Visual acuity

1. Stimulus factor s as illumination and

contast.

2. Diopteric factors as normal cornea

and lens

3. Retinal factors as F.C. is maximum.


Effect of lesion in Effect of lesion in visual pathwayvisual pathway::


11 ( (Lesion in right optic Lesion in right optic nervenerve::

a)Blindnessa)Blindness b) No direct light reflex. b) No direct light reflex.

a)Blindness a)Blindness b) No direct light reflex. b) No direct light reflex. 2) Lesion in center of optic chiasma2) Lesion in center of optic chiasma::

Bitemporal Hemianopia Bitemporal Hemianopia Causes: Pituitary tumor.Causes: Pituitary tumor.


33 ( (Lesion in both sides of Lesion in both sides of optic chiasmaoptic chiasma::

Binasa! Hemianopia

4-Lesion on right optic tract L.G.B. optic radiation:

a-Homonyrnus Hemianopia

b) No light reflex (if lesion in optic tract).


55 ( (Lesion in right area 17Lesion in right area 17:: Cause :Vascular due to Cause :Vascular due to

thrombosis in posterior thrombosis in posterior cerebral artery, it is either:cerebral artery, it is either:

a- Lesion in whole area:a- Lesion in whole area: i.e. i.e. lesion in macula (in lesion in macula (in posterior occipital pole) + posterior occipital pole) + Periphery (anterior part)Periphery (anterior part)

This causesThis causes Homonymus hemianpoiaHomonymus hemianpoia


b-Lesion in anterior part b-Lesion in anterior part (only periphery)(only periphery)

Homonymus hemanopia with macular sparingHomonymus hemanopia with macular sparing. .

Also it is called Telescopic vision Also it is called Telescopic vision..


c-Lesion above calcarine fissurec-Lesion above calcarine fissure::

Affect only upper portion of retina. Affect only upper portion of retina.

d-Lesion below calcarine fissure: d-Lesion below calcarine fissure: affects only lower portion of affects only lower portion of retina.retina.

N.B:N.B: Causes of macular sparing: Causes of macular sparing:1-Separate and wider cortical 1-Separate and wider cortical

representation of macula(100 times representation of macula(100 times larger than periphery)larger than periphery)

2-Double blood supply of the macula, 2-Double blood supply of the macula, posterior and middle cerebral posterior and middle cerebral arteries.arteries.


Objectivs-NS&SSObjectivs-NS&SSLecture 16 : Light reflex, and retinal Lecture 16 : Light reflex, and retinal

function (dark adaptation, and function (dark adaptation, and electrophysiology of Rods and Cones)electrophysiology of Rods and Cones)

By the end of the lecture you By the end of the lecture you should be able to: should be able to:

list the properties of the retinalist the properties of the retina explain the mechanism of light reflexexplain the mechanism of light reflex describe the mechanism of dark describe the mechanism of dark

adaptationadaptation explain the mechanism of rods and explain the mechanism of rods and

cones stimulationcones stimulation explain the spectral sensitivities of explain the spectral sensitivities of

rods and cones rods and cones


PUPILLARY LIGHT REFLEXPUPILLARY LIGHT REFLEX

Nervout Pathway ol pupillary Light Reflex 1. RetinaNervout Pathway ol pupillary Light Reflex 1. Retina2. Optic nerve 3. Optic chiasma 4. Optic tract 5. 2. Optic nerve 3. Optic chiasma 4. Optic tract 5. Superior colliculus 6. Prelectal area 7. Aqueduct of Superior colliculus 6. Prelectal area 7. Aqueduct of Sylvtus 8.Sylvtus 8. Edinger westphal nucleus 9. Cilary Edinger westphal nucleus 9. Cilary ganglion 10. Short ciliary nerves 11. Occipital cortex.ganglion 10. Short ciliary nerves 11. Occipital cortex.


Definition:Definition: It is constriction of It is constriction of both pupils when one eye is both pupils when one eye is exposed to light. The response exposed to light. The response in exposed eye is called direct in exposed eye is called direct light reflex, while in the other light reflex, while in the other eye is called indirect or eye is called indirect or consensual reflexconsensual reflex..N.B.: Consensual light reflexN.B.: Consensual light reflex results from partial crossing of results from partial crossing of fibers at optic chiasma, thus fibers at optic chiasma, thus impulses from one eye activate impulses from one eye activate pretectal and Edinger-Westifal pretectal and Edinger-Westifal nuclei at both sidesnuclei at both sides..


Functions:Functions: 1) Regulation of amount of light entry. 1) Regulation of amount of light entry.2) Diagnosis of nervous disease and localization of 2) Diagnosis of nervous disease and localization of

lesion in visual pathway:lesion in visual pathway:

a)a) Lesion in right optic nerve: Lesion in right optic nerve: Left eye Right eyeLeft eye Right eye

DD C C D C D C present Lost present Lost Lost present Lost present

b) Lesion in right optic tract:b) Lesion in right optic tract: If light fell on the blind half of each retina (right temporal & left E nasal)If light fell on the blind half of each retina (right temporal & left E nasal)

But if light fell on right nasal & left temporal half of each retina normal But if light fell on right nasal & left temporal half of each retina normal response.response.

c) Lesion beyond optic tract (right L.G.B optic radiation, area 17): > c) Lesion beyond optic tract (right L.G.B optic radiation, area 17): > No effect on light reflex.No effect on light reflex.

Right eyeRight eye Left eye Left eye


This is used to differentiate between This is used to differentiate between lesion in the optic tract (lost light lesion in the optic tract (lost light reflex) from those in distant parts of reflex) from those in distant parts of optic pathway (normal light reflex)optic pathway (normal light reflex)

N.B:N.B: If light falls on temporal or nasal If light falls on temporal or nasal halves only on each retina( direct halves only on each retina( direct light reflex and consensual light light reflex and consensual light reflex)reflex)

CauseCause:: Impulses from one half of retina Impulses from one half of retina activate pretectal nucleus of one side activate pretectal nucleus of one side activate Edinger Westfal nuclei of activate Edinger Westfal nuclei of both sides so consensual light reflex both sides so consensual light reflex results from:results from:

1-Partial crossing of optic nerve fibers 1-Partial crossing of optic nerve fibers at optic chiasma if lightat optic chiasma if light

directed into one eye.directed into one eye.2-Partial crossing around aquiduct of 2-Partial crossing around aquiduct of

Sylvius if light directed into one half Sylvius if light directed into one half of retina.of retina.


Pathway of Pupillary Pathway of Pupillary DilatationDilatation

Cilio-spinal reflex:Cilio-spinal reflex: Pinching neck skin stimulate the sympathetic to the Pinching neck skin stimulate the sympathetic to the

eye causing pupillary constriction.eye causing pupillary constriction.

Horners syndrome:Horners syndrome:

CauseCause:: Cervical sympathectorny. Cervical sympathectorny.

Effects:Effects: on same side of lesion: Ptosis, Miosis, Anhydrosis,on same side of lesion: Ptosis, Miosis, Anhydrosis, Enophthalmos and flushing of the face.Enophthalmos and flushing of the face.

Reaction of pupil to anesthesia Reaction of pupil to anesthesia

Stages 1.2:Stages 1.2: Dilatation due to emotions.Dilatation due to emotions.

Stage 3:Stage 3: Constriction due to 3rd nerve release from corticalConstriction due to 3rd nerve release from cortical inhibition.inhibition.

Stage.4:Stage.4: Dilatation due to medullary paralysis (3rd cranialDilatation due to medullary paralysis (3rd cranial nerve nucleus paralysis)nerve nucleus paralysis)


Te-differentiate between Te-differentiate between stages 2,4stages 2,4: :

By corneal reflex, light R, lacrimation and eye By corneal reflex, light R, lacrimation and eye movement. movement. All are present in stage 2 and absent in stage 4.All are present in stage 2 and absent in stage 4.

MiosisMiosis MydrasisMydrasis (Pupillary dilatation) (Pupillary constriction)(Pupillary dilatation) (Pupillary constriction)

11--Near visionNear vision22--Light adaptationLight adaptation

33--Horners syndromeHorners syndrome44--SleepSleep

55--Pontine HePontine He..66--Stage 3 of anaesthiaStage 3 of anaesthia77--Stimulation of S.C.CStimulation of S.C.C

88 - -Drugs :acetyl cholineDrugs :acetyl choline Morphine α- blockersMorphine α- blockers . .

1- Far vision1- Far vision2-Dark2-Dark3-3rd nerve lesion3-3rd nerve lesion4-Emotions4-Emotions5- Cilio-spinal R. 5- Cilio-spinal R. 6- Stages 1,2,46- Stages 1,2,47-Painful stimulus 7-Painful stimulus 8- Adrenaline, Atropine, 8- Adrenaline, Atropine, CocaineCocaine


Ophthalmoscope


Ophthalmoscope Examination For Vision conditions

1) Emmotropic = Relaxed eye

Emmetropia is the optical term for

normal vision .The light from an object is focused directly onto the retina forming a perfect image.

Road normal


2 (Hypermetropic eye ( Far sightedness)Cases :-1- short anterio-posterior diameter .2- Weak lenss.Correction with Biconvex lens (+ve)

lens.


Myopic eye ( short sightedness)

Cases-: 1 -Long anterio-posterior diameter.

2 -Strong lenss.Correction with Biconcave lens (-ve) lens.


Astigmatism

In equality of curvature of cornea and may be lens.

Correction with cylendrical concave

or convex lens.

It is either Regul

ar

Non regular Myoopic

Hypermetropic


Presbyobia-:

Loss of accommodation in old age due to loss of elasticity of lens protein by continuous lossing of H2o .

Corrected by biconvex lens.

Wich person need’nt to use glasses after 45 years old?

A) Myopic Person.B) Hypermetropic Person.?



Ophthalmoscope and Fundus Examination-:

Its uses :-1.Fundus examination.2.Diagnosis of errors of refraction and

its magnitude.3.Diagnosis of atherosclerosis (dilated

and tortuous retinal blood vessels ) = more cupping

4.Diagnosis of glocoma increase Intraocular pressure (I.O.P.)

5.Diagnosis of I . Cranial pressure = flattening or clupping.


6.Diagnose of Diabetus melitus.(diabetic retinopathy).

7.Diagnos of retinitis pigmentosa.


N.B. Blood supply of retina

Retinal vessel to B.C, G.c

Choroidal vessels to receptor .

So Retinal detachment affects receptor only.



THE RETINATHE RETINA

It is formed of 10 layers and contains beside It is formed of 10 layers and contains beside photo-receptorsphoto-receptors

(Rods & Cons) 4 types of neurons :(Rods & Cons) 4 types of neurons : 1-Bipolar ( B ).1-Bipolar ( B ). 2-Ganglion ( G )2-Ganglion ( G ) 3-Horizontal ( H ). 4-Amacrine cells (A).3-Horizontal ( H ). 4-Amacrine cells (A). Layers of retina:Layers of retina: 1) Pigmented layer:1) Pigmented layer: It contains melanin pigment to prevent It contains melanin pigment to prevent

reflection of light to the retina. They are the reflection of light to the retina. They are the storage of Vitamin A. storage of Vitamin A.

The Albino always complain of weak vision The Albino always complain of weak vision due to deficiency of melanin pigment. The due to deficiency of melanin pigment. The light has to penetrate the layers of the retina light has to penetrate the layers of the retina till it reach the rods and cones and stimulating till it reach the rods and cones and stimulating them when they are hyperpolarized.them when they are hyperpolarized.

The image formed in the retina is inverted but The image formed in the retina is inverted but the brain by certain mechanism that will the brain by certain mechanism that will upright the picture. (Blind eye see nothing).upright the picture. (Blind eye see nothing).


2) Photo-receptor2) Photo-receptors:s:

Any rods or cones has similar structure ,4 Any rods or cones has similar structure ,4 segments:segments:

1- Outer layer: Contain photopigments, In 1- Outer layer: Contain photopigments, In rods Rhodopsine=scotopsine) , in cones rods Rhodopsine=scotopsine) , in cones (Idopsin = photopsin) (Idopsin = photopsin)

2- Inner segment: There is mitochondria for 2- Inner segment: There is mitochondria for energy supply, cytoplasm contain vitamin A energy supply, cytoplasm contain vitamin A and other organelles.and other organelles.

3-Nuclear part.3-Nuclear part.4-Synaptic zone: with horizontal and bipolar 4-Synaptic zone: with horizontal and bipolar

cells.cells.

Photochemistry of rods:Photochemistry of rods: Visual purple which is composed of: Visual purple which is composed of:

Scotopsin & Retinine (A1aldehyde) II Cis.Scotopsin & Retinine (A1aldehyde) II Cis.


Excitation of rhodopsine Excitation of rhodopsine decompositiondecomposition::

In the dark ,Na channels are open and In the dark ,Na channels are open and leakage back Na to inner segment, so leakage back Na to inner segment, so they add +ve charge to inside lead to they add +ve charge to inside lead to decrease in -ve charge. The -ve will be = -decrease in -ve charge. The -ve will be = -30 mV.30 mV.

On exposure to light:On exposure to light: Na+ channel are going to be closed Na+ channel are going to be closed

most probably by movement of Ca most probably by movement of Ca++++ ions, ions, so no Na ions can enter again and Na so no Na ions can enter again and Na accumulated in outer segment makes accumulated in outer segment makes outside +ve to inside provides a state of outside +ve to inside provides a state of hyperpolarization which is actually the hyperpolarization which is actually the stimulus of rods and cones.stimulus of rods and cones.

N.B:N.B: Mitochondria present in the inner Mitochondria present in the inner segment pump Na+ to outside.segment pump Na+ to outside.


RhodopsineRhodopsine light energy light energy

pre-lumi rhodopsinepre-lumi rhodopsine dark dark

lumi rhodopsinelumi rhodopsineOpsineOpsine meta rhodopsine meta rhodopsine

isomeraseisomerase

all cis retinol all cis retinol all transretinalall transretinal

(only form able to form rhodopsine(only form able to form rhodopsine).).


Action of light on Action of light on RhodopsineRhodopsine::

Action of light on Rhodopsine:Action of light on Rhodopsine: The whole pigment (Rhodopsine) is The whole pigment (Rhodopsine) is

the only which can absorb lightthe only which can absorb lightN.BN.B stimulatesstimulates

Meta rhodopsine II transducineMeta rhodopsine II transducine

PhosphodisterasePhosphodisterase Closure of Na channel Closure of Na channel decrease decrease cGMPcGMP

release of-synaptic transmitterrelease of-synaptic transmitter

action potential in ganglion cellsaction potential in ganglion cells


Difference between rods and consDifference between rods and consNumberRods

120-150 millionsCones5.5 - 7 millions

Siteperipheral distributioncentral part of retina

Fovea centralis

Not presentonly cones

Photo pigment

Rhodopsinevisual purple(scotopsine)

lodopsine: 1) Erythrolabe (red)2) Chlorolabe(green)3) Cyanolabe (blue)

Connectionmany rods (100-300) converge to one Bipolar cell

In fovea one to one connection

Functiona-Scotopic:(dim light vision)b-Peripheral vision.c-More sensitive to light.d- less accurate vision.e-Can not differentiate colours, they are sensitive to black, gray and whiteThey respond to allradiations even ultraviolet(if lens is removed)

a- phototopic (day light vision) b-central vision c-less sensitive to light d-more accurate vision (visual acuity) e-colour vision.


The peripheral retina is more The peripheral retina is more sensitive to weak light than the sensitive to weak light than the

center (fovea centralis). becausecenter (fovea centralis). because: :

a-AII rhodopsine has maximal absorption at a-AII rhodopsine has maximal absorption at minimal wave lengths.minimal wave lengths.

B- Convergence and summation between nerve B- Convergence and summation between nerve fibers.fibers.

While central part (F.C) has highest visual While central part (F.C) has highest visual acuity (more details; as there is no acuity (more details; as there is no convergence.convergence.

N.B: Both rods and cones produce receptor N.B: Both rods and cones produce receptor potential and not action potential and synaptic potential and not action potential and synaptic transmission is by electreotonic current and transmission is by electreotonic current and not chemically. There is convergence of 140 not chemically. There is convergence of 140 rods and 6 cons on each optic nerve rods and 6 cons on each optic nerve fiber( 900000 optic nerve fiber) fiber( 900000 optic nerve fiber)


Function of Horizontal cells: Function of Horizontal cells: (Inhibitory).(Somethetic focusing )(Inhibitory).(Somethetic focusing )..

1-They lie in inner nuclear layer of retina.1-They lie in inner nuclear layer of retina.

2- They are excited directly by 2- They are excited directly by rods .cones, in turn transmit signals rods .cones, in turn transmit signals laterally to bipolar cells located in areas laterally to bipolar cells located in areas lateral to excited zone, causing its lateral to excited zone, causing its inhibition. Thus excited rods and cones inhibition. Thus excited rods and cones transmit excitatory signals in a direct transmit excitatory signals in a direct line through the bipolar cells in the area line through the bipolar cells in the area of excitation. But transmit inhibitory of excitation. But transmit inhibitory signals through the surrounding cells. signals through the surrounding cells. So horizontal cells enhances contrast in So horizontal cells enhances contrast in the visual scene and help to the visual scene and help to differentiate colours.differentiate colours.


Stimulation and function of Stimulation and function of Amacrine cells Amacrine cells

(Excitatory)(Excitatory)

They are excited, by bipolar cells, They are excited, by bipolar cells, then stimulates ganglon cells. They then stimulates ganglon cells. They respond first very strongly, and send respond first very strongly, and send strong signals to brain, then signals strong signals to brain, then signals die away in a fraction of second to die away in a fraction of second to indicate sudden change in light indicate sudden change in light intensity i.e. level of illumination of intensity i.e. level of illumination of retina.retina.

Stimulation of Ganglon cells : ( G.C.)Stimulation of Ganglon cells : ( G.C.)By Bipolar cells. G.ceils transmits By Bipolar cells. G.ceils transmits

signals to the brain. signals to the brain.


Transmission of colour Transmission of colour signals by G.Csignals by G.C:.:.

Signals to G.C may be from a number of cones or Signals to G.C may be from a number of cones or from one cone only. All signals stimulate the same from one cone only. All signals stimulate the same ganglon cell, the signals are the same for any ganglon cell, the signals are the same for any colour, so plays no role in colour detection, just a colour, so plays no role in colour detection, just a white signal (lumenisty signal)white signal (lumenisty signal)

On the other hand some ganglion cells are On the other hand some ganglion cells are

stimulated by one colour cone (e.g. Red) and stimulated by one colour cone (e.g. Red) and inhibited by another colour cone (e.g. Green) , this inhibited by another colour cone (e.g. Green) , this is called Reciprocal-excitation relationship, and it is called Reciprocal-excitation relationship, and it plays role in colour contrast.plays role in colour contrast.

GREEN [G.C] REDGREEN [G.C] RED--- --- Indirect by H.C. + ++ Direct by B.CIndirect by H.C. + ++ Direct by B.C..

Therefore the process of colour analysis Therefore the process of colour analysis begins in begins in the retinathe retina and not entirely a function of the brain .and not entirely a function of the brain ...

RED GREEN BLUE

Cones

One B.C. One G.C (colour intensity)


N.B. Optic disc :N.B. Optic disc : It lies 3 mm medial to post. Pole , 1.5 mm diemeter. It is the site It lies 3 mm medial to post. Pole , 1.5 mm diemeter. It is the site

of optic nerve exit and entry of retinal blood vessels. It is called of optic nerve exit and entry of retinal blood vessels. It is called the blind spot (no visual receptors)the blind spot (no visual receptors)

Night Blindness : (Nyctalopia)Night Blindness : (Nyctalopia) It occurs in severe vit. A deficiency causing decrease in It occurs in severe vit. A deficiency causing decrease in

rhodopsin synthesis, also decreased rhodopsin in cones → rhodopsin synthesis, also decreased rhodopsin in cones → dark adaptation is slow and incomplete → night blindness. dark adaptation is slow and incomplete → night blindness.

Q-What is the effect of avitaminnosis A ?Q-What is the effect of avitaminnosis A ? In the dark, we can not recognize colours and shape (as no In the dark, we can not recognize colours and shape (as no

rhodopsin is found) . rhodopsin is found) .

Purkinje shift phenomena :Purkinje shift phenomena :

In bright light, yellow part of the spectrum is the In bright light, yellow part of the spectrum is the most bright, while in dim light sensitivity or luminisity most bright, while in dim light sensitivity or luminisity shift toward the blue green part of the spectrum e.g shift toward the blue green part of the spectrum e.g in a garden, the yellow flowers are the most bright in in a garden, the yellow flowers are the most bright in day light, while at dark (dim light), the blue flowers day light, while at dark (dim light), the blue flowers appear shinning, while red flowers appear black, as appear shinning, while red flowers appear black, as red spectrum of wave length 700 ml.µ is out of red spectrum of wave length 700 ml.µ is out of scotopic visibility curve .scotopic visibility curve .


Scotopic visionPhotopic vision

Dim light vision (twi light vision)

1-function of rods. 2-Details and

boundaries are not seen 3-No colour vision.

visibility curve: i.e retinal sensitivity to different wave lengths, is most sensitive to wave length 500 nm. (blue-green), so blue part of the spectrum has maximal luminsity.

Day light vision1-function of cones.

2-details and boundaries are seen (visual acuity).

3-Colours are seen

Visibility curve: In good illumination (photopic vision),the retina is most sensitive to wave-length 550 nm., soyellow part of the spectrum has maximal luminisity


Scolopic (Low intensity)Scolopic (Low intensity) and and photopic (High intensity) visionphotopic (High intensity) vision..


Autonomic regulation of retina sensitivity Autonomic regulation of retina sensitivity 1-1-Retinal adaptation :Retinal adaptation :It can change its sensitivity to different It can change its sensitivity to different

intensities of light (adaptation), i.e. intensities of light (adaptation), i.e. increased sensitivity in dark and decreases increased sensitivity in dark and decreases on exposure to bright light.on exposure to bright light.

II- II- Light adaptation :(short duration 3-5 Light adaptation :(short duration 3-5 min.)min.)

Increased visual threshold (decreased Increased visual threshold (decreased retinal sensitivity) in bright light by retinal sensitivity) in bright light by bleaching of retinal photopigments of both bleaching of retinal photopigments of both rods and cones, occurs for generation of rods and cones, occurs for generation of nerve impulse. nerve impulse.

General changes during light adaptation are General changes during light adaptation are : : 1-Myosis 2-breakdown of rhodopsin and1-Myosis 2-breakdown of rhodopsin and lodopsin .lodopsin .3- decreased retinal sensitivity 3- decreased retinal sensitivity 4- visual acuity is greater.4- visual acuity is greater.N.B.:N.B.: pupillary constriction causes fall of light pupillary constriction causes fall of light

on central part of retina (only) = cones.on central part of retina (only) = cones.


III-Dark adaptation of retinaIII-Dark adaptation of retina::

• • Is the function of retina but not CNS.Is the function of retina but not CNS.• • Its increased sensitivity of the eye to Its increased sensitivity of the eye to

light (decreased light threshold).light (decreased light threshold).• • Regeneration of retinal pigments of Regeneration of retinal pigments of

both rods and cones occurs.both rods and cones occurs.• • From light to dark, at first nothing is From light to dark, at first nothing is

seen, then after few minutes, there is seen, then after few minutes, there is certain degree of vision. certain degree of vision.

N.B.:N.B.: Light adaptation takes 3-5 min., Light adaptation takes 3-5 min., while dark takes 30 min. while dark takes 30 min.


'Changes' occur during dark 'Changes' occur during dark adaptation: adaptation:

1-Mydriasis1-Mydriasis2- Regeneration of rhodopsin and 2- Regeneration of rhodopsin and

iodopsiniodopsin3- ↑↑ in retinal sensitivity (100,000 3- ↑↑ in retinal sensitivity (100,000

times).times).4- Visual acuity is decreased.4- Visual acuity is decreased.

Two Components of dark Two Components of dark adaptation:adaptation:

Cone adaptation which is rapid and Cone adaptation which is rapid and small small

Rod adaptation which is slow and Rod adaptation which is slow and greater.greater.


Q-Why rods arc important for dark Q-Why rods arc important for dark adaptation ?adaptation ?

1-due to convergence (spatial summation) 1-due to convergence (spatial summation) → → high sensitivity.high sensitivity.

2 Rod adaptation continue for longer time (30-2 Rod adaptation continue for longer time (30-45 min.) (same time needed for 45 min.) (same time needed for regeneration of rhodopsin).regeneration of rhodopsin).

So, dark adaptation is slower if person So, dark adaptation is slower if person previously exposed to intense illumination, previously exposed to intense illumination, that is why during war Night-Fight Pilots that is why during war Night-Fight Pilots wear red gogles (glasses) when in day wear red gogles (glasses) when in day (bright light), it absorbs all colours except (bright light), it absorbs all colours except red, rhodopsin is not sensitive to longer red, rhodopsin is not sensitive to longer wave lengths, so it is not bleached, when wave lengths, so it is not bleached, when entering the dark, adaptation rapidly entering the dark, adaptation rapidly occurred by removing the goggles. occurred by removing the goggles.

* * Factors affecting dark adaptation : it is Factors affecting dark adaptation : it is reduced byreduced by : :

1-hypoxia 1-hypoxia 2- vit. A deficiency2- vit. A deficiency 3-tobacco3-tobacco 4- CO4- CO 5-Anesthesia5-Anesthesia 6-Myopia .6-Myopia .


Flicker Flicker Intermittent retinal stimulationIntermittent retinal stimulation

1- When retina is stimulated intermittently by a series of 1- When retina is stimulated intermittently by a series of light flashes. light flashes.

2- Upon increasing the frequency (2- Upon increasing the frequency (number/secnumber/sec.) of .) of light stimuli .fusion results and flicker disappears light stimuli .fusion results and flicker disappears (i.e. continuous sensation) . The frequency at which (i.e. continuous sensation) . The frequency at which this occurs is called: critical fusion frequency (C.F.F.)this occurs is called: critical fusion frequency (C.F.F.)

-It is a function of CMS and not of retina.-It is a function of CMS and not of retina.

3-Light stimuli have a stimulation frequency above 3-Light stimuli have a stimulation frequency above "C.F.F." (24-60) are perceived as a continuous "C.F.F." (24-60) are perceived as a continuous moving stimuli.moving stimuli.

-It is the idea of TV. (60 frames / sec.) while motion -It is the idea of TV. (60 frames / sec.) while motion pictures flashes at 24 frames/sec.pictures flashes at 24 frames/sec.

Light intensity :Light intensity :1-At low intensity (dark), C.F.F 2-6/sec.1-At low intensity (dark), C.F.F 2-6/sec.2-ln bright illumination , C.F.F. 60 frames/sec, as cones 2-ln bright illumination , C.F.F. 60 frames/sec, as cones

which work in illumination can detect much more which work in illumination can detect much more rapid alteration .rapid alteration .


According to Free-Part low :According to Free-Part low :-C.F.F. is directly proportional -C.F.F. is directly proportional

to Log. of light intensity .to Log. of light intensity .-So , in high intensity of -So , in high intensity of

illumination ,illumination ,high C.F.F. -> continuous high C.F.F. -> continuous

motion .motion .If C.F.F. is low -» flicker If C.F.F. is low -» flicker

sensation .sensation .C.F.F. is depressed by :C.F.F. is depressed by :a-Alcohol b-Low Oa-Alcohol b-Low O22 tension . tension .c-Barbiturates c-Barbiturates d-Diabetes.d-Diabetes.

Q-When does a movie begin Q-When does a movie begin to flicker?to flicker?

When the projectors slow When the projectors slow down, so rate of perception down, so rate of perception of the pictures is equal to of the pictures is equal to C.F.F.C.F.F.


Colour visionColour vision

It is subject sensation It is subject sensation The spectrum of light to which the human The spectrum of light to which the human

retina is sensitive ranges from 700 mµ to retina is sensitive ranges from 700 mµ to 400 mµ.400 mµ.

So, colour vision is the power of the eye to So, colour vision is the power of the eye to discriminate stimuli according to their wave discriminate stimuli according to their wave lengths. lengths.

Cones are the receptors for colour vision.Cones are the receptors for colour vision.N.B. N.B. Below 400 mµ (ultraviolet) and above Below 400 mµ (ultraviolet) and above

700 mµ (infra-red) the receptors are not 700 mµ (infra-red) the receptors are not stimulated. stimulated.

Primary colours : Red - Green – Blue Primary colours : Red - Green – Blue They are called primary colours because They are called primary colours because

white colour or any other spectral can be white colour or any other spectral can be formed by mixing various proporions of formed by mixing various proporions of these 3 colours these 3 colours


Complementary colours:Complementary colours:They are 2 particular colours They are 2 particular colours which when mixed together which when mixed together produce white light. e.g. Red + produce white light. e.g. Red + Green → white.Green → white.

Qualities of colours:Qualities of colours: 1-Hue = the actual colour.1-Hue = the actual colour. 2- Brightness = light or dark.2- Brightness = light or dark. 3- Saturation = degree of 3- Saturation = degree of

freedom from dilution with whitefreedom from dilution with white


Colour perceptionColour perception: :

(1) Retinal mechanism :(1) Retinal mechanism :-It depends upon the presence of certain -It depends upon the presence of certain

cone-pigments which absorb colours .cone-pigments which absorb colours .-One type of cone stimulation causes -One type of cone stimulation causes of of

ganglioniccell while another type of cone ganglioniccell while another type of cone causes inhibition to the same ganglionic causes inhibition to the same ganglionic cell → signals to lateral geniculate body of cell → signals to lateral geniculate body of thalamus → cerebral cortex .thalamus → cerebral cortex .

(2) Cortical mechanism :(2) Cortical mechanism :-For interpretation of light e.g. perception of -For interpretation of light e.g. perception of

sensation of yellow when red light falls on sensation of yellow when red light falls on right eye and green light on left eye ."So , right eye and green light on left eye ."So , this integration is done in brain and not in this integration is done in brain and not in retina .retina .


- - After image phenomenon :After image phenomenon :(A) -ve after image :(A) -ve after image :

If you concentrate vision to yellow for If you concentrate vision to yellow for long time and then shiftlong time and then shiftyour vision to white screen, it will not your vision to white screen, it will not appear white butappear white butappears blue (complementary appears blue (complementary colour) due to retinalcolour) due to retinaladaptation to the 1st colour.adaptation to the 1st colour.

(B) +ve after image :(B) +ve after image :It is seeing the same colour after It is seeing the same colour after

removing it from seeing (after removing it from seeing (after discharge phenomenon).discharge phenomenon).

N.B.:N.B.: Perception of white light: Perception of white light:By equal By equal of the 3 types of cones . of the 3 types of cones .


Theories of colour visionTheories of colour vision: : (1) Young-Helmhotz-Theory (Trichromatic (1) Young-Helmhotz-Theory (Trichromatic

Theory )Theory )- Colour vision is subserved by 3 types of - Colour vision is subserved by 3 types of cones and each is containing different cones and each is containing different photosensitive pigment which is maximally photosensitive pigment which is maximally stimulated by one of the 3 primary colours stimulated by one of the 3 primary colours (red , green blue).,(red , green blue).,

-These pigments are:-These pigments are:a-Erythrolabe (red-sensitive)a-Erythrolabe (red-sensitive)b-Cyanolabe (blue-sensitive)b-Cyanolabe (blue-sensitive)

c-Chlorolabe (green-sensitive)c-Chlorolabe (green-sensitive)-The different colour sensations are produced -The different colour sensations are produced

by stimulation of the 3 types in different by stimulation of the 3 types in different degrees.degrees.


--Objections against this Objections against this theorytheory: :

1-Histological studies have not shown any 1-Histological studies have not shown any difference in structure of various cones.difference in structure of various cones.

2-The visual field for red , green and blue 2-The visual field for red , green and blue colours are not the same.colours are not the same.

(2) Polychromatic theory (Granit):(2) Polychromatic theory (Granit):-Studied the discharge in single nerve fiber of -Studied the discharge in single nerve fiber of

optic nerve in response to different wave optic nerve in response to different wave lengths of light when various colours of lengths of light when various colours of light are directed through the pupil of the light are directed through the pupil of the eye into retina.eye into retina.


- The photo pigments absorb light.- The photo pigments absorb light.- The absorption characteristic of the pigments - The absorption characteristic of the pigments

in the 3 types of cones .in the 3 types of cones .

- From the curve, a red light wave length of 600 - From the curve, a red light wave length of 600 nm transmitted into the eye stimulate red nm transmitted into the eye stimulate red cones at an intensity of 91 % , stimulates cones at an intensity of 91 % , stimulates green cones to an intensity 8 % and blue green cones to an intensity 8 % and blue Colour of intensity Colour of intensity

0-1 %0-1 %Interpretation of the colour:Interpretation of the colour: Occurs in the brain where above particular Occurs in the brain where above particular

ratio of impulses have transmitted. So, it is ratio of impulses have transmitted. So, it is not the retina that discriminate colours but it is not the retina that discriminate colours but it is cortical integration of colour sensation .cortical integration of colour sensation .

-Granit said that -Granit said that 2 2 broad categories of broad categories of cones : cones :

A)A) Dominators :Dominators : which are stimulated by the which are stimulated by the wide range of the whole spectrum , their wide range of the whole spectrum , their visibility curve coincides with the photopic visibility curve coincides with the photopic visibility curve with maximal sensitivity at 550 visibility curve with maximal sensitivity at 550 nm composed of several types of cones nm composed of several types of cones which are all connected to a single ganglion which are all connected to a single ganglion cell.cell.


B) Modulators :B) Modulators :narrownarrow band , 3 types : band , 3 types :

1-red modulators (1-red modulators (ed by wave ed by wave lengths 580 - 600 nm) . lengths 580 - 600 nm) .2-green modulators (2-green modulators (ed by wave ed by wave lengths 520 - 550 nm) . lengths 520 - 550 nm) .3-blue modulators (3-blue modulators (ed by wave ed by wave lengths 450 - 470 nm) . lengths 450 - 470 nm) .

N.B.: The colour perceived by eye depend on relative degree of of the different types of cones in retina


--Colour blindnessColour blindness : :--It is inability for discrimination of light of different colours or It is inability for discrimination of light of different colours or

to a portion of the spectrumto a portion of the spectrum . .--It is classified according to Young-Helmholtz intoIt is classified according to Young-Helmholtz into : :

))I) Trichromatic vision (Anomulous): 6%I) Trichromatic vision (Anomulous): 6%--The person has 3 cone systems intact, but one is The person has 3 cone systems intact, but one is

weak . e.gweak . e.g-- Protanomaly = red colour weakness Protanomaly = red colour weakness . .-- Deutranomaly = green colour weakness Deutranomaly = green colour weakness . .-- Tritanomaly = blue colour weakness Tritanomaly = blue colour weakness . .--So , he can recognize deep colour but not pale colourSo , he can recognize deep colour but not pale colour..

))II) Dichromatic vision : 1%II) Dichromatic vision : 1%-- Individuals have only 2 cone systems with one cone Individuals have only 2 cone systems with one cone

deficient.deficient.--e.g. Protanopia (red blind), it is coloured green , it is called e.g. Protanopia (red blind), it is coloured green , it is called

red-green blindness. red-green blindness.

(III) Monochromatic vision : 1%(III) Monochromatic vision : 1%11 - -Rod monochromatic vision : all colours are missing, he Rod monochromatic vision : all colours are missing, he

can see only white , black and graycan see only white , black and gray . . 22--Cone monochromatic vision : have only one cone systemCone monochromatic vision : have only one cone system


Causes of colour blindness : Causes of colour blindness :

l)-Genetic colour blindness :l)-Genetic colour blindness :-It is sex-linked recessive trait due to -It is sex-linked recessive trait due to

absence of colour gene in the absence of colour gene in the X-chromosome (more in males) .X-chromosome (more in males) .-It is transmitted from females to their male -It is transmitted from females to their male

children .children .-2% of men are red blind , 6% are green blind -2% of men are red blind , 6% are green blind

..-N.B : The eye is apparently healthy . -N.B : The eye is apparently healthy .

II) Acquired colour blindness :II) Acquired colour blindness :-In one or both eyes , which are not normal, -In one or both eyes , which are not normal,

they show other symptoms , due to some they show other symptoms , due to some diseases as : diseases as :

a-Glaucoma b-Optic neuritis a-Glaucoma b-Optic neuritis c-Diabetic retinopathy d-Tobaccoc-Diabetic retinopathy d-Tobaccoe-retinal detachment. e-retinal detachment. III-Psychological colour blindness:III-Psychological colour blindness:- A man who was colour-blind suddenly recovered - A man who was colour-blind suddenly recovered

normal colour vision after a motor car accident.normal colour vision after a motor car accident.


Tests for colour visionTests for colour vision (1) Ishihara test colours :(1) Ishihara test colours :- Some charts are designed to be read easily - Some charts are designed to be read easily

by the normal eye but not coloured blind by the normal eye but not coloured blind subjects and some others can read only by subjects and some others can read only by the colour blind subject. Some charts are the colour blind subject. Some charts are interpreted differently by normal and colour interpreted differently by normal and colour blind people e.g. normal person reads 74 blind people e.g. normal person reads 74 while red-green blind reads 21 .while red-green blind reads 21 .

(2) Coloured wool test:(2) Coloured wool test:-The person is given many small tufts of wool -The person is given many small tufts of wool

with colours covering the entire visual with colours covering the entire visual spectrum . Then , asked to place tufts with spectrum . Then , asked to place tufts with same colours together.same colours together.


Distribution of colours Distribution of colours in retinain retina: :

1-The very central part of the retina is 1-The very central part of the retina is tritanopia due to complete absence tritanopia due to complete absence of the cones .of the cones .

2-Outekie the fovea (red + green 2-Outekie the fovea (red + green blindness). So , not all parts of retina blindness). So , not all parts of retina receive colours with the same receive colours with the same magnitude because cones are magnitude because cones are unequally distributed.unequally distributed.

3-ln the periphery, all colours 3-ln the periphery, all colours sensations are lost since no cones sensations are lost since no cones found there. (rod monochromatism).found there. (rod monochromatism).


Binocular VisionBinocular Vision It is the ability of using both eyes to see certain part of It is the ability of using both eyes to see certain part of

the outside world at the same time without the the outside world at the same time without the occurrence of diplopia (double vision). Although, we occurrence of diplopia (double vision). Although, we have 2 eyes , 2 optic nerves , and 2 visual centers , yet have 2 eyes , 2 optic nerves , and 2 visual centers , yet we don't see 2 objects .we don't see 2 objects .

Although an image is formed upon each retina , the 2 Although an image is formed upon each retina , the 2 images are fused in consciousness into a single images are fused in consciousness into a single impression.impression.

In animal, with eyes placed laterally (rabbit), the visual In animal, with eyes placed laterally (rabbit), the visual fields are completely separated (monocular vision). fields are completely separated (monocular vision).

Factors necessary for binocular vision :Factors necessary for binocular vision :1-The visual fields must overlap to a greafand same extent.1-The visual fields must overlap to a greafand same extent.2-The 2 images must be approximately identical as regard 2-The 2 images must be approximately identical as regard

size , shape , intensity and colour.size , shape , intensity and colour.3-The 2 images must fall on corresponding points, on the 23-The 2 images must fall on corresponding points, on the 2

retina, lie on nasal half of one retina and temporal half of retina, lie on nasal half of one retina and temporal half of the other retina . the other retina .

4-The refractive power of both eyes and the extra-occular 4-The refractive power of both eyes and the extra-occular exactly the same .exactly the same .


Advantages of Advantages of Binocular vision :Binocular vision :

1-Visual field of both eyes together is 1-Visual field of both eyes together is larger than each eye separately.larger than each eye separately.

2-Refractive errors , or pathological 2-Refractive errors , or pathological changes in one retina are masked by changes in one retina are masked by the other normal eye .the other normal eye .

3-lmportant for stereoscopic vision to 3-lmportant for stereoscopic vision to see the 3 dimensions of objects see the 3 dimensions of objects (width, length and depth).(width, length and depth).

4-Depth distance perception .4-Depth distance perception .


EXTERNAL PROTECTION EXTERNAL PROTECTION OF THE EYEOF THE EYE

(l)-Eve brows :(l)-Eve brows :-helps to protect eye balls from sweat and from direct rays of. Sun-helps to protect eye balls from sweat and from direct rays of. Sun

(I) Eye Lids : (I) Eye Lids : Functions :Functions :1- Protection from injuries & foreign bodies. 1- Protection from injuries & foreign bodies. 2- Protection from excessive light.2- Protection from excessive light.3- Continuous blinking spreads lacrimal fluid over the cornera. 3- Continuous blinking spreads lacrimal fluid over the cornera.

Types of eye lid movement:Types of eye lid movement:1-Voluntary1-Voluntary2-Spontaneous: Subconscious (20 times/min).2-Spontaneous: Subconscious (20 times/min).3-Reflex:3-Reflex:a-Corneoc-onjunctical reflex (afferent 5a-Corneoc-onjunctical reflex (afferent 5thth, efferent 7, efferent 7thth ), ),b-A shinning bright light on the eye (afferent optic, efferent 4b-A shinning bright light on the eye (afferent optic, efferent 4thth))c-Auditory impulses (afferent 8c-Auditory impulses (afferent 8thth).).Functions of tears :Functions of tears :1-Clears , lubricates and moistens eye balls .1-Clears , lubricates and moistens eye balls .2-Bactericidal action (lysozyme enz.).2-Bactericidal action (lysozyme enz.).- Rate of secretion : 1ml./day .- Rate of secretion : 1ml./day .- Physical characters - Physical characters : pH = 7.4 , O.P. = 0.9% NaCI. : pH = 7.4 , O.P. = 0.9% NaCI. R.I. = 1.33R.I. = 1.33-Composition : 98.2% water,1.8 %=solids,Na,Cl, glucose, proteins -Composition : 98.2% water,1.8 %=solids,Na,Cl, glucose, proteins

and HCOand HCO33––

N.B.:N.B.: Vitamin A deficiency leads to Xerophthalmia → Blindness Vitamin A deficiency leads to Xerophthalmia → Blindness

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