physiology:-special senses:-vision(eye)

*vision:-

-eye -has three layers 
:sclera- anteriorly called as cornea
-choroid
-retina-have receptors

-visual receptors(5 marks)
teloreceptors -stimulated from distance,stimulated by light,present more at fovea centralis
-cells:cone&rod


*rod:-
rod shaped
-less in number
-concentrated more toward periphery
-pigment present is rodopsin
-for dim light


*cone cell:-
coneshaped
-more in number for visual aequity about 120 million
-concentrated more toward fovea centralis
-pigments:-red-porphyropsin
                  green-iodopsin
                  blue-cynopsin
-bright light vision

*aqueous humor(5/2mark)
its atranspanrent liquid presemt in anterior diameter &posterior chamber infront of lens
-it is secreted in cilliary body and goes to posterior chamber through the pupil it enters into anterior chamber.
-it is drained at canal of schelmma which is at junction of sclera- corneal junction
-function:-provides nutritionand o2 to the avascular tissue lens & cornea 
                -maintains inraocular pressure within eyeball 
                  n.v=16-20mmhg
if it is increased condition is called glaucoma which leads to detachmentwhich leads to blindness
maintains the shape of eyeball

*dark adaptation:-
-the subject is going to bright to dark room
-requires more than -20min
-resynthesis of rodopsin-retinol+opsin
-pupil dialation occurs

*light adaptation:-
subject going from dark room to bright light
-require less time-5 
-cleavage of rodopsin-opsin& retinol
-pupil constriction occurs

*optic pathway:-(5marks)

flow chart:-
resceptors-rods &cones
             |            1st order neuron
bipolar cells
             |
ganglionic cells
            |
optic nerve
            |
optic chiasma
           |
optic tract
         |    2nd order neuron
synapse in thalamus
        |
optic cradiation
         |3rd order neuron
visual cortex(17,18,19)


*refractive errors of vision:-
-myopia
-hypermyopia
-presbiopia
-astigmatism


*myopia
-can see nearby objects ,cant see far off objects
-anterior posterior dimensions of eyeball increases,light rays are focusses infront of retina
-correction by using bi-concave lens,it diverges the rays &focus on retina

*hypermetropia:-
can see far objects ,not near objects
-anterior posterior dimension of eyeball decreases,so light rays are focussed behind retina
-correction by using convex lens ,it converges the rays &focus on retina

*presbyopia:
due to ageing (after 40 years )
-cause-due to weakening of cilliary muscles which hols lens
symptom:-can ssee far objects  cant read read books
-correction-bifocal lens

*astigmatism:-
cause -corneal surface is not uniform or uneven
symptoms blurred vision 
correction-cylindrical lens

*pupillary reflex:-
1)accomadation reflex
2)light reflex
1)accomadation reflex:-
human eye is set for distant region 
- changes occur in eye during near vision is called accomadation reflex
-they are: medial rotation of eyebrows
                constriction pupil
                convexity of lens increases

flow chart:-

retina
    |
opticnerve 
     |
optic tract
      |
thalamus 
     |
visual cortex
    |
visual motor neuron
     |-
iii cranial nerve
     |
medial rectus
    |
cilliary nerve



*`light reflex-
beam of light thrown /focussed into the eye if constriction of pupil occurs then it is called direct light reflex
-if constriction of pupil occurs opposite eye is called indirect light reflex.

-significance:
-regulation of entry of light
-to diagnosis of encephalitis /neurosyphilis

pathway-
                 retina
                   |
                 optic nerve
                  |
                optic chiasma
                  |
                optic tract
                 pre tectal nucleaus in medulla 
                    |
                 3rd cranial nerve(edinger westpal nuc.)
                     |
                  ciliary nerve 
                   |
                 sphincter pupillar muscle
                   |
                 constriction of pupil

note:-constriction of pupil occurs on both sides becuase fibers from PTN(PRE TECTAL NUC.)pass to both sides to edingar westpal nuc. of 3rd cranial nerve get excited & constricted of pupil occur on both sides 

*argyl robertsons pupil:-

accomadation reflex is present ,light reflex is absent becuase there is lesion in pretectal nucleas that is the center of light reflex 

EG:neurosyphilis

*visual acuity:-its the resolving power of eye to different 2 points 

test:-1)snellers chart:-meant for distant region (6 METERS)

         2)JAEGARS CHART:-meant for near region(30 cm)

colour vision:-

unable to appreciate primary colours(blue,green,red)

it is a sex linked disorder females are carriers male are suffers)

Test:wool matching test 

        edridge green lantern test