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Structure of eye
eye
Constrictor pupillae :-
Also called the iris sphincter muscle or sphincter pupillae.
Formed of circular muscle fibres .
Contraction causes the constriction of pupil.
Dilator pupillae:-
Also called the pupillary dilator muscle.
Formed of radial muscle fibers.
Contraction of this muscle causes dilatation of pupil.
Parasympathetic preganglionic fibers arises from Edinger Westphal nucleus of 3rd cranial nerve.
Passes through 3rd cranial nerve & reaches the ciliary ganglion.
Post ganglionic fibers arises & passes through ciliary nerves.
Supplies the ciliary muscle & constrictor pupillae.
Sympathetic preganglionic fibers arises from lateral horn of 1st thoracic segment of spinal cord.
Passes through sympathetic chain & reaches the superior cervical ganglion.
Post ganglionic fibers arises & run along with carotid artery & its branches.
Supplies the intrinsic muscles of the eyeball.
Intraocular fluid:-
Fluid present in the space within the eyeball.
Maintenance of shape of eyeball
Two types of fluid
1. vitreous humor
2. aqueous humor
Vitreous humor :-
Also known as vitreous body.
Present behind lens in the space b/w lens & retina.
Viscous & Gelatinous.
Formed by a fine fibrillar network of proteoglycan molecules .
Major substances are albumin & hyaluronic acid entering from blood by means of diffusion.
Maintain the shape of eyeball.
Aqueous humor:-
Thin fluid present in front of lens in the space b/w lens & cornea.
Properties of Aqueous humor:-
Volume : 0.13 ml.
Alkaline with a pH of 7.5
Viscosity : 1.029
Refractory index : 1.34
Composition of aqueous humor:-
Water : 98.7 %
Solids : 1.3%
a) 0rganicb) inorganicAlbuminGlobulinGlucosePyruvateLactateureaSodiumCalciumPotassiumMagnesiumChloridesPhosphatesbicarbonatesLESIONS OF VISUAL PATHWAY
Visual defects
Anopia
Right anopia
Left anopia
Hemianopia
Homonymous hemianopia
Heteronymous hemianopia
Right Homonymous hemianopia
Left Homonymous hemianopia
Binasal Heteronymous hemianopia
Bitemporal Heteronymous hemianopia
1) LESIONS OF OPTIC NERVE :
Causes:
optic atrophy
indirect optic neuropathy
acute optic neuritis
traumatic avulsion of optic nerve.
Characterised by: complete blindness in affected eye.
Eg. Right optic nerve
involvement
3)Central lesions of chiasma (sagittal)
causes:
suprasellar aneurysm
tumors of pituitary gland
craniopharyngioma
suprasellar meningioma & glioma of 3rd ventricle.
third ventricular dilatation due to obstructive hydrocephalus.
chronic chiasmal arachnoiditis.
Characterised by:
Bitemporal hemianopia
4)Lateral chiasmal lesions :
causes:
Distension of 3rd ventricle causing pressure on each side of optic chiasma
Atheroma of carotids & posterior communicating artery.
Characterised by
Binasal hemianopia
5)Lesions of optic tract :
Causes:
Syphilitic meningitis/ gumma.
Tuberculosis
Tumors of optic thalamus
Aneurysm of superior cerebellar or posterior cerebral arteries.
Characterised by :
homonymous hemianopia
6)Lesions of lateral geniculate body :
leads to homonymous hemianopia.
7)Lesions of optic radiations :
Causes:
Vascular occlusion
Primary & secondary tumors
Trauma
Characterised by :
TOTAL OPTIC RADIATION INVOLVEMENT
COMPLETE HOMONYMOUS HEMIANOPIA( sometimes sparing macula)
8)Lesions of upper or lower part of visual cotrex
leads to inferior or superior homonymous hemianopia.
PUPILLARY REFLEXES :-
They are the visceral reflexes which alter the size of pupil .
They are classified into 3 types :
Pupillary reflexes
Light reflex
Ciliospinal reflex
Accommodation reflex
LIGHT REFLEX :- (Pupillary light reflex) It is the reflex in which the pupils constricts when light is flashed into the eyes. It is of 2 types :
1. Direct light reflex :
There is constriction of pupil when light is thrown into that eye.
2. Indirect light reflex :
Constriction of pupil in both eyes. ie, constriction of pupil occurs in the opposite eye also even though no light rays falls on that eye.
LIGHT REFLEX :-
COLOR BLINDNESS:-
Failure to appreciate one or more colors.
It is common in 8% of males & 0.4% of females.
It can be hereditary or acquired.
Mostly it is an inherited sex linked recessive condition.
Causes of acquired color blindness:-
1. Trauma of eye due to stroke or accidents
2. Chronic diseases :
Glaucoma
Degeneration of macula
Retinitis
Sickle cell anaemia
Leukemia
Diabetes
Liver diseases
Parkinsons disease
Alzheimerss disease
Multiple sclerosis
3. Alcoholism
4. Drugs:
Antibiotics
Antihypertensive drugs
Anti tuberculosis drugs
Barbiturates
Drugs used to treat to treat psychological problems & neural disorders.
5. Industrial toxins or stong chemicals :
Fertilizers
Carbon monoxide
Carbon disulphide
Chemicals with high lead content.
6. Aging : occurs after 60 yrs
Test for color blindness:-
By using Ishiharas color charts
By using colored wool
By using Edridge Green lantern.