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) inorganicAlbuminGlobulinGlucosePyruvateLactateureaSodiumCalciumPotassiumMagnesiumChloridesPhosphatesbicarbonates

LESIONS 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

Color blindness1. Monochromatism ( achromatopsia)2. Dichromatism 3. Trichromatism Rod Monochromatisma. Protonopia a. Protanomaly b. Cone Monochromatismb. Deuteranopia b. Deuteranomaly c. Tritanopia c. Tritanomaly

Test for color blindness:-

By using Ishiharas color charts

By using colored wool

By using Edridge Green lantern.