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Sight and the eye
By
Shahzad Bashir
RN, BScN
(NMC ION)
Objectives
By the end of this presentation you The Eye
will able to:
Describe the gross structure of eye. The eye is the organ of sense of sight
Structure related to vision It is supplied by optic,
Describe the structure and function oculomotor,trochlear, abducent nerves
of ear. (2nd,3rd,4th and 6th cranial nerves)
Transmission through ear. It is spherical in shape and is about 2.5
Physiology of Hearing and balance cm in diameter.
Structure Structure inside the eyeball
are the lens,aqueous fluid
There are three layers of tissue in the
wall of eye: (humour) and vitreous body
The outer fibrous layer: sclera and (humour)
cornea
The middle vascular layer or uveal
tract:choroid, ciliary body and iris
The inner nervous tissue layer:
retina
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Accessory Structures of the The Fibrous Tunic (layer)
Eye
Lacrimal apparatus – keeps the Most external layer of the eyeball
surface of the eye moist Composed of two regions of connective tissue
Lacrimal gland – produces lacrimal Sclera – White, opaque region
fluid Provides shape and an anchor for eye muscles
Lacrimal sac – fluid empties into Cornea – The transparent circular part of front of the
eye, it refracts the light to entering in the eye.
nasal cavity
Limbus – junction between sclera and cornea
The Fibrous Tunic (layer)
The Fibrous Tunic (layer)
The middle coat of the eyeball
Composed of choroid, ciliary body, Ciliary body – thickened ring of tissue
and iris – encircles the lens
Choroid – vascular, darkly Composed of ciliary muscle
pigmented membrane Ciliary processes – posterior surface of the
Prevents scattering of light rays within ciliary body
the eye Ciliary zonule (suspensory ligament)
Attached around entire circumference of the
Choroid corresponds to the lens.
arachnoid and pia maters
The Iris Medial View of the Eye
Visible colored part of the eye
Attached to the ciliary body
Composed of smooth muscle
Pupil – the round, central opening
Sphincter pupillae muscle (constrictor or
circular)
Dilator pupillae muscle (dilator or
radial)
Act to vary the size of the pupil
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Posterior View of the Anterior
Half of the Eye Pupillary dilation and
constriction
The Sensory Tunic (layer Microscopic Anatomy of the
) (Retina) Retina
Retina – the deepest tunic
Composed of two layers
Pigmented layer – single layer of
melanocytes
Neural layer – sheet of nervous tissue
Contains three main types of neurons
Photoreceptor cells
Bipolar cells
Ganglion cells
Photoreceptors
Photoreceptors
Two main types
Rod cells – more sensitive to light
Allow vision in dim light
Cone cells – operate best in bright light
Enable high-acuity, color vision
Considered neurons
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Blood Supply of the Retina
Retina receives blood from two sources
Outer third of the retina – supplied by
capillaries in the choroid
Inner two-thirds of the retina – supplied
by central artery and vein of the retina
Internal Chambers and Fluids
Internal Chambers and Fluids
Anterior segment
The lens and ciliary zonules divide the Divided into anterior and posterior
eye chambers
Anterior chamber – between the cornea and
Posterior segment (cavity) iris
Filled with vitreous humor Posterior chamber – between the iris and
Clear, jelly-like substance lens
Transmits light Filled with aqueous humor
Supports the posterior surface of the lens Renewed continuously
Helps maintain intraocular pressure Formed as a blood filtrate
Supplies nutrients to the lens and
cornea
Internal Chambers and Fluids The Lens
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The Eye as an Optical Device Visual Pathways
Structures in the eye bend light rays
Light rays converge on the retina at a
single focal point Most visual information travels to the
Light bending structures (refractory cerebral cortex
media) Responsible for conscious “seeing”
The lens, cornea, and humors Other pathways travel to nuclei in the
Accommodation – curvature of the lens is midbrain and diencephalon
adjustable
Allows for focusing on nearby objects
Visual Pathways to the Visual Pathways to the
Cerebral Cortex Cerebral Cortex
Pathway begins at the retina
Optic tracts send axons to:
Light activates photoreceptors
Lateral geniculate nucleus of the thalamus
Photoreceptors signal bipolar cells
Synapse with thalamic neurons
Bipolar cells signal ganglion cells
Fibers of the optic radiation reach the
Axons of ganglion cells exit eye as the
primary visual cortex
optic nerve
Visual Pathways to the Brain
and Visual Fields Regional Specializations of the
Retina
Macula lutea – contains mostly cones
Fovea centralis – contains only cones
Region of highest visual acuity
Optic disc – blind spot
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The Ear: Hearing and Equilibrium
The ear – receptor organ for hearing and
equilibrium it is supplied by 8th cranial
The Ear nerve that is vestibulocochlear nerve.
Composed of three main regions
Outer ear – functions in hearing
Middle ear – functions in hearing
Inner ear – functions in both hearing and
equilibrium
The Outer (External) Ear
The Outer (External) Ear
Composed of:
The auricle (pinna)
Helps direct sounds
External acoustic meatus
Lined with skin
Contains hairs, sebaceous glands, and
ceruminous glands
Tympanic membrane
Forms the boundary between the external and
middle ear
The Middle Ear Structures of the Middle Ear
The tympanic cavity
A small, air-filled space
Located within the petrous portion of the
temporal bone
Medial wall is penetrated by:
1.Oval window
2.Round window
Pharyngotympanic tube (auditory or
eustachian tube)
Links the middle ear and pharynx
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The Middle Ear
Ear ossicles – smallest bones in
the body
Malleus – attaches to the eardrum
Incus – between the malleus and stapes
Stapes – vibrates against the oval window
The Inner (Internal) Ear The Inner (Internal) Ear
The Inner (Internal) Ear
The Inner (Internal) Ear
Membranous labyrinth
Series of membrane-walled sacs and Membranous labyrinth (continued)
ducts Filled with a clear fluid – endolymph
Fit within the bony labyrinth Confined to the membranous labyrinth
Consists of three main parts Bony labyrinth is filled with perilymph
A. Semicircular ducts Continuous with cerebrospinal fluid
B. Utricle and saccule
C. Cochlear duct
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The Membranous Labyrinth The Vestibule
The central part of the bony labyrinth
Lies medial to the middle ear
Utricle and saccule – suspended in
perilymph
Two egg-shaped parts of the
membranous labyrinth
House the macula – a spot of sensory
epithelium
The Vestibule
Macula – contains receptor cells
Monitor the position of the head when
the head is still
Contains columnar supporting cells
Receptor cells – called hair cells
Synapse with the vestibular nerve
The Semicircular Canals The Semicircular Canals
Lie posterior and lateral to the vestibule
Anterior and posterior semicircular canals
Lie in the vertical plane at right angles
Lateral semicircular canal
Lies in the horizontal plane
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The Semicircular Canals The Cochlea
Semicircular duct – snakes through
A spiraling chamber in the bony
each semicircular canal
labyrinth
Membranous ampulla – located within
bony ampulla
Houses a structure called a crista
ampullaris
Cristae contain receptor cells of
rotational acceleration
Epithelium contains supporting cells and receptor
hair cells
The Cochlea The Cochlea
The cochlear duct (scala media) –
contains receptors for hearing The cochlear duct (scala media) –
Lies between two chambers contains receptors for hearing
The scala vestibuli Organ of Corti – the receptor
The scala tympani epithelium for hearing
The vestibular membrane – the roof of the Consists of:
cochlear duct
Supporting cells
The basilar membrane – the floor of the
Inner and outer hair cells (receptor cells)
cochlear duct
Equilibrium and Auditory
Pathways References
•Tortora, J. G., Derrichson, B.
The equilibrium pathway (2006).Principles of Anatomy and
Transmits information on the position Physiology. (11th ed). USA: New
and movement of the head York. John Willey 7 sons , Inc.
Most information goes to lower brain
centers (reflex centers)
•Ross and Wilson, Anatomy and
Physiology (ninth edition) in health
The ascending auditory pathway
and illness.
Transmits information from cochlear
receptors to the cerebral cortex
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