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EYE
EYE
ACCESSORY STRUCTURES
EYEBROWS
Two sets of directional hairs
Direct sweat
Away from eye
LACRIMAL APPARATUS
Responsible for
Production of tears
Stimulated by parasympathetic fibres
of Facial (VII) nerve
Response to
Strong smells
Irritants
Emotion
Overstimulation
Fill nasal cavity with fluid
Excess tears drain down nasolacrimal duct
Distribution of tears
Structure
Lacrimal duct
Lacrimal gland
Lacrimal punctum
Lacrimal canals
Lacrimal sac
Nasolacrimal duct
EYELASHES
Protect eyeballs from
Sweat
Foreign objects
Sunlight
Sebaceous ciliary glands
Located at base of eyelash follicle
Release fluid to lubricate eyeball
EXTRINSIC EYE MUSCLES
There are 6
Medial rectus
Bring pupil closer to midline (nose)
Inferior rectus
Depression & lateral eye rotation
Superior oblique
Internal rotation & depression
Superior rectus
Elevation
Inferior oblique
External rotation
Each move eye in different direction
Lateral rectus
Lateral movement
EYELIDS
Sheets of voluntary muscle
Tarsal Plate
Dense connective tissue
At free edge
Row of sebaceous glands
Meibomian glands
Secrete the lipid layer of tear film
Delays the evaporation of tears from eyeball
Upper eyelid
More mobile than the lower eyelid
aka Palpebra
Both eyelids
Lined with mucous membrane
Called conjunctiva
Continuous from the edge
To eyeball
ANATOMY
SCLERA (FIBROUS LAYER)
Made up of
Collagen fibres
Fibroblasts
Function
Gives shape and rigidity to eyeball
Gives eye it's white colour
Cornea
Anterior sclera
Transparent
Covers iris
Canal of Schlemm
Drains aqueous humour
UVEA (VASCULAR LAYER)
Structure
Highly vascularised
Choroid layer
Function
Provides nutrients to retina
Contains melanocytes
Produce melanin
Absorb stray light that enters eye
Maintain sharpness of image on the retina
Anterior portion
Choroid layer becomes the ciliary body
Ends in ciliary processes
Contain capillaries
Secrete aqueous humour
Into anterior chamber
Suspensory ligaments
Hold lens in place
Ciliary muscle
Circular and radial smooth muscle
Changes shape of the lens
Focuses the eye
IRIS
Structure
Coloured
Doughnut shaped arrangement of
Circular and radial smooth muscle
Position
Attached to ciliary processes
Suspended between cornea and lens
Function
Regulate the amount of light entering the eye
By changing size of the pupil
Stimulation
Sympathetic
Dim light
Radial muscles of iris contract
Pupil dilates
Parasympathetic
Response to bright light
Circular muscles of iris contract
Pupil constricts
RETINA
Position
Posterior segment of eye
Structure
Highly vascularised
Appears red under light
Where it joins choroid is pigmented with melanin
Absorbs scattered light that enters eye
3 Layers of neurons
Photoreceptor neurons
Rods
Light perception
Found at edge of retina
Essential for dark function
Cones
Colour vision
Essential for bright light function
Fovea centralis
Bipolar neurons
Ganglion neurons
Pass signals from retina to optic nerve fibres
Optic nerve
Leaves back of eye at optic disc
Blind spot
Central retinal artery & central retinal vein both enter and leave
EYE CAVITIES
ANTERIOR CAVITY
Front the eye
Consists of anterior and posterior chambers
Posterior Chamber
Located between iris and lens
Filled with aqueous humour
Replaced with every 90 mins
Maintains the intraocular pressure
Between 16-25 mmHg
Anterior Chamber
Located between cornea and iris
Filled with aqueous humour
Replaced with every 90 mins
Maintains the intraocular pressure
Between 16-25 mmHg
POSTERIOR CAVITY
Back of the eye
Contains vitreous humour
Jelly-like
Hold the retina flush against choroid
Made up of
Water
Collagen fibres
Hyaluronic acid
Phagocytic cells
Remove debris
e.g. Dead retinal cells
Floaters
Cast a shadow onto cornea
Harmless debris
Stagnant
