Structure and Function of the Eye Flashcards
Label the anterior view of the eye
Upper eyelid Palpebral fissure Lateral canthus Medial canthus Lower eyelid Pupil Iris Sclera Caruncle Limbus
What are the types of tears
Basal tears
Reflex tears
Crying/emotional tears
Describe the reflex pathway for tears
Afferent - corner CN V1 (ophthalmic branch of the trigeminal)
Efferent - parasympathetic
NT - acetylcholine
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What are the functions of the tear film
Maintains smooth cornea-air surface
Provides oxygen supply
Removal of debris
Bactericide
Describe the structure of the tear film
Superficial oily
Aqueous tear film
Mucinous later on the corneal surface
Describe the conjunctiva
Thin, transparent tissue that covers the outer surface of the eye
Begins at the outer edge of the cornea, covers the visible part of the eye and lines the inside of the eyelids
Nourished by tiny blood vessels (invisible to the eye)
In which conditions may the vessels of the eye become visible
Conjunctivitis
Uveitis
Label a sagittal section of the eye
Cornea Iris Ciliary body Rectus muscle Retina Choroid Sclera Optic nerve Optic disc Vitreous Lens
Describe the coat of the eye
Anterio-posterior diameter - 24mm 3 layers Sclera - hard and opaque Choroid - pigmented and vascular Retina - neurosensory tissue
Describe the sclera
Tough, opaque tissues that serves as the eye’s protective outer coat
High water content
Describe the cornea
Transparent, dome-shaped window covering the from
Refractive surface, providing 2/3 eye focusing power
Low water content
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Describe the layers of the cornea
1 - epithelium 2 - Bowman's membrane 3 - stroma 4 - Descemet's membrane 5 - endothelium
Describe the storm layer of the cornea
Regularity contributes to transparency
Corneal nerve endings provides sensation and nutrients for healthy tissue
No blood vessels in normal cornea
Describe the endothelial layer o the cornea
Pumps fluid put of the cornea and prevents
Describe the uvea
Vascular coat of the eye ball
Lies between sclera and retina
Composed of iris, ciliary body and choroid
They are connected and a disease of one part will affect the others
Describe the choroid
Lies between retina and sclera
composed of layers of blood vessels that nourish the back of the eye
Describe the iris
Coloured part of the eye
Controls light levels in the eye
Embedded with tiny muscles that dilate and constrict the pupil size
Describe the structure of the lens
Outer acellular capsule
Regular inner elongated cell fibres - transparency
May lose transparency with age e.g. cataracts
Descriebe the function of the lens
Transparency (regular structure) Refractive power (1.3 power, higher refractive index than aqueous fluid and vitreous) Accommodation (elasticity)
What are lens zonules
Lens is suspended by a fibrous ring (lens zonules) consisting of passive connective tissue
Describe the retina
Thin layer of tissue lining the inner part of the eye
Responsible for capturing light rays that enter the eye
Light impulses are then sent to the brain via the optic nerve
Describe the optic nerve
Transmits electrical impulses from the retina to brain
Connects to the back of the eye near the macula
Visible portin = optic disc
Describe the macula
Located roughly in the centre of the retina. temporal to the optic nerve
Small and highly sensitive part of the retina - central vision
Fovea is the centre of the macula
Allows for appreciating detail (reading)
Describe the anterior chamber
Froms the lens forwards
Between cornea and lens
Filled with clear aqueous fluid
Supplies nutrients
What is the ciliary body made up of
Ciliar muscle
Ciliary epithelium
Dilator
Sphincter
What are the functions of the ciliary body
Secretes aqueous fluid into the eye
Aqueous fluid supplies nutrients
Describe the ciliary body
Intraocular fluid flow anteriorly into the anterior chamber along
Normal pressure = 12-21
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Canal of scheme - 80-90%
Uveal -sclera outlaw
What is glaucoma
Medical condition of sustained raised intraocular pressure
Retinal ganglion cell death and enlarged optic disc cupping
What can glaucoma lead to
Visual field loss
Blindness
What are the types of glaucoma
Primary open angle glaucoma
Closed angle glaucoma
What is the blind spot
Where the optic nerve meets the retina there are no light sensitive cells. It is a blind spot.
Describe primary open angle glaucoma
Trabecular Meshwork Dysfunction
Describe closed angle glaucoma
Increased pressure pushing the iris/lens complex forwards, blocking the trabecular meshwork – vicious cycle
Risk factors - small eye (hypermetropia), narrow angle at trabecular meshwork
May present with sudden painful red eye with acute drop in vision
Can be treated with peripheral
laser iridotomy to create a drainage hole on the iris
Describe the fovea
most sensitive part of the retina.
Has the highest concentration of cones, but a low concentration of rods.
Describe central vision
Detail Day Vision, Colour Vision – Fovea has the highest concentration of cone photoreceptors
to navigate in environment, patient may
need white stick even with perfect visual acuity
Describe peripheral vision
Shape, Movement, Night Vision – Navigation Vision – Assessed by Visual Field Assessment – Extensive loss of Visual Field – unable Central and Peripheral Vision –
Describe the structure of the retina
Outer Layer – Photoreceptors (1st Order Neuron) – Detection of Light Middle Layer – Bipolar Cells (2nd Order Neurons) – Local Signal Processing to
improve contrast sensitivity, regulate sensitivity
Inner Layer – Retinal Ganglion Cells (3rd Order Neurons) – Transmission of Signal from the Eye to the Brain
macula and fovea
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Describe the rod receptor
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Describe the cone receptor
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Whichisthe commonest form of colour vision deficiency in humans
Red-green confusion
