Visual System Anatomy Flashcards
What is the Limbus?
The border between the cornea and the sclera
What produces tears?
Lacrimal gland
Where do the afferent nerves travel from the eye?
Cornea
Cranial Nerve V1 - ophthalmic trigeminal
What neurotransmitter operates within the lacrimal system?
Acetylcholine * due to parasympathetic efferent nerves
Where do the tears drain?
through two puncta - which are openings on medial lid margin
Where do tears flow through?
Superior and inferior canalculi and gather in the tear sac
They exit the tear duct into the nasal cavity
Where is the lacrimal gland located?
Located within the orbit - latero-superior to the globe
It is innervated by the parasympathetic nerve
What is basal tear?
Tear even in the absence of irritation or stimulation
What is reflex tear?
Increased tear productions in response to ocular irritation
What is the tear film?
The healthy cornea is covered in the tear film which is a thin layer of FLUID
Made of three layers : - mucous area - thick watery layer - thin lipid layer it allows a smooth cornea to air surface
What are the functions of the tear film?
Oxygen supply to cornea as cornea has no blood vessels
It contains factors against harmful bacteria
- both functions of the aqueous tear film layer in the middle
What is the top lipid layer of the tear film responsible for?
Protecting tear film from rapid evaporation
Where does the lipid layer of the tear film come from?
The lipid layer is secreted by Meibomian glands which are situated along the eyelid margins
What is the layer adhered to the eye surface used for?
The bottom mucinous layer ensures that tear film sticks to eye surface
Mucin molecules act by binding water molecules to the hydrophobic corneal epithelial cell surface
What is the conjuctiva?
The thin transparent tissue that covers the outer surface of the eye
begins at outer edge of cornea, covers visible part of the eye AND lines the EYELIDS
Nourished by tiny blood vessels which are more prominent when inflammed
What is the eyeball made up of outside to inside?
Sclera : hard and opaque
Choroid : pigmented and vascular
Retina: neurosensory tissue lining inner part of the eye
What is the function of the sclera?
Protecting and maintaining shape of the eye
has a high water content
What is the function of the choroid?
Providing circulation * especially to the back of the eye
and shields out unwanted scattered light
What is the function of the retina?
conversion of light to neurological impulses to be transmitted to the brain via optic nerve
What is the cornea?
Transparent dome like window covering front of the eye
Low water content
Powerful refracting surface 2/3 of eyes focusing power
Made of 5 layers
What 5 layers is the cornea made of?
1 – Epithelium
2 – Bowman’s membrane
3 – Stroma – its regularity contributes towards transparency
4- Descemet’s membrane
5- Endothelium – pumps fluid out of corneal and prevents corneal oedema