Anatomy of the Eye and Orbit Flashcards
What are the 3 coats of the eyeball?
Fibrous coat
Vascular coat
Sensory coat
What is included in the fibrous coat of the eyeball?
Cornea
Sclera
What is included in the vascular coat of the eyeball?
Ciliary body
Iris
Choroid
What is included in the sensory coat of the eyeball?
Optic nerve
Retina
Describe the cornea
Anterior 1/6th which is transparent
Is a window to allow light rays to enter the eyeball
Describe the sclera
Is the opaque posterior 5/6th
Gives attachments to muscles moving the eyeball
Describe the ciliary body
Suspends the lens and produces the aqueous humor
Describe the iris
Controls the diameter of the pupil and thereby controls the amount of light rays entering the eyeball
Describe the choroid
Supplies blood to outer layers of the retina
Describe the retina
Has light sensitive rods and cons which enables us to see
What does the sensory coat contain?
Vitreous humor (VH) in posterior segment
Describe the crystalline lens
Is transparent
Bio-convex structure which is suspended by zonules (suspensory ligaments) from ciliary body
It can change shape
What are the 2 segments of the eye?
Anterior is in front of lens and Posterior segment is behind lens
Anterior - AH
Posterior - VH
What is the function of the aqueous humor?
Helps maintain intraocular pressure
Watery fluid
What is the function of the vitreous humor?
Transparent gel posterior to the lens and helps cushion retina
Prevents detachment
Where is the anterior and posterior chambers?
Anterior - in front of iris
Posterior - behind iris but in front of lens (narrow)
Describe the angle of anterior chamber
If blocked, the AH can’t be drained into trabecular meshwork on sclera
AH drains out of the Schlemm’s canal
What 7 bones make up the bony orbit?
Frontal, sphenoid, lacrimal, ethmoid, maxillary, zygomatic, and palatine
What are the 3 foramina of the orbit?
Optic foramen
Superior orbital fissure
Interior orbital fissure
Describe orbital depth and support
AP length of eyeball - 24mm
AP length of orbit - 40mm
Orbital fats cushions the globe
Describe the eyelids
Skin on outside and mucus membrane called conjunctivae on inside
Eyelashes with sebaceous glands
Muscles, hard palate to keep shape and oil secretory glands for tear film
What are the oily secretory glands of the eyelids called?
Meibomian glands
What are the muscles of the eyelids?
Orbicularis oculi
LPS - levator palpebrae superioris
Where is the conjunctiva?
Is transparent - Covers surface of inner eyelids and loops back over the sclera
Not cover the cornea
Describe the lacrimal apparatus
Lacrimal gland is situated on orbit laterally and ducts open into conjunctival sac
During each blink eyelids spread tears evenly on surface of cornea
Tears drain into punctae sitting over lacrimal bone where its reabsorbed
Drain through nasolacrimal duct into inferior meatus of nasal cavity
What is the nerve control of the lacrimal gland?
Parasympathetic - facial nerve
What are the 2 types of ocular muscles?
Intrinsic (start and end in the eyeball) - control pupil diameter and helps alter lens curvature to enable to see
Extrinsic - move the eye
What are the intrinsic muscles of the eye?
Ciliaris muscle and constrictor pupillae - parasympathetic
Dilator pupillae - sympathetic
What are the 6 extrinsic muscles of the eye?
4 straight - medial, lateral, inferior, superior rectus
2 oblique - superior and inferior oblique
Where do the extrinsic muscles arise from?
Recti muscles - from apex of orbit from an annular fibrous ring
Superior oblique - roof of orbit posteriorly
Inferior oblique - floor of oblique anteriorly
What nerves supply the muscles of the eye?
Trochlear nerve supplies the SO
Abducent nerve supplies the LR (lateral retcus)
Everything else is the oculomotor nerve
What is the origin and insertion of the LPS?
Origin - roof of orbit
Insertion - upper eyelid
What is the origin and insertion of the recti muscles?
Origin - tendinous ring
Insertion - sclera anteriorly
What is the origin an insertion of the inferior and superior obliques?
SO - origin is lesser wing of sphenoid and inserts in sclera posteriorly
IO - origin is medial part of orbit floor and inserts in sclera posteriorly
Describe the function of the optic nerve in the eyeball
Carries visual impulses from the eyeball and leaves through the optic foramen
Describe the oculomotor nerve
Supplies all muscles going to eye except 2 and also supplies levator muscle of the eyelid
Carrie parasympathetic fibres which synapse at ciliary ganglion in orbit
What are some branches of the ophthalmic division of the trigeminal nerve?
Nasociliary nerve
Frontal branch - largest branch
Lacrimal branch - smallest branch
Describe the ophthalmic artery
Large branch of ICA
Supplies all structures in the orbit and also branches to nasal cavities and forehead
Enters through the optic foramen with optic nerve
Where does the central retinal artery supply?
Supplies inner layers of retina
Travels within substance of optic nerve
Where does the short posterior ciliary arteries supply?
Posterior part of the choroid and outer retina
Where does the long posterior ciliary arteries supply?
The anterior choroid ciliary body and iris
Describe an ophthalmoscope
Fundus picture
Can see optic disc - start of optic nerve and physiological blind spot
4 quadrants - superonasal, inferonasal, supero-temporal, infero-temporal
Describe venous drainage of the eye
Superior and inferior ophthalmic veins which drain into cavernous sinus - posterior to apex of orbit
What are the cavernous sinus contents?
Loop of internal carotid artery and nerves
Beside pituitary gland
Layers of dura mater covered by endothelium
What does the eye develop from?
Neurectodermal
Where do optic vesicles grow out from?
From diencephalic part of neural tube towards surface ectoderm
Describe the formation of the optic vesicles
Reach surface ectoderm - cells of surface ectoderm thicken - lens placode
Lens placode pushes inwards causing optic vesicle to form an optic cup - 2 layers
Describe the lens vesicle and optic cup
Lens vesicle looses connection with surface ectoderm
Choroid fissure forms as blood vessels pass through fissure in inferior wall of optic cup
What does surface ectoderm form?
Eyelids, conjuctiva, corneal epithelium
What does mesenchyme form?
Forms choroid, stroma of cornea, sclera and extraocular muscles
What does lens fibres form?
Epithelium of lens vesicle and later loose their nuclei
