Eye Flashcards
What are the 3 layers of the eye and their components?
Outer fibrous layer - sclera and cornea
Medial vascular layer - choroid, ciliary body and iris
Inner neural layer - retina
How many bones contribute to the bony orbit?
7:
Frontal Sphenoid Ethmoid Lacrimal Maxilla Zygomatic Palatine
Describe the boundaries of the bony orbit:
Superior:
- frontal
- sphenoid (lesser wing) near apex
Inferior:
- maxilla
- zygomatic
- palatine
Lateral:
- frontal
- sphenoid (greater wing)
- zygomatic
Medial:
- frontal
- sphenoid
- ethmoid
- lacrimal
Apex (internal):
- lesser wing of sphenoid
Describe the 3 anatomical features of the external eye:
Palpebrae (eyelids)
- cover anterior eyeball
- internal surface: palpebral conjunctiva
- protect cornea from dust and light
- keep cornea moist by spreading lacrimal fluid
Eyelashes
- protect eye from foreign bodies and initiates automatic blink response when object is near
Ciliary glands
- at base of eyelashes
- secrete anti-bacterial sebaceous substance that lubricates eyelashes
What are the conjunctiva?
Mucous membranes covering the eylelid and sclera of the anterior eyball
Palpebral - lines eyelid
Bulbar - lines sclera
Conjunctival Fornix - where two conjunctiva meet (inner fold of eyelid)
What are the tarsal plates?
Thick bands of connective tissue that stabilize and support the eyeballs structurally
Superior and inferior tarsal plates
Tiny tarsal glands within tarsal plates secrete lipid based substance that lubricates edges of eyelids
What are the 5 features of the lacrimal apparatus? Describe the function of this apparatus.
Lacrimal glands - in lacrimal fossa of supero-lateral orbit. Secrete lacrimal fluid
Lacrimal ducts - up to 12, open into superior conjunctival fornix in inner fold of superior eyelid
Lacrimal lake -triangular space at medial aspect of eye where lacrimal fluid collects
Lacrimal sac - upper portion of nasolacrimal duct
Nasolacrimal duct - conveys fluid from lacrimal lake /sac to nasal cavity, draining into inferior nasal meatus
Function of the lacrimal apparatus is to secrete lacrimal fluid (tears). Lacrimal fluid is secreted by the lacrimal glands, distributed by the lacrimal ducts into the superior conjunctival fornix, sweeps from lateral to medial across the sclera and cornea of the anterior eye, collects in the lacrimal lake, and drains into the lacrimal sac and nasolacrimal duct into the inferior nasal meatus.
What are the components of the outer fibrous layer of the eye?
Sclera (whites of eye) - posterior 5/6ths eyeball
Cornea - anterior 1/6 eyeball, overlying lens and iris
What are the components of the middle vascular layer of the eye?
Choroid - dark brown membrane covering posterior 5/6ths eyeball (intermediate membrane between sclera and retina). Contains blood vessels and pigment which absorbs excess light
Ciliary body - anterior continuation of choroid, and connects choroid with circumference of iris. Has a vascular and a muscular part:
Vascular - ciliary processes secrete aqueous humour which fills anterior and posterior chambers
Muscular - ciliary muscle controls shape of the lens: accommodated (fatter / contracted) for short distance, and non-accommodated (thinner / non-contracted) for long distance. Contraction via CN III Oculomotor via Edinga-Westphall nucleus in rostral midbrain.
Lens suspended from ciliary body (posterior to iris) by suspensory ligaments
Iris - coloured portion of eye. Thin muscular diaphragm.
What are the anterior and posterior chambers of the eye?
Anterior - between iris and cornea
Posterior - between iris and lens
(both chambers filled with aqueous humour secreted by ciliary processes of ciliary body)
What is the pupil and what controls its circumference?
Aperture (hole) in iris, adjusts size to regulate amount of light entering retina.
Controlled by two circular muscles: sphincter pupillae (parasympathetic) - constricts pupils dilator pupillae (sympathetic) - dilates pupils
Innervation via CN III oculomotor through Edinga-Westphall nucleus in rostral midbrain
Describe the difference between accommodated & non-accommodated vision, and how this occurs.
Accommodated - ciliary muscle (in ciliary body) contracts around the lens to make the lens fatter. For short vision.
Non-accommodated - ciliary muscle is non-contracted. Lens is thinner. For long distance vision.
Contraction of ciliary muscle via CN III Oculomotor nerve, via Edinga-Westphall in rostral midbrain.
Describe the features of the inner neural layer of the eye.
Retina - 10 layers of thin neural membrane covering the inside of the posterior 2/3rds of the eyeball. Receives visual images and transmits via optic nerve to the brain
Optic disc - where ganglion cells converge to form CN II Optic nerve moving towards the brain (Primary Visual Cortex of Occipital lobe). No photoreceptors cover the optic disc so this is a blind spot in the vision.
Macula - oval shaped indentation of retina responsible for central vision.
Fovea - area of macula with greatest density of cones.
Photoreceptors - rods (peripheral) and cones (central) transmit visual signals via bipolar cells to ganglion cells.
What are the photoreceptors of the eye?
Rods - 100 million per eye. Located peripherally. Responsible for peripheral vision & black/white vision.
cones - 7 million per eye. Located centrally. Responsible for central vision andcolour vision.
transmit visual images via bipolar cells to ganglion cells, which converge to form CN II optic nerve.
Located in the retina in the neural layer (inner layer) of the eye.
What are the 7 muscles of the eye?
Levator Palpebrae superioris
4 recti muscles - superior, inferior, lateral & medial
2 oblique muscles - superior and inferior
