The Orbit and Eye Flashcards
Bony Orbit
Bilateral, symmetrical cavities containing the eyeballs and associated structures
Bony Orbit Bones (7)
- Frontal bone
- Sphenoid bone
- Ethmoid bone
- Lacrimal bone
- Palatine bone
- Maxilla
- Zygomatic bone
Bony Orbit Fissures (3)
- Superior orbital fissure:
-CN 3, 4, 5 (opthalmic division) and 6 - Optic canal:
-CN 2 - Inferior orbital fissure
3 Layers of the Eye
- Outer fibrous layer- sclera and cornea
- Middle vascular layer- uvea (iris, ciliary body, choroid)
- Inner neural layer- retina
Outer Fibrous Layer (2)
- Cornea:
-clear outer layer
-first refraction of light entering eye
-directs light to lens
-avascular - Sclera:
-supportive outer white layer
-attachment site for extraocular muscles
-covered by mucous membranes (conjunctiva) to lubricate eye
-vascular
*Limbus= transition zone between cornea and sclera
Middle Vascular Layer (4)
- Iris:
-contains pupillary dilator and sphincter muscles
-controls pupil size depending on light and nervous system signals
-colour is determined by amount of melanin - Ciliary body:
-produces aqueous humour (to help provide nutrients)
-contains ciliary muscles
-helps focus lens using zonular fibers and ciliary muscles - Choroid:
-between sclera and retina
-nourishes retina
-maintains eye temperature and volume
*3 make up uvea
- Lens:
-focuses light on retina
-majority of refraction in lens
Intraocular Muscles of Middle Layer (2)
- Ciliary Muscles:
-ring around entire eye
Contract= lens bulges
Relax= lens pulled in and flatten
- Pupillary Muscles:
a) Sphincter Pupillae- concentric muscle fibers, constricts pupil when contracted, parasympathetic NS *inner ring
b) Dilator Pupillae- muscle fibers run longitudinally towards margins of iris, enlarges pupil when contracted, sympathetic NS *outer ring
*more light comes in/brighter/PSNS signals= pupil constricts (less light needs to come in)
*dim light/SNS signals= pupil dilates (more light needs to come in)
Ciliary Muscles Distant vs. Near Objects
Distant object:
-ciliary muscles relax
-zonular fibers tighten
-lens flattens
Near object:
-ciliary muscles contract
-zonular fibers relax
-lens thickens
Inner Neural Layer (1)
- Retina
-captures light to send to brain
Components of Retina (5)
- Macula- highest concentration of photoreceptor cells (sharpest vision, photoreceptors= rods (low light, no colour) and cones- high light, high colour)
- Fovea- centre of macula
- Optic disc- where optic nerve exits the eye, blind spot= no photoreceptors
- Ora serrata- anterior border of retina
- Optic nerve- accumulation of retinal axons
Clinical Connection: Sightedness
- Normal vision
- Myopia (Near-Sightedness)
-Lens or eyeball too long/bulbous, image focused in front of fovea - Hyperopia (Far-Sightedness)
-Lens or eyeball too short/flat
-Image focused behind fovea
Chambers of the Eye (3)
- Anterior Chamber
-between cornea and iris, filled with aqueous humour - Posterior Chamber
-between iris and lens, important for production and circulation of aqueous humour
*both in anterior cavity
*aqueous humour- maintains ocular/eye pressure, replaced every 90 mins through post. chamber -> anterior chamber -> limbus
- Vitreous Chamber
-filled with gel-like vitreous humour
*in posterior cavity
*vitreous humour maintains shape of eye, nourishes eye, attached to retina, makes up about 80% of eye volume and does not regenerate
Extraocular Muscles (6)
- Superior rectus
- Inferior rectus
- Lateral rectus
- Medial rectus
- Superior oblique
- Inferior oblique
Movements of Extraocular Muscles
- Superior rectus- up
- Inferior rectus- down
- Lateral rectus- laterally
- Medial rectus- medially
- Superior oblique- down and out (pulled through trochlea)
- Inferior oblique- up and out
Innervation of Extraocular Muscles
All oculomotor nerve (CN 3) except SO4LR6 “SOLR”
Superior oblique= trochlear nerve (CN 4) *trochlea= “pulley”
Lateral rectus= abducens nerve (CN 6) *ABducens ABducts
