Anatomy Of Eye & Adnexa Flashcards
Purpose of vision
Taking in info from surroundings
Energy from environment is converted to neural activity via conversion of photon into electrical signal in the retina
Vision of carnivores
More binocular, less peripheral
herbivore vision
Opposite of carnivores, less binocular and more peripheral vision
Bony orbit in species
Dog & cat - incomplete, finished w orbital ligament
Herbivores - complete by postorbital bar
Supraorbital fossa
Space dorsal & caudal to orbit
Houses extension of retrobulbar fat pad
Coronoid process of mandible extends into space
Pterygopalatine fossa
Bony orbital rim
Houses globe & adnexa, contains specific for foramina transmitting arteries, veins & nerves serving the globe & adnexa
Nerves that travel through pterygopalatine fossa
CN II
(Orbital fissure)
CN III, IC, V- ophthalmic, VI
Rostral alar foramen
CNV - maxillary
Eyelids
Palpebrae
Superior eyelid
Inferior eyelid
Internal - palpebral fissure
Lateral and medial canthus
Respective edges where two lids meet
Form the medial and lateral angles of the eye
Palpebrae stuctures
Levator palpebrae superior
Orbicularis oculi
Tarsal glands
Medial and lateral palpebral ligaments
Anchoring eyelids medially & laterally so they close in a horizontal line rather than a circle when the orbicularis oculi contracts
Levator palpebrae superioris
Narrow strip of muscle running longitudinally into upper lid
Contraction raises the upper lid
Innervated by CNIII
Simultaneous contraction of two muscles that ensure globe rotates upward & upper lid is raised
Muscles of eyelid
Various other small muscles
Levator anguli oculi medialis
Retractor anguli oculi lateralis
Orbital adnexa
Third eyelid
Cartilage supported by connective tissues that is anchored in medial canthus
Cartilage often t-shaped but shape varies
Can be carried across the anterior globe like a windshield wiper
Bulbar surface well-provided with lymphoid tissue
Mechanism of third eyelid movement
Held in traction by tonic contraction of the orbitalis (SM)
Contraction is under sympathetic control
Motion over the eye is passive
When eye is retracted into the orbit, 3rd lid slides over globe
Lacrimal apparatus
Flow of tears from Dorso lateral to Ventrolateral
Exit of tears from eye through medial canthus to nasal vestibule via nasolacrimal duct
Apparatus structures
Tear producing glands
Duct system conducting tears from medial canthus into nasal vestibule for evaporation
Tear producing glands
Scattered small accessory glands within eyelids
Glands of 3rd eyelid
Lacrimal gland
Positioned dorsolaterally within orbit
Secretion into conjunctival sac from Dorso lateral aspect
Blinking distributes secretions across globe in a ventromedial direction
Secretion washes over bulbar conjunctiva towards medial canthus
Lacrimal lake
Accumulations of tear fluid near medial canthus
Lacrimal caruncle
Lump in the lake
Lacrmal puncta - superior and inferior
One tiny duct opening in each lid at medial -most margin of lid
Minor species variation
Only pigs dorsally
Lacrimal canaliculi - superior and inferior
Tiny ducts, one from each punctum going medially from each punctum
Two canaliculi fuse
Enlargement called the lacrimal sac is present at the fusion site
Nasolacrimal duct
With or without the sac, two canaliculi fuse into the larger duct, nasolacrimal duct
NLD passes rostrally to empty into the nasal vestibule
Introduction of tears into the nasal vestibule provides evaporative space
Lacrimal apparatus
Lacrimal gland
Lacrimal puncta
Lacrimal canaliculi
Lacrimal sac
Nasolacrimal duct
Nasolacrimal orifice
Extraocular muscles
Trochlea
Fossa for lacrimal sac
Ventral oblique
Dorsal oblique
Maxillary foramen
Levator palpebrae
Retractor bulbi
Dorsal rectus
Lateral rectus
Oblique muscles
Both start medially at pterygopalatine fossa
Two take a general course that crosses orbit obliquely, both insert on respective (dorsal & ventral) lateral aspect of globe
Dorsal (superior) oblique muscle
Starts near optic canal (medially)
Passes rostrally on the Dorso medial orbit wall
Turns around the trochlea, U-shaped cartilage in dosromedial orbit wall
Tendon turns almost 90 degrees (laterally)
Tendon passes to insertion of Dorso lateral side of globe
Isolated action would rotate the dorsal part of globe medially
Ventral inferior oblique muscle
Originates medially in pterygopalatine fossa, more ventrally than dorsal oblique
Passes laterally to insert on Ventrolateral side of globe
Isolated action would be to move the dorsal side of globe laterally
Retractor bulbi
Originates near optic canal
Radiates out as cone that surrounds optic nerve & attaches to globe in a circle just posterior to equator
Contraction retracts globe deeper into orbit, facilitates protrusion of 3rd eyelid.
ABSENT in birds & primates
Muscle that turns globe
Medial rectus - turns globe nasally
Lateal rectus - turns globe temporally
Arteries
Primarily delivered through external ophthalmic artery, vessel itself is a branch of maxillary artery as it courses through the pterygopalatine fossa via rostral alar foramen
Blood delivered to eye via
External ophthalmic artery
Motor nerves of eye (non autonaumic)
Oculomotor nerve innervates
Levator palpebrae superioris
Dorsal, ventral & medial recti
Ventral oblique
Part of retractor bulbi
Trochlear nerve
Motor nerve of dorsal oblique
Abducens nerve
Nerve of lateral rectus and most of retractor bulbi
Palpebral nerve
Terminal branch of auriculopalpebral nerve
Supplies orbicularis oculi
Optic nerve
Sensory to retina (rods & cones)
Ophthalmic
Maxillary
O: sensory to upper lid & frontal region
M: general sensory to lower lid, variable area from caudal to eye to midline of frontal region, upper muzzle
Sympathetic innervation of eye in mammals
Pupillary dilator
Orbitalis muscle (SM)
Common affects of sympathetic innervation
Horners syndrome
Ptosis, miosis, enophthalmos, protrusion of 3rd eyelid
Sunken eye, small pupil, drooping upper lid
PSNS innervation of eye
Pupillary constrictor
Ciliary body - acts on lens for accommodation of vision
