eye anatomy Flashcards
Describe the vision of carnivores/predators vs. herbivores/preys relative to binocular and peripheral vision/
Carnivores/predators: more binocular, less peripheral
Herbivore/preys: more peripheral, less binocular
What bone connects the frontal bone to the zygomatic arch, forming a COMPLETE orbit? (Ruminants & Equine-only)
Postorbital bar
What region near the eye moves “in and out” when horses chew?
The Supraorbital fossa (space dorsal and caudal to orbit)
Identify region and function:
Pterygopalatine Fossa - contains foramina transmitting VAN supplying globe and adnexa
What is the ocular adnexa?
all the supporting/protected structures of the globe (eyelids, extraocular muscles, lacrimal system, etc.)
What structures help close the eyelids into a horizontal line when the orbicularis oculi contracts?
Medial and lateral palpebral ligg.*
-> Orbicularis oculi = muscle that closes the eyelids (tested with dazzle reflex)
What muscle lifts the top eyelid and what innervates it?
Levator palpebrae superioris m. - CN III (occulomotor)
Which species have lower and upper cilia?
Equine and ruminants
Where is the third eyelid anchored?
in the medial canthus
What controls the contraction of the third eyelid that keeps it in retraction?
SYMPATHETIC (mydriasis) innervation of the ORBITALIS MUSCLE (a vestigial, smooth muscle)
-> movement of 3rd eyelid over globe = passive
“A vestigial structure is a biological structure that has lost a major ancestral function and is usually drastically reduced in size.”
How do tears exit the globe?
lacrimal duct (dorsolateral to eye) -> tears move over eye -> Medial canthus -> superior & inferior lacrimal puncta -> lacrimal canaliculli -> nasolacrimal duct system -> nasal vestibule
Where is the lacrimal gland located?
Dorsolaterally (relative to the globe)
What nerves innervate which extraocular muscles?
Dorsal Oblique (CN IV = trochlear)
Lateral Rectus and Retractor Bulbi (CN VI = Abducens)
Dorsal Rectus, Ventral Rectus, Medial Rectus, Ventral Oblique, Levator Superioris (CN III = Oculomotor)
What artery supplies the eye and part of the adnexa?
External Ophthalmic Artery (branch from maxillary a.)
(external carotid -> maxillary a. -> external ophthalmic a.)
What nerve supplies the orbicularis oculi? Sympathetic or parasympathetic nerve fibers?
Palpebral Nerve – terminal branch of CN VII (Facial) via PARASYMPATHETIC nerve fibers
What two branches of the trigeminal nerve provide general sensation to the eye in carnivores?
Ophthalmic (V1) –> upper eyelid sensation
Maxillary (V2) –> lower eyelid sensation
What acts on the lens to accommodate vision (i.e. focus/de-focus the lens), how, and what is it innervated by?
CILIARY BODIES via relaxing the suspensory ligg. of the lens (ZONULAR FIBERS) that attach onto lens capsule – innervated by PARASYMPATHETIC nerve fibers
Describe the order of the tissue layers (tunics) of the globe
Fibrous tunic (external) -> vascular tunic (uvea/middle) -> nervous tunic (internal)
What two structures are within the fibrous tunic? What is the distinct junction at which they are separate? Is it an complete or incomplete structure?
Cornea (anterior) and sclera (posterior)
Cornea projects from the sclera; distinctly demarcated form sclera @ corneoscleral junction (limbus)
COMPLETE structure (lines the inner cornea)
What structures are within the uvea (the vascular tunic)? Is it complete or incomplete?
Iris, ciliary bodies, choroid; is an incomplete structure (because it does not line the inner cornea)
What condition is this?
Uveitis (inflammation of the uvea / vascular layer) - green color = typical for this condition
Identify 1, 2 and 3 structures.
1 = lens
2 = ciliary body
3 = choroid (covered by pigmented outer layer of retina)
What are corpora nigra / iridic granules in ungulates?
Proliferation of normal iris tissue; allow for a rounder POV; help with reducing glare
Which intra-ocular muscle causes mydriasis? Miosis?
Mydriasis = dilator muscle
Miosis = sphincter muscle
What causes vertical pupils in small cats during miosis?
DV orientation of sphincter muscle fibers -> extend at iris periphery -> intersect at pupil extremities
What is the most posterior portion of the vascular tunic? Function?
Choroid- lines the most posterior & circumferential parts of globe (fundus).
HIGHLY VASCULAR LAYER that brings oxygen and nutrients to the eye. Lays between retina and sclera.
What structure is a part of all mammals’ choroid (except for pigs’) that gives the “eye shine” at night / improves low-light vision? How?
Tapetum lucidum - provides retina with extra opportunity for photon-photoreceptor stimulation
What internal portion of the globe is visible through the pupil via ophthalmoscope?
Fundus (with retina, choroid, vessels, and optic disc)
What structure makes up the nervous tunic? Is it a complete or incomplete structure?
Retina (3 parts), incomplete (because it does not line the inner cornea)
What structure detects light and transforms photons into neural signals?
The retina (composed of tissue originally derived from the developing brain)
What chamber lies posterior to the lens? Function?
The vitreous chamber - maintains eyeball shape, shock absorber, assists with vision (light passes thru this chamber to the retina)
How does glaucoma form?
Ciliary EPITHELIUM produces aqueous humor from posterior -> anterior chamber, and returned to venous circulation @ SINOUS VENOUS SCLERAE (spaces of Fontana) –> GLAUCOMA OCCURS WHEN THESE SPACES BECOME PLUGGED due to RAISE IN INTRAOCULAR PRESSURE -> OPTIC N. COMPRESSION
Identify layers of nervous tunica
Purple: Pars optica retina (visual part)
Lavender: pars ciliaris (avisual)
Blue: pars iris (avisual)
Lavendar + blue = pars ceca retinae (avisual)
