Eye Flashcards
What is the function of the orbit?
Protects eye and adexa, & serves as attachment site for extrinsic muscles
Bones of the orbital margin:
frontal, maxillary, zygomatic, lacrimal, ethmoid
The bony orbit is complete in the horse, ox, and goat. What does this mean?
the temporal process of the frontal bone joins the zygomatic arch to complete the orbit
What completes the orbit in the dog?
orbital ligament- spans the region b/t the zygomatic process of the frontal bone and the frontal process of the zygomatic bone
Structures contained within the orbit:
periorbita, eyeball, ocular adnexa, trochlea
Periorbita
cone-shaped sheath of connective tissue that surrounds the caudal eyeball and ocular adnexa
Ocular adnexa
accessory structures for protection (palpebrae, third eyelid, conjunctiva, retrobulbar fat), tear production (lacrimal gland/appartatus, gland of third eyelid), blood supply and innervation
Trochlea
- a pulley-shaped cartilage that is attached to the dorsomedial wall of the orbit
- directs the course of the dorsal oblique muscle
Three tunics of the eye:
Tunica externa (fibrous tunic) Tunica media (vascular tunic, choroid) Tunica interna (retina)
Fibrous tunic:
- comprised of two regions: Cornea (transparent anterior 1/4) & Sclera (opaque posterior 3/4)
- continuous w/ dural layer of the CNS
Vascular tunic
Composed of 3 regions: -Choriod -Ciliary body -Iris Continuous w/ pia-arachnoid layers of the CNS
Choriod
- highly vascularized and pigmented; provides nourishment to globe
- black areas for light absorption
- tapetum lucidum is a brightly colored region, located superior to the optic disk, that reflects light
Ciliary body
ciliary mm. and ciliary ligaments control the shape of the lens
Iris
circular and radial mm. regulate the size of the pupil
Iridic granulae
horse has “black bodies” (sunglasses) on pupillary margin
Internal tunic
the retina, divided into two regions:
- Optical part (visual part covers the choroid)
- Blind part (non-visual part, covers ciliary body and iris) Cannot distinguish blind retina from ciliary body
The optic retina has two layers:
- pigmented (outer) layer (stratum pigmentosum)
- nervous (inner) layer (pars nervosa retina) divided into nine layers
- divisions of retina can only be seen histologically
The neuron processes of the ganglion cells of the retina converge to form the
optic nerve
Ganglion cells
-bi-polar neurons whose cell bodies are located within the ganglion cell layer of the retina
The optic nerve begins at the ______
optic disk, where these axonal processes exit the caudal aspect of the globe of the eye
“blind spot”
-retinal vessels also enter & leave here
Anterior compartment
-located b/t the lens and cornea
-filled with aqueous humor
-divided by the iris into 2 chambers:
anterior chamber and posterior chamber
Posterior compartmenT
- Located b/t the lens and fundus
- Contains the vitreous body
- helps maintain shape of eye
- maintains necessary intraocular pressure to prevent retinal detachment
Vitreous body
- established during development and is maintained w/in the posterior compartment of the eye to maintain intraocular pressure
- degeneration (liquefaction) of the vitreous body may predispose to retinal detachment
Aqueous humor
- continuously produced and reabsorbed
- secreted by ciliary body epithelium
- drained via the venous sinuses of the sclera at the iridocorneal angle
- increased fluid results in increased intraocular pressure (glaucoma)
Intrinsic muscles of the eye
ciliary muscles and pupillary muscles
Ciliary Muscles
- regulates shape of the lens
- contraction relaxes tension of the suspensory ligaments and the lens fattens (accommodation)
- regulated by the oculomotor nerve (PSNS)
Pupillary muscles
- constrictor pupillae (circular)
- regulated by the oculomotor by the oculomotor nerve (PSNS)
- Dilator pupillae (linear, radial)
- regulated by the SNS (neuron processes from cranial cervical ganglion)
Adnexa of the eye
- Palpebrae: superior and inferior eyelids- palpebral fissure is the space b/t these
- conjunctiva: palpebral and bulbar; continuous at the fornix
- third eyelid: cartilage, superficial gland of the third eyelid
- Lacrimal appartaus
- Extrinsic muscles of the globe
Both eyelids (palpebrae) are lined by haired skin externally and ____ internally
mucous membrane
What anchors the commisures of the eyelids?
Medial and lateral palpebral ligaments
-medial ligament is more developed
The ______ is a continuous mucous membrane that lines the inner palpebrae and part of the globe
conjunctiva
Palpebral conjunctiva
- lines internal surface of palpebrae
- continuous w/ outer skin of palpebrae and w/ bulbar conjunctiva at fornix
- third eyelid is a fold of the inferior palpebral conjunctiva
Bulbar conjunctiva
- reflects onto the surface of the globe at the fornix
- continuous w/ palpebral conjunctiva
Concave fold of palpebral conjunctiva that protrudes from the medial angle of the eye
plica semilunaris (third eyelid)
Plica semilunaris
- supported by a T-shaeped cartilage
- superficial gland of the third eyelid
- accessory lacrimal gland (mucous and serous secretions)
- surrounds cartilage “stem”
- deep gland also in cattle and swine
Secretions of the _____ keep the surface of the eye moist and clean, and provide nourishment to the eye
lacrimal gland
Process of lacrimal gland
- lacrimal gland secretes serous fluid into the superior conjunctival sac
- secretion flows over cornea (blinking)
- Passes through puncta and into lacrimal gland ducts
- lacrimal lake
- drains into nasolacrimal duct
- dissipated via convection in nasal cavity
Extrinsic muscles of the eye
- muscles of the globe: dorsal rectus, ventral rectus, lateral rectus, medial rectus, dorsal oblique, ventral oblique, retractor bulbi
- muscles of the eyelids (palpebrae): levator palpebrae superioris, orbicularis oculi, retractor anguli oculi lateralis, levator anguli oculi medialis
Function of the retractor bulbi m.
retract the eyeball deep into the orbit (protective mechanism, surrounds the optic nerve)
