Eye Flashcards
Bony orbit
bounded by:
- medially – ethmoid paranasal sinuses
- inferiorly – maxillary paranasal sinuses
Structures and muscles of eyes
Eyebrows & (Eyelids (palpebrae) – separated by palpebral fissure,
reinforced by dense CT bands or tarsi:
- Meet each other at M & L angles (canthi).
- Levator palpebrae superioris lifts S eyelid.
- Orbicularis oculi close eyelids
Conjunctiva
transparent mucous membrane, covers inner surfaces of eyelids (palpebral) and A surfaces of eyeball (bulbar)
Lacrimal apparatus
keeps eye surface moist, its glands make lacrimal fluids (tears), lies in a fossa in SL orbit, ducts convey fluid to conjunctival sac
lacrimal canaliculi – connect to nasolacrimal duct, passage conveys lacrimal fluid to NC, CN VII nerve
Accessory eye glands
Meibomian glands – sebaceous gland in upper and lower eyelid, secretes oily substance, meibum, coats surface of eye, prevents drying of eye
Moll’s glands – base of eyelashes, modified
apocrine sweat glands secrete sebum which coats eyelash, keeps it healthy
Eyeball anatomy
optical apparatus of visual system.
Components of eye:
- protect and support photoreceptors
- gather, focus, and process light into precise images.
- 3 layers: fibrous, vascular, and inner
- Internal cavity – contains fluids (humors)
Fibrous external eye layer
2 regions of CT, shape and resistance
- cornea – A 1/6th of fibrous coat, transparent – allows light to enter eye
- sclera – P 5/6 of coat:
- white, opaque region
- protects the eyeball and provides shape and sturdy anchoring site for extrinsic and intrinsic eye
Vascular middle eye layer
Choroid – darkly pigmented membrane:
- lines most of sclera
- prevents scattering of light rays within eye.
- Ciliary body – ring-like muscular and
vascular thickening, provides attachment to lens, SM control thickness and thus focus of lens
Vascular middle layer part 2
Iris – visible colored part of eye: thin contractile diaphragm w/central aperture.
- Pupil – round, central opening of the
iris: allows light to enter eye
- iris contains SM fibers that act to vary size of pupil
SM of iris and ciliary body
sphincter pupillae constricts pupil (PS) and radially arranged dilator pupillae (S) to dilate pupil, dilation takes longer
Inner eye layer (retina)
site where light-sensitive photoreceptor cells are located, 2 parts:
- optic layer (sensitive to visual light rays: 2 layers – neural and pigmented)
- non-visual layer (A continuation of pigmented area)
Inner layer
- Optic disc: distinct circular area of retina, sensory fibers and vessels conveyed by optic nerve (CN II) enter the eyeball, no
photoreceptors, insensitive to light, blind spot - Macula of retina (macula lutea, L. yellow spot): a small area w/special photoreceptor cones, acuity of vision.
- Fovea centralis (L. central pit): depression at center of macula characterized as area of most acute vision
Photoreceptors
rod cells – more sensitive to light.
- allow vision in dim light.
- don’t provide sharp images or color vision.
- cone cells – operate best in bright light.
- enable high-acuity color vision
Lens
- A: filled with aqueous humor: clear watery solution, provides nutrients for
avascular lens and cornea. - P: filled w/vitreous humor: transmits light, holds retina in place, supports lens
light waves path to retina
- Cornea
- Aqueous humor
- Lens
- Vitreous humor
Retinal attachment
layers of developing retina separated in embryo by intraretinal space.
- early fetal period- fusion of layers usually
eliminates space, but pigmented cell layer isn’t firmly attached to neural layer
- Retinal detachment - may result from
a blow to eye and seepage of fluid
between 2 layers, takes days or weeks after trauma for detachment to occur, patients present w/flashes of light or specs floating
in front of eye
Extra-ocular Orbit muscles
levator palpebrae superioris: elevates S eyelid, CN III
- 4 recti: S, I, M, & L
- 2 obliques: S & I
- All originate from walls of orbit
Recti muscles (eye)
4 recti muscles mainly run A to attach to S, I, M, and L aspects of eyeball, primary actions are elevation, depression, adduction, and abduction of eyeball
Oblique muscles (eye)
obliques take an indirect path through orbit
- S oblique: originates P, runs A along M orbital wall, loops through trochlea in AM part of orbital roof to insert on PL eye surface
- Due to attachment position, S oblique abducts eyeball (i.e. turns the pupil L) and
depresses it
- I oblique abducts and elevates pupil
Nerves of orbit
General sensory: CN V1 nerves
- Special sensory: CN II for vision
- Branchial motor: CN VII to orbicularis oculi – closure of eyelids
- Somatic motor:
1. CN III to levator palpebrae superioris, S rectus, I rectus, M rectus, and I OM
2. CN IV to superior oblique
3. CN VI to lateral rectus
Orbit arteries
orbit receives arterial blood supply from branches of ophthalmic artery off internal carotid artery.
- The central retinal artery is a terminal branch; occlusion results in instant blindness (blockage usually unilateral)
