The Eye and Orbit Flashcards
Describe the shape and boundaries of the orbit. (5)
Pyramid shape Base of pyramid: orbit opening Lateral wall: sphenoid and zygomatic Medial wall: ethmoid and lacrimal - nasal cavity. Roof: frontal - anterior cranial fossa Floor: maxilla - maxillary air sinuses.
What are the three openings at the back of the orbit? (3)
Optic canal
Superior orbital fissure
Inferior orbital fissure
Describe the neurovascular supply to the orbit. (6)
Artery: opthalmic
Vein: superior and inferior opthalmic veins into cavernous sinus, pterygoid plexus and facial vein.
General sensory (inc conjunctiva and cornea): ophthalmic branch of trigeminal Vc
Special sensory: optic
Motor: occulomotor, trochlear, abducens.
Describe orbital ‘blow out’ fractures. (4)
Caused by increased pressure inside the orbit (punch) or inside the maxillary sinus (sinusitis) just below the floor, which can burst the weak inferioromedial wall and cause orbital contents to leak into the sinus. Presents with trapping of the extraoccular muscles so can’t look up.
Describe the structure of eyelids. (6)
Skin, subcutaneous sptissue, tarsal plate containing Meibomian glands, muscles like aponeurosis of levator palpebrae superioris, and sebaceous glands assocaited with lash follicles. The tarsal plate gives shape and the glands produce the tear film.
Explain the differences between styles and Meibomian cysts. (2)
Styes - blocked eyelash follicles causing infection.
Meibomian cysts - blocked Meibomian glands - not infectious.
Describe the septum of the eye. (2)
Thin sheet of fibrous tissue that runs from orbital rim to tarsal plates to stop superficial infections from spreading into the orbit.
Describe periorbital or preseptal cellulitis. (3)
Secondary to wounds of infections, confined superficial so doesn’t affect eye movements. Usually no treatment needed.
Describe orbital or postseptal cellulitis. (6)
Infection within the orbit which can cause exophthalmos, reduced eye movements and reduced visual acuity. Potential route for infection to spread intracranial via venous drainage causing meningitis or cavernous sinus thrombosis. Needs abx and surgical drainage.
Describe the lacrimal apparatus. (4)
Structures involved in tear film production (lacrimal gland) and drainage (lacrimal sac, canaliculi and nasolacrimal ducts). Obstruction can lead to epiphora (overflow of tears).
Describe the anatomy of the eyeball (6)
Eyeball has 3 layers:
Anteriorly the conjunctiva.
Outer sclera (white) continuous anteriorly as the transparent cornea.
Middle choroid, ciliary body and iris - the vascular layer.
Inner retina (photosensitive layer on outer pigmented layer).
Describe how the eyeball position is maintained. (3)
Suspensory ligament, extra-ocular muscles and lots of orbital fat.
Describe the conjunctiva and two pathologies of it. (4)
Anterior surface (except cornea) covered in conjunctiva which covers whites of eyes and lines the eyelids, creating a conjunctival sac.
Conjunctivitis - inflammation and redness
Subconjunctival haemorrhage - wholly red by asymptomatic patch.
What is the macula? (1)
The area at the back of the eye where light is focussed.
Describe the differences between rods and cones. (6)
Rods: active at low levels of light, not colour vision, abundant at peripheries.
Cones: high definition colour vision at high levels of light only, concentrated within the macula. Fovoa = only cones.
Explain why older people tend to hold books further away to read them. (5)
Things that are closer have more divergent light rays, so more effort is undertaken to focus them on the macula.
This is beyond the cornea, so the eye accommodates - pupil constricts (less light) lens becomes more convex (ciliary muscle contraction)
As we age, lens gets stiffer in presbyopia so you can’t focus on near things. Through occipital higher thinking, they hold stuff away so the rays are less divergent to start with.
Describe 3 causes of vision blurring. (6)
Transparency of structures anterior to the retina is reduces (cataracts)
Ability to refract light is reduced (presbyopia, shape of eyeball)
Retina or optic nerve pathology (retinal detachment, optic neuritis).
Explain the pinhole thing. (3)
When decreased visual acuity is due to a refracted error, viewing things through a pin hole can help because all the light travels perpendicular to the retina so doesn’t need to be refracted.
Describe the chambers of the eyeball (3)
Vitreous chamber is behind the lens and is filled with vitreous humour.
Anterior chamber is between cornea and iris
Posterior chamber is between iris and ciliary muscle.
Describe the production of aqueous humour. (3)
Describe its purpose, and it’s draininage. (4)
Secreted by the ciliary processes within the ciliary body. Flows from posterior chamber through pupil to anterior chamber.
Nourishes the avascular lens and cornea.
Drains through the iridocorneal angle (iris to cornea) via The trabecular meshwork of Canal of Schlemm.
Describe glaucoma. (10)
Optic nerve damage secondary to raised intraocular pressure due to a blockage in drainage of the aqueous humour from the anterior chamber.
Chronic = open angle glaucoma: trabecular meshwork deteriorates with age, asymptomatic but with optic cupping. Gradual but irreversible loss of peripheral vision.
Acute = closed angle glaucoma: narrowing of iridocorneal angle leading to an emergency presenting with irregular, oval and fixed pupil, a halo around lights (corneal oedema), nausea and vomiting.
Describe the actions and innervation of Superior rectus (4)
Elevates
Intorts and adducts
Occulomotor
Describe the actions and innervation of Inferior rectus (4)
Depresses
Extorts and abducts
Occulomotor
Describe the actions and innervation of Medial rectus. (2)
Adducts
Occulomotor
