Ophthalmology Anatomy Flashcards
What bones make up the orbit?
Frontal Sphenoid Ethmoid Maxilla Zygomatic Lacrimal
Which parts of the orbit are particularly susceptible to fracture?
Inferior and Medial parts
What muscles move the eyelids and what innervates each muscle?
Orbicularis Oculi - facial nerve (VII)
Levator Palpabrae Superioris - oculomotor nerve (III)
What makes up the lacrimal apparatus?
Lacrimal glands
Lacrimal ducts
Lacrimal canaliculi
How can injury to the facial nerve lead to excess tear production?
Orbicularis oculi paralysis –> eyelid partially open and lose protective blinking –> cornea dry and unprotected from dust –> irritation of eyeball lead to excess tear formation
How may patients with a blowout fracture present?
Sunken orbits - pain
Reduced eye movement
Double vision
Loss of sensation to cheeks and upper gum - lose infraorbital nerve
What is seen on X-Ray in a blowout fracture?
Teardrop sign
What vasculature is important in ophthalmology?
Ophthalmic artery - from internal carotid
Central retinal artery - from ophthalmic artery - internal surface of retina
Ophthalmic vein - drain into cavernous sinus
What are the foramen in the orbit?
Optic canal - optic nerve and ophthalmic artery
Superior orbital tissue - CN III, IV, VI, ophthalmic branch of trigeminal, superior orbital vein
Inferior orbital fissure - inferior orbital vein
How do tears flow through the lacrimal apparatus?
Gland produce components of tears and secrete onto eye through the lacrimal duct
Pass through lacrimal lake at medial angle of eye
Pass to nasal cavity through nasolacrimal duct
Swallowed
What are the components of the tear film?
Surface lipid layer - secreted by meibomian glands
Middle aqueous layer - secreted by lacrimal gland and accessory lacrimal glands
Inner mucus layer - secreted by goblet cells of the conjunctiva and epithelial cell surface
Lipid layer of the tear film prevents underlying aqueous component from evaporating and drying out
What are the layers of the eyeball?
Outer protective layer - sclera and cornea
Middle - choroid, ciliary body and iris, with a rich network of blood vessels
Inner layer - retina with optic and non-visual parts
What are the chambers of the eyeball?
Anterior chamber - between cornea and iris
Posterior chamber - between iris and ciliary body and lens
What does the ciliary body secrete?
Aqueous humour filling the chambers of the eye
What contracts to change the shape of the lens?
Muscle fibres of the ciliary body
What contracts to change the shape of the pupil?
Sphincter and dilator pupillae
What is the vitreous humour?
Transparent jelly like substance
Cavity behind the lens filled with it, supports lens and holds retina in place
What is the structure of the retina?
Neural layer - light receptive
Pigmented layer
Retina supplied by the central artery of the retina
Drained by. the corresponding vein
What are the muscles of the orbit?
Levator palpebrae superioris
Four recti
Two oblique - superior and inferior
Supplied by 3 (oculomotor), 4 (trochlear) and 6 (abducens)
Respectively
What are the muscles of the orbit?
Levator palpebrae superioris
Four recti
Two oblique - superior and inferior
Supplied by 3 (oculomotor), 4 (trochlear) and 6 (abducens)
Respectively
Recti muscles arise from common tendinous ring - annulus of zinn.
What are the main arteries of the orbit?
Ophthalmic artery - gives of central artery to the retina
Ophthalmic veins drain into cavernous sinus
What are the roles of the cornea?
Maintain transparency
Ocular protection, including the corneal reflex
Refraction of incoming light, along with overlying tear film
What are the layers of the cornea?
Epithelium - non-keratinised, sloughed off in tear film
Bowman’s membrane - acellular, any trauma below this level is scarring, as epithelium regenerates
Stroma - connective tissue layer, keratinocytes
Descemet’s membrane - basement membrane
Endothelium - hydration so cornea is transparent
What innervates the cornea?
Rich nerve supply mainly from ophthalmic branch of trigeminal via long ciliary nerve
What maintains intraocular pressure?
Balance between rate of production of aqueous and rate of drainage.
Aqueous humour is responsible for maintaining an adequate pressure in the eye.
What is the flow of aqueous humour?
Produced by ciliary body
Flows up between iris and anterior surface of lens
Through the pupil
Flows out through the drainage angle of the eye
Between cornea and peripheral iris
Through trabecular meshwork
Into canal of schlemm
Drains into episcleral vessels and into the systemic venous circulation
What is the normal IOP?
Intraocular pressure
Measured by determining force needed to flatten pre-determined area of the corneal surface using a tonometer
Greater force needed = higher pressure
Normal - 11-21mmHg
Above 21 - ocular hypertension
Does not necessarily equate to diagnosis of glaucoma (can have normal IOP too)
What receptors control IOP?
Adrenergic
Alpha 2 - reduces IOP by reducing aqueous production, increase uveoscleral outflow
Beta 2 - increases IOP by increasing aqueous production
What is the function of timolol?
Beta blocker
Reduces production of aqueous
What is the function of apraclonidine/brimonidine?
Alpha agonists
Reduces aqueous production
Small increase in drainage
What is the function of latanoprost?
Prostaglandin analogues
Increases uveoscleral outflow of aqueous
What is the function of dorzolamide?
Carbonic anhydrase inhibitors
Reduces production of aqueous
What is the function of pilocarpine?
Parasympathetic
Increases outflow of aqueous by ciliary muscle contraction, opening trabecular meshwork
How can the pupil change size?
Mydriasis - conditions of low light or sympathetic activation - dilation by dilator pupillae
Bright light - miosis, constricts by sphincter pupillae
Stimulated by parasympathetic activation, fibres by inferior division of 3rd nerve
What drugs can have an effect on the pupil?
Tropicamide - antimuscarinic - mydriasis
Phenylephrine - sympathomimetic - mydriasis
Pilocarpine - muscarinic agonist - miosis
What is the function of the ciliary body?
Accommodation, aqueous humour production secreted into the posterior chamber, providing attachment for the lens zonules (suspensory ligaments)
What is the function of the choroid?
Allows nerves and vessels to reach anterior eye
Removes waste products from outer retina
Supplies essential nutrients to outer half of retina
Absorbs any light passing through the retina, preventing it from reflecting back and interfering with vision
How does the choroid attach to the retina?
Basement membrane - Bruch’s membrane
Important in age related macular degeneration
What supplies blood to the outer half of the retina?
Rich capillary bed of the choroid - choriocapillaris
What is the vitreous cavity?
Fills 2/3 volume of the eye
Attached to posterior lens capsule and retina
99% water, 3x more viscous than water
What are the layers of the retina?
Inner neural layer and outer retinal pigment layer
Subretinal space fuses during foetal life, and attached to Bruch’s membrane
Neural retina attached to optic nerve head and anteriorly at termination - ora serrata
Retinal detachment causes separation to reform
What are the components of the neural retina?
Inner retina - photoreceptors (but many neural cell types)
Rods - contrast, motion
Not good for detail
Black and white
To see in darker environments
Cones - finer detail
Colour vision
What is the blood supply of the retina?
Inner 2/3 central retinal artery
Outer 1/3 supplied by choroidal blood supply
Central retinal artery divides into 4, each supplies a segment of the retina - end-arteries
What is the visual pathway?
Light striking temporal retina comes from nasal field, and vice versa
Temporal and nasal fibres come together at optic nerve, to optic chiasm
Nasal retinal fibres (temporal visual field) decussate at chiasm
Optic tract synapses at lateral geniculate nucleus
Then forms optic radiations through the temporal and parietal lobes
Terminates at occipital visual cortex
What is the pathway of pupil reflexes?
Afferent pupillary fibres travel with retinal fibres up until the LGN
Then synapse with pretectal nucleus and travel to both Edinger-Westphall nuclei (3rd nerve nucleus)
Meaning stimulation causes a bilateral response
Efferent fibres leave EWN and gravel to ciliary ganglion via inf division of oculomotor
to sphincter pupillae - constriction of pupil.
