Opthalmology Anatomy Flashcards
Describe the opthalmoscope view of the retina in terms of temporal and nasal
Temporal - Macula and Fovea
Nasal - Optic disc and vessels
Name three roles of the eyelid
Protect cornea and eyeball from injury
Keep cornea moist
Contain glands
What are the three main glands of the eyelid?
Meibonium - secretes lipid into tear film
Glands of Moll - Modified sebaceous glands
Glands of Zeiss - Sebaceous Glands
Describe the lacrimal pathway
- Tears drain from lacrimal gland into excretory lacrimal ducts
- From the ducts the tears drain into lacrimal lake
- Lacrimal canaliculi into lacrimal sac
- Nasolacrimal duct into inferior meatus
Describe the innervation of the lacrimal gland
Somatic supply from lacrimal nerve (branch of Opthalmic)
Parasympathetic increases production
Sympathetic decreases production
Why does Epiphora occur? Why is this a danger?
There isn’t an anastomotic pathway in the lacrimal system
Obstruction will give rise to overflow of tears
Stagnant tears can predispose to infection
The tear film is regenerated every time blinking occurs. Give three roles
-Anti bacterial
-Lubrication
- Creates smooth ocular surface for light to be refracted unifrp,
Y
What are the three components of the tear film?
- Surface Lipid- Meibomian secretion
- Middle Aqueous - Lacrimal and Accessory Lacrimal secretion
- Inner Mucous - Goblet cells of conjunctiva/epithelial surface
What is the outer protective layer of the eyeball?
Sclera and Cornea
Fibrous attachment for extraocular muscles
What is the middle layer of the eyeball?
Choroid, Ciliary Body and Iris
Rich vasculature
What is the inner layer of the eyeball?
Retina (optic and non visual parts)
What is the Iris?
Thin contractile diaphragm
Central pupil to allow light through
Size controlled by sphincter (parasympathetic) and dilator (sympathetic) papillae muscles
What is the Lens?
Transparent biconvex structure enclosed in a capsule
Attached to ciliary body by suspensory ligaments
Size of lens changed by ciliary contraction
What are the two layers of the retina?
Neural Layer (light receptive) Pigmented Layer
What is the optic disc?
Depression on the fundus of the eye
Where optic nerve leaves the eye
Contains nerve fibres and NO photoreceptors (blind spot)
Lateral to the optic disc is the macula and fovea. What are these?
Macula - photoreceptors cells specialised for visual acuity
Fovea - centre of macula (highest visual acuity)
What muscle opens the eye?
Levator Palpebrae Superioris
Inserts into skin and tarsal plate
Inner gated by oculomotor
What are the four recti muscles of the eye?
Superior, Inferior, Medial, Lateral
All arise from common tendinous ring around optic nerve and insert on sclera
What are the two oblique muscles of the eye?
Superior and inferior
Work synergistically with recti
What is the role of the optic nerve?
Transmit all visual information
Light reflex
Accommodation reflex
What are the subdivisions of the Opthalmic Nerve (from trigeminal)?
Lacrimal
Frontal
Nasociliary
Ciliary
What does the Lacrimal Nerve innervate?
Supplies Lacrimal gland
Sensory to lacrimal gland, upper outer conjunctiva, lateral eyelid and lateral forehead
What does the frontal nerve innervate?
Skin of forehead
Upper eyelids
Mucosa of frontal sinus
What does the Ciliary branch of the Opthalmic nerve innervate?
Sensory innervation of eyeball
Dilator pupillae
Describe the arterial supply of the eye
Mainly from the Opthalmic artery
Retina is supplied by the central retinal artery branch
Describe the venous drainage of the Eye
Opthalmic veins that drain into cavernous sinus
What is the cornea?
A transparent layer of the eye that separates the tear film and the anterior chamber
Give three roles of the Cornea
Maintaining transparency
Protecting the eye (eg corneal reflex)
Refraction of incoming light
What are the five sub layers of the cornea
Epithelium Bowmans Stroma Descemets Membrane Endothelium
How is the corneal epithelium repaired when damaged?
Cells migrate from basal layer to replace, and from periphery to centre
Cells on the surface spread out to cover defect before basal cell layer replaces
Regenerates within 14 days (longer if central as stem cells are peripheral)
What is the Bowmans layer of the cornea?
Acellular layer
Trauma below this layer - corneal scarring
What is the Endothelium of the cornea?
Maintains hydration of cornea so it is transparent
Doesn’t regenerate - loss is replaced by change in size/shape
Describe the pathway of humour drainage
Produced by ciliary processes of ciliary body
Flows between iris and anterior surface of lens through the pupil
Flows through iridocorneal angle (trabecular meshwork and canal of schlemm)
Through episcleral vessels and into systemic venous circulation
What is the unconventional drainage of aqueous humour?
Into root of iris before draining into Scleral vascular system
How is Intraocular Pressure Measured?
Measured by the force needed to flatten the corneal surface using a tonometer
The greater the force required, the higher the pressure
What is the normal range of intraocular pressure?
11-21 mmHg
Note: Correlation factor of corneal thickness
Describe the autonomic control of IOP
Alpha 2 Adrenoreceptors - reduce IOP by reducing production and increasing flow
Beta 2 Adrenoreceptors - increase IOP by increasing production and reducing flow
Name 6 classes of drugs targeting Aqueous Humour
Beta Blockers (Timolol) Alpha Agonists (Brimonidine) PG Anologues (Latanoprost) Carbonic Anhydrase Inhibitors (Dorzolamide) Parasympathomimetic (Pilcarpine)
How does Timolol work?
Reduces humour production
How do Alpha Agonists work?
Reduces production and increase drainage
How does Latanoprost work?
Increases uveoscleral flow
How does Dorzolamide work?
Reduces aqueous humour production
What are the roles of the Lens?
Refract light (less powerfully than cornea)
Changing refraction by accommodation (capsule changes shape)
Describe the composition of the Lens Epithelium
Undergoes mitosis throughout whole life
Newest lens (softest in the outside)
Fibres tightly packed and organised to maintain transparency
Name three roles of the ciliary body
Accommodation
Aqueous humour production
Attachment for lens zonules
Name four roles of the Choroid
- Allows nerves and vessels to anterior eye
- Removes waste products to outer retina
- Supplies nutrients to outer retina
- Absorbs any light passing through retina to prevent reflection and obscured vision
What is affected in Anterior Uveitis?
Iris and/or ciliary body
What is affected in Intermediate Uveitis?
Posterior part of ciliary body and nearby peripheral choroid and retina
What is affected in Posterior Uveitis?
Inflammation of retina and choroid
What is the Vitreous?
Cavity filled with aqueous humour
Attached to the posterior lens capsule and retina at several points
Holds retina in place and supports lens
What is the relevance of cataract surgery and the vitreous?
Cataract surgery can cause disruption of the posterior lens capsule and vitreous membrane allowing humour flow into anterior chamber
What happens to the vitreous as you age?
Fluid fills in potential space between vitreous and retina
Can detach where it is weakly bound
Vitreous detachment can predispose to retinal detachment
What is the role of the neural retina?
Converts light stimulus to nervous impulses
Travels along ganglion cells in axons to be processed in visual cortex
What are Rods?
Photoreceptors that sense contrast and motion, and assist in dark environments
Not good for detail (B&W)
What are Cones?
Used for fine detail and colour vision
The Retina is a metabolically active tissue so requires a good blood supply. Describe this
Outer 1/3 - Choroidal
Inner 2/3 - Central Retinal Artery (giving off four end arteries)
Macula has a dense capillary network
Fovea is capillary free (reliant on underlying choreocapillaris)
Describe the pupillary light reflex
Afferent fibres leave visual pathway and synapse on pretectal nucleus
Fibres travel to both EWN nuclei
Efferent fibres leave EWN and synapse on ciliary ganglion (activating sphincter pupillae)
What bones make up the walls of the orbital cavity?
Roof - Frontal Bone
Lateral - Zygomatic bone
Posterior - Greater wing of Sphenoid
Inferior - Maxilla
Tears are composed of water, protein, salts, lipids and mucins . Give four roles
Hydration
Immunology
Nourishment
Lubrication
