022 the eye Flashcards
what are the external/visible structures of the eye?
- upper and lower eyelids
- palpebral fissure between the eyelids (endpoints called medial and lateral cathus)
- medial canthus = has lacrimal caruncle and plica semilunaris
- sclera, cornea, iris and pupil
what are the medial and lateral canthus of the eye?
end points of the eye
what is the lacrimal caruncle and plica semilunaris of the eye?
- remnants of the ‘3rd eyelid’ which many animals have
- inner pink part of eye
- lacrimal caruncle is most inner, then plica semilunaris
what is the conjunctiva?
- thin transparent film that covers inside of eyelids and visible part of sclera (but not cornea/iris)
what is the purpose of the conjunctiva?
- secretes oils and mucous to lubricate eye and keep it clean
what is the anatomical location of the conjunctiva and what is it attached to?
- covers inside of eyelids and sclera, but not cornea/iris
– attaches on the corneal boundary/limbus
what is the innervation and blood supply of the conjunctiva?
- ophthalmic division of trigeminal nerve
- ophthalmic artery
what is subconjunctival hemorrhage?
- blood in eye
- caused by blood vessel bursting between conjunctiva and sclera (not in cornea)
- can be causing by high blood pressure in head e.g. from coughing, vomiting, sneezing, head injury, lifting heavy things
- not serious, goes away by itself
what is hyphaema?
- blood in between the cornea and iris
- often due to trauma, surgery, tumours or vascular anomalies
- can be serious –> cause vision loss, increased intraocular pressure and atrophy of optic nerve
what is viral conjunctivitis?
- inflammation of the conjunctiva of the eye often due to infection/allergies
- also called pink eye
- makes eyes red and itchy and may produce pus
what are the layers of the eyelids?
superficial to deep:
- skin
- subcutaneous tissue
- orbicularis oculi muscle
- levator palpebrae and superior tarsal muscle (upper)
- orbital septum
- tarsus / tarsal gland
- sebaceous gland of eyelash
- conjunctiva
what is the orbital septum?
- extension of periosteum into both upper and lower eyelids
- levator palpebrae superiors and tarsus muscle atatch here
what are the tarsal plates?
- fibrous tissue in the upper and lower eyelids
- stiffen eyelids
- the conjunctiva adheres to the deep surface of the tarsal plates and tarsal muscle
what glands are in the eyelids?
ciliary = behind the roots of eyelashes (infection of these cause styes)
tarsal = on deep surface of tarsal plates, their ducts open onto lid margin
what is the innervation of the upper eye lid?
ophthalmic division of trigeminal nerve
what is the innervation of the lower eye lid?
maxillary division of trigeminal nerve
what is ptosis?
- drooping of upper eyelid
- sometimes called a lazy eye
- can be unilateral or bilateral
what causes ptosis?
- muscle weakness of the eyelid muscles levator palpebrae and superior tarsal muscle (associated with old age or congenital)
- oculomotor nerve palsy e.g. stroke
- Horner’s syndrome
what is Horner’s syndrome caused by?
- usually due to damage of the sympathetic trunk in the neck
what are symptoms of Horner’s syndrome?
- ipsilateral = same side as the side of the sympathetic trunk lesion
- ptosis, drooping of eyelid due to denervation of superior tarsal muscle
- miosis, pupillary constriction due to denervation of superior tarsal muscle
- anhidrosis, absence of sweating due to deneravation of sweat glands
what is the lacrimal apparatus made up of?
- lacrimal gland and its ducts
- puncta
- lacrimal canaliculi
- lacrimal sac
- nasolacrimal duct
what is the function of the lacrimal apparatus?
- production, movement and drainage of fluid from the surface of the eyeball
what is the location of the lacrimal gland?
- above the eyelid on the lateral side
what is the location of the puncta, lacrimal canaliculi, lacrimal sac, nasolacrimal duct?
- puncta = medial inner pink region of eye, opening through which fluid enters each lacrimal canaliculus
- the lacrimal canaliculi then join the lacrimal sac which is connected to the nasolacrimal duct
what is the lacrimal gland innervated by?
- ophthalmic division of trigeminal nerve
- facial nerve
what are the 3 wall layers of the eye?
outer to inner:
- sclera
- choroid
- retina
what is the eye divided into?
- anterior and posterior cavity
what is in the anterior cavity of the eye?
- divided into anterior and posterior chamber
- anterior chamber = lens
- posterior chamber = everything in front of the lens : pupil, iris
-all filled with aqueous humour ( more watery)
what is in the posterior cavity of the eye?
- filled with vitreous humour (more jelly like)
- behind the lens
- retina/fovea at back
what is a?
sclera
what is b?
choroid
what is c?
retina
what is d?
fovea centralis
what is e?
optic disc
what is f?
optic nerve
what is g?
central retina artery and vein
what is h?
hyaloid canal
what is i?
ora serrata
what is j?
ciliary process of the ciliary body
what is k?
ciliary muscle of the ciliary body
what is L?
lacrimal sac
what is m?
limbus
what is n?
scleral venous sinus
what is o?
suspensory ligament
what is p?
lens
what is q?
iris
what is r?
cornea
what is s?
pupil
what is t?
posterior chamber of the anterior cavity
what is u?
anterior chamber of anterior cavity
describe the structure of the cornea
- a transparent layered structure that covers the iris, covered with stratified epithelium epithelium
- epithelium contains no stem cells, new cells migrate from periphery
- contains no blood vessels or lymphatics
- continuous with the sclera
what is the function of the cornea?
- refracts light entering the eye
- responsible for 40 out of 60 diopters refractive power if the eye
- sensory = corneal reflex
what happens if the cornea is misshapen?
- can no longer refract light into the eye properly
- affect vision
- vision more blurry
- need cornea transplant
what is the structure of the sclera?
- outermost layer of the eye
- fibrous connective tissue
- continuous with the cornea
- provides shape and support
- white part of eye
- attachment for extraocular muscles
what is the choroid?
- middle layer of the eye wall
- part of the vascular layer of the eye
- supplies the retina with nutrition and gas exchange from ciliary arteries (branch of ophthalmic artery)
-part of uveal tract (iris, ciliary body, choroid) - contains melanin, limits uncontrolled reflection of light
what is in the vascular layer of the eye?
- choroid, the ciliary body, iris
what is the cornea reflex?
- touching the cornea causing a reflex to blink/shut eyelids
describe the pathway of the cornea reflex
- stimulus on cornea –>nasociliary nerve of ophthalmic division of trigeminal nerve (CNVi)
–> spinal trigeminal nucleus –> interneuron –> facial nucleus
–> facial nerve –> orbicularis oculi muscles to close eyelids
what is the ciliary body?
- 2 parts:
- ciliary muscle = collection of smooth muscle fibres, radial, longitudinal and circular
- ciliary processes = longitudinal ridges projecting from the ciliary body, attach ciliary muscle to lens
- overall control shape of lens for vision and also formation of aqueous humour
What is the function of the ciliary muscle?
- change the shae of the lens for focusing vision
what is the function of the ciliary processes?
- attach zonular fibres (which forms the suspensory ligament) to the lens of the eye
- also contributes to the formation of aqueous humour
describe accommodation for near vision
-ciliary muscle contraction = decreases size of ring formed by ciliary body, which reduces tension on suspensory ligament –> lens becomes more rounded/relaxed = accommodation for near vision
- pupil diameter is also smaller because of this
- both under parasympathetic innervation (CNIII)
describe the flow of aqueous humour in the anterior cavity of the eye
- aqueous humour is secreted in the ciliary process in the posterior chamber and flows from their through the pupil into the anterior chamber
- the posterior limiting lamina of the cornea contains many small openings in the pectinate ligament into the scleral canal/sinus which it drains out of into the episcleral veins
what is glaucoma?
- increased pressure in the eye, causing damage to the optic nerve
- causes blurry/distorted vision and halos around lights
what causes glaucoma?
- blockage of the drainage of aqueous humour out of the eye
= increased eye pressure and damage the optic nerve
describe the structure of the iris
- circular structure with an opening in the centre (pupil)
- 2 rings of muscles, outer dilator ring and inner sphincter ring
- coloured part of eye
describe how the iris constricts the pupil
- circularly arranged sphincter muscle of the iris receives innervation from parasympathetic nerves from CNIII to contract muscle and constrict pupil
= short ciliary nerves
describe how the iris dilates the pupil
- radially arranged dilator muscle of the iris receives innervation from sympathetic nerves from superior cervical ganglion through CNVi
= long ciliary nerves
what is the structure/attachment of lens?
- avascular and a-sensory
- onion like lamella structure
- suspended behind iris from the ciliary process and muscle via the suspensory ligament
- resting lens is flat and long = long vision
what is cataracts?
when the lens in the eye becomes opaque
- due to old age, too much UV exposure, trauma
- can easily be replaced with artificial lens
what is the sympathetic pathway supply to the eye?
- originate in hypothalamus –> down into upper thoracic cord (T1,2) (thoracic trunk)
–> back up into superior cervical ganglion –> carotid plexus –> long ciliary nerves via CNVi = dilate pupil
what is the parasympathetic pathway supply to the eye?
- originate in midbrain –> ciliary ganglion –> short ciliary nerves via CNIII= constrict pupil and accommodate for short distance vision
what are the 4 parasympathetic ganglia of the head and neck?
- ciliary ganglion = eye (1)
- submandibular ganglion = salivary glands of mandible (2)
- pterygopalatine ganglion = lacrimal glanfs of eye and nasal glands (3)
- otic ganglion = parotid gland (4)
describe common features of the parasympathetic ganglia of the head and neck
- autonomic
- paired
- non-terminal
- all have a motor root which synapses within the ganglia to the postsynaptic fibres to the postsynaptic fibres to the target organs
- all receive postsynaptic sympathetic fibres via a sympathetic root which pass through (don’t synapse)
- all receive a sensory root which also just pass through ( no synapsing) for general sensory
describe the structure of the retina
- inner most wall layer of the eye
- 2 cellular layers:
- neural layer = consists of photoreceptors, located posteriorly and laterally (optic part)
- pigmented layer = lies beneath neural layer, attached to choroid layer, supports neural layer and continues around the whole inner surface of the eye (non-visual part) - ora serrata = junction between the optic part and the non-visual part of the retina
- also have optic disc, macula lutea, fovea centralis and rod and cone cells
what is the macula lutea?
- centre of retina
- has a depressed area where the fovea centralis lies
- yellow in colour and highly pigmented
- area of maximal retinal resolution power (most accurate vision)
- vulnerable to degeneration as it is mainly avascular to have more rod and cone cells
what is the fovea centralis?
- depression in the macula in the retina at the back of the eye
- high concentration of cone and rod light detecting cells
- lower concentration of rod cells and higher concentration of cone cells
what is the fovea centralis?
- depression in the macula in the retina at the back of the eye
- high concentration of cone and rod light detecting cells
- lower concentration of rod cells and higher concentration of cone cells
what is the function of rod cells?
- light senstitive receptor cell
- function in dim light
- insensitive to colour
( black and white, night vision)
what is the function of cone cells?
- light sensitive receptor cells
- function in bright light
- sensitive to colour
(colourful, day time)
what is the optic disc?
- where the optic nerve leaves the retina in the back of the eye
- no light-sensitive receptor cells here, so called ‘blindspot’
what is the distribution of rod and cone cells?
- rod cells = high density across retina except dramatic decrease at the fovea
- cone cells = low density across the retina and a dramatic increase at the fovea
what is ophthalmoscopy?
- using an ophthalmoscope to look at the back of the eye (fundus), including retina, optic disc, choroid and blood vessels
