PBL 43 Flashcards
What are glaucomas?
A group of eye diseases characterised by optic nerve damage that can lead to irreversible loss of vision
What is the leading cause of blindness worldwide?
Cataracts
What causes glaucoma? (Pathophysiology)
Imbalance in production and drainage of aqueous humor
Aqueous humor is produced by what?
Ciliary body behind the iris in the posterior chamber
The build up of fluid in the eye causes an increased pressure which causes damage to what?
Optic nerve
What is the difference between primary and secondary glaucoma?
Primary is when the cause is unknown, secondary is when the cause is known
What are possible causes of secondary glaucoma?
- Infection
- Inflammation
- Tumours
- Large cataracts
- Cataract surgery
- Drugs
- All of ^ keep the fluid from draining freely, which leads to increased pressure and optic nerve damage
What are the 2 types of glaucoma?
- Open-angle
2. Closed-angle
Explain the rate of open-angle glaucoma (acute vs chronic)
Chronic, develops slowly
Explain the cause of open-angle glaucoma
Trabecular meshwork is clogged, the canals are not visibly blocked, but drainage through them is still inadequate, this explains the slow onset nature
What are the symptoms of open-angle glaucoma
- Gradual vision loss –> Peripheral vision loss first then central
- Development of blind spots/patches of vision loss which grow larger and merge over months to years
Explain the rate of closed-angle glaucoma (acute vs chronic)
Acute, medical emergency
Explain the cause of closed-angle glaucoma
The iris is forced against the trabecular meshwork, which closes the anterior chamber angle, blocking drainage.
Explain the symptoms of closed-angle glaucoma
- Sudden vision loss/blurring
- Red eye
- Severe eye/head pain
- Nausea/vomiting
- People can lose vision as quickly as 2 to 3 hours after symptom onset
Risk factors for glaucoma
- Age older than 40
- African ethnicity
- FHx
- Nearsightedness (open-angle glaucoma)
- Farsightedness (closed-angle glaucoma)
- Diabetes
- High blood pressure
- Long term corticosteroid use
- Previous eye injury or surgery
Treatment for glaucoma
- Beta-blockers = inhibit the ciliary epithelium beta-receptors to reduce aqueous humor production
- Alpha 2-AR agonists = produce vasoconstriction and reduce aqueous humor production
- Carbonic anhydrase inhibitors = decrease production of aqueous humor
- Prostaglandin analogues = increased uveoscleral outflow
- Miotics = increased trabecular outflow
What is a cataract?
A clouding (opacity) of the lens of the eye that causes a progressive, painless loss of vision
Explain the cause of cataracts (pathophysiogy)
Proteins and fibers in the lens begin to break down, causing vision to become hazy or cloudy
Risk factors for cataracts
- Trauma
- Prolonged corticosteroid use
- Prolonged X-ray exposure / UVB
- Diabetes
- Nutrition
- Smoking
- Alcohol use
Signs and symptoms of cataracts
- Seeing halos and starbursts around lights (glare)
- Needing more light to see well
- Problems distinguishing between dark blue and black
- Blurred vision
- Colours seeming more yellow and less vibrant
- Mild double vision (LESS COMMON)
Prevention of cataracts
- Consistently wearing eye-glasses or sunglasses with a coating to filter UV light
- Not smoking
- Reducing alcohol consumption
- If diabetic, keeping blood sugar controlled
- Eating a diet high in vitamin C, vitamin A and substances known as carotenoids (dark leafy vegetables such as spinach)
Treatment of cataract
- Eyeglasses and contact lenses to improve vision
- Surgery to remove the cataract and place an intraocular lens
What are the three layers of the eye?
Fibrous layer
Vascular layer
Neural layer
What constitutes the fibrous layer of the eye?
- Cornea
- Sclera
What constitutes the vascular layer of the eye?
Iris
Ciliary body
Choroid
What constitutes the neural layer of the eye?
Retina
What is the role of the ciliary body?
Control the shape of the lens (ciliary processes contract and relax) and contribute to formation of aqueous humor in the eye
What is the light detecting component of the eye?
The retina
The retina is composed of 2 layers, what are they?
Pigmented (outer) layer
Neural (inner) layer
Which layer of the retina contains photoreceptors?
The neural layer
The centre of the retina is marked by an area known as the …
Macula
The macula contains a depression called the … , which has a high concentration of light detecting cells and is repsonsible for … … …
Fovea centralis
High acuity vision
What is the anterior chamber of the eye located between?
The cornea and the iris
What is the posterior chamber of the eye situated between?
The iris and the ciliary processes
Where does aqueous humor drain?
Through trabecular meshwork at the base of the cornea, near the anterior chamber (INTO SHLEMM’S CANAL)
Vascular supply to the eye?
Ophthalmic artery, a branch of the internal carotid
Superior and inferior ophthalmic veins
What are the extraocular muscles of the eye?
- Levator palpebrae superioris
- Superior rectus
- Inferior rectus
- Medial rectus
- Lateral rectus
- Superior oblique
- Inferior oblique
What is the action and innervation of levator palpebrae superioris?
Action – elevates the upper eyelid
Innervation: CN3
What is the action and innervation of the superior rectus?
Action: Main movement is elevation. Contributes to adduction and medial rotation of the eyeball
Innervation: CN3
What is the action and innervation of the inferior rectus?
Action: main movement is depression. Also contributes to adduction and lateral rotation of the eyeball
Innervation: CN3
What is the action and innervation of medial rectus?
Action: ADDucts the eyeball
Innervation: CN3
What is the action and innervation of the lateral rectus?
Action: ABDucts the eyeball
Innervation: CN6 (LR6, SO4, R3)
What is the action and innervation of the superior oblique?
Action: depresses, abducts and medially rotates the eyeball
Innervation: CN4
What is the action and innervation of the inferior oblique?
Action: Elevate, abducts and laterally rotates the eyeball
Innervation: CN3
What is the main role of the ciliary body and the iris?
To adjust the amount of light that goes in and out of the eye
What is the role of miosis and mydriasis?
Complementary systems which help focus images on the back of the eye
Explain miosis
- Pupil constriction
- Iris sphincter is active
- Iris dilator is relaxed
- Reponse to light increase
- Parasympathetic control
- Relaxed state
Explain mydriasis
- Pupil dilation
- Iris sphincter is relaxed
- Iris dilator is active
- Response to light decrease
- Sympathetic control
- Elevated: emotional/aroused state
- Lets in more light
Sympathetic control of the eye leads to …
Dilation
Parasympathetic control of the eye leads to…
Constriction
How do rods and cones work?
They are sensitive to and absorb light, transducing light signals into electrical signals which then pass to the other layers towards the ganglion cell axons, which send off axons to the optic nerve and the brain
Cones are more sensitive in … light
Bright
Rods are mainly used for … light
Dim light for night vision
Cones are found in the … of the eye whereas rods are found in the … of the eye
- Center
- Periphery
SIgnals from different types of cone are compared to differentiate what?
Colour
The external ear is divided into two parts?
Auricle
External acoustic meatus which ends at the tympanic membrane
What is the function of the auricle?
Capture and direct sound waves towards the external acoustic meatus, to convert acoustic energy to kinetic energy
The external acoustic meatus is what shape?
Sigmoid shaped
What is the function of the tympanic membrane/ear drum?
Vibrates in response to sound pressure waves and thus transmits sound energy from the ear canal to bones of the middle ear
Vasculature of the external ear?
External carotid artery which branches into the:
- Posterior auricular artery
- Superficial temporal artery
- Occipital artery
- Maxillary artery
Nervous supply to the ear?
Greater auricular nerve (branch of the cervical plexus)
Lesser occipital nerve (branch of the cervical plexus)
Auriculotemporal nerve (branch of the mandibular nerve)
Branches of the facial and vagus nerves
The middle ear spans from?
The tympanic membrane to the lateral wall of the inner ear
What is the function of the middle ear?
Transmit vibrations from the tympanic membrane to the inner ear via the auditory ossicles
What is the middle ear divided into?
Tympanic cavity
Epitympanic recess
What is found within the tympanic cavity?
The three auditory ossicles: malleus, incus, stapes
What is the role of the auditory ossicles?
Transmit sound vibrations through the middle ear
What are mastoid air cells and what is their role?
They are air-filled spaces in the mastoid process of the temporal bone
Role: Act as a buffer system, releasing air into the tympanic cavity when the pressure is too low
What are the two protective muscles of the middle ear?
The tensor tympani
Stapedius
What is the role of the middle ear protective muscles? ACOUSTIC REFLEX
They contract in response to LOUD noise, inhibiting the vibrations of the malleus, incus and stapes, to reduce transmission of sound to the inner ear.
The inner ear houses the vestibulocochlear organs, what are its two main functions?
- Convert mechanical signs from the middle ear into electrical signals, which can transfer information to the auditory pathway in the brain
- To maintain balance by detecting position and motion
The inner ear has 2 main components, what are they?
Bony labyrinth
Membranous labyrinth
What constitutes the bony labyrinth?
Cochlea
Vestibule
Semi-circular canals
What is the name of the fluid found within the structures of the bony labyrinth?
Perilymph
Wha is the name of the fluid found within the membranous labyrinth?
Endolymph
There are 3 semi-circular canals, what are they called?
Anterior, lateral and posterior
What do they semi-circular canals contain and what are they responsible for?
Semi-circular ducts, responsible for balance
The inner ear is innervated by which nerve?
CN8
What are the 2 types of hearing loss?
Conductive
Sensorineural
Explain conductive hearing loss
Problem conducting sound waves through the outer ear, eardrum or middle ear
How can a problem with solely air conduction be fixed?
Circumvention by bone conduction which take sound through the petrous part of the temporal bone straight to the middle ear
What are common causes of conductive hearing loss?
- Earwax
- Otitis externa & media
- Perforated ear drum
- Fluid in middle ear
- Damage to bones of middle ear
What is sensorineural hearing loss?
Problem in the cochlea (Organ of Corti), vestibulocochlear nerve or auditory cortex of the brain
- A PROBLEM WITH BOTH AIR AND BONE CONDUCTION
What are common causes of sensorineural hearing loss?
- Congenital
- Presbycusis
- Inflammatory disease e.g measles, mumps, meningitis, syphillis
- Ménières disease
- Ototoxc drugs (gentamycin, furosemide, cisplatin, some NSAIDs)
- Physical trauma
- Noise-induced
- Benign tumour on auditory nerve
Why is otitis media so common in children?
The eustachian tube is smaller and more horizontal, therefore it can be more easily blocked by conditions such as large adenoids and infections.
- Until the eustachian tube changes in size and angle as the child grows, children are more susceptible to otitis media
