The eye Flashcards
What bones make up the floor of the orbit?
Part of zygomatic bone, maxilla bone
What bones make up the lateral wall of the orbit?
the zygomatic bone and the greater wing of the sphenoid bone
What bones make up the roof of the orbit?
the frontal bone and a small part of the sphenoid bone
What 4 bones make up the medial wall of the orbit?
the maxilla, lacrimal, ethmoid and part of the sphenoid bone
Where are the paranasal sinuses?
The ethmoid bone, frontal bone, sphenoid bone and maxilla bone
When do orbital blow out fractures occur and which part of the orbit fractures?
Direct trauma to the orbit causing a rise in intraorbital pressure- eg a fist or ball. The floor fractures as this is the weakest part.
This pt got into a fight on a night out. Why can his right eye not look up and has parasthesia over the right cheek
he has an orbital blow out frcature. the orbital contents havr porlapsed into the maxillary sinus and inferior oblique muscles and have become trapped.
He cannot feel over the right cheek because CN Vb which runs in the orbital floor has been damaged also.
What is the orbital septum?
Fascia that arises from the orbital rim (bone) and bends with the tarsal plates. It seperates intra orbital contents from the eyelid fat and obicularis oris muscle
Which muscles open and close the eyelids and what is their innervation?
Open:
- levator palpebrate superioris: oculomotor nerve
- Superior tarsal msucle: sympathetics via the end of the oculomotor nerve
Close:
- orbital part of obicularis oculi: facial nerve
What is the role of the tarsus superior and tarsus inferior?
Give the eyelid firmness/ structure and shape
What is wrong with this pt? What may have caused it?
Pre- septal orbital cellulitis. This may be due to bites, cuts, stings ect.
What is wrong with this pt?
post- septal orbital cellulitis, this is much more severe that pre septal
Give 2 complications of post septal orbital cellulitis
Cavernous sinus thombus (spread by inf and sup opthalmic veins)
abcesses
What is this? Which glands is affected?
Stye- gland of zies (at base of hair follicle) blocked.
What is this? Which gland is affected?
Meibominan cyst- blocked meibomian glands
Which, of stye and meibomian cysts tend to be painful and which is more commonly infected?
Stye is more commonly painful and can be infected by staph aureus
How are stye and meibomian cysts tretaed?
Hot compression may help speed up recovery, most are self limiting. If they persist you may need to cut them out.
What makes up the lacrimal aparatus?
lacrimal glands, lacrimal ducts, lacrimal caniculi
Describe the creation and drainage of lacrimal fluid.
- lacrimal glands are stimulated by parasymapthetics from the facial nerve to secrete lacrimal fluid
- these travel to conjunctiva by lacrimal ducts and they drain across the eye from superiorlateral-> medial, this is aided by blinking
- The fluid drains into the superior and lateral punctum and into the lacrimal caniculi
- The fluid collects in a lacrimal sac before draining into the nose via the nasolacrimal duct
Describe the consequence of the superior punctum being blocked by a hair?
Less drainage of lacrimal fluid= more fluid building up on conjunctiva= weeping/ tears being produced
When can corneal abrasions and ulcers occur?
When dust is trapped under the tarsal plates
Why are superficial corneal abrasaions less severe than corneal ulceration to deeper structures?
The cornea is always undergoing mitosis so can easily recover, deeper structures dont so cant recover easily, leading to permenant damage
Why can contact lenses no get lost behind the eye?
The conjunctiva (thin and transparent layer of cells on top of the sclera) reflects onto the inner surface of the upper and lower eyelids
What type of organism usually causes conjunctivitis? Is it contagious?
Usually viral, very contagious.
you also get allergic conjunctivitis
What my pts with conjunctivitis complain of?
Concomfortable/ gritty sensation
Tearing
Red eye
Sometimes blurred vision
Itching if allergic cause
How can you differentiate between uveitis and conjunctivitis?
Uveitis is painful and made worse by looking at bright lights.
What is the pathology shown in the image? How is it managed?
Subconjunctival haemorrhage- bleeding from the vessels in the conjunctiva, looks bad but will resolve by themselves
What holds the eye ball in the orbit?
Lots of orbital fat
Rectus muscles
a suspensory ligament
Describe the layers of the eyeball from out to in??
- White sclera, which is continious with the transparent cornea at the front. It is continious with the dural shealth of the optic nerve at the back and provides attachment for muscles.
- Middle layer is made up of choroid which is continious with the cilary body and iris anteriorly
- Innermost layer is the retina, there are two layers to the retina; the innermost neural layer and deep to this a pigmented (non photosensitive) layer
What causes uveitis?
Normally associate with autoimmune disease- causes inflammation of the choroid layer.
It is rare
How is uveitis treated?
refferal to an opthalmologist for steroids
What role does melanine have in the eye?
It is produced in the epithelial cells of the retinas innermost pigmented/ non photosensitive layer. It absorbs scattered light, reducing reflection and helping us to focus images on the retina.
How are the two types of cells found within the retinas neural layer distributed?
Cones are found centrally at the macula, cones more peripherally
What is the difference in function of rods and cones?
cones detect colour and high definition, rods detect black and white and work well in low light conditions
What is the optic disc?
A collection of axons bundling together to make the optic nerve, there are no rods and cones here- thus it is our blind spot.
Why do you need to wear sunglasses if you have albinism?
Because you cant produce melanin so you need sunglasses to absorb the scattered light for you
What colours do the 3 types of cones detect?
Red, green and blue- deficiency in any of the 3 leads to colour blindness
What is retinal detachment and how does it occur?
When the two layers of the retina detach. May be due to trauma or spontaneously (almost always in short sited ppl)
What is the consequence of retinal detachment?
Photoreceptors no longer able to function because they loose their blood supply so you get visual disturbances- blind/black spots/ areas. If not promptly reattached it may lead to retinal detachment.
Describe the 3 chambers of the eyeball
The vitruous chamber (big one filled w/ vitreous humour (jelly like)
Anterior chamber (between cornea and iris)
Posterior chamber (between lens and iris- communicates with the anterior chamber via the pupil)
Describe the normal flow of aqueous humour through the anterior and posterior chambers of the eye ball
Aqueous humour produced from cillary body in the posterior chamber flows out posterior chamber through the pupil and into the anterior chamber. Here it flows though the trabecular meshwork at the idiocorneal angle and into the canal of schlemm where its recycled.
What is the role of aqueous humour?
It supplies the cornea and lens with nutrients as they dont get their own blood supply.
What is the difference between open and closed angle glaucoma?
Open= blocked drainage at the trabecular meshwork
Closed= acute narrowing of the iridocorneal angle meaning access to the trabecular meshwork is blocked
Describe the difference in onset between open and closed onset glaucoma?
Closed angle is acute conditon, meaning rapid rise in intraocular pressure
Open angle glaucoma develops over time as the trabecular meshwork gets progressively blocked
Describe the difference in presentation between open and closed angle glaucoma?
Open angle= painless, slow onset of blurred vision
Closed angle= sudden painful, onset red eye, burred vision, nausia, vomiting, irregular and irresponsive pupil and halos around objects (due to odema)
How are open and closed glaucoma managed?
Closed: Urgent refferal to opthalmologist to correct the irido- corneal angle as sight will be lost in hours
Open= medicines can be given to reduce aqueous humour production and later surgery if needed. If left untreated it leads to optic nerve damage
What nerve controls the thickness of the lens?
Autonomics from the oculomotor nerve
How is the thickeness of the lens increased to look at nearby objects?
Parasympathetic stimulation= contraction of cillary body, this reduces tension on the suspensory ligaments, meaning the lens is able to become fatter and so more refractive
Describe the 3 parts to the accomodation reflex?
Objects close by to look at=
- pupil contracts so less light allowed in
- eyes converge (contaction of medial rectus) so both retina loooking in one place
- thickening of lens for more refractive power
When viewing objects at a normal distance, where does most light refraction take place within the eye?
The cornea.
Refraction also occurs as the light goes from air-> lacrimal fluid and at the lens at through the vitreous humour, but less so
What causes cateracts?
As we age, proteins denaturing in the lens cause it to become clouded and less transparent- can be treated by surgery
What is presbyopia?
The lens becoming less elastic as we age, reducing our ability to focus on nearby objects. It can be corrected with glasses.
What is the difference between short and long sight?
Short sight= can only see objects up close (eye too long (myopia), or cornea too curved) so that image focuses infront of retina
Long site: can only focus on obects far away (old age, lens dysfunction, long eye (myeropia)
Which 2 extra ocular muscles of the eye are not innervated by the oculomotor nerve?
the lateral rectus muscle = Abduces nerve
The superior oblique muscle= Trochlear nerve
LR6 SO4
Describe the individual and combined movements of inferior oblique and superior rectus
Inferior oblique moves eye up and out and extorts
Superior rectus moves the eye up and in and intorts
Together theyll move the eye straight up due to their opposing horizontal actions
What is intortion and extortion and which muscles do them?
Intortion is rotating the eye inwards from the top: Superior oblique and superior rectus
Extorition is rotating the eye outwards from the top: Inferior oblique and inferior rectus
How are the oblique muscles tested on eye movement testes?
The eye is moved medially, in order to fix the action of the rectus muscles so that vertical movement is done by the obliques only. Superior oblique moves the eyeball down, inferior oblique moves it up
What will the result of a oculomotor nerve palsy? (3)
Eye down and out- as superior oblique and lateral rectus are the only muscles working
Ptosis as lack of innervation ot the levator palpebrae superioris muscle to open eyelid
Dilated pupil as lost parasympathetics to sphincter pupillae
What may cause an occulomotor nerve palsy?
raised ICP, vasular disease (eg diabetes, hypertension), tumours, aneuysms, cavernous sinus thrombus
What will be the result of a trochlear nerve palsy? (3)
Loss of superior oblique=
- loss of intortion leading to head tilt,
- eyes held in up and in position
- difficulty looking down and in (stairs, books)
What may cause a trochlear nerve injury?
Tumour, trauma, raised ICP, vascular disease, congenital
What would be the result of an abducens nerve palsy? (3)
loss of lateral rectus=
- eyeball held in wards
- unable to move eye laterally
- diplopia on horizontal gaze
Why do ppl with graves get wide eyes and bilateral eyelid retraction?
increased expression of noradrenaline receptors on superior tarsal muscle
