8.1.2 Orbital Contents, Lacrimal Apparatus and Vision Flashcards
What are the contents of the orbital cavity?
Nerves (CNII,III,IV,Va,VI)
Blood vessels (opthalmic artery and vein)
Fat +++
Lacrimal apparatus
Eyeball (globe)
Extra-ocular muscles
What is the tear film and lacrimal apparatus?
Structures involved in tear production and drainage
What are the layers of the tear film?
Meibomian-Oily
Lacrimal-Water
Goblet cells in conjuctiva-Mucus
What does blinking do?
Protects eye
Distributes tear film across surface of eye, rinsing and lubricating conjuctivae and cornea
What does the lacrimal apparatus do?
Collects and drains tear fluid, obstruction to drainage can cause epiphora (overflow of tears over lower eyelid)
Outline tear production to drainage
- Lacrimal gland produces tears
- Drains to lacrimal punctum
- Lacrimal canaliculus
- Nasolacrimal duct
- Inferior meatus of nasal cavity
How can the nasolacrimal duct become obstructed?
Infection
Injury
Stenosis
How is the position of the eyeball maintained?
Suspensory ligament (sits underneath like a sling)
Extra-ocular muscles
Orbital fat
What is the outer surface of the eyeball covered with?
Transparent mucous membrane, conjuctival membrane reflects onto inner surface of lids
Why can’t contact lenses slip behind the eye?
Conjuctiva reflects on itself, contact lenses unable to go beyond this point
What part of the outer anterior eyeball is not covered by conjuctivae?
Cornea- conjuctiva goes to the limbus (area where the sclera and cornea meet) and no further
What does the conjuctival membrane contain?
Blood vessels
What is conjuctivitis?
Inflammation of the conjuctiva,
* Uncomfortable “gritty”
* Watery, may have discharge
* Typically viral cause e.g. adenovirus
* Highly contagious
What is a sub-conjuctival haemorrhage?
Burst blood vessel in the conjuctiva
Painless
No other symptoms
Often no cause- spontaneous
What are the three layers of the eye?
Label the image
Outer: sclera (continues posteriorly as the dura mater and the cornea anteriorly)
Middle: choroid (vascular), continuous with ciliary body and Iris (=uveal tract)
Inner: retina (photosensitive layer)
What is the macula and what does it do?
Point of highest acuity vision (thinnest part of retinal layer with many cones) for central vision
Appears as a darker spot as thinnest part of the retina so can see the highly vascular choroid layer through it
Where is the fovea?
At the back of the eye, the indent
What are the different layers of the back of the eye?
Retinal ganglion cells, axons merge together forming the optic nerve
Rods and cones
Pigment epithelium to absorb excess light
What happens in a central retinal artery occlusion?
Sudden painless loss of sight in one eye developing over seconds
Due to embolus causing occlusion
How does a central retinal artery occlusion appear on a fundoscope?
Pale retina due to ischaemia
Cherry redspot as the macula is the thinnest part and you can see the vascular choroid layer beneath which is unaffected
How does aqueous humour flow and drain?
Flows from posterior chamber through pupil into anterior chamber
Nourishes lens and cornea
Drains through iridocorneal angle (between iris and cornea)
Via trabecula meshwork into canal of schlemm (circumferential venous channel draining into venous circulation)
How does glaucoma occur?
Drainage of aqueous humour from anterior chamber blocked, causes rise in intra-occular pressure
How does glaucoma appear on fundoscopy?
Glaucomatous cupping- lighter region of optic disc increases in size
How can light reach the macula?
- Transparent lens and cornea
- Pupil- regulates light entering
- Tear film and cornea refract light to bring into focus
- Shape of the eye ball, too long (short sighted, myopic) too short (long sighted, hypermetropic)
What happens to the lens as we age?
Lens becomes stiffer with age and less able to alter shape, older people hold things further away to see more easily
