8.1.2 Orbital Contents, Lacrimal Apparatus and Vision

Question 1

What are the contents of the orbital cavity?

Answer 1

Nerves (CNII,III,IV,Va,VI)
Blood vessels (opthalmic artery and vein)
Fat +++
Lacrimal apparatus
Eyeball (globe)
Extra-ocular muscles

Question 2

What is the tear film and lacrimal apparatus?

Answer 2

Structures involved in tear production and drainage

Question 3

What are the layers of the tear film?

Answer 3

Meibomian-Oily
Lacrimal-Water
Goblet cells in conjuctiva-Mucus

Question 4

What does blinking do?

Answer 4

Protects eye
Distributes tear film across surface of eye, rinsing and lubricating conjuctivae and cornea

Question 5

What does the lacrimal apparatus do?

Answer 5

Collects and drains tear fluid, obstruction to drainage can cause epiphora (overflow of tears over lower eyelid)

Question 6

Outline tear production to drainage

Answer 6

1. Lacrimal gland produces tears
2. Drains to lacrimal punctum
3. Lacrimal canaliculus
4. Nasolacrimal duct
5. Inferior meatus of nasal cavity

Question 7

How can the nasolacrimal duct become obstructed?

Answer 7

Infection
Injury
Stenosis

Question 8

How is the position of the eyeball maintained?

Answer 8

Suspensory ligament (sits underneath like a sling)
Extra-ocular muscles
Orbital fat

Question 9

What is the outer surface of the eyeball covered with?

Answer 9

Transparent mucous membrane, conjuctival membrane reflects onto inner surface of lids

Question 10

Why can’t contact lenses slip behind the eye?

Answer 10

Conjuctiva reflects on itself, contact lenses unable to go beyond this point

Question 11

What part of the outer anterior eyeball is not covered by conjuctivae?

Answer 11

Cornea- conjuctiva goes to the limbus (area where the sclera and cornea meet) and no further

Question 12

What does the conjuctival membrane contain?

Answer 12

Blood vessels

Question 13

What is conjuctivitis?

Answer 13

Inflammation of the conjuctiva,
* Uncomfortable “gritty”
* Watery, may have discharge
* Typically viral cause e.g. adenovirus
* Highly contagious

Question 14

What is a sub-conjuctival haemorrhage?

Answer 14

Burst blood vessel in the conjuctiva
Painless
No other symptoms
Often no cause- spontaneous

Question 15

What are the three layers of the eye?
Label the image

Answer 15

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)

Question 16

What is the macula and what does it do?

Answer 16

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

Question 17

Where is the fovea?

Answer 17

At the back of the eye, the indent

Question 18

What are the different layers of the back of the eye?

Answer 18

Retinal ganglion cells, axons merge together forming the optic nerve

Rods and cones

Pigment epithelium to absorb excess light

Question 19

What happens in a central retinal artery occlusion?

Answer 19

Sudden painless loss of sight in one eye developing over seconds

Due to embolus causing occlusion

Question 20

How does a central retinal artery occlusion appear on a fundoscope?

Answer 20

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

Question 21

What is the globe of the eye filled with?

Answer 21

Aqueous humour (watery)
Vitreous humour (firm jelly-like)

Question 22

How is the lens attached to the ciliary body?

Answer 22

Suspensory ligaments attached to ciliary muscle

Question 23

What does the ciliary body contain?

Answer 23

Ciliary muscle
Ciliary processes- produces the aqueous humour

Question 24

How does aqueous humour flow and drain?

Answer 24

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)

Question 25

What is glaucoma?

Answer 25

Optic nerve damage secondary to raised intraocular pressure

Question 26

How does glaucoma occur?

Answer 26

Drainage of aqueous humour from anterior chamber blocked, causes rise in intra-occular pressure

Question 27

What is chronic: open-angle glaucoma?

Answer 27

Most common and many asymptomatic * Trabecular meshwork deteriorates with age * Increased intraocular pressure, causes optic disc cupping * Gradual loss of peripheral vision

Question 28

What is acute: closed-angle glaucoma?

Answer 28

Less common - Narrowing of iridocorneal angle - **Opthalmological emergency as sight threatening**

Question 29

How does glaucoma appear on fundoscopy?

Answer 29

Glaucomatous cupping- lighter region of optic disc increases in size

Question 30

How does acute closed angle glaucoma present?

Answer 30

Older patient- 55+ Acutely painful red eye Irregular oval shaped pupil (fixed) Blurred vision Halos around lights (due to corneal oedema) Nause and vomiting Treat with drugs to reduce IOP then surgery

Question 31

For us to see what must happen?

Answer 31

Light must reach and be focused onto the macula

Question 32

How can light reach the macula?

Answer 32

* 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)

Question 33

What is the accomodation reflex?

Answer 33

To see closer objects, greater refraction needed to focus onto retina beyond capabilities of cornea 1. Pupil constricts, limits light coming through 2. Eyes converge, ensure image remains focused on same point of retina in both eyes 3. Lens becomes more biconvex (fatter) by contraction of ciliary muscle

Question 34

What happens to the lens as we age?

Answer 34

Lens becomes stiffer with age and less able to alter shape, older people hold things further away to see more easily

Question 35

What is presbyopia?

Answer 35

Age-related inability to focus on near objects

Question 36

What part of the eye refracts the most light?

Answer 36

Tear-lined cornea

Question 37

What is phototransduction?

Answer 37

Photoreceptors convert light into action potentials

Question 38

What are the two type of photoreceptors?

Answer 38

Cones Rods

Question 39

What do cones do?

Answer 39

**C**olour vision High definition Active at high light levels Many at macula and fovea

Question 40

What do rods do?

Answer 40

Non-colour vision Low acuity Active at low light levels Many at peripheral **r**etina

Question 41

What happens after action potentials are produced?

Answer 41

APs propagated via retinal ganglion cells RCG axons collect in area of optic disc forming optic nerve (optic disc=no photoreceptors, blind spot) APs propagates along visual pathway to occipital lobe for interpretation