Anatomy of the Eye

Question 1

Which bones make up the orbital cavity?

Answer 1

Floor: mainly maxilla, part of zygomatic bone

Roof: the frontal bone, part of sphenoid

Medial wall: Lacrimal, Ethmoid, part of maxilla

Lateral wall: mosty zygomatic bone, part of sphenoid

Question 2

Which bones of the orbit are the weakest and therefore the most vulnerable to fracture in orbital trauma?

Answer 2

The floor and the medial walls of the orbit are the weakest

Question 3

What is the main arterial blood supply and the venous drainage of the orbital cavity?

Answer 3

Artery: opthalmic artery (branch of internal carotid)

Vein: superior + inferior opthalmic veins which drain to the cavernous sinus, pterygoid plexus and facial vein

Question 4

Which nerves give general sensory, special sensory and motor innervation to the eye?

Answer 4

General sensory: Opthalmic branch of Trigeminal (Va)

Special sensory: Optic

Motor Nerves: Occulomotor, Abducens and Trochlear

Question 5

What is an orbital blow out fracture?

Answer 5

Something that causes a sudden increase in intra-orbital pressure fracturing the floor of the maxilla

Orbital contents can proplapse and bleed into the maxillary sinus

Question 6

What can happen to the eye in an orbital blow out fracture and why?

Answer 6

Fractured site can trap structures e.g. soft tissue and extra occular muscles in the floor of the orbit, tethering the eye.

When asked to look up, the patient can’t

Question 7

Why do you get numbness over the cheek, lower eyelid and upper lip on the affected side of an orbital blow out fracture?

Answer 7

The infraorbital nerve (branch of maxillary) runs through the floor of the orbital cavity. If damaged will affect sensation from Vb nerve dermatome

Question 8

Which muscles make up the eyelid and what are their respective actions?

Answer 8

• Orbicularis oculi - closes the eyelid
• Levator palpebrae superioris - retracts eyelid

Question 9

What components make up the eyelid

Answer 9

• Skin
• Subcutaneous tissue
• Tarsal plate (connective tissue gives shape to eye)
• Muscles
• Glands

Question 10

Which glands are in the eyelid and what do they secrete?

Answer 10

Meibomian glands - inside tarsal plate, secrete oily component of tear fluid

Sebaceous glands - associated with lash follicle

Question 11

What pathology can occur with the glands of the eyelid?

Answer 11

Stye - blockage of sebaceous glands located near the eyelash follicle, self limiting

Meibomian Cysts- blockage of meibomian gland, deeper in the eyelid, tends to be painless

Question 12

What is blepharitis?

Answer 12

Inflammation of the eyelids

Including: skin, lashes, and Mebomian glands

Question 13

What is the orbital septum?

Answer 13

A thin sheet of fibrous tissue from the orbital rim periosteum, that blends with the tarsal plates

Question 14

What is the function of the orbital septum?

Answer 14

Acts as a barrier against superficial infections spreading from pre-septal to post- septal space

Question 15

What is periorbital (pre-septal) cellulitis?

Answer 15

An infection of eyelid tissue superficial to the septum

• secondary to superficial infection (bites, wounds)
• Confined to tissue superficial to orbital septum
• Ocular function remains unaffected as protected by septum

Question 16

What is an orbital (post- septal) cellulitis?

Answer 16

An infection within the orbit, posterior to the orbital septum

• Causes proptosis (eyeball pushed forward), expothalmus
• Reduced, painful eye movement
• Reduced visual acuity (may involve optic nerve)

Question 17

Why is orbital ceullitis so dangerous?

Answer 17

Orbital veins drain to the cavernous sinus, pterygoid venous plexus and facial veins giving a potential route for infection to spread intracranially. Potential to cause:

• Cavernous sinus thrombosis
• Meningitis

Question 18

What is the lacrimal apparatus?

Answer 18

Structures involved in tear film production and drainage

1. lacrimal gland
2. lacrimal sac
3. lacrimal ducts (tear drainage)

Question 19

Where do tears drain to?

Answer 19

The nasal cavity

Question 20

What is epiphora?

Answer 20

Any obstruction in the drainage of tears that leads to the overflow of tears over the lower eyelid

Question 21

What are the 3 layers of the eye and what is found in each?

Answer 21

Outer Fibrous tunic: Sclera & Cornea

Middle Vascular tunic: Choroid, Ciliary body, Iris

Inner: Retina

Question 22

What 3 things maintain the eyeball position within the orbital cavity?

Answer 22

• suspensory ligaments
• extra-ocular muscles
• orbital fat

Question 23

What is the conjunctiva of the eyeball?

Answer 23

A transparant mucus membrane that prodcues a component of tear film, covers the sclera but does not over the cornea

Highly vascular with small blood vessels within the membrane

Question 24

What is conjunctivitis?

Answer 24

Inflammation or infection of the conjuctiva

Causes the eye to become very red

Question 25

What is a **subconjunctival haemorrhage?**

Answer 25

Haemorrhage from blood vessles in the conjuctiva

Question 26

Which point in the eye is light focused onto?

Answer 26

The **Macula**

Question 27

Which structures **refract** light in the eye? Which is the main one?

Answer 27

* Cornea and it's assoicated tear film → **main refractor** * Lens * Aqueous humour * Vitreous humour

Question 28

How can the shape of the eye affect refraction?

Answer 28

* **Myopia** = short sightedness. Eyeball is **too long** bringing point of focus **infront** of the retina * **Hypermetropia** = long sightedness. Eyeball is **too short** lighy focused **after** the retina

Question 29

What is the accomodation reflex?

Answer 29

Focusing **near** objects requires **greater refraction** of light Eye accommodates by: * **pupil constriction** to limit amount of light coming through * **Eyes converging** ensures image focused at the same point in both eyes * **Lens** becomes more **biconcave** (fatter) by **contraction** of ciliary muscle

Question 30

What is **presbyopia?**

Answer 30

Natural **stiffening** of the lens with age, means the lens is **less able** to change shape so focusing near objects becomes harder

Question 31

What are the 2 types of photoreceptor found in the retina? What does each do and how do they differ in location?

Answer 31

**Rods:** active at **low light levels**, do **not** see colour. * Abundant in **peripheral** parts of the retina **Cones:** see in **high definition** and **colour** * concentrated in the **macula** of the reina * The fovea (middle point) of macula is **only cones**

Question 32

How do rods and cones respond to light?

Answer 32

* Generate action potentials in response to light passing through **retinal gandlion cells** * RGC axons collect in an area of the optic disc forming the **optic nerve** (no photoreceptors here → **blindspot**) * Action potentia propogate along a visual pathway to the occipital lobe for interpretation

Question 33

How do you can you get blurred vision?

Answer 33

Pathology affecting * **transparancy** of lens e.g cateracts * ability to **refract** light * irregular corenal surface * ability of lens to change shape * shape of eyeball * Retinal detachment * Macular degeneration * Optic neuritis

Question 34

What are the different chambers of the eye and the fluid in them?

Answer 34

Anterior and Posterior chambers: contain **Aqeuous Humour** Vitrous Chamber contains **Vitrous humour** (more firm and jelly like)

Question 35

What is the function of fluid in the eye?

Answer 35

Helps maintain **shape** and keeps **retina** pushed against all the other layers

Question 36

Describe the production and drainage of aqueous humour

Answer 36

1. Produced by cilliary processes of **ciliary bodies** 2. Flow from **posterior → through pupil → into anterior chamber** 3. Nourishes lens and cornea 4. Drains through **iridocorneal angle** (between irish and cornea) via the **trabecular meshwork** into the **canal of Schlemm**

Question 37

What is Glaucoma? What are the two types?

Answer 37

**Optic Nerve Damage** secondary to raised intracocular pressure due to a blockage in the **drainage** of aqeous humour from the eye Acute = **closed angle** glaucoma (less common) Chronic= **open angle** glaucoma (most common)

Question 38

Explain what happens in **open angle glaucoma?**

Answer 38

* **Blockage of the trabecular network** which detriorates with age * Aqeous humour unable to drain * Increases ***intra-ocular pressure*** causing **optic disc cupping** * Causes **gradual** loss of peripheral vision * Iridocorneal angle is ***not*** affected

Question 39

Explain what happens in **closed angle glaucoma**?

Answer 39

* **_Narrowing_ of the iridocorneal angle** * Iris is pushed forward closing the angle * Aqueous humour cannot drain * Raises intra ocular pressure more **rapidly** * **Opthalological emergency**

Question 40

How does a patient with acute closed angle glaucoma usually present?

Answer 40

* Older patients 55 yrs + * Acutely painful **red eye** * Irregular **oval shaped** pupil * Blurring of vision * Halo's around lights due to corenal oedema * Nausea and Vomiting

Question 41

How do you treat closed angle glaucoma?

Answer 41

Medical drugs to reduce IOP then surgical treatment * **diueretics** - reduces aqeous humour production * **muscarinic eye drops-** pupillary constriction opens the irido-corneal angle * strong analgesia

Question 42

What is uvetitis?

Answer 42

Inflammation of the **choroid layer** in the eye Associated with autoimmune conditions e.g. anklyosing spondyltitis and IBD

Question 43

Explain what happens in colour blindness?

Answer 43

There are 3 types of cones: red, green and blue senstivie **Absence/ Dysfunction** of any of these can lead to colour blindness

Question 44

A patient is diagnosed with Grave's Disease. On examinatio they have **bilateral eye retraction** with a **wide eye appearance**. How would you explain the clinical findings?

Answer 44

* Increased levels of circulating thyroid hormone increases the expression of **adrenergic receptors** of sympathetic tissues * In this case, **increased noradrenaline receptors on the superior tarsal muscle** causes excessive retration of the lid and lid lag