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S3 AHNNAS > Functional Antomy Of The Orbit And Eye > Flashcards

Functional Antomy Of The Orbit And Eye Flashcards

1
Q

Describe the orbital cavity, which bones make it up, what fissures are present?

A

Pyramidal shaped with apex pointing posteriorly

Superior to inferior:
Frontal 
Sphenoid 
Ethmoid 
Lacrimal 
Zygomatic
Nasal
Maxillary

Superior orbital fissure and inferior orbital fissure below optic canal

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2
Q

Describe the blood

supply to the orbit

A

Main arterial supply (ICA->) ophthalmic A & it’s branches (-> orbital canal-> central retinal A)

Ophthalmic veins (superior and inferior) drain venous blood into cavernous sinus, pterygoid plexus and facial vein

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3
Q

Describe the nervous innervation to the eye

A

General sensory - trigeminal ophthalmic N (Va)

Special sensory vision from retina - optic N (2CN)

Motor nerves to muscles - oculomotor (3), abducens, trochlear (4), abducens (6)

CN 2,3,4,5,6

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4
Q

What are the weakest parts of the orbital cavity and why?

A

Medial wall and floor of orbit bc these are where the ethmoid paranasal sinus and maxillary paranasal sinus sit retrospectively

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5
Q

What is an orbital blow out fracture? Symptoms and signs

A

Sudden increase in intra-orbital pressure e.g. from retropulsion of eye ball by fist - fractures floor of orbit

Orbital contents can prolapse and bleed into maxillary sinus, Fracture site can trap structures e.g. soft tissue, extra ocular muscle located near orbit floor

  • prevents upward gaze on the affect side (get pt to follow finger)
  • history of trauma to orbit
  • periorbital swelling, sinful
  • double vision (worse on vertical gaze)
  • numbness over cheek,lower eyelid and upper lip (and upper teeth and gums) on affected side due to injury to intra-orbital N (branch maxillary)
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6
Q

What are the eyelids made of

A

Consist of skin, subcutaneous tissue, tarsal plate,

muscles e.g. orbicularis oculi (palpebral part) - closes eyelids and levator palpebrae superioris - retracts eyelids

& glands e.g. meibomian (oily fluid come out end tarsal plate), sebaceous glands associated with lash follicle

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7
Q

How do you get a meibomian cyst? Treatment, location

A

Meibomian glands secrete oily (lipid- rich) substance onto eye lids, prevents evaporation of tear film and tear spillage - if blocked -> cyst

Deeper at the back of the lid -> can have excused or just goes with blood eye hygiene (clean lids with warm soapy water)

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8
Q

How do you get a stye?location, treatment

A

Eyelash follicle or its associated sebaceous gland can also block (infection- staphylococcus) causing styes

Edge of lid near eyelashes

Normally self- limited

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9
Q

What’s inflammation of the eyelids called, symptoms, treatment?

A

Blepharitis including skin, lashes, meibomian glands

Foreign body sensation and crusty

Goes with good hygiene, clean lids with warm soapy water

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10
Q

What is the orbital septum ?

A

Thin sheet of fibrous tissue originating from orbital rim periosteum blends with tarsal plates

Separates components/ contents orbital fossa and superficial structures (along with tarsal plates)

Just posterior to orbicularis occuli

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

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11
Q

What is periorbital cellulitis? Cause

A

Periorbital/pre-septal

Infection occurring within eyelid tissue superficial to orbital septum

Secondary to superficial infections e.g. bites, wounds, bacterial sinusitis in children

Confined to tissues superficial to orbital septum and tarsal plates

Ocular function unaffected

Difficult to differentiate between peri-orbital and more severe orbital cellulitis, of in any doubt refer urgently (high dose IV antibiotics+ surgical drainage)

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12
Q

What is orbital cellulitis? Signs, spread of infection.

A

More severe
Orbital/ post-septal

Infection within the orbit (orbital tissue/ fat/ extraocular muscles)

Signs:
Proptosis/ exophthalmos (pushes eyeball forwards)

Reduced +/- painful eye movements

Reduced visual acuity

Orbital veins (superior/ inferior ophthalmic veins) drain to cavernous sinus, pterygoid venous Plexus and facial veins - potential route for infection to spread intracranial e.g. cavernous sinus thrombosis, meningitis

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13
Q

Contents of the orbital cavity

A

Eyeball
Fat

Associated extra-ocular muscles (LPS, S oblique, IO, S rectus, MR, LR, IR)

Nerves and blood vessels (optic/ ophthalmic N, ophthalmic V/A

Lacrimal apparatus (production and drainage of tears)

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14
Q

What is the lacrimal apparatus?

A

Structures involved in tear film production and drainage

  • lacrimal gland (tear production), lacrimal sac and ducts (tear drainage)
    Ducts= canaloculi and nasolacrimal duct
  • blinking (orbicularis oculi palpebrae)distributes tear film across front of eye, rinsing and lubricating conjunctivae and cornea
  • tears ultimately drained into nasal cavity
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15
Q

What is epiphora?

A

Obstruction to the drainage system leads to epiphora (overflow of tears over lower eyelid)

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16
Q

What are the three layers of the eyeball?

A

Outer: sclera (whit elf eye) continuous anteriorly as transparent cornea ‘fibrous tunic’

Middle: choroid, ciliary body and iris (vascular) ‘vascular tunic’

Inner: retina (inner photosensitive layer lying on an outer pigmented layer)

17
Q

How is the eyeball maintained in position?

A

Suspension ligament (sits underneath)

Extra-ocular muscles

Orbital fat

18
Q

What is the conjunctiva, where is it located?

A

Anterior surface of eyeball is covered with a conjunctival membrane (except for cornea)

Transparent mucous membrane -> mucous component of tear film

Covers white of eye (sclera) and lines inside of eyelids (forming a conjunctival sac)

Highly vascular small BVs within membrane

19
Q

What is the limbus?

A

Junction of conjunctivae with cornea (cornea has its own epithelial covering)

20
Q

What is a subconjunctival haemorrhage?

A

Haemorrhage from Bvs readily visible

|&raquo_space; dense than conjunctivitis

21
Q

Which structures refract light? Where do they refract light to?

A

All transparent:
Cornea and associated tear film (main)

Lens (behind pupil)

Aqueous humour and vitreous humour

Refract to macula on the retina

22
Q

What is myopia and what causes it?

A

Short-sighted

Eyeball length too long so focal point anterior to retina

23
Q

What is hypermetropia? What causes it?

A

Long- sighted

Eyeball too short so focal point posterior to retina

24
Q

Explain the accommodation reflex. What’s the term for age-related inability to do this and what causes it?

A

Focusing near objects required greater refraction of light bc rays are more divergent so ….

  • Pupils constrict (limit amount of light coming through
  • eyes converge (image remains focused on same point of retina on both eyes)
  • lens more biconvex/ fatter contraction by ciliary muscle

As we age lens becomes stiffer and less able to change shape - presbyopia (age related inability to focus near objects)

25
Q

Describe the route of light signals within the eye to reach the sclera

A 
Nerve fibres to optic nerve 
Ganglion cell 
Amacrine cell 
Bipolar cell 
Horizontal cell 
Cone 
Rod 
Pigment epithelium 
Choroid
Sclera
26
Q

Where are rods and cones found?

A

Outermost layer of retina

27
Q

Compare rods and cones

A

Cones - more anterior, high definition, colour vision, active at high light levels, concentrated within the macula of the retina and fovea = only cones

Rods - more posterior, active at low light levels, don’t mediate colour vision, abundant in peripheral parts of retina (open eyes wide in dark)

28
Q

How do we see?

A

Light hits photoreceptors and action potentials generated -> retinal ganglion cells -> collect in area of optic disc forming the optic nerve -> visual pathway -> occipital lobe interprets

29
Q

What are some pathological causes of blurry vision?

A
  • transparency of structures anterior to retina e.g. opacity in lens cataracts
  • Ability of structures to refract light e.g. irregular corneal surface (astigmatism), ability of lens to change shape (presbyopia) or shape of eyeball
  • retina/ optic nerve pathologies e.g. retinal detachment, age-related macular degeneration (most common cause adult blindness Uk) , optic neuritis

Decreased acuity

30
Q

How can you test to see if blurry vision is due to errors of refraction?

A

Errors of refraction will have no effect on light travelling perpendicular to cornea/ lens

So acuity will improve with pin-hole testing

(If doesn’t improve problem with retina/ optic N/ transparency)

31
Q

How is the shape of the eyeball maintained (not the position)?

A

Several chambers filled with fluid

Aqueous humour fills anterior and posterior chambers* (provides O2, glucose)

Vitreous humour within vitreous Chamber (more firm, transparent, helps keep the retina pushed back)

*anterior and posterior to iris

32
Q

Where’s the blind spot?

A

The optic disc as there are no photoreceptors (where retinal ganglion cells axons meet forming the optic nerve)

33
Q

Explain the production and drainage of aqueous humour

A

Aqueous humour secreted by ciliary processes within ciliary body

Flows from posterior chamber through pupil into anterior chamber

Nourishes lens and cornea

Drains through iridocorneal angle (between iris and cornea through trabecular meshwork into canal of schlemm (circumferential venous channel) -> venous circulation

34
Q

Explain the pathology of chronic open- angle glaucoma (most common type) and the less common acute closed-angle

A

Drainage of aqueous humour from anterior chamber is blocked causing a rise in intra-ocular pressure

Chronic open- angle: trabecular meshwork deteriorates with age (many asymptomatic) -> increases IOP -> optic disc cupping (optic cup: disc ratio decreased slide 29) -> gradual loss of peripheral vision

Acute closed-angle: narrowing of iridocorneal angle -> iris listed forwards and closes-> , ophthalmic emergency. Intra-ocular pressure rises much more rapidly -> sight-threatening

35
Q

How can you test for glaucoma?

A

Tonometry measure intra-ocular pressure when warm air is blown on the eyes

36
Q

Signs and symptoms of acute angle- closure glaucoma. Treatment

A

> 55yrs

Acutely painful red eye

Fixed Irregular oval shaped pupil

Blurry vision

Halo’s around lights (corneal oedema)

Nausea and vomiting

✅Medical (drugs to reduce IOP) -> surgical treatment

S3 AHNNAS (19 decks)

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