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Head and Neck > Lecture 16 - Anatomy of the eye > Flashcards

Lecture 16 - Anatomy of the eye Flashcards

1
Q

Orbital cavity borders

A

roof : anterior cranial fossa
floor : maxilla
Medial wall : ethmoid and lacrimal bone
Lateral wall : maxillary

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2
Q

Orbit

A

Protects and contains the eyeball, muscles, nerves and vessels + most lacrimal apparatus

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3
Q

Holes in the orbit

A

Superior orbital fissure - CN III, IV, Va, VI and superior opthalmic vein
Optic canal - optic nerve and opthalmic artery
Inferior orbital fissue - Vb branch and inferior opthalmic vein
Lacrimal fossa

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4
Q

Blood supply of orbit

A

Artery: opthalmic artery branches (from ICA)

Vein: Inferior and superior opthalmic veins which drain into the cavernous and pterygoid plexus and facial vein

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5
Q

Innervation to orbit

A

General sensory: Va (including cornea and conjunctiva)
Motor of eye: CN III, IV, VI
Special sensory: CN II

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6
Q

Weakest parts of orbit

A

The inferior and medial walls are the weakest (maxillary and ethmoid bone)

Most prone to fracture as thin due to sinuses

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7
Q

Orbital blow out fracture

A

Sudden increase in intra-orbital pressure fractures the floor of the orbit

Maxillary sinus fills with blood

Fracture site can trap tissues, fat and muscles located near the orbital floor

Prevents upward gaze on affected side as tethered

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8
Q

Presentation of orbital blow out fracture

A
  • History of trauma to orbit
  • Periorbital swelling
  • Pain
  • Diplopia
  • Numbness over cheek, lower eyelid and upper lip, teeth and gums (due to infraorbital nerve and superior alveolar nerve lesion Vb)
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9
Q

Eyelid

A

Consists of:

  • Skin
  • tarsal plate
  • subcutaneous tissue
  • muscles - levator palpebrae superioris and obicularis oculi
  • Levator aponeurosis attaches to tarsal plate
  • Melbomian glands
  • Sebaceous glands
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10
Q

Orbicularis oculi

A

Closes eyelid
Innervated by facial nerve
If CN VII lesion: Lagophthalmos

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11
Q

Levator palpebrae superioris

A

Opens eyelid
Innervated by occulomotor nerve
Lesion causes complete ptosis

[Superior tarsal muscle innervated by sympathetics can cause partial ptosis if disrupted]

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12
Q

Meibomian glands

A

Secrete oily, lipid rich tear fluid on to the edges of the eyelid.

Prevents evaporation of tear film and tear spillage

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13
Q

Stye

A

Blockage or infection (staph) of sebaceous gland or hair follicle on outer part of the eyelid where follicles are found

Painful

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14
Q

Meibomian cyst

A

Block meibomian cyst
Oily secretions build up
Deeper

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15
Q

Blepharitis

A

Inflammation of eye lids, including the skin, lashes and meibomian glands.

Can crust around edges
Foreign body sensation

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16
Q

Orbital septum

A

Thin sheet of fibrous tissue originating from the orbital rim periosteum blending into the tarsal plate

Separates subcutaneous tissue and the orbicularis oculi from intra-orbital contents.

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17
Q

Tarsal plate

A

Dense bands of connective tissue
Strengthens and gives shape to the eyelid
Contains meibomian glands

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18
Q

Periorbital cellulitis

A

Infection occuring within eyelid tissue, superficial to the orbital septum

Secondary to superficial infections e.g. via bites or wounds or bacterial sinusitis (fronto-ethmoidal sinuses in children)

Ocular function unaffected

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19
Q

Orbital cellulitis

A

Infection within the orbit deep to the orbital septum

More serious as can spread intracranially via the cavernous or pterygoid plexus causing meningitis ad venous thrombosis

Hard to distinguish between peri-orbital cellulitis

Presentation:

  • proptosis
  • exopthalmos
  • reduced eye movements
  • reduced visual acuity
  • +/- pain eye movements

Treat with IV antibiotics and drainage

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20
Q

Lacrimal apparatus

A

Lacrimal gland - tear production
Lacrimal sac
Lacrimal ducts and nasolacrimal duct - drains tears into nasal cavity

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21
Q

Epiphora

A

Overflow of tears due to duct obstruction

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22
Q

Blinking

A

Due to orbital part of orbicularis oculi innervated by the facial nerve

Covers eye in tear film lubricating fluid which rinses the eye, conjuctiva and cornea and sweeps dust

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23
Q

Layers of the eyball

A

Outer - Sclera (white) and cornea anteriorly (transparent)

Middle (uvea): Iris, choroid and ciliary body

Inner - retina containing rod and cone cells

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24
Q

How is the eyeball position maintained?

A

By suspensory ligaments
Extra-ocular muscles
Fat

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25
Q

Lacrimal gland

A

Secretes lacrimal fluid (tears)

Under parasympathetic innervation via the facial nerve greater pertrosal

Lies in fossa on the superolateral orbit

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26
Q

Lacrimal ducts

A

Allows tears to be drained into the conjuctival sacs via the lacrimal lakes medially

Drained into the lacrimal sacs via lacrimal caniculi and then to the nasolacrimal duct to the nasal cavity

27
Q

Lacrimal gland to nasal cabity

A
  1. Lacrimal gland secreted lacrimal fluid
  2. Lacrimal ducts
  3. Conjunctival sac
  4. Lacrimal lake
  5. Lacrimal caniculi
  6. Lacrimal sac
  7. Nasolacrimal duct
  8. Nasal cavity
28
Q

Conjunctiva

A

Thin, transparent mucous membrane

The anterior surface of the eye is covered in a conjunctival membrane covering the sclera and lines inside of the eyelid

Forms a conjunctival sac

Secretes mucous component of the lacrimal fluid

Highly vascular with small blood vessels within its membrane

29
Q

Limbus

A

Junction between the conjunctiva and cornea as the cornea has its own epithelial lining

30
Q

Conjunctivitis

A

Inflammed conjunctiva causes small blood vessels to dilate and eye looks red

  • Viral aetiology
  • Feels gritty
  • Teary
  • Contagious
31
Q

Subconjunctival heamorrhage

A

Small blood vessel rupture in the conjunctiva
Not dangerous or site threatening
Spontaneous
Painless

32
Q

Red eye

A

Conjunctivitis or subconjunctival haemorrhage

33
Q

Uveitis

A

Inflammation of the choroid

  • Red, painful eye
  • Worse when focusing or looking at bright light
  • Associated with autoimmune conditions such as ankylosing spondylitis and inflammatory bowel disease
34
Q

Sclera

A

Opaque white covering
Gives eyeball shape
Attachment site for extraocular muscles
Continues with dural sheath covering the optic nerve

35
Q

Conjunctivitis in neonate

A

Infective organism - chlamydia from mother’s vaginal mucosa

Treat with: erythromycin

36
Q

Structures that refract ligh to focal point

A

Cornea and tear film
Lens
Aqueous and vitrous humour

37
Q

Myopia

A

Short sighted

38
Q

Hypermetropia

A

Long sighted

39
Q

Accomodation reflex

A
  1. Pupil constriction - limits amount of light entering pupil which ensures light from near objects pass through centre to fovea via the iris (PS stimulation)
  2. Eyes converge - ensures image remains focused on the same point of retina in both eyes
  3. Lens becomes more biconvex (fatter) by contraction of circular ciliary muscles (PS innervation) and loosening of the suspensory ligaments
40
Q

Why do we need the accomodation reflex

A

Light from nearer objects diverges more which surpasses the refraction power of the cornea

41
Q

Presbyopia

A

Ageing causing the lens to become stiffer therefore cannot refract as much light onto retina

Can’t focus on near objects as well

42
Q

Iris

A

Provides colour to eye
Thin, contractile diaphragm with the pupil being the central aperture
Anterior to lens

Muscles: control size of pupil
Sphincter pupilae
Dilator pupilae

43
Q

Lens

A

Transparent
Focuses light on back of eye

Posterior to iris
Biconvex
Enclosed in capsule
Avascular and no nerves as transparent - receives nutrients from the aqueous humour
Edges of the lens is attaches to the ciliary body via the suspensory ligaments

44
Q

Cataracts

A

Ageing causes gradual degradation of proteins

Therefore lens becomes cloudy

45
Q

Rod cells

A

Active at low light intensity
No colour vision
Located in the periphery of the retina
20 x more rod cells

46
Q

Cone cells

A 
Active at high light intensity 
Colour vision
High definition
Located centrally (macula of retina)
In fovea, only cone cells are present
47
Q

Fovea

A

Centre of macula

48
Q

Macula

A

Dark region in retina lateral to the optical disc where vision is centred

49
Q

Tyoes of cone cells

A

Blue sensitive
Red sensitive
Green sensitive

50
Q

Optic disc

A

Blind spot as no photoreceptors

Area where there is accumulation of retinal axons that leave the eye at the optic nerve

51
Q

Layers of retina

A

Neurosensory - senses light

Pigmented - contains melanin

52
Q

Pigmented layer

A

Absorbs scattered light
Reduces reflection
Focuses images onto the retina

53
Q

How we see

A
  1. APs generated in response to light via rod and cone cells pass via the retinal ganglion cells
  2. The retinal ganglion cell axons accumulate at the optic dics to form the optic nerve
  3. APs propagate along the visual patheay wo the primary visual cortex in the occipital lobe for interpretation
54
Q

Astigmatism

A

Irregularity of corneal surface, decreasing the ability to refract light

55
Q

Optic nueritis

A

Inflammation of the optic disc causes blurring of vision

56
Q

Pin - hole testing

A

Refraction of light does not affect light passing into the pupil perpendicularly to the lens as does not need to be refracted.

Therefore, if make small hole and look through it where only perpendicular light passes through the pupil, vision acuity should improve if there is a refractive error

If does not improve:
Problem with optic nerve or retina

57
Q

Chambers of eye

A

Anterior - between cornea and iris
Posterior - between iris and lens
Vitreous

58
Q

Aqueous humour

A

Secreted by the ciliary proccessus inside the ciliary body in the posterior chamber
Fills anterior and posterior chamber
Flows into the anterior chamber via the pupil
Provides nutrients to lens and cornea
Contributes to shape of eyeball with vitreous humour

Drains into the irido-corneal angle via the trabecular meshwork into the canal of Schlemm back to venous circulation

59
Q

Aqeous humour in elderly

A

Drainage of aq humour can become obstructed
Increases intraocular pressure
Can cause glaucoma if untreates

60
Q

Glaucoma

A

Irreversible damage and death of optic nerve fibres leading to impairment of vision and blindness

61
Q

Chronic open angle glaucoma

A

Most common
Painless
Insidious

The trabecular meshwork deteriorates due to age decreasing aq humour drainage.

Increased intra-ocular pressure causes disc cupping and loss of peripheral vision gradually.

62
Q

Acute closed angle glaucoma

A

Irido-corneal angle decreases
Trabecular meshwork is blocked leading to increased intra-ocular pressure
Medical emergency as sight threatening in hours

Acutely painful red eye
Seen in 55+ yr old patients [common = 70 - 80 yr olds]

Irregular oval shaped pupil - sluggish and dilated
Blurry vision
Halos around objects due to corneal oedema
Nausea and vomiting
Eye is hard and tender to palpate through upper eyelid

63
Q

How to treat acute closed angle glaucoma

A

Diuretics - reduce aq humour production

Muscarinic eye drops - pupillary constriction which opens the irdo-corneal angle

Strong analgesia

Laser eye surgery - iridotomy

64
Q

Risk factor for closed angle glaucoma

A

Long sited
Middle aged
Shallow chambers

Head and Neck (15 decks)

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