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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
Lacrimal gland
Secretes lacrimal fluid (tears) Under parasympathetic innervation via the facial nerve greater pertrosal Lies in fossa on the superolateral orbit
26
Lacrimal ducts
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
Lacrimal gland to nasal cabity
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
Conjunctiva
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
Limbus
Junction between the conjunctiva and cornea as the cornea has its own epithelial lining
30
Conjunctivitis
Inflammed conjunctiva causes small blood vessels to dilate and eye looks red - Viral aetiology - Feels gritty - Teary - Contagious
31
Subconjunctival heamorrhage
Small blood vessel rupture in the conjunctiva Not dangerous or site threatening Spontaneous Painless
32
Red eye
Conjunctivitis or subconjunctival haemorrhage
33
Uveitis
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
Sclera
Opaque white covering Gives eyeball shape Attachment site for extraocular muscles Continues with dural sheath covering the optic nerve
35
Conjunctivitis in neonate
Infective organism - chlamydia from mother's vaginal mucosa Treat with: erythromycin
36
Structures that refract ligh to focal point
Cornea and tear film Lens Aqueous and vitrous humour
37
Myopia
Short sighted
38
Hypermetropia
Long sighted
39
Accomodation reflex
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
Why do we need the accomodation reflex
Light from nearer objects diverges more which surpasses the refraction power of the cornea
41
Presbyopia
Ageing causing the lens to become stiffer therefore cannot refract as much light onto retina Can't focus on near objects as well
42
Iris
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
Lens
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
Cataracts
Ageing causes gradual degradation of proteins | Therefore lens becomes cloudy
45
Rod cells
Active at low light intensity No colour vision Located in the periphery of the retina 20 x more rod cells
46
Cone cells
``` Active at high light intensity Colour vision High definition Located centrally (macula of retina) In fovea, only cone cells are present ```
47
Fovea
Centre of macula
48
Macula
Dark region in retina lateral to the optical disc where vision is centred
49
Tyoes of cone cells
Blue sensitive Red sensitive Green sensitive
50
Optic disc
Blind spot as no photoreceptors Area where there is accumulation of retinal axons that leave the eye at the optic nerve
51
Layers of retina
Neurosensory - senses light | Pigmented - contains melanin
52
Pigmented layer
Absorbs scattered light Reduces reflection Focuses images onto the retina
53
How we see
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
Astigmatism
Irregularity of corneal surface, decreasing the ability to refract light
55
Optic nueritis
Inflammation of the optic disc causes blurring of vision
56
Pin - hole testing
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
Chambers of eye
Anterior - between cornea and iris Posterior - between iris and lens Vitreous
58
Aqueous humour
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
Aqeous humour in elderly
Drainage of aq humour can become obstructed Increases intraocular pressure Can cause glaucoma if untreates
60
Glaucoma
Irreversible damage and death of optic nerve fibres leading to impairment of vision and blindness
61
Chronic open angle glaucoma
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
Acute closed angle glaucoma
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
How to treat acute closed angle glaucoma
Diuretics - reduce aq humour production Muscarinic eye drops - pupillary constriction which opens the irdo-corneal angle Strong analgesia Laser eye surgery - iridotomy
64
Risk factor for closed angle glaucoma
Long sited Middle aged Shallow chambers

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