The eye and the visual stream Flashcards
(58 cards)
1
Q
Features of the orbit
A
- conical
opens into the midline of the face - points back into the head
2
Q
Bones of the orbit
A
- ) Orbital margin:
- frontal
- zygomatic
- maxilla
3
Q
Walls of the orbit
A
- ) Lacrimal
- ) Ethmoid
- ) Sphenoid: body/lesser & greater wings
4
Q
Holes of the orbit
A
- ) Optic canal
- ) Superior orbital fissure
- ) Inferior orbital fissure
- ) Nasolacrimal fossa
5
Q
Clinical: what can occur to the orbit
A
A blowout fracture
6
Q
Layers of the eyelid
A
- ) Anterior skin
- ) Orbicularis oculi
- ) Levator superioris (have levator aponeurosis here)
- ) Tarsal plate
- ) Meibomian gland (lipid tear film)
- ) Posterior conjunctiva (mucous membrane)
- ) Puncta and canaliculi
7
Q
Clinical link: what happens in facial palsy?
A
- Inability to close eyelid
- Drooping of mouth
8
Q
What makes up the conjunctiva?
A
- ) Tarsal (back of eyelid)
- ) Forniceal (superior and inferior)
- ) Bulbar (covers globe)
- ) Limbus (stem cells)
- ) Lateral (canthus)
- ) Medial (canthus): has caruncle and pilca semilunaris
9
Q
Histology of the tear film
A
Has:
- ) columnar epithelium
- ) goblet cells
10
Q
What makes up the surface layer of the conjunctiva?
A
Lipid: Meibomian glands
11
Q
What makes up the middle layer of the conjunctiva?
A
- ) Aqueous: lacrimal glands
- ) Lysozyme
- ) Lactoferrin
- ) Antibodies
12
Q
What makes up the deep layer of the conjunctiva?
A
Mucin: goblet cells
13
Q
Clinical link: Sjogren’s syndrome. What are the features of this?
A
- ) Xerostomia (dryness of mouth)
2. ) Deep red tongue
14
Q
What makes up the globe?
A
- ) The cornea
2. ) The sclera
15
Q
What epithelium does the cornea have?
A
Non-keratinising squamous epithelium
16
Q
What is the stroma of the cornea made up of?
A
Regular lamellae
17
Q
What is the function of the endothelium in the cornea
A
It pumps fluid out of stroma
18
Q
Features of the sclera
A
- ) Strong
- ) It is where the insertion of eye muscles is
- ) Has holes
19
Q
What does the sclera have holes for?
A
- ) Optic nerve
2. ) Neurovascular bundle
20
Q
Clinical link: what is keratoconus
A
- disorder of the eye which results in progressive thinning of the cornea.
- May result in blurry vision, double vision, astigmatism, and light sensitivity.
21
Q
What four features make up the middle layer of the globe
A
- ) The uveal tract
- ) Iris
- ) The ciliary body
- ) The choroid
22
Q
What features does the iris have?
A
- ) Pupil
- ) Sphincter + dilator muscles
- ) Pupil reflexes
23
Q
What features does the ciliary body have?
A
- ) Ciliary epithelium: aqueous
- ) Ciliary muscle: accommodation
- ) Pars plana
24
Q
What features does the choroid have?
A
- ) Highly vascular
2. ) Highly pigmented
25
Clinical link: what is coloboma?
A hole in one of the structures of the eye
26
What is within the inner layer of the globe?
1. ) Inner retina
| 2. ) Outer retina
27
What makes up the inner retina?
1. ) Internal limiting membrane
2. ) Nerve fibre layer
3. ) Ganglion cell layer
4. ) Inner plexiform layer
5. ) Inner nuclear layer
6. ) Outer plexiform layer
7. ) Outer nuclear layer
8. ) Outer limiting membrane
28
What makes up the outer retina?
1. ) Photoreceptors
| 2. ) Retinal pigment epithelium
29
What are the two parts of the retina?
1. ) The central retina
| 2. ) Peripheral retina
30
What structures make up the central retina?
1. ) Macula lutea
2. ) Foveal centralis
3. ) Cone photoreceptors
4. ) Fine visual resolution
5. ) Colour vision
6. ) Photopic vision
31
What structures make up the peripheral retina
1. ) Rod photoreceptors
2. ) Peripheral visual field
3. ) Motion detection
4. ) Scotopic vision
32
Clinical link: what is a central retina artery occlusion
where the flow of blood through the central retinal artery is blocked
33
Key features of the lens
1. ) Continually grows
2. ) Contained within elastic capsule
3. ) Natural shape: almost spherical
4. ) Shape controlled by ciliary muscle in the ciliary body vis zonules
5. ) Allows for accommodation
6. ) Fades with age
34
What are zonules
Suspensory ligaments
35
Clinical link: what is cataract surgery
Removing the natural lens of the eye and replacing it with a plastic one
36
What are the two segments of the globe?
1. ) The anterior segment
| 2. ) The posterior segment
37
What makes up the anterior segment of the globe?
1. ) Anterior chamber
2. ) Cornea
3. ) Iris
4. ) Pupil
5. ) Lens
6. ) Posterior chamber
7. ) Aqueous humour circulated from ciliary body (via pupil) into AC. Leaves via the trabecular meshwork in the 'angle'
38
What makes up the posterior segment of the globe?
Has vitreous humour
39
Clinical link: what is angle closure
- When the flow of aqueous humour out of the eye is blocked - Pressure inside the eye becomes too high very quickly
40
What are the two parts of the humours of the globe?
1. ) Aqueous
| 2. ) Vitreous
41
Features of the aqueous part of the humours
- Produced by ciliary epithelium in ciliary body
- Maintains intraocular pressure between 12 + 20 mmHg above atm pressure
- Circulates around lens
- Low protein 'plasma'
- High vitamin C
- Nourishment for avascular structures
42
What are the key features of the vitreous part of the humour?
- Made up of a collagen matrix
| - Has hyaluronic acid and water
43
What are the extraocilar muscles?
1. ) Rectus muscles: horizontal (lateral + medial)
2. ) Rectus muscles: vertical (superior and inferior)
3. ) Oblique muscles: superior and inferior
44
Features of the extraocular muscles
1. ) Muscles arise from the orbital APEX
2. ) Muscles insert anteriorly into sclera
3. ) Nerve supply
45
What is the nerve supply to the extraocular muscles
3rd: MR/LR/SR/LO
4th: SO
5th: LR
46
Actions of the horizontal recti muscles
1. ) Abduction
| 2. ) Adduction
47
Actions of the vertical recti
1. ) Elevation
| 2. ) Depression
48
Actions of the oblique muscles
1. ) Intorsion
| 2. ) Extorsion
49
How does the transmission of light take place in the visual system?
Reasons:
1. ) Wavelength (UV absorbed)
2. ) Eyelids separated (ptosis)
3. ) Normal tear film (dry eye)
4. ) Transparent cornea (scarring, swelling)
5. ) Clear aqueous (inflammation, blood)
6. ) Normal pupil (too large, too small, incorrect position, occluded)
7. ) Clear lens (cataract)
8. ) Clear vitreous (blood, inflammation)
9. ) Normal inner retina (swelling, blood)
50
How does the refraction of light take place in the cornea?
1. ) Interfaces:
- air/tear film
- tear film/cornea
- corneal/aqueous
- aqueous/lens
- lens/vitreous
- vitreous/retina
2. ) Cornea is most significant (45D)
3. ) Lens allows for change in focus (15-20D
51
Clinical link: refractive error
- Emmetropia: normal
- Myopia: near sighted
- Hyperopia: far sighted
- Astigmatism: irregular vision
52
How is light detected in the visual system?
- Process of light detection: transduction
1.) Photoreceptor outer segments
2.) Discs contain rhodopsins
3.) Respond to different wavelengths
4.) Change in structure of retinal
5.) Opens Na/K channels
6.) Hyperpolarisation of membrane
7.) Closes Ca channels
8.) Reduces glutamate release
Bipolar cells respond
53
Clinical link: what is dyschromatopsia?
Colour blindess
54
Clinical link: what is dyschromatopsia?
Colour blindness
55
Describe the afferent pathway
- Images temporal to midline fall on nasal retina
- Images nasal to midline fall on temporal retina
- Optic nerves transmit from each eye but maintain orientation
- Splits at chiasm:
- Nasal fibres (temporal field) cross
- Tracts now have information from opposite field but from each eye
56
Describe the efferent pathway
```
Pupillary reflexes to light:
- Light sensitive ganglion cells
- Optic nerve, chiasm, tract
- Synapse in midbrain (3rd n)
- 3rd n to ciliary ganglion (orbit)
- Fibres to sphincter muscle
- Light stimulus in one eye therefor causes both pupils to constrict
(direct and consensual response)
- Afferent pupil defect
- Efferent pupil defect
```
57
Clinical link: what is horners sydrome
- loss of sweating on face
2. ) Partial drooping of upper eyelid
3. ) Small pupil
58
Clinical link: what is Horner's syndrome
- loss of sweating on face
2. ) Partial drooping of upper eyelid
3. ) Small pupil
