Visual system Flashcards
Anatomy of optic pathway:
Eye - optic nerve - optic chiasm - optic tract - lateral geniculate nucleus - optic radiation - primary visual cortex (V1)
V1 is located in
Occipital love
Where is the lateral geniculate nucleus?
Thalamus
What information goes to the left hemisphere?
Right visual field from right and left eye
What information goes to right hemisphere?
Left visual information from right and left eye
eye can be divided into which regions in terms of visual field?
Temporal retina and nasal retina
Nasal retina information
Decussates in optic chiasm
Temporal retina information
Remains ipsilateral in optic chiasm/ doesn’t cross
Lesion in optic nerve leads to:
Monocular blindness in eye of nerve (loss of peripheral vision - keep the part (nasal) which is covered by both eyes)
Lesion at optic chiasm:
Bi-temporal hemionopsia (tunnel vision)
What leads to tunnel vision?
Losing the temporal fields (carried by nasal fibers)
Another name for tunnel vision =
Bi-temporal hemionopsia
Lesion in optic tract =
Homonymous hemionopsia on same side
Ex of lesion in optic radiation
Meyer’s loop
Meyer’s loop supplies
Upper visual field
Lesion in fiber of optic radiation =
Quadranopsia
Lesion in occipital lobe =
Contralateral homonymous hemianopsia with macular sparing
Why is there macular sparing in occipital lobe lesion?
Dual blood supply
3 main layers of eye:
- Fibrous
- Vascular/uvea
- Neural
Fibrous layer =
Sclera
Cornea
Where do muscles attach?
Sclera
Uvea =
Choroid
Ciliary body
Iris
Choroid =
layer of connective tissue and blood vessels. nourish outer layers of retina
Ciliary body consists of =
Ciliary muscles
Ciliary processes
Zonules
Function of ciliary body =
Control shape of lens
Formation of aqueous humor
Iris lies between the
Lens and cornea
Neural layer =
Retina
Center of retina in marked by the
Macula and fovea
Fovea =
High concentration of photo receptors. Visual acuity
Purpose of eye movements:
To move or maintain visual target on fovea (with highest res vision)
Eye movements can be:
Conjugate
Disconjugate
Purpose of eye movements can be:
Gaze stablising
Gaze shifting
Conjugate eye movements:
Vestibulo-ocular
Optokinetic
Saccade
Smooth pursit
Vestibulo-ocular:
Gaze stabalisation
Rapid/breif head movement
Optokinetic:
Gaze stabalisation
Slow head movements
Saccade:
Gaze shifting
Directs eyes towards visual target
Smooth pursuit:
Gaze shifting
Follows moving visual target
Disconjugate eye movement and purpose:
Vergence
Adjusts eyes for different viewing distance
Extraocular muscles:
- Lateral rectus
- Medial rectus
- Superior rectus
- Inferior rectus
- Superior oblique
- Inferior oblique
SO4 LR6
Superior oblique 4
Lateral rectus 6
Elevation by
Superior rectus
Inferior oblique
Depression by
Inferior rectus
Superior oblique
Intorsion by
Superior rectus
Superior oblique
Extorsion by
Inferior rectus
Infectior oblique
Adduction by
Medial rectus
Abduction by
Lateral rectus
Zonules =
Attach cilliary body to lens
Muscles within what help the pupil to change size
Iris
Pupil constriction =
Miosis
Pupil dilation =
Mydriasis
Miosis what is active and relaxed
Iris sphincter
Dilator relaxed
Miosis is under what control
Parasympathetic (relaxed state)
Mydriasis is under what control
Sympathetic
Tropicamide:
Anti-muscarinic, causes dilation
Atropine:
anti-muscarinic: causes dilation
Condition in which 2 pupils are different sizes =
Anisocoria
Where does ocular motor nerve originate in brainstem?
Edinger-Westphal nucleus
Ocular motor nerve carries what innervation
Parasympathetic to sphincter
Synapse of oculomotor n =
Cilliary ganglion
Short cillary nerve
What nerve carries innervation to dilator muscle?
Opthalmic nerve (V1)
When an object is distant, light rays are what so lense is what
Parallel
Flatter
When an object is near, light rays are what so lense is what
Diverging
Rounder
Accommodation reflex =
Focus on near objects
Accommodation reflex is under what control?
Parasympathetic control
Where is aqueous humor located primarily?
Anterior chamber
Function of aqueous humor
- Nourishment to outer layers
- Intraocular pressure
- Vitamin C to front (antioxidant)
- Protection against dust and wind
What drains aqueous humour
Trabecular meshwork
Schlemm’s canal
2 main types of blood flow:
- Retinal artery
2. Choroid
World-leading causes of blindness:
- Cataracts
- Uncorrected refractive error
- Glaucoma
- Age-related macular degeneration
- Diabetic retinopathy
- Corneal opacities
Cataracts effect which part of the eye?
Lens
Cataracts -
Opacification of lense caused by compaction and protein deposition.
Risk factors for cataracts:
- Age
- Traume
- Diabetes
- Smoking
- UVB light
- Genetic
Treatment of catracts:
Outpatient surgery, lense removed and replaced with artificial
Glaucoma:
Group of eye diseases in which optic nerve is damaged by pressure inside eye
Risk factors of glaucoma:
- Age
- Recent surgery or trauma
- High IOP
- High BP
- Severe myopia
- Long-term corticosteroid use
2 types of glaucoma:
Primary open angle
Acute closed angle
Which type of glaucoma is more common and chronic?
Primary open angle
Cause of primary open angle glaucoma:
BLockage of trabecular meshwork
Symptoms of primary open angle glaucoma:
Gradual loss of vision starting in peripheries
Cause of acute closed angle glaucoma
Iris bows, closes the antierior chamber angle and blocks drainage
Symptoms of acute closed angle glaucoma:
Sudden, severe stabbing pain Sudden vision loss Red eye Head pain Nausea/vomiting
3 tests for glaucoma
Tonometry - measure IOP
Peripheral fields
Fundus photography
What might you see in fundus photography in a patient with glaucoma?
Cupping
Treatments for glaucoma:
- Reduce aqueous humor: beta blockers, alpha blockers, carbonic anhydrase inhibitors.
- Increase trabecular outflow: muscarinic agonists
- Increase uveoscleral outflow: prostaglandin agonists
Pilocarpine:
Muscarinic agonist
Ex of beta-blocker
Betatoxolol
Retinal cell types in order:
Ganglion cells - Biopolar cells + horizontal cells - photoreceptors, rods and cones - pigmented epithelium
Cones:
High density in fovea
Daytime vision
Colour (red, green, blue)
Which cone detects highest wavelength
Red
Rods:
Non in center, lots outside center
Night vision
Very sensitive to light
Grey scale
Which photoreceptor is most sensitive to light?
Rods
Red/green colour blindness is what (genetic)
X linked
Blue colour blindness is what (genetic)
Chromosome 7
Only have 2 cone types =
Dichromats
Protanopes
Deuteranopes
Tritanopes
No Red
No Green
No Blue
Have 3 cone types but sensitivity of one is shifted towards others:
Anomalous trichromats
Protanomalous trichromat
Deuteranomalous trichromat
Tritanomalous trichromat
Red shifted
Green shifted
Blue shifted
Information from fovea is processed where in occipital lobe?
Back
Information from peripheral is proccessed where in occipital lobe?
Anteiror
V4
Colour
V5
Motion
Problem with V4 can cause:
Achromatopsia
Problem with V5 can cause:
Akinetopsia
‘where’ pathway - what lobe
Posterior-parietal cortex
‘what’ pathway - what lobe
Inferio-temporal
Lesion to dorsal stem/posterior parietal lobe =
Optic ataxia
Lesion of ventral stem/inferior temporal lobe =
Visual agnosia
Visual agnosia =
The man who mistook his wife for a hat!