Neuro - Visual System pt.1 Flashcards
Name some of the anatomical structures of the eye.
When are tears produced?
→ basal tear
→ reflex
→ emotional (crying)
What are the afferent pathways of the lacrimal system?
→ cornea
→ ophthalmic branch of trigeminal nerve
What are the efferent pathways of the lacrimal system?
parasympathetic
What is neurotransmitter used in the lacrimal system?
acetylcholine
How are tears produced and released?
→ tears produced by lacrimal gland
→ drain through the 2 puncta (opening on medial lid margin)
→ flow through superior + inferior canaliculi
→ gather in tear sac
→ exit tear sac through tear duct into nasal cavity
Where is the lacrimal gland located?
within the orbit, later-superior to the globe
What is the “basal tear”?
tears produced at constant level, even in the absence of irritation + stimulation
What is tear film?
thin layer of fluid that constantly covers the healthy cornea
How is the tear film arranged?
arranged in 3 layers:
→ superficial lipid layer - reduces tear film evaporation
→ aqueous tear film
→ mucinous layer corneal surface - maintains surface wetting
How is the superficial lipid layer produced?
by row of Meibomian Glands along lid margins
What is the purpose of the tear film?
→ maintains smooth cornea-air surface → maintains oxygen supply to cornea (normal cornea has no blood vessels) → removal of debris through blinking → bactericide → maintains clear vision
What is the conjunctiva?
→ thin, transparent tissue that covers outer surface of eye
→ begins at outer edge of cornea
→ covers visible part of eye
→ lines inside of eyelids
→ nourished by tiny blood vessels (almost invisible)
What is the coating of the eye made up of?
→ sclera (hard + opaque)
→ choroid (pigmented + vascular)
→ retina (neurosensory tissue)
What is the sclera?
→ “white of the eye”
→ tough, opaque tissue
→ protective outer coat
→ high water content
What is the cornea?
→ transparent, dome-shaped window covering front of eye
→ low water content
→ powerful refracting surface, providing 2/3 of eye’s focusing power
→ like a crystal, gives clear window to look through
What are the 5 layers of the cornea? (EBSDE)
→ epithelium
→ bowman’s membrane
→ stroma - regularity contributes with transparency
→ descemet’s membrane
→ endothelium - pumps fluid out of corneal + prevents corneal oedema
What happens if you hydrate the cornea?
turns white
What is the uvea?
→ vascular coat of eyeball
→ lies between sclera + retina
How is the uvea arranged?
composed of 3 parts: → iris → ciliary body → choroid intimately connected (disease of one part affects the rest of the uvea too)
What is the choroid?
What are its functions?
→ lies between the retina + sclera
→ composed of layers of blood vessels that nourish back of eye
What is the iris?
What are its functions?
→ controls light levels inside the eye
→ round opening int he centre for pupil
→ embedded w tiny muscles that dilate + constrict pupil size
What is the structure of the lens?
→ Outer acellular capsule
→ Regular inner elongated cell fibres – transparency
→ May loose transparency with age – cataract
What is the function of the lens?
→ Transparency → Regular structure → Refractive Power → 1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous → Accommodation → Elasticity
What is the retina?
very thin layer of tissue that lines the inner part of the eye
What is the function of the retina?
→ responsible for capturing the light rays that enter the eye
→ light impulses are then sent to the brain for processing, via optic nerve
What is the function of the optic nerve?
→ connects to the back of the eye near the macula
→ transmits electrical impulses from the retina to the brain
What is the visible portion of the optic nerve called?
optic disc
What is the blind spot?
part where optic nerve meets retina + there are no light sensitive cells
What is the macula?
→ small + highly sensitive part of the retina responsible for detailed central vision
→ allows us to appreciate detail and perform tasks that require central vision such reading
Where is the macula located?
roughly in the centre of the retina, temporal to the optic nerve
What is fovea?
→ very centre of the macula
→ most sensitive part of retina
→ highest conc. of cones but lowest conc. of rods (to perceive things in detail)
What are two parts of vision?
→ central vision
→ peripheral vision
What is central vision?
→ Macular Vision
→ responsible for detailed central fine vision + daytime colour vision
→ reading + facial recognition
How is central vision assessed?
visual acuity assessment
What is peripheral vision?
→ shape
→ movement in the environment
→ night vision
→ navigation vision
How is peripheral vision assessed?
visual field assessment
What does loss of foveal vision result in?
poor visual acuity
What does extensive loss of visual field result in?
→ unable to navigate in environment
→ patient may need white stick even with perfect visual acuity
How many layers are in the retina?
3 layers:
→ outer layer
→ middle layer
→ inner layer
What does the outer layer of the retina consist of?
→ photoreceptors (1st order neurones)
→ detection of light
What does the middle layer of the retina consist of?
→ bipolar cells (2nd order neurones)
→ local signal processing to improve contrast sensitivity, regulate sensitivity
What does the inner layer of the retina consist of?
→ retinal ganglion cells (3rd order neurones)
→ transmission of signal from the eye to the brain
What are the two different types of photoreceptors?
→ rods
→ cones
What are the main features of rod cells?
→ longer outer segment with photo-sensitive pigment
→ 100 times more sensitive to light than cones
→ slow response to light
→ responsible for night vision + spatial recognition
→ 120 million rods
What are the main features of cone cells?
→ less sensitive to light but faster responses
→ responsible for daylight vision, fine vision, and colour
→ 6 million cones
What is Scotopic Vision? What cells are responsible for this?
→ peripheral + night vision
→ rod cells
What is Photopic Vision?What cells are responsible for this?
→ central vision, day light vision, colour vision, fine vision
→ cone cells
Where are rods mostly concentrated?
→ widely distributed across the retina
→ highest density just outside the macula
→ density tails off towards the periphery
→ none in the macula
Where are cones mostly concentrated?
only distributed within the macula
What are the 3 different types of cone cells? What are their colours?
→ S-Cones : Blue (short wavelength)
→ M-Cones : Green (medium wavelength)
→ L-Cones : Red (large wavelength
What is deuteranomaly?
→ most frequent form of colour blindness
→ don’t perceive the colour red
What is achromatopsia?
→ full colour blindness
How are colour vision deficits caused?
shift in the photo-pigment peak sensitivity
What is the clinical name for colour vision deficits?
Anomalous Trichromatism
What is anomalous trichromatism?
→ colour vision deficit caused by shift in photo-pigment peak sensitivity
→ results in not being able to see one or more primary RBG colours
What is the most common form of anomalous trichromatism?
deuteranomaly - can’t see colour red
What is dichromatism?
only two cone photo-pigment sub-types are present
What is the condition where you experience a complete absence of colour?
monochromatism
achromatopsia
