Anatomy of the Visual System Flashcards
How many types of tears are there? What are they called?
3 types
Basal
Emotional
Reflex
What are the afferent components of the lacrimal system?
Cornea, cranial nerve V1 (ophthalmic division of trigeminal) supplies it
What are the efferent components of the lacrimal system?
Parasympathetic
What neurotransmitter is involved with the lacrimal system?
Acetylcholine
What produces tears?
Lacrimal gland
What do tears drain through?
The 2 puncta, these are the opening on the medial lid margin, they then flow through superior and inferior canaliculi
Where do tears gather and then exit?
Gather the tear sac amd then exit through tear duct into nasal cavity
What is the role of the tear film? (4)
Maintain a smooth cornea to air surface
Provide oxygen supply to the cornea
Allow removal of debris alongside blinking
Bactericide
What is the blood supply to the cornea?
There is no blood supply to the cornea
How may layers are there to the tear film? What are they called?
3 layers (from superficial to deep they are): Lipid layer (reduces tear evaporation- oil produced by row of meibomian glands along lid margins) Water layer (aqueous tear film) Mucin layer (maintains surface wetting)
What is the conjunctiva?
A thin, transparent tissue that covers the outer surface of the eye
Starts at the cornea and lines inside of the eyelid
What is the blood supply to the conjunctiva?
Supplied by tiny blood vessels that we can’t see
How many layers are there in the coat of the eye? What are they called?
3 layers (from outer to innermost they are):
Sclera- hard and opaque
Choroid- pigmented and vascular
Retina- has neurosensory tissue
What is the sclera?
‘White of the eye’
Tough, opaque tissue that serves as eyes protective outer coat
High water content
How many layers does the cornea have? What are they called?
5 layers: Epithelium (outermost) Bowman's membrane Stroma Descement's membrane Endothelium
What is the cornea?
The transparent dome shaped window covering the front of the eye
Describe the water content of the cornea
Low
What is the role of the cornea?
It is a powerful refracting surface (2/3 of the eyes refracting power)
What is the significance of the endothelium of the cornea?
It pumps fluid out of the cornea and prevents corneal oedema
What is the uvea?
It is the vascular coat of the eyeball
What does the uvea lie between?
The sclera and the choroid
How many layers are there in the uvea? What are they called?
3 layers
Iris
Ciliary body
Choroid
Describe the role of the iris
It controls how much light is let into the eye, and has an opening in the middle which is the pupil. Muscles allow the pupil to constrict and relax
What is the choroid composed of?
Tiny blood vessels that nourish the eye
What is the role of the lens?
To allow transparency
Has refractive power also (1/3 of the eye)
Describe the structure of the lens
Outer acellular capsule
Inner elongated cell fibres
What is it called when lens transparency is lost with age?
Cataract
Describe the retina and where its found
It is a very thin layer of tissue that lines the back of the eye
What is the role of the retina?
To capture light rays that enter the eye
What happens to light rays that are captured by the retina?
They are sent to the brain for processing via the optic nerve
What is the optic disc?
The visible part of the optic nerve that connects to the retina
Where does the optic nerve connect to the eye?
At the back near the macula
What is formed where the optic nerve meets the retina?
A blind spot, there are no sensitive light cells here
How many layers are there to the retina? What are they called and what are their roles?
3 layers
Outer layer: photoreceptors, 1st order neurons, detect light
Middle layer: Bipolar cells, 2nd order neurons, local signal processing to improve contrast sensitivity
Inner layer: retinal ganglion cells, 3rd order neurons, transmits signals from eye to brain
What type of cell is found in the outer layer of the retina?
Photoreceptors
What type of cell is found in the middle layer of the retina?
Bipolar cells
What type of cell is found in the inner layer of the retina?
Retinal ganglion cells
What is the macula?
A small highly sensitive part of the retina that is responsible for detailed central vision and allows us to appreciate detail for tasks such as reading
What is the fovea?
The centre of the macula, the most sensitive part of the retina
What type of cells are found in the fovea?
Highest conc of cones (allows perception of detail) and lowest conc of rods
What does central vision include?
Detailed vision during the day
Colour vision
Reading
Facial recognition
How is central vision assessed?
Visual acuity assessment
What does peripheral vision include?
Shape, movement, night vision, navigation vision
How is peripheral vision assessed?
Visual field assessment
What happens if there is a loss of visual field?
This is an impairment in peripheral vision and so people cannot navigate
May need a stick even with perfect visual acuity
What are photoreceptors for?
Visual processing
What are the 2 types of photoreceptors?
Rods and cones
Describe rods
They have a long outer segment which is photo-sensitive
They have a slow response to light but are 100x more sensitive to light than cones
They are responsible for night vision
120 million rods
What is the scientific name for night vision?
Scotopic vision
Out of rods and cones which is more sensitive to light?
Rods
Describe cones
Less sensitive to light but fast response to light
Responsible for day vision and colour vision
6 million cones
What is the scientific name for day vision?
Photopic vision
How does the eye see colour?
Through different photoreceptors
S cones= blue
M cones= green
L cones= red
What colours are rods sensitive to?
No colours
What is deuteranomaly?
Aka daltonism
Partial colour blindness (the most common form) where they don’t perceive red
What do we call full colour blindness?
achromatopsia
What test is used to diagnose colour blindness?
Ishihara test
What is the function of the lens?
Transparency Regular structure Refractive power 1/3 of eye focusing power- higher refractive index that aqueous fluid and vitreous Accommodation Elasticity
