Visual System - Anatomy Flashcards
Fill in the missing labels on the diagram below:
Upper eyelid, Pupil, Iris, Palpebral fissure, Lateral canthus, Sclera, Medial Canthus, Caruncle, Limbus, Lower eyelid
What is the lacrimal system composed of?
What is the function of the lacrimal system?
Lacrimal system - lacrimal gland, puntum, canaliculi, tear sac, tear duct
Function = produce basal (continuous), reflexive and emotional tears
Tears produced in the lacrimal gland, tear film drains through the two puncta (two tiny holes in the medial upper and lower lid margins), flows through the superior and inferior canaliculi, gathers in tear sac, leaves via tear duct into the nasal cavity
What are the innervations of the tear reflex pathway?
Reflex pathway = afferent, CNS, efferent
Afferent = sensory fibres of the ophthalmic branch of the trigeminal nerve (V1) innervates the cornea
Efferent = motor parasympathetic nerves that innervate the lacrimal gland
NT = acetylecholine
What is the tear film?
What is its function?
Most superficial part of the eye - fluid made of 3 layers: mucus layer, aqueous layer, lipid layer (outermost)
3 functions - removal of debris (tear film and blinking), bactericide, oxygen supply to cornea
Cornea has no blood vessels, oxygen diffuses into the cornea via tear film
Which layer in the tear film protects the tear film from rapid evaporation?
Lipid layer
What is the conjunctiva?
Thin, transparent tissue that covers outer surface of the eye and lines the inside of the eyelids
Supplied by tiny blood vessels
Where is the eyeball located?
What are the 3 layers of the coat of the eye(ball) and what are their features?
Under the conjunctiva
Made of 3 layers: s
Sclera (hard and opaque) - white, protective outer coat, high water content
Choroid (pigmented vascular)
Retina (neurosensory tissue)
How does the sclera link to the cornea?
What is the cornea and its function?
What are the 5 layers of the cornea?
Sclera stops at the limbus, then it becomes the cornea
Cornea = thin, transparent, dome-shaped window covering the front of the eye, low water content
Function of cornea = powerful refracting surface, providing 2/3 of eye’s focusing power
5 layers = 1. epithelium 2. Bowman’s membrane 3. Stroma (transparency) 4. Descemet’s membrane 5. Endothelium
What happens if the cornea is hydrated?
It turns white
What is the uvea?
What are the 3 parts of the uvea?
The next layer of the eyeball (between sclera and retina)- vascular coat of the eyeball
3 parts;
Iris = controls light levels inside the eye, has muscles to constrict / dilate pupil
Ciliary Body = connects iris to choroid
Choroid = composed of blood vessels supplying back of eye
What is the lens of the eye?
What is its function?
What is a cataract?
Composed of an outer acellular capsule with regular elongated cell fibres on the inside (transparent)
Function = transparency, regular structure, 1/3 of refractive power of the eye, accommodation, elasticity
Lens loses transparency with age, becomes more opaque
What is the retina?
What is its function?
What is a common dysfunction of the retina?
Retina = thin layer of tissue lining inner part of the eye at the back
Function = captures light ray entering the eye, light impulses then sent to the brain for processing via the optic nerve (phototransduction)
Dysfunction of phototransduction = colour blindness
What is the optic nerve?
What is its function?
What is the blind spot?
CN II - connects to the back of the eye, visible portion is called the optic disc
Transmits electrical impulses from the retina to the brain
Where the optic nerve meets the retina = no light sensitive cells = blind spot
What is the macula?
What is its function?
Where is the fovea?
Macula = located at the centre of the retina, temporal to the optic nerve
Function = small and highly sensitive for detailed central vision
Fovea = centre of macula
What does the fovea contain?
Most sensiive part of the retina - contains highest concentration of cones, but low concentration of rods
Only fovea has the concentration of cones to perceive detail
What are the differences between central and peripheral vision?
How is the loss in these visions tested?
Central vision = detailed, day colour vision; high visual acuity; reading; facial recognition
Peripheral vision = shape, movement, night vision; navigation vision
Visual acuity assessment = central vision; loss of visual acuity = loss of foveal vision
Visual field assessment = peripheral vision; loss of visual field = loss of navigation
What is the structure of the retina? What structures are found in each of the outer, middle and inner layers?
Outer layer = photoreceptors (1st order neuron) = detection of light
Middle layer = Bipolar cells (2nd order neuron) = local signalling to improve contrast sensitivity
Inner layer = Retinal ganglion cells (3rd order neuron) = axon runs along optic nerve = transmission of signal from the eye to brain
What are the 2 main classes of photoreceptors and what are their properties?
Rods = longer outer segment with photo-sensitive pigment, 100x more sensitive to light than cones, slower response to light, responsible for night vision AKA scoptopic vision and peripheral vision, higher spatial and temporal summation, recognises motion (120M rods)
Cones = Less sensitive to light but faster response, responsible for daylight fine and colour vision, recognises colour and detail (6M cones)
Where can the highest concentration of rod photorecceptors be found?
20-40 degrees away from the fovea
What are the different types of cone cells and what colours do they detect?
What causes red-green colour blindness?
Are rod cells sensitive to the same colours?
S cones = blue, M cones = green, L cones = red
If the M cone peak shifts towards the L cone peak, it can cause red-green confusion
Rods = night vision and spatial recognition = not sensitive to any particular light
What is Deuteranomaly?
What is Achromatopsia?
What is the colour blindness test called?
Frequent for of colour blindness, partial colour blindness as they don’t perceive the colour red
Achromatopsia - full colour blindness
Ishihara test
