Visual System - Anatomy

Question 1

Fill in the missing labels on the diagram below:

Upper eyelid, Pupil, Iris, Palpebral fissure, Lateral canthus, Sclera, Medial Canthus, Caruncle, Limbus, Lower eyelid

Answer 1

Question 2

What is the lacrimal system composed of?

What is the function of the lacrimal system?

Answer 2

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

Question 3

What are the innervations of the tear reflex pathway?

Answer 3

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

Question 4

What is the tear film?

What is its function?

Answer 4

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

Question 5

Which layer in the tear film protects the tear film from rapid evaporation?

Answer 5

Lipid layer

Question 6

What is the conjunctiva?

Answer 6

Thin, transparent tissue that covers outer surface of the eye and lines the inside of the eyelids

Supplied by tiny blood vessels

Question 7

Where is the eyeball located?

What are the 3 layers of the coat of the eye(ball) and what are their features?

Answer 7

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)

Question 8

How does the sclera link to the cornea?

What is the cornea and its function?

What are the 5 layers of the cornea?

Answer 8

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

Question 9

What happens if the cornea is hydrated?

Answer 9

It turns white

Question 10

What is the uvea?

What are the 3 parts of the uvea?

Answer 10

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

Question 11

What is the lens of the eye?

What is its function?

What is a cataract?

Answer 11

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

Question 12

What is the retina?

What is its function?

What is a common dysfunction of the retina?

Answer 12

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

Question 13

What is the optic nerve?

What is its function?

What is the blind spot?

Answer 13

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

Question 14

What is the macula?

What is its function?

Where is the fovea?

Answer 14

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

Question 15

What does the fovea contain?

Answer 15

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

Question 16

What are the differences between central and peripheral vision?

How is the loss in these visions tested?

Answer 16

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

Question 17

What is the structure of the retina? What structures are found in each of the outer, middle and inner layers?

Answer 17

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

Question 18

What are the 2 main classes of photoreceptors and what are their properties?

Answer 18

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)

Question 20

Where can the highest concentration of rod photorecceptors be found?

Answer 20

20-40 degrees away from the fovea

Question 21

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?

Answer 21

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

Question 22

What is Deuteranomaly?

What is Achromatopsia?

What is the colour blindness test called?

Answer 22

Frequent for of colour blindness, partial colour blindness as they don’t perceive the colour red

Achromatopsia - full colour blindness

Ishihara test