1b Visual System Flashcards
What is the palpebral fissue?
The line of the eye where the eyelashes sit
What is the limbus?
The border between the cornea and the slcera?
What is the caruncle?
The inner most fleshy corner part of the eye
What is the medial canthus?
Where the caruncle meets the sclera
What neurotransmiter controls the release of tears?
Acetylcholine
Where are tears produced?
Lacrimal gland
Where are tears drained from?
Puncta - opens on the medial lid margin
What do the tears flow through in order to gather in the tear sac?
Gather in the tear sac
How to the tears exit the tear sac?
Through the tear duct - into the nasal cavity
What is the function of the tear film?
Maintains smooth cornea-air surface and regulates the oxygen supply to the cornea - as the normal cornea has no blood supply
What are the secondary functions of the tear film?
Bactericidal properties
Removal of Debris - through tear film and blinking
What are the three layers of the tear film called?
Most superficial = Lipid Layer
Water layer
Mucinous Layer
What is the function of the superficial lipid layer?
Reduce tear film evapouration
What is the lipid layer of the tear film produced by?
Meibomian glands
what is the water layer of the tear film do?
Thickest layer so acts as a lubricant
What is the role of the mucinous layer of the tear film?
Maintains surface wetting and keeps the tear on the eye
What is the conjunctiva?
Thin, transparent tissue which covers the outer surface of the eye
What are the three layers of the eye?
Sclera - hard and opaque
Choroid - pigmented and vascular
Retina - Neurosensory tissue
What is the sclera?
The white of the eye - tough and opaque tissue which serves as the eyes protective outer coat
What is the water content of the sclera?
High
What is the cornea?
The transparent, dome-shaped window covering the front of the eye.
What is the water content of the cornea like?
Low water content
What is the function of the cornea?
Powerful refracting surface, providing 2/3 of the eye’s focusing power. Like the crystal on a watch, it gives us a clear window to look through
What are the five layers of the cornea?
1 – Epithelium
2 – Bowman’s membrane
3 – Stroma – its regularity contributes towards transparency
4- Descemet’s membrane
5- Endothelium – pumps fluid out of corneal and prevents corneal oedema
What happens if the cornea becomes hydrated?
becomes cloudy
What is the uvea?
Vascular coat of eyeball and lies between the sclera and retina.
What are the three parts of the uvea called?
Composed of three parts – iris, ciliary body and choroid.
What is the choroid?
Choroid - lies between the retina and sclera. It is composed of layers of blood vessels that nourish the back of the eye.
What is the function of the iris?
Controls the amount of light which is entering into the eye - has tiny muscles which dilate and constrict the eye
What is the structure of the lens?
It is composed of an outer acellular thin capsule,
encasing a core of regular elongated cell fibres.
What percentage of the eyes refractory power comes from the lens?
1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous
What is a cataract?
The lens may loose its transparency with age,
resulting in an opaque lens, known as Cataract.
What is the retina?
Thin layer of tissue which lines the inner part of the eye
Responsible for capturing the light rays which enter into the eye - light impulses are then sent to the brain for processing via the optic nerve
What is the function of the optic nerve?
Transmits electrical impulses from the retina to the brain
What is the visible portion of the optic nerve called?
The optic disc
Where does the optic nerve connect to the back of the eye?
Near the macula
What is the blind spot?
Where the optic nerve meets the retina, there are no light sensitive cells
What is the macula?
A small and highly sensitive part of the retina responsible for detailed central vision - located roughly in the centre of the retina
what is the structure found at the center of the macula?
Fovea
Which part of the eye allows us to perform tasks which require central vision like reading?
Fovea
What is the concentration of cones and rods like in the fovea?
Cones are high, rods and low
Why is the fovea particularly important?
Only the fovea has the highest concentration of cones in order for us to perceive high detail
What is the anatomical land mark for the physiological blind spot?
Optic disc
What is central vision?
Detailed, day vision - only the fovea
what is peripheral vision for?
Shape, movement and night vision, as well as navigation
What is the result of extensive loss of visual field?
Unable to navigate in an unfamiliar environment,
What is found in the outer layer of the retina?
Photoreceptor cells - involved in the detection of light
What is found in the middle layer of the retina?
Bipolar cells (2nd order neurones)
What is the function of the bipolar cells?
Local signal processing to improve contrast sensitivity
What does the inner layer of the retina contain?
Retinal ganglion cells (3rd order neurones)
What is the function of the retinal ganglion cels
Transmission of signal from the eye to the brain
What is the structural differences between the cones and the rods?
Rods = Longer outer segment
Cones = Shorter outer segment
What is the difference between rods and cones?
Rods = More sensitive to light, but slower response
Cones = Less sensitive to light, but faster response
Which photoreceptor cell is responsible for day light fine vision and colour?
Cones
Which photoreceptor cells is responsible for night vision?
Rods
What is scotopic vision?
Peripheral and night vision
Where can one find the highest concentration of Rod photoreceptors in the retina?
20-40 degrees away from fovea
Which cones are used for blue?
S-Cones
Which cones are used for Green?
M-Cones
Which cones are used for Red?
L-Cones
What colour are rods sensitive to?
Rods are used for night vision and spatial recognition and are not really sensitive to any particular colour
What is dueteranomaly, or Daltonsim?
most common type of colour blindness - red colourness
What is achromatopsia?
Full colour blindness
What is the name of the colour blindness test?
Ishihara test
what is refraction?
Then light goes from one’s medium to another, it changes velocity
What is the index of refraction and how is it calculated?
Ratio of speed of light in a vacuum to speed of light in a medium
What can the index of refraction be used for?
Help identify a material
What happens to the path of light when it changes from one medium to another?
Path changes
What is the angle of incidence?
Equal to the angle of reflection, is the angle at which light is reflected off the new medium
What are the two types of lenses?
Concave and convex
What does a convex lens do to light?
Takes the light rays and brings to a single focal point
What does a concave lease do?takes light rays and spreads them out
What is an example of an application of a converging lens?
A camera
What is emmetropia?
Perfect eye - adequate correlation between the axial length and refractive power
Parallel light rays fall on the retina without the need for accomodation
What is ametropia?
Mismatch between axial length and refractive power so parallel light rays do not fall onto the retina
What is myopia?
Near sightedness