The Human Eye Flashcards
Name the layers found in The Eye
Sclerotic coat (sclera) - outermost layer
Choroid - middle layer
Retina - innermost layer
What are the functions of the tear gland?
It secretes tears to
- wash away dust particles
- moisten the cornea for the absorption of dissolved oxygen
- lubricates the conjunctiva to reduce friction when the eyelids move
What is the pupil and its function?
The pupil is a hole in the centre of the iris that allows the entry of light entering The Eye, its size is controlled by muscles in the iris
What is the cornea and its function?
A dome shaped transparent layer that refracts light rays into The Eye
What is the function of the eyelid?
To protect the cornea from mechanical damage; squinting also prevents excessive entry of light which may damage the retina
Blinking spreads tears over the eyes so that dust can be wiped off
What is the function of the eyelash?
To shield The Eye from dust particles
What is the iris and its function?
A circular sheet of two sets of involuntary and antagonistic muscles ; circular and radial
Contains a pigment which gives The Eye its colour
What is the conjunctiva and its function?
Thin mucus membrane covering the sclera
Secretes mucus to keep the front of the eyeball moist
What is the sclerotic coat and its functions?
Tough white outer covering of the eyeball that is continuous with the cornea
Eye muscles are attached to this layer, facilitating the movement of the eyeball
Protects the eyeball from mechanical damage
What is the choroid and its function?
Black pigmented middle layer of the eyeball
Prevents the internal reflection of light
Contains blood vessels which transports oxygen and nutrients to the eyeball and removes metabolic waste products
What is the retina and its function?
The innermost layer of The Eye wall containing light-sensitive cells known as photoreceptors - consists of rods and cones which have different functions
Connected to nerve fibres from the optic nerve
What is the function of photoreceptors in the retina?
Converts light waves into nerve impulses which relays information to the brain
What are the functions of cones in the retina?
There are 3 different types of cones which contains either red blue and green pigment that each absorbs light of different wavelengths work together to enable one to see a variety of colours in bright light
What are the functions of rods?
Stimulated by very dim light, enables one to see in dim light but only in black or white
Contains a pigment called visual purple which becomes bleached in bright light preventing nerve impulses from being transmitted to the brain
What is the fovea and its function?
A small yellow depression where images are focused ,
Contains only cones
Enables a person to have detailed colour vision in bright light
Vision is sharpest here
What is the blind spot and its function?
Region where the optic nerve leaves The Eye
Does not contain photoreceptors and thus is not sensitive to light
Function of the optic nerve?
Transmits nerve impulses to the brain when the photoreceptors are stimulated
What are the lens and its function?
Transparent circular biconvex structure
Shape or thickness can be changed in order to refract light onto the retina
What is the ciliary body and its function?
contains ciliary muscles which control the curvature and thickness of the lens
What are Suspensory ligaments ?
Ligaments that attaches the edge of the lens to the ciliary body
What is the aqueous chamber and its function?
Space between the lens and the cornea
Is filled with aqueous humour
What is aqueous humour and its function?
A transparent watery fluid that
Keeps the front of the eyeball firm and
Refracts light onto the pupil
What is the vitreous chamber?
The space behind the lens
Contains vitreous humour
What is the vitreous humour and its function?
A transparent jelly-like substance that
Keeps the eyeball firm and refracts light onto the retina
What is pupil reflex and its function?
A reflex response to changes in light intensity; protects The Eye from excessive light exposure , which could damage the retina
Pathway of pupil reflex?
Stimulus (change in light intensity) -> receptor ( retina ) -> sensory neurone in the optic nerve -> brain -> motor neurone -> effector (iris muscles)
What is the pathway for the formation of an upright image at the brain?
The inverted image is formed on the retina
Light sensitive cells (rods and cones) are stimulated
Nerve impulses generated are transmitted through the optic nerve
Nerve impulses reach the optic centre of the brain
Te brain interprets the information and forms an upright image
What happens when one tries to focus on a nearby object?
The light rays from a near object are divergent. A greater angle of refraction is needed to bring them into focus on the retina.
The ciliary muscles contract, relaxing their pull on Suspensory ligaments. The Suspensory ligaments slacken , relaxing their pull on the lens.
The lens become thicker and more convex, decreasing the focal length
Light rays are sharply focused on the retina , stimulating the photoreceptors
Nerve impulses generated are transmitted to the brain via the optic nerve
The brain interprets the impulses and the person sees the near object
What happens when one tries to focus on a far object?
Light rays from a distant object are almost parallel, thus a smaller angle of refraction is needed to bring them into focus. The ciliary muscles relax, pulling on Suspensory ligaments
The Suspensory ligaments becomes taut, pulling on the edge of the lens
Causing it to become thinner and less convex, increasing the focal length
Light rays are sharply focused on the retina
Nerve impulses generated are transmitted to the brain via the optic nerve
The brain interprets the impulses and the person sees the far object
