Eye Flashcards
What is the purpose of the eyelids?
Protection of the eye
Blink reflex
Ensures front of the eye is lubricated with tear fluid
Where is tear fluid produced from?
Lacreal glands above the eye, the tear fluid then drains through canals
Describe the part of the eye we can see?
Sclera - white of the eye
Pupil - hole in the middle, controls the amount of light received by the eye
Iris - coloured portion of the eye
What is the conjunctiva?
Membrane that covers, protecting the eye. Tear fluid then sits at the front allowing outer surface protection
What is the purpose of the cornea?
Circular transparent window at the front of the eye
Ensures the refraction of light as it enters
What is the purpose of the anterior chamber?
The anterior chamber is the front part of the eye between the cornea and the iris and provides the aqueous humour.
What is the purpose of the aqueous humour?
It provides oxygen and nutrients to the transparent organs within the eye as well as maintaining the intraocular pressure which keeps the eye inflated.
Describe the production and supply of the aqueous humour.
To ensure constant intraocular pressure within the eye, turnover is required. It is produced from the ciliary body, it flows across the front of the lens, out through the pupil and the drains into the canal of Schlemm (circular production pathway).
Which muscle is the iris composed of?
Smooth muscle which aids pupil response to light.
What is the main purpose of the lens?
It is a transparent organ with its primary focus to fine focus the light on to the retina. The lens is held in place by suspensory ligaments which attaches it to the ciliary body which contains smooth muscle which aids fine focusing.
Where is vitreous humour found?
In the chamber of the eye and is responsible for absorbing energy, important for protecting the neural retina.
What are the two parts of the retina?
The retina is found at the back of the eye and is divided into two parts:
Neural retina which is light sensitive
Retinal pigment epithelium
When light enters the eye where is it focused on?
The fovea at the back of the eye due to having the highest visual acuity.
Where is the choroid found and what is its function?
It is found behind the retina. It is pigmented ensuring light absorption and highly vascular. Provides a blood supply for the outer layers of the retina.
What is the purpose of the optic disk?
This is the point where all the axons meet to form the optic nerve to transmit information to the brain. This is also the point that blood come in supplying the inner retina.
Where is the blind spot located?
At the optic disk as they are no light sensitive cells here.
What are the two types of smooth muscle controlling pupil size?
Circular smooth muscle (fibres run in a circular fashion) and radial smooth muscle
Explain in what circumstances circular muscle contraction occurs.
In response to light, circular smooth muscle contraction occurs stimulated by the parasympathetic nervous system. This causes pupil constriction - restricting the amount of light entering the pupil.
Explain in what circumstances radial smooth muscle contraction occurs.
In darkness, radial smooth muscle contraction occurs stimulated by the sympathetic nervous system. This results in the radial fibres becoming shorter leading to pupillary dilation.
What is the first point of focusing light?
The cornea which enables the greatest degree of refraction. To ensure the refraction occurs evenly the cornea surface must be very smooth - astigmatism results due to unsmooth cornea.
What occurs in laser corrective surgery?
The curvature of the cornea is altered which in turn then changes the plane of focus - how light is focused on to the retina.
Explain what is meant by the concept of accommodation.
Accommodation of the eye refers to the eye’s ability to adjust its focus to see objects clearly at different distances. This is achieved by changing the shape and curvature of the eye’s natural lens to bring images into sharp focus on the retina, remember unable to change the curvature of the cornea.
Explain the concept of fine focusing in relation to far vision.
For far vision the circular ciliary muscle is relaxed, the intraocular pressure pulls the lens taut (thin and flat) resulting in less curvature and therefore is able to focus parallel light coming from a distant point.
Explain the concept of fine focusing in relation to near vision.
For near vision, more curvature is required so the circular ciliary muscle contracts, the suspensory ligaments become slack which enables the lens to become more rounded more refraction to ensure light is focused from a close source. This is mediated under the control of the parasympathetic nervous system which innovates the ciliary muscle of contraction.
Is accommodation mediated by the sympathetic or parasympathetic nervous system?
Parasympathetic nervous system innovates ciliary muscle contraction for fine focusing on near vision. Whilst the sympathetic nervous system activation does enable some ciliary muscle relaxation enabling fine focusing on far vision this is mainly mediated by the switching off of the parasympathetic nervous system.
How is light reflected on to the fovea?
It presents as upside down and back to front which is then sorted by the brain.
What occurs in the condition presbyopia?
The lens becomes less flexible with age, can’t focus on near vision as the lens is unable to become as rounded as it once was.
What causes the condition myopia?
Myopia also known as short-sightedness occurs as a result of the eyeball being too long so when light becomes in from a distant object it is focused in front of the retina meaning it becomes blurred.
Can see close images but not far away.
What causes the condition hyperopia?
Hyperopia is when the eyeballs are too short, unable to see near objects and as light is reflected behind the retina.
Can’t see close images but able to see far away.
What is the purpose of the retina?
It is the light sensitive part of the eye which is responsible for visual transduction, converting light energy to electrical signals within neurons.
What is the purpose of photoreceptors?
They are responsible for converting light energy to electrical signals.
Describe the two different types of photoreceptors.
Rods which are responsible for black and white (grayscale vision) and cones which are responsible for colour.
Describe the visual pathway that occurs within the retina.
When light hits the back of the retina photoreceptors both cones and rods are responsible for converting light energy into an electrical synapse. These then synapse with bipolar cells which then synapse with ganglion cells and it is the extended axons of these ganglion cells which then form the fibres of the optic nerve and transmit the electrical signals to the brain.
Light enters at the front of the retina and travels to the back which is the opposite direction of visual processing which starts at the back of the retina.
