Structure and function of eye pdf
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Eye anatomy and function
Special cells called cones and rods are located in the retina. These cells are known as photoreceptors and help absorb light. The majority of the cones are located in the macula, or central area, of the retina.
Cone cells help us see colour and detail. Similarly, the macula allows us to read and clearly recognize people's facial details, such as eye colour and whether they have freckles. The majority of the rods are located in the peripheral, or outer area, of the retina. Rod cells allow us to see in poor lighting and give us our night vision. To understand the vision of someone with an eye condition, it can be helpful to know what normal vision is like.
Imagine a scenario where two people are sitting on the couch in front of you. If you look directly at Person A, you are able to use your macula, or central vision, to see the details of their head and face. Maybe they have freckles, brown eyes and black hair. At the same time, you are aware that Person B is sitting on the couch beside Person A. However, you are not able to see the same amount of detail on their face.
For example, you may only see dark areas where their eyes are. To see Person B, you are using the rest of your retina or peripheral vision.
Seeing clearly and sharply in the centre, and blurry in the periphery is considered normal vision. A problem with any part of the eye can cause vision problems. There are many types of eye conditions that can affect vision in different ways. In some cases, the lens does not focus correctly, or the shape of the eyeball is not round, so the image will appear blurry.
This can often be corrected with prescription glasses or contact lenses. When an image is focused behind the retina, this is referred to as far-sightedness.
When an image is focused in front of the retina, this is referred to as near-sightedness myopia. Some eye conditions affect the retina. For some people, only their peripheral vision is affected, which can cause tunnel vision.
For others, only their central vision is affected, which can lead to the formation of blind spots scotomas. Finally, other eye conditions that may cause vision problems include cloudiness in the lens cataract , increased eye pressure glaucoma , damage to the cornea, or problems with the eye muscles.
Visual field VF is the term used to describe the width of our peripheral vision. Normally, we see with a VF of degrees or half a circle. When looking straight ahead, we should be able to sense motion off our right or left shoulder. Occasionally, a manual test called a Goldmann VF exam is used. Next, a light source is brought into their field of vision from the side. The person then pushes a button when they see the light. The results of the VF test determine whether a person has tunnel vision and blind spots.
Visual fields can be measured in one eye at a time or using both eyes at once binocular fields. A person with blind spots in both eyes may need to have a binocular visual field test to make sure that one eye sees in an area that is a blind spot in the other.
This is important information when determining whether someone has a VF that meets the government standards for driving see below. Visual acuity VA is defined as the clarity of the image seen by the eye. VA is tested using an eye chart at a distance of 20 feet six metres. From testing many patients, eye doctors have determined what the average VA is for most people when standing 20 feet away from an eye chart.
This measurement is called "normal" vision. Young children who are unable to read the letters on the chart will have their vision checked using preferential looking tests where cards with lines or pictures are held up for a child to look at. The cards will get progressively more difficult to see, and the test continues until the child stops responding.
It is average vision. There are other vision skills that contribute to overall visual ability. These include:. The person's VF must be at least degrees and not interrupted by blind spots. The VF must also be at least 15 degrees above and below the fixation point with both eyes open. An ophthalmologist is required by law to report any patient that does not meet the MOT guidelines.
Such a person is classified as "legally blind for assistive devices. Low vision aids include hand-held magnifiers, magnification in reading glasses and telescopes. Ask your bank for details. Skip to main content.
The pupil, or black dot at the centre of the eye, is an opening through which light can enter the eye. The iris, or coloured part of the eye, surrounds the pupil.
It controls how much light enters the eye by changing the size of the pupil. The cornea, a clear window at the front of the eye, covers the iris and the pupil. A clear lens, located behind the pupil, acts like a camera lens by focusing light onto the retina at the back of the eye. The retina is a light-sensitive inner lining at the back of the eye. Ten different layers of cells work together in the retina to detect light and turn it into electrical impulses.
The retina Special cells called cones and rods are located in the retina. Cones The majority of the cones are located in the macula, or central area, of the retina. Rods The majority of the rods are located in the peripheral, or outer area, of the retina.
How the eye sees For people with normally functioning eyes, the following sequence takes place: Light reflects off the object we are looking at. Light rays enter the eye through the cornea at the front of the eye. The light passes through a watery fluid aqueous humor , and enters the pupil to reach the lens. The lens can change in thickness to bend the light, which will focus it onto the retina at the back of the eye.
On the way to the retina, the light passes through a thick, clear fluid called a vitreous humor. The vitreous humor fills the eyeball and helps maintain its round shape. The light then reaches the back of the eye and hits the retina.
The retina translates the light into electrical impulses which are then carried to the brain by the optic nerve. What normal vision is like To understand the vision of someone with an eye condition, it can be helpful to know what normal vision is like. Vision problems A problem with any part of the eye can cause vision problems.
Structure and Function of the Human Eye
The orbit is the bony cavity that contains the eyeball, muscles, nerves, and blood vessels, as well as the structures that produce and drain tears. The eye is roughly analogous to a self-regulating, self-cleaning camera. Associate Professor Bruce Hadden. It provides attachment surfaces for eye muscles Choroid Eyes Structure and Function The eye transmits visual stimuli to the brain for interpretation and, in doing so, functions as the organ of vision. It helps to shield the rest of the eye from germs, dust, and other harmful matter. It is one of the important human eye facts that they help us view our surroundings.
Both modes require fibroblast growth factor 2 FGF2. So I'm just drawing that in. Move your left hand to unblock your left eye and the gap re-appears. Melanin, the pigment present in the RPE, reduces the scatter of light to the photoreceptors, shielding, them from excessive light exposure Marmor and, Wolfensberger, This article uses the mammalian eye as a primary model and follows the path that light takes on its journey through the functional eye, detailing the essential components of one of the smallest, yet most complex organs in the body. Our findings therefore suggest a functional role of Fam3c in the regulation of osteoblast differentiation.
With longer wavelengths in the IR spectrum and the availability of InGaAs detectors and cameras, OCT scanners now penetrate even deeper into the human, We report a Talbot bands-based optical coherence tomography OCT system capable of producing longitudinal B-scan OCT images and en-face scanning laser ophthalmoscopy SLO images of the human retina in-vivo. Spectrogram graphs based on short time Fourier transform STFT were considered to evaluate the power spectrum analysis in each EEG channel of transition or steady state. The spatial separation of the two beams facilitates collection by an SLO channel of optical power originating exclusively from the retina, deprived from any contribution from the reference beam. Human eye, specialized sense organ in humans that is capable of receiving visual images, which are relayed to the brain. The vitreous humour is also in contact with, the retina, though it only adheres to it at the optic nerve, disc; it helps hold the retina in place by exerting a pressure, on it against the choroid.
Eyes. Structure and Function. The eye transmits visual stimuli to the brain for interpretation and, in doing so, functions as the organ of vision. The eyeball.
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Members of the animal kingdom use different strategies to detect light and focus it to form images. Human eyes are "camera-type eyes," which means they work like camera lenses focusing light onto film. The cornea and lens of the eye are analogous to the camera lens, while the retina of the eye is like the film. To understand how the eye sees, it helps to know the eye structures and functions:.
Eyes are organs of the visual system. They provide animals with vision , the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons.
How the Human Eye Works
The structures and functions of the eyes are complex. Each eye constantly adjusts the amount of light it lets in, focuses on objects near and far, and produces continuous images that are instantly transmitted to the brain. The orbit is the bony cavity that contains the eyeball, muscles, nerves, and blood vessels, as well as the structures that produce and drain tears. Each orbit is a pear-shaped structure that is formed by several bones. The outer covering of the eyeball consists of a relatively tough, white layer called the sclera or white of the eye. Near the front of the eye, in the area protected by the eyelids, the sclera is covered by a thin, transparent membrane conjunctiva , which runs to the edge of the cornea.