Structure of the eye and its functions pdf

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structure of the eye and its functions pdf

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The lens is a transparent biconvex structure in the eye that, along with the cornea , helps to refract light to be focused on the retina. By changing shape, it functions to change the focal length of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known as accommodation see also below.

Anatomy and function of the eye

The eye is a sensory organ. It collects light from the visible world around us and converts it into nerve impulses.

The optic nerve transmits these signals to the brain, which forms an image so thereby providing sight. Human eyes primarily consist of two globe-shaped structures, the eyeballs, which are surrounded by the the bony sockets of the skull, the orbits. The orbits are covered with fatty and fibrous tissue to protect the eye. Additional structures protecting the eye include the eyelids, the outer coating layer of the eye fibrous tunic , the conjunctiva, and the lacrimal glands.

Six special muscles that insert at different sites outside the eyeball work together to control eye movement. The following chapters will explain anatomy and function of the three coats as well as of the inner part of the eyeball.

The eyeball is surrounded by a three-layered wall, the three coats of the eye. They consist of different tissue and serve different functions. It is also known as the fibrous tunic. The fibrous tunic is composed of the sclera and the cornea. The sclera covers nearly the entire surface of the eyeball. The transparent cornea occupies the front center part of the external tunic. The anterior, visible part of the sclera as well as the inner surface of the eyelids are covered by the conjunctiva, a mucous membrane that helps lubricating the eye together with the tears made by the lacrimal glands, thus protecting the eye from drying out.

The choroid takes up the posterior five-sixths of the bulb and is mainly comprised of blood vessels. Its major functions are oxygen supply and nutrition for the eye. A dark pigment, melanin, occurs throughout the choroid in order to help limiting uncontrolled reflection within the eye, which would potentially result in the perception of confusing images. The anterior part of the choroid passes into the ciliary body , one function of which is anchoring the lens in place.

The ciliary body contains a muscle ciliary muscle , which can change the shape of the lens for adjustment to far or near sight, respectively, thereby controlling the so-called refractive power of the lens accomodation. The iris , which is connected to the anterior part of the ciliary body, covers the top of the lens. Similar to the aperture of a camera, it controls how much light is let into the eye.

The iris forms a circular, thin structure within the eyeball that regulates the size and the diameter of the pupil. For example, in children with blue eyes, the iris contains less pigment than in brown-eyed kids. The third and inner coat of the eye is the retina, which is responsible for the perception of images — vision.

The retina is a light-sensitive layer of nervous tissue composed of multiple sensory cells, so-called light- or photoreceptor cells , as well as associated nerve cells and other types of cells, all working together to make a person see. For vision, there are two types of photoreceptor cells: rods and cones. Rods provide the perception of black-and-white vision, mostly in dim light, whereas cones help to see colors in daylight. The light and colour impulses received by these photoreceptors are transmitted to the associated nerve cells of the retina, which, on their part, send these signals — via the optical nerve — to the visual centre visual cortex of the brain.

Its central part fovea centralis is densely packed with cone cells for colour perception. At this point, the sense of vision is the most accurate and detailed.

The inner part of the eyeball consists of the lens, the vitreous body and the two eye chambers. The lens is a transparent olive-shaped structure in the eye that has no blood vessels. Lens and cornea see above work together to focus the light rays passing through the eyeball to the back of the eye, that is, to the retina, by bending or refracting them, thereby creating clear images of the environment perceived from different distances.

By adjusting its shape and size, the lens can change the focus. This process is called accomodation. The vitreous is a clear gelatinous mass held by collagen fibers. It is situated between lens and retina and comprises about two thirds of the entire eyeball. By pushing the retina towards the choroid, the vitreous promotes keeping the retina in place. The anterior chamber of the eye is located between the iris and the cornea see above.

The posterior chamber is the space between parts of the iris and the lens. Both chambers are filled with aquaeous fluid to nourish cornea and lens.

The human eye is a complex optical system that basically works like a camera: the iris serves as the aperture that controls the amount of light rays reaching cornea and lens photographic objective , and the retina works as the film. Bending of light rays by cornea and lens serves to create sharp images on the retina. These images ultimately trigger nerve impulses, which are transmitted to the brain where the images are perceived and interpreted. English translations are still in development.

Table of contents Layers of the eye The inner part of the eyeball How the eye works.

Structure and Function of the Eyes

Human eye , in humans, specialized sense organ capable of receiving visual images, which are then carried to the brain. The eye is protected from mechanical injury by being enclosed in a socket, or orbit, which is made up of portions of several of the bones of the skull to form a four-sided pyramid, the apex of which points back into the head. Thus, the floor of the orbit is made up of parts of the maxilla, zygomatic, and palatine bones, while the roof is made up of the orbital plate of the frontal bone and, behind this, by the lesser wing of the sphenoid. The optic foramen , the opening through which the optic nerve runs back into the brain and the large ophthalmic artery enters the orbit, is at the nasal side of the apex; the superior orbital fissure is a larger hole through which pass large veins and nerves. These nerves may carry nonvisual sensory messages—e. There are other fissures and canals transmitting nerves and blood vessels. The eyeball and its functional muscles are surrounded by a layer of orbital fat that acts much like a cushion, permitting a smooth rotation of the eyeball about a virtually fixed point, the centre of rotation.

Iris: The iris is the colored part of the eye that regulates the amount of light entering the eye. Lens: The lens is a clear part of the eye behind the iris that helps to focus light, or an image, on the retina. Macula: The macula is the small, sensitive area of the retina that gives central vision.

Anatomy of the Eye

Jump to content. The five senses include sight, sound, taste, hearing and touch. Sight, like the other senses is closely related to other parts of our anatomy. The eye is connected to the brain and dependent upon the brain to interpret what we see. How we see depends upon the transfer of light.

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.

Lens (anatomy)

Structure and Function of the Eyes

The eye is a sensory organ. It collects light from the visible world around us and converts it into nerve impulses. The optic nerve transmits these signals to the brain, which forms an image so thereby providing sight.

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.

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Structure and Function of the Human Eye

Key points

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.

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.

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