the human eye structure and function pdf

The human eye structure and function pdf

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human eye structure and function pdf

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To browse Academia. Skip to main content. By using our site, you agree to our collection of information through the use of cookies. To learn more, view our Privacy Policy. Log In Sign Up. Download Free PDF. Colin Willoughby. Download PDF. A short summary of this paper. All MPS types have a progressive course and involve multiple organs. They share several common clinical features, but with variable degrees of severity.

Typical features of the MPS include coarse facial fea-tures, affected hearing and vision, cardiorespiratory problems, reduced joint mobility, organomegaly and skeletal deformities dysostosis multiplex, dwarfism Fig. Patients with MPS IV Morquio syndrome show bony lesions specific for that disorder dwarfism with short trunk and neck. There is a wide spectrum of phenotypes and progression rates within any one MPS type.

Characteristic ocular features in patients with MPS include corneal clouding, glaucoma, retinopathy, optic disc swelling and optic atrophy. The outer region consists of the cornea and the sclera. The cornea refracts and transmits the light to the lens and the retina and protects the eye against infection and structural damage to the deeper parts.

The sclera forms a connective tissue coat that protects the eye from internal and external forces and maintains its shape. The cornea and the sclera are connected at the limbus.

The visible part of the sclera is covered by a transparent mucous membrane, the conjunctiva. The middle layer of the eye is composed of the iris, the ciliary body and the choroid. The iris controls the size of the pupil, and thus the amount of light reaching the retina; the ciliary body controls the power and shape of the lens and is the site of aqueous production; and the choroid is a vascular layer that provides oxygen and nutrients to the outer retinal layers.

The inner layer of the eye is the retina, a complex, layered structure of neurons that capture and process light. The three transparent structures surrounded by the ocular layers are called the aqueous, the vitreous and the lens. It is the most densely innervated tissue of the body, and most corneal nerves are sensory nerves, derived from the ophthalmic branch of the trigeminal nerve. The cornea is avascular and the branches of the anterior ciliary arteries stop at the limbus where they form arcades that supply the peripheral cornea.

The mucous layer interacts with the epithelial cells, allowing the tear film to spread with each eyelid blink. The cells of the corneal epithelium are renewed every days from a pluripotent stem cell population, which resides in the palisades of Vogt at the corneoscleral limbus.

The stem cells differentiate into transient amplifying cells when they migrate to the central cornea. The latter is secreted by the basal cells and mainly consists of type IV collagen and laminin. Because innervations are essential for the physiology of the epithelium, Figure 2. Schematic illustration of the structure of the eye and the ocular barriers.

The primary physiologic blockage against instilled drugs is the tear film. Cornea is the main route for drug transport to the anterior chamber I. The retinal pigment epithelium and the retinal capillary endothelium are the main barriers for systemically administered drugs II. Intravitreal injection is an invasive strategy to reach the vitreous III.

The administered drugs can be carried away from the anterior chamber either by venous blood flow after diffusing across the iris surface 1 or by the aqueous outflow 2. Drugs can be removed away from the vitreous through diffusion into the anterior chamber practically all epithelial cells are in contact with nerve cells.

The corneal lamellar stroma mm-thick provides structural integrity to the cornea. Stromal keratocytes secrete collagen and proteoglycans, which are ultimately fundamental for the transparency of the cornea and hydration. The stroma is separated from the epithelium by the Bowman's layer, an acellular zone of mm beneath the basal lamina.

The bulk of the stromal extracellular matrix consists of collagen fibrils arranged in parallel lamellae that run from limbus to limbus. In the pre-pupillar cornea, the fibrils are packed more compact than in the peripheral cornea, probably contributing to the mechanical strength and dioptric stability in the cornea.

These proteoglycans have an important structural function and help regulate hydration. Keratocytes are the predominant cell type in the stroma and play a role in maintaining its organization. These stellar-shaped cells contact to each other by long cytoplasmatic extensions morphologic and functional syncytium and also interact with the corneal epithelium.

The corneal endothelium consists of a single layer of five-to seven-sided cuboidal cells with little or no self-renewing potential. They secrete the Descemet's membrane that separates the endothelium from the stroma. This elastic membrane thickens with age and is composed of an anterior layer with a banded appearance and a posterior layer with an amorphous texture.

Corneal oedema may develop if deturgescence is disturbed for some reason. Incident light on the cornea can be transmitted, absorbed or scattered. In a normal transparent cornea, visible light is not absorbed and scattering is negligible. Only irregularities with dimensions similar to the wavelength of visible light nm will affect the retinal image. An increase of corneal scattering can arise in case of corneal oedema, the relaxation of collagen fibrils, haze extracellular matrix production by keratocytes or irregularities due to surgery.

During embryogenesis, the vertebral retina develops from the optic cup. The latter is formed by invagination of the optic vesicle, which is an outgrowth of the embryonic forebrain. The inner wall of the optic cup surrounding the vitreous cavity ultimately becomes the neural retina; the outer wall surrounded by the choroid and sclera becomes the retinal pigment epithelium RPE. The cells of the neural retina are arranged in several parallel layers Fig. The inner nuclear layer has plexiform layers at both sides.

In the outer plexiform layer, the photoreceptors connect with bipolar and horizontal cells, whereas in the inner plexiform layer, bipolar and amacrine cells synapse with ganglion cells. The nuclei of the ganglion cells lie in the ganglion layer, their axons in the nerve fibre layer. The apical processes form the outer limiting membrane by making junctional complexes with one another and with photoreceptors. The apposed end-feet of the vitreal processes form the inner limiting membrane.

In humans, rods are approximately 20 times more abundant than cones. For this purpose, the membranes of the outer segment discs of the photoreceptors contain pigments. Cones, which are responsible for colour vision, have pigments with absorption peaks in the blue, green or yellow parts of the spectrum. Pigments of the rods have an absorption peak in the blue-green part of the spectrum. Rods are active with low light levels, and are not involved in colour vision. The density of rods and cones varies between different regions of the retina.

The macula lutea refers to an area in the retina between the temporal vascular arcades containing xanthophylls pigment Figs 2,5. The excavation near the centre of the macula is called the fovea Fig.

This area of the retina is responsible for sharp central vision and contains the largest concentration of cones in the eye. Due to the high density of cone cells in the foveola, the cone synaptic terminals and the ganglion cells to which they connect are pushed away from its centre, resulting in elongations between the nuclei and synaptic terminals of the cone cells, called Henle's fibres.

No photoreceptor cells are present at the optic disc or optic nerve head where the axons from the ganglion cells exit the eye to form the optic nerve Fig. The RPE is a monolayer of cuboidal epithelial cells intercalated between the photoreceptors and the choriocapillaris, a layer of capillaries adjacent to the innermost layer of the choroid. The RPE incorporates about 3. At the apical side, the cells of the RPE form long microvilli that reach up between the outer segments of rod photoreceptors.

The retina receives its blood supply from two circulatory systems: the retinal and the choroidal blood vessels. The outer avascular retinal layers receive their nutrients by diffusion from the choroid vessels. The choriocapillaris is fenestrated, which allows leakage of molecules to the RPE. Specialized transport systems in the RPE control the transportation of fluid and nutrients to the photoreceptors.

Retinal function depends on several factors, including the region of the retina being illuminated, the wavelength and intensity of the light stimulus and the state of light adaptation. As visual images are inverted as they pass through the lens, the right half of the image is projected on the nasal retina of the right eye and the temporal retina of the left eye , whereas the left half of the image is projected on the temporal retina of the right eye and the nasal retina of the left eye.

The neurons of the neural retina translate the visual information into nerve impulses, which travel through the optic nerve to the brain. The photoreceptors, the bipolar cells and the ganglion cells form a direct pathway to the brain Fig.

The horizontal and amacrine cells form lateral pathways that modify and control the signal that passes through the direct pathway. The optic nerve extends from the eye to the optic chiasm.

The next synapses lie deep in the brain, in the lateral geniculate nuclei LGN. This is due to a hemidecussation of both optic nerves in the optic chiasm, before they reach the LGN. Neurons from the LGN send their axons to the ipsilateral primary visual cortex.

The left primary visual cortex receives information from the right visual field, and vice versa. A lesion in one or both optic nerves will result in visual loss in one or both eyes, respectively. This will be apparent in the optic disc, which may become swollen or develop pallor optic atrophy. Increased intracranial pressure results in the swelling of both optic discs papilloedema that may cause optic atrophy when untreated.

The hallmarks of chiasmal lesions are defects that affect the temporal visual field in each eye. A lesion behind the optic chiasm is characterized by homonymous visual field defects occurring in both eyes e.

These barriers can hamper the delivery of topical ocular drugs i. Topical ocular drugs, mostly given as eyedrops, are the most frequently used dosage forms for treating ocular diseases. The first barrier to cross for these drugs is the tear film, which rapidly removes instilled compounds from the eye, resulting in low bioavailability.

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In short, we will say that this topic is very interesting and enhance our knowledge about the human eye. Therefore, we will be providing you human eye short notes PDF by that you can easily understand this topic. Friends, on our site we provide you complete study material for all Competitive Exam. Here, on this site we will provide you daily new free study materials which helps you score good marks in your competitive exam. So, please daily visit our site, for free study material and other updates regarding exams. For daily current affairs, latest govt. Friends, for any assistant, queries, and questions related to exams ask in our Telegram Group and follow us on Facebook and also comment on this post.

To browse Academia. Skip to main content. By using our site, you agree to our collection of information through the use of cookies. To learn more, view our Privacy Policy. Log In Sign Up. Download Free PDF. Colin Willoughby.

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. Accommodation is similar to the focusing of a photographic camera via movement of its lenses. The lens is more flat on its anterior side than on its posterior side.

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Lacrimal glands are located in the outer corner of eye. The various parts of the eye perform different functions that contribute to this purpose. This gives them a larger field of view for avoiding predators.

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.

human eye structure and function pdf

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.

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.

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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.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. The intricacy and seeming perfection of the eye, both as an object of anatomical beauty and as a working machine, have worried and intrigued scientists, philosophers and zealots, especially during the intellectual upheavals of the nineteenth century. For William Paley, such a mechanism argued for a supreme designer; for Darwin, the eye was a test case for natural selection; and for Helmholtz, it was a brilliant compromise — a flawed device to a brass and glass instrument-maker, but a structure nonetheless capable of resolving at the limits that physics allow.

structure and function of eye pdf

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4 comments

  • Jemina Z. 01.06.2021 at 11:23

    In short, we will say that this topic is very interesting and enhance our knowledge about the human eye.

    Reply
  • Prudens P. 02.06.2021 at 10:21

    Components of the Eye 8 The Cornea and the Sclera 9 The Limbus and the Anterior Chamber 10 The Iris and the Pupil 11 The Ciliary Body​.

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