eye final ppt

Category: Education

Presentation Description

A presentation on human eye.


Presentation Transcript



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We perceive shapes, distance, movement, color and depth by our sense of sight. The eye is the sensory organ of the vision or sight. Location- It is situated in the orbital cavity of skull. The eye alone cannot make sight possible. It works with brain and on the outside, needs light to be present. The eye is connected to brain through optic nerve (II). Eyes detect light and convert it to electro-chemical impulses in neurons.

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ACCESSORY STRUCTURES OF EYE- The accessory structures of the eye include- Eye-lids Eye lashes Eyebrows Conjunctiva Lacrimal apparatus Extraocular muscles of eye (extrinsic eye muscles).

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EYEBROWS- They are two arches of thick skin over the eyes. They contain thick hairs. They protect the eye from sweat, dust and other foreign bodies. EYE-LIDS- There are upper and lower eyelids which protect the eyes. The upper eyelid is large and more motile. Both eyelids are covered externally by skin and line internally by conjunctiva. Conjunctiva- The conjunctiva is a mucous membrane that covers the exposed front portion of the sclera and lines the inside of the eyelids. The conjunctiva helps to lubricate the eye and keep it moist. The conjunctiva also contains many blood vessels and nociceptors. EYE LASHES -Eye lashes are short hair which project from the free margin of eyelids. It helps to keep airborne particles from reaching the eye surface and provide some protection from excessive light.

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6. LACRIMAL APPARATUS- It is concern with the production and removal of tears. It consists of- A Lacrimal Glands- It is situated at the superior, lateral end of upper eyelid. This gland secreted tears. Lacrimal duct, Lacrimal sac and nasolacrimal duct through which tear is carried to the nasal cavity. Tears perform an important function in keeping the anterior surface of the eye moist and in washing away foreign particles. An antibacterial enzyme ( lysozyme ) in tears helps to reduce the chance of eye infection. 7. EXTRAOCULAR MUSCLES OF EYE- The eyeball is moved by six muscles. These are four straight (rectus) muscles and two oblique muscles. Name Action Medial Rectus Rotate eyeball inwards Lateral Rectus Rotate eyeball outwards Superior Rectus Rotate eyeball upwards Inferior Rectus Rotate eyeball downwards Superior oblique Rotate eyeball upwards & outwards Inferior oblique Rotate eyeball downwards & outwards

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STRUCTURE OF EYEBALL- Diameter- The human eyeball is approximately 2.5 cm in diameter with a 6 mm diameter pupil . There are three layers of tissue in the walls of the eye. They are- Fibrous Tunic-Formed by the sclera and cornea . Anterior- Iris & Ciliary body Vascular Tunic- Posterior- choroid The inner nervous tissue layer- Retina

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FIBROUS TUNIC- The fibrous tunic is the superficial layer of the eyeball and consists of the anterior cornea and posterior sclera. CORNEA- The cornea is the anterior outermost layer of the eye. It is a transparent coat that covers the coloured iris. It is also known as window of the eye. It is not supplied with blood vessels but is well supplied with sensory nerves. There are 3 layers to the cornea. The outermost layer is formed of non-keratinized stratified epithelium. The outer layer acts as a kind of shield to the elements and can usually repair itself within a few days of suffering a minor injury. The middle layer is formed by collagen fibers & fibroblast. The inner layer is made up of simple squamous epithelium . The inner layers exist mainly to strengthen the eye. Function- It permits light to enter the eye. It also protect the inner structure.

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SCLERA- The posterior outer part and the white part of the eye is called the sclera. The sclera is composed of tough, dense connective tissue (which is commonly fibroblast & collagen fibers). The sclera covers the entire eyeball except the cornea. It gives shape to the eyeball, make it more rigid, protects its inner parts and serves as a site of attachment for the extrinsic eye muscles. Function- It protects the inner working of the eye and forms the outer coating of the eyeball. At the junction of the sclera and cornea is an opening known as the scleral venous (Canal of Schlemm ). A fluid called aqueous humor drains into this sinus.

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VASCULAR TUNIC- The vascular tunic or uvea is the middle layer of eyeball. It is composed of three parts- choroid, ciliary body and iris- CHOROID- The middle layer of the eye is called the choroid. This layer is the posterior portion, highly vascular, pigmented tissue (deep chocolate brown) that provides nourishment and oxygen supply to the outer layers of retina. It is richly supplied with blood vessels. Note- The choroid also contains melanocytes that produce the pigment melanin, which causes this layer to appear dark brown in color. Function- Light enters the eye through the pupil, stimulates the sensory receptors in the retina and is then absorbed by the choroid.

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CILIARY BODY- The Ciliary body is the anterior continuation of the choroid consisting of ciliary muscle (smooth muscle fibres) and secretory epithelial cells. It gives attachment to the suspensory ligament ( zonular fibers) which, at its other end, is attached to the capsule enclosing the lens. The ciliary muscle is a circular band of smooth muscle. Contraction and relaxation of the ciliary muscle changes the thickness of the lens, which bends light rays entering the eye to focus them on the retina and adapting it for near or far vision. The ciliary body is formed by a thickening of the choroid.

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IRIS- The iris is continuous with the ciliary body. The iris is a circular, pigmented (colored) muscular structure that gives color to the eye. It is shaped like a flattened donut. It is suspended between the cornea and the lens and is attached at its outer margin to the ciliary processes. It consists of melanocytes and circular and radial smooth muscle fibers. The amount of melanin in the iris determines the eye color. The eyes appear brown to black when the iris contains a large amount of melanin, blue when its melanin concentration is very low, and green when its melanin concentration is moderate. The iris separates the anterior cavity into anterior and posterior chambers.

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  Anterior chamber Anterior Cavity- Contain aqueous humor Posterior chamber Posterior Cavity- It contain vitreous humor (Produced by cells in the non-pigmented portion of the ciliary body). 1 . Anterior Cavity Anterior chamber- It is present between cornea and iris. This is the space which is anterior to the iris but posterior to the cornea. Posterior chamber- It is present between iris and lens. This is the space which is anterior to the lens but posterior to the iris. This chamber filled with a clear, watery fluid called aqueous humor. Aqueous humor helps to give the cornea its curved shape. 2. Posterior Cavity- The posterior cavity of the eye is larger than the anterior cavity. It occupies all the space posterior to the lens, suspensory ligaments and Ciliary body. The posterior cavity filled with a jelly like substance called vitreous humor. Vitreous humor maintain sufficient pressure inside the eye to prevent the eyeball from collapsing.

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Pupil- The pupil is the dark circular hole in the centre of the iris. It is the opening in the iris. The amount of light entering the pupil is regulated through the contraction of radial and circular muscles in the iris. Lens- It is biconvex transparent body. It is located behind the pupil and between iris and retina. It is attached to Ciliary body by suspensory ligaments. It is made up by the crystalline protein that arranged in layers like the onion. It is enclosed by a capsule which is made up of connective tissue. Function- It helps in focusing clear image on retina to facilitate clear vision for both near and distant objects by changing its convexity.

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RETINA- It is the innermost layer of eyeball, it covers ¾ posterior part of eye ball. It is between the choroid & lens. It contains blood vessels which bring nutrients to the nerve cells. The macula is at the very center of the retina and contains the fovea. The photoreceptor cells of the retina are the rods and cones. The cones perceive color and finer elements. The photoreceptors send light and images to a large nerve called the optic nerve. This carries the information to the occipital lobe of the brain where they are interpreted.

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Retina is made by two layers 1. Pigmented layer- Pigmented layer is a sheet of melanin containing epithelial cell which is present between the choroid and the neutral layer of retina. The melanin in the pigmented layer of the retina, like in the choroid, also helps to absorb stray light rays. 2. Neural layer- Retinal neuronal layer contains three distinct cells- Bipolar cell Photoreceptor cell cone cell Rod cell Ganglion cell

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1. Bipolar cells- Bipolar cells are the cells of retina. bipolar cells exist between photoreceptors (rod cells and cone cells) and ganglion cells. They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells.

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2. Photoreceptor Cell- There are two types of photoreceptor cell: Rods and cones. Cone cell Number – 6 million in each retina Rod cell Number – 120 million in each retina Rod & cone cell is made up by the photo pigment i.e., made up by the glycoprotein ( opsin ) & retinol (Vitamin A) Glycoprotein opsin is 4 types - One in the rod cell known as rodopsin . Remaning three in the cone cell photopsin . Three types of cone cell 1. Red cone cell- these cells responds most to light of long wavelength (564-580 nm). 2. Green cone cell- these cells responds most to light of medium wavelength (534-545 nm). 3. Blue cone cell- these cells responds most to light of short wavelength (420-440 nm). Function of rod cell- Vision in the dim light For night vision Function of cone cell – Vision in the bright light For colour vision  

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3. Ganglion Cells- A retinal ganglion cell ( RGC ) is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells. Retina amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and making it so that ganglion cells can observe a small dot moving a small distance. Retinal ganglion cells collectively transmit image-forming and non-image forming visual information from the retina in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon , or midbrain.

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Optic disc- is the site where the optic nerve (II) exits the eyeball. The optic disc is also called the blind spot.Because it is the part of retina at where no rod & cone cell present. We cannot see an image that strikes the blind spot. Bundled together with the optic nerve are the central retinal artery (a branch of the ophthalmic artery) and the central retinal vein. Macula lutea (a small, flat spot)- is in the exact center of the posterior portion of the retina, at the visual axis of the eye. Fovea- A small depression in the center of the macula lutea , it contains only cone cells.

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PHYSIOLOGY OF THE EYE- Human eye acts like a camera Light energy enters into the eye from the object through cornea & pupil after entering pupil accommodate according to light intensity.   Lens focus the image onto the retina (Image is inverted on retina)   The light stimulates the photoreceptor cells (rod and cone cells) of retina   The photoreceptor cells transmit the signals to the bipolar cells (transmit signals from the photoreceptors to the ganglion cells).   The ganglion cells of retina receive the impulses from bipolar cells and forming visual information in the form of action potential After getting the impulses, optical nerves of the retina processes the image & send the messages to the brain through cranial nerve II (Optic nerve)   Thalamus Cerebral cortex   Cerebral cortex process the image   Vision

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