ppt on eye

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A PRESENTATION ON EYE DISSECTIONBY MISS SHANU : 

A PRESENTATION ON EYE DISSECTIONBY MISS SHANU

Special Senses: The Eye : 

Special Senses: The Eye

Anatomy of the Eye : 

Anatomy of the Eye

Human Visual System : 

Human Visual System Basic Anatomy, Visual Function, Common Conditions and Common Diseases

Basic Anatomy of Human eye : 

Basic Anatomy of Human eye

Sclera : 

Sclera The white part of the eyeball is called the sclera. The sclera is made of a tough material and has the important job of covering most of the eyeball.

Sclera : 

Sclera Opaque, mechanically tough Forms the posterior 5/6 of the outer coat of the eye Consists of irregularly arranged collagen fibres Functions include Maintains the constancy of ocular shape Maintenance of intraocular pressure Barrier to infection and trauma

CORNEA : 

CORNEA The part of the sclera in front of the colored part of the eye is called the cornea . Unlike the rest of the sclera, which is white, the cornea is transparent, or completely clear, which lets light travel through it. The cornea helps the eye focus as light makes its way through. It is a very important part of the eye, but you can hardly see it because it's made of clear tissue. Like clear glass, the cornea gives your eye a clear window to view the world through

IRIS : 

IRIS Behind the cornea are the iris and the pupil. The iris is the colorful part of the eye. When we say a person has blue eyes, we really mean the person has blue irises!

PUPIL : 

PUPIL The iris is a muscle. This allows the iris to control how much light goes through the pupil . The pupil is the black circle in the center of the iris, and it lets light enter the eye. The pupils will get smaller when a light shines near them and they'll open wider when the light is gone.

Crystalline lens : 

Crystalline lens A biconvex structure with a clear outer acellular capsule Consists of very tightly packed hexagonal fibres The cortex contains the more recently formed fibres, the nucleus contains the older non-dividing cells Has a relatively low water (66%) and high protein (35%) content

Slide 14: 

Between the iris and cornea is the anterior chamber. This chamber is filled with a special transparent fluid that gives the eye oxygen, protein, and glucose (a type of sugar in the body) to keep it healthy.

Basic Eye Structures : 

Basic Eye Structures Cornea The cornea transmits and focuses light into the eye Iris - The iris helps regulate the amount of light Pupil - Response to various degrees of illumination to control the amount of light that is let into the eye. Lens - the transparent structure behind the iris that focuses light rays onto the retina Basic Eye Structures

Basic Eye Structures : 

Basic Eye Structures Retina - the nerve layer that lines the back of the eye. The retina senses light and creates impulses that are sent through the optic nerve to the brain Optic Nerve - the nerve that connects the eye to the brain. It carries the impulses formed by the retina to the brain, where it is interpreted as images Basic Eye Structures

Extrinsic Eye Muscles : 

Extrinsic Eye Muscles 4 rectus: superior, inferior, lateral, medial 2 oblique: superior, inferior Origins: annular ring in posterior orbit Insertions: fibrous tunic (layer) of eyeball (outermost layer)

Slide 18: 

Rectus muscles

External Features of the Eye : 

External Features of the Eye Conjunctiva: transparent mucous membrane Lines eyelids, anterior eye Vitamin A deficiency stops mucus production Conjunctivitis: inflammation Lacrimal apparatus: produces tears Mucus, antibodies, lysozyme Flushes out particulates, bacteria, viruses

The Vascular Tunic : 

The Vascular Tunic Middle layer, carries blood vessels, 3 regions Choroid: posterior, highly vascular, melanin (pigment) absorbs light Ciliary body: continuous with the choroid and encircles the lens, smooth muscle, focuses lens Iris: base attached to ciliary body, most anterior, eye color (melanin), opening = pupil Muscles: sphincter relaxes (constrict), dialator contracts (opens), ANS

The Sensory Tunic (Retina) : 

The Sensory Tunic (Retina) Deepest layer, posterior, 2 layers Pigmented layer: outer thin layer, dark brown (pigmented), single cell layer, absorbs light Neural layer: inner thick layer, plays direct role in vision, 3 cell types From external to internal (photoreceptors, bipolar neurons, ganglion cells)

Specialized Regions of the Retina : 

Specialized Regions of the Retina Ora serrata retinae: neural layer ends anteriorly at ciliary body, pigmented layer extends to cover posterior iris Macula lutea: directly on eye’s posterior pole, “yellow spot”, mostly cones, Fovea centralis: central pit of macula, only cones, visual acuity straight on Optic disc: blind spot, no rods or cones, optic nerve exits, medial and inferior to fovea centralis

RETINA Transparent At least 11 layers Converts light energy into nervous impulses - transduction Photoreceptors 120 million rods (monochromatic) 6 million cones (colour vision)

Sections of the Eye : 

Sections of the Eye Lens: thick, transparent, biconvex disc, focuses light on the retina Collagen fiber layers Shape controlled by suspensory ligament, ciliary body

Segments of the Eye : 

Segments of the Eye Lens divides eye into 2 segments: Anterior segment: between cornea and lens Filled with aqueous (watery) humor Filtrate of blood plasma Fluid replaced continually by ciliary process cells Drains thru scleral venous sinus (Canal of Schlemm) and returns to blood Build-up of aqueous humor causes glaucoma “Clouding” of lens = cataract

Aqueous HumourAqueous formation Active secretion by the epithelium of the ciliary processes of the ciliary bodyAqueous drainage- 90% through the trabecular meshwork into the canal of Schlemm in anterior chamber angle, then via aqueous veins and into the general circulation- 10% through uveoscleral (unconventional) outflow : 

Aqueous HumourAqueous formation Active secretion by the epithelium of the ciliary processes of the ciliary bodyAqueous drainage- 90% through the trabecular meshwork into the canal of Schlemm in anterior chamber angle, then via aqueous veins and into the general circulation- 10% through uveoscleral (unconventional) outflow

Physiology – Aqueous HumourFunctions are to: - Maintain intraocular pressure - Contribute to ocular transparency- Provide metabolic support for the lens, cornea and vitreous- Constituents essentially similar to plasma but only 1% of the plasma protein : 

Physiology – Aqueous HumourFunctions are to: - Maintain intraocular pressure - Contribute to ocular transparency- Provide metabolic support for the lens, cornea and vitreous- Constituents essentially similar to plasma but only 1% of the plasma protein

Drainage Of Aqueous Humour : 

Drainage Of Aqueous Humour

Intra-ocular pressure (IOP) : 

Intra-ocular pressure (IOP) Maintained at 10-21 mm Hg Dynamic balance between secretion and drainage of aqueous humour High IOP (glaucoma) Leads to loss of visual field and eventual blindness

Segments of the Eye (continued) : 

Segments of the Eye (continued) Anterior segment has 2 divisions Anterior chamber: anterior to iris Posterior chamber: posterior to iris Posterior segment: posterior to lens Filled with vitreous humor (fluid) Jelly-like, transmits light, holds retina in place, maintains pressure Formed only before birth

VITREOUS HUMOUR : 

VITREOUS HUMOUR Firm gel - 4 ml / 80% of the globe volume Composition: Collagen type II, arranged in fibrils Few cells (hyalocytes) - secreting glycosaminoglycan Functions are to: Maintain transparency Protect the ocular structures Passive "transport and removal" of metabolites

The Eye : 

The Eye Accessory structures: eye lid, eye brow, eye lashes, muscles, lacrimal apparatus

Photoreceptors : 

Photoreceptors

RODS : 

RODS Rods see in black, white, and shades of gray and tell us the form or shape that something has. Rods can't tell the difference between colors, but they are super-sensitive, allowing us to see when it's very dark.

CONES : 

CONES Cones sense color and they need more light than rods to work well. Cones are most helpful in normal or bright light.

Slide 41: 

RETINAL IMAGE FORMATION The formation of image on the retina requires four basic process, all concerned with the focusing light rays. Refraction of light Accommodation of light Constriction of pupil Convergence of eyes.

REFRACTION OF THE LIGHT RAYS: When light rays pass through a transparent medium (such as air) pass in to second transparent substance with a different density (such as water) they bend at the surface of two medium. This bending is called refraction. As light rays pass from one medium to another medium that has different density will bend .the eyes has four medium up to retina these are anterior & posterior surface of cornea, the aqueous humor, lens, and vitreous body. The degree of refraction take place attach of the structure will be very much minute. When the object is 20 ft away from the eyes than the rays are parallel to each other and enter to the eyes. But when the distance of the object is more than 20 ft than the coming rays from object will be divergent and this process will automatically take place and known as accommodation : 

REFRACTION OF THE LIGHT RAYS: When light rays pass through a transparent medium (such as air) pass in to second transparent substance with a different density (such as water) they bend at the surface of two medium. This bending is called refraction. As light rays pass from one medium to another medium that has different density will bend .the eyes has four medium up to retina these are anterior & posterior surface of cornea, the aqueous humor, lens, and vitreous body. The degree of refraction take place attach of the structure will be very much minute. When the object is 20 ft away from the eyes than the rays are parallel to each other and enter to the eyes. But when the distance of the object is more than 20 ft than the coming rays from object will be divergent and this process will automatically take place and known as accommodation

Accommodation of the Lens: The Lens curved according to the distance of the object. When the object is too far from the eyes than the lens will curve less to bend the rays toward center of central fovea. This process is known as accommodation. In the nearby object the suspensory ligaments are release and decrease the tension on lens and vice versa. : 

Accommodation of the Lens: The Lens curved according to the distance of the object. When the object is too far from the eyes than the lens will curve less to bend the rays toward center of central fovea. This process is known as accommodation. In the nearby object the suspensory ligaments are release and decrease the tension on lens and vice versa.

CONSTRICTION OF PUPIL: The circular muscle fibers of the iris also have a role in the formation of clear retinal images. Part of the accommodation mechanism consists of the contraction of the circular muscles of the iris to constrict the pupil. In case of bright light our pupil will be constricted to decrease the passes of the rays of light and in case of dim light the pupil will be dilated. : 

CONSTRICTION OF PUPIL: The circular muscle fibers of the iris also have a role in the formation of clear retinal images. Part of the accommodation mechanism consists of the contraction of the circular muscles of the iris to constrict the pupil. In case of bright light our pupil will be constricted to decrease the passes of the rays of light and in case of dim light the pupil will be dilated.

CONVERGENCE: This is the process of the movement of the eye ball medially for the light rays for the object to hit the same point on the both retina. In case of human being both eyes focus on the one set of the objects –a characteristic called single binocular vision. This feature of our visual system allows the perception of the depth and an appreciation of the three dimensional nature of the objects. : 

CONVERGENCE: This is the process of the movement of the eye ball medially for the light rays for the object to hit the same point on the both retina. In case of human being both eyes focus on the one set of the objects –a characteristic called single binocular vision. This feature of our visual system allows the perception of the depth and an appreciation of the three dimensional nature of the objects.

OPTIC NERVE : 

OPTIC NERVE Contains over 1 million fibres Nerve fibres are myelinated only after leaving the eye Nasal fibres decussate at the optic chiasm Optic disc The entry of the optic nerve into the eye (1.5 x 1.5 mm) Corresponds to the blind spot of the visual field as does not contain any overlying photoreceptors

OPTIC TRACT : 

OPTIC TRACT Extends from the optic chiasm to the LGN Contains uncrossed and crossed fibres from the temporal and nasal retinas respectively About 30% of the fibres leave the visual pathway in the optic tract before the LGN, including those subserving the pupillary light reflex which pass to the pretectal nuclei

PHYSIOLOGY OF VISION Rods and cones were name for the different appearance of each’s outer segment- the distal end of the photoreceptor next to the pigment epithelium. The outer segment of the rods is cylindrical or rod shaped, whereas those of cones are tapered or cone shaped. The first in visual transduction is absorption of the light by a photopigment. The single type of photopigment in rod is rhodopsin. There different cone photopigment are present in the retina, one in each of three types of cones. : 

PHYSIOLOGY OF VISION Rods and cones were name for the different appearance of each’s outer segment- the distal end of the photoreceptor next to the pigment epithelium. The outer segment of the rods is cylindrical or rod shaped, whereas those of cones are tapered or cone shaped. The first in visual transduction is absorption of the light by a photopigment. The single type of photopigment in rod is rhodopsin. There different cone photopigment are present in the retina, one in each of three types of cones.

Photopigment respond to light in the following cyclical process:-- In darkness retinal has a bent shape, called cis-retinal which fits snugly into opsin portion of the photopigment. When cis-retinal absorbs a photon of light, it straightens out to a shape called isomerization and is the first step in the visual transduction. --In about a minute, trans-retinal completely separates from opsin. The final products look colorless, so this portion of the cycle is called bleaching of photopigment.--The cis-retinal then can bind to opsin, reforming a functional photopigment. This portion of the cycle resynthesis of a photopigment- is called regeneration. : 

Photopigment respond to light in the following cyclical process:-- In darkness retinal has a bent shape, called cis-retinal which fits snugly into opsin portion of the photopigment. When cis-retinal absorbs a photon of light, it straightens out to a shape called isomerization and is the first step in the visual transduction. --In about a minute, trans-retinal completely separates from opsin. The final products look colorless, so this portion of the cycle is called bleaching of photopigment.--The cis-retinal then can bind to opsin, reforming a functional photopigment. This portion of the cycle resynthesis of a photopigment- is called regeneration.

VISUAL PATHWAYS : 

VISUAL PATHWAYS

Slide 51: 

Thank You