Explain full structure of an eye?

  • 0

Structure of the Eye

In general the eyes of all animals resemble simple cameras in that the lens of the eye forms an inverted image of objects in front of it and projects it onto the sensitive retina, which corresponds to the film in a camera.

The front of the eye mainly contains an elaborate array of structures which are mainly concerned with the refraction (ie bending) of light rays and bringing them into focus on the retina. The structure most directly involved is the lens.

The eye changes light rays into electrical signals then sends them to the brain, which interprets these electrical signals as visual images via the optic nerve.

Structure of human eye and refion of retina 

  • 3

Eye is like a camera. The external object is seen like the camera takes the picture of any object. Light enters the eye through a small hole called the pupil and is focused on the retina, which is like a camera film. Eye also has a focusing lens, which focuses images from different distances on the retina. The colored ring of the eye, the iris, controls the amount of light entering the eye. It closes when light is bright and opens when light is dim. A tough white sheet called sclera covers the outside of the eye. Front of this sheet (sclera) is transparent in order to allow the light to enter the eye, the cornea. Ciliary muscles in ciliary body control the focusing of lens automatically. Choroid forms the vascular layer of the eye supplying nutrition to the eye structures. Image formed on the retina is transmitted to brain by optic nerve. The image is finally perceived by brain. A jelly like substance called vitreous humor fill the space between lens and retina. The lens, iris and cornea are nourished by clear fluid, aqueous humor, formed by the ciliary body and fill the space between lens and cornea. This space is known as anterior chamber. The fluid flows from ciliary body to the pupil and is absorbed through the channels in the angle of anterior chamber. The delicate balance of aqueous production and absorption controls pressure within the eye.


  • 0

 Eye is like a camera. The external object is seen like the camera takes the picture of any object. Light enters the eye through a small hole called the pupil and is focused on the retina, which is like a camera film. Eye also has a focusing lens, which focuses images from different distances on the retina. The colored ring of the eye, the iris, controls the amount of light entering the eye. It closes when light is bright and opens when light is dim. A tough white sheet called sclera covers the outside of the eye. Front of this sheet (sclera) is transparent in order to allow the light to enter the eye, the cornea. Ciliary muscles in ciliary body control the focusing of lens automatically. Choroid forms the vascular layer of the eye supplying nutrition to the eye structures. Image formed on the retina is transmitted to brain by optic nerve. The image is finally perceived by brain. A jelly like substance called vitreous humor fill the space between lens and retina. The lens, iris and cornea are nourished by clear fluid, aqueous humor, formed by the ciliary body and fill the space between lens and cornea. This space is known as anterior chamber. The fluid flows from ciliary body to the pupil and is absorbed through the channels in the angle of anterior chamber. The delicate balance of aqueous production and absorption controls pressure within the eye.


  • 2

 Medical illustration showing the anatomy of the eyeCiliarybody - part of the eye, above the lens, that produces the aqueous humor.

  • 0

 Ciliary body - part of the eye, above the lens, that produces the aqueous humor.

Cornea - the outer, transparent structure at the front of the eye that covers the iris, pupil and anterior chamber; it is the eye's primary light-focusing structure.

Iris - the colored ring of tissue behind the cornea that regulates the amount of light entering the eye by adjusting the size of the pupil.

  • 2

Lens - the transparent structure suspended behind the iris that helps to focus light on the retina; it primarly provides a fine-tuning adjustment to the primary focusing structure of the eye, which is the cornea.

Optic nerve - the bundle of nerve fibers at the back of the eye that carry visual messages from the retina to the brain.

 Pupil - the adjustable opening at the center of the iris through which light enters the eye.

Retina - the light sensitive layer of tissue that lines the back of the eye.

  • 2

 Anterior chamber - the region of the eye between the cornea and the lens that contains aqueous humor.

  • 2

Drawings of the Eye

Drawing of the eye 

Cross section drawing of the eye - (side view) with major parts labeled.

Drawing of the eye 

Cross section drawing of the eye - (rear view).


Drawing of the eye in its socket 

Cut-away view of the eye in its socket showing the: bony socket, orbital muscles, eyelids and eyelashes.


Drawing of the eye 

The lacrimal system - (tear ducts) produce tears to clean, moisten and lubricate the eyes and then drains the excess fluid into the nose.

Drawing of the optic pathways 

Our Eyes and brain divide what we see into a right and left half. In the drawing above, light gray represents the left half; dark gray represents the right half. The eyes invert the image and the left side of what we see ends up in the right side of our brain and visa versa. This all works out because the right side of our brain controls the left side of our bodies and visa versa.

Anterior Chamber
The space between the cornea and iris filled with Aqueous Humor.
Aqueous Humor
A water like fluid, produced by the ciliary body, it fills the front of the eye between the lens and cornea and provides the cornea and lens with oxygen and nutrients. It drains back into the blood stream through the canals of schlemm.
Brain
The brain is where the electrical signals sent from our eyes are processed into vision. Damage to the brain can lead to vision loss if the visual cortex or optic pathways are damaged. The majority of nerve fibers in the optic tract connect to the LGN. Several nerve fibers leave the optic tract before the LGN to connect to sub cortical structures through out the brain. These parts of the brain regulate things like: eye and head movements, pupillary light reflex - (pupil size), and circadian rhythms - (light/dark cycle). Damage to these parts of the brain often leads to vision disorders too.
Canals of Schlemm
These canals are located around the perimeter of the iris. They allow aqueous fluid to drain back into the blood stream. The Trabecular Meshwork along with the Canals of Schlemm regulate the eyes internal pressure. In the eye disease called glaucoma, these canals become blocked leading to increased pressure. The increased pressure, from this condition, destroys the optic nerve.
Choroid
The choroid is a layer of blood vessels between the retina and sclera; it supplies blood to the retina. In the disease called Macular Degeneration, abnormal blood vessels grow into the space between the retina and choroid damaging the macula.
Ciliary Body
This is where the Aqueous Humor is produced.
Ciliary Muscle
The eye can bring the fine print in a phone book into focus, or focus in on the moon over ¼ million miles away. The ciliary muscle changes the shape of the lens - (this is called accommodation). It relaxes to flatten the lens for distance vision; for close work it contracts rounding out the lens. Everyone will develop an eye condition called presbyopia. As we age, the ciliary muscle and crystalline lens lose their elasticity. This is why most people need reading glasses by their 40's.
Conjunctiva
The conjunctiva is a thin, clear membrane covering the front of the eye and inner eyelids. Cells in this lining produce mucous that helps to lubricate the eye. This is the eyes first layer of protection against infection. Inflammation of this membrane is called conjunctivitis, or pink eye.
Cornea
The cornea is a clear, dome-shaped surface that covers the front of the eye. It is the first and most powerful lens in the eye's optical system. To keep it transparent the cornea contains no blood vessels. Tears that flow over it and aqueous humor in the chamber behind it keep it nourished. When you hear of eye banks and eye transplants, it is the cornea that is being replaced. The cornea can be damaged from: accidents, infections, and genetic defects.
Crystalline Lens
The eye's crystalline lens works like the adjustable lens in a camera. Positioned just behind the cornea; it is responsible for keeping images in focus on the retina. It is adjustable for distance and close work. A cataract is the lens clouding up. This happens to most people as they age. A few people are even born with cataracts. Modern surgery has all but eliminated cataracts as a cause of blindness in the developed world.
Eyeball
The eye is like a little video camera measuring about 1 inch or 2.5 cm. in diameter. If someone's eyeball is larger then this, they will be nearsighted (myopic); if it is smaller then this, they will be farsighted (hyperopic). Having two eyes gives us binocular vision - (depth perception). This is due to the fusing of both images in the visual cortex.
Eyelashes and Eyebrows
These specialized hairs protect the eyes from particles that may injure them. They form a screen to keep dust and insects out. Anything touching them triggers the eyelids to blink.
Eyelids
Our eyelids protect and lubricate our eyes. Small oil-producing glands line the inner edge of our eyelids. These oils mix with tears when we blink, keeping the eye moist and clean.
Eye Socket
The orbit or eye socket is a cone-shaped bony cavity that protects the eye. The socket is padded with fatty tissue that allows the eye to move easily.
Fovea - (small pit)
The fovea is an indentation in the center of the macula. Its diameter is only 1.5 mm or about 1/16 inch. This small part of our retina is responsible for our highest visual acuity. It is the center of our central vision.
Lacrimal Gland - (Tear Duct)
This gland continually releases tears and other protective fluids onto the surface of the eye. It lubricates and keeps the cornea from becoming dehydrated.
Lacrimal Sac
The lacrimal sac is a tiny pump that drains tears and other debris from the eye. The fluids flow down the nasolacrimal duct into the nose where they help keep the nasal linings moist. This is why your nose runs when you cry.
Lateral Geniculate Nucleus - (LGN)
This part of the brain acts as a relay station; it decodes visual information from the optic tract before sending it to the visual cortex for final processing.
Lens Sack or Capsule
During modern cataract surgery the outer membrane of the lens is left in place. The artificial intraocular lens is placed in this sack.
Iris
This is the colored part of the eye: brown, green, blue, etc. It is a ring of muscle fibers located behind the cornea and in front of the lens. It contracts and expands, opening and closing the pupil, in response to the brightness of surrounding light. Just as the aperture in a camera protects the film from over exposure, the iris of the eye helps protect the sensitive retina.
Macula - (yellow spot)
This part of the retina is the most sensitive. Its diameter is only 7 mm or about 1/4 inch. It is responsible for our central, or reading vision. This part of the retina gives us 20/20 vision. Without the macula, you would be blind - Legally Blind that is. People with eye diseases like Macular Degeneration have vision from 20/200 to 20/800.
Optic Chiasm
This is the first part of the brain to receive visual input. Each eye takes a slightly different picture of the world. At the optic chiasm each picture is divided in half. The outer left and right halves continue back toward the visual cortex. The inner left and right halves cross over to the other side of the brain then continue back toward the visual cortex. See Drawing of optic pathways.
Optic Disk
The optic disk is the spot on the retina where the optic nerve leaves the eye. There are no sensory cells here, creating a blind spot. Each eye covers for the blind spot of the other eye and the brain fills in the missing information.
Optic Nerve
Each optic nerve has about 1.2 million nerve fibers. This is the cable connecting the eye to the brain.
Optic Tract
The nerves that connect the optic chiasm to the LGN are called the optic tract. If one of these tracts is damaged, vision will be lost in one side of each eye.
Orbital Muscles
Six muscles are in charge of eye movement. Four of these move the eye up, down, left and right. The other two control the twisting motion of the eye when we tilt our head. Defects in these muscles and the nerves that control them lead to conditions like Nystagmus and Amblyopia (Lazy Eye).
Photoreceptor Cells
The retina is composed of two types of photoreceptor cells. When light falls on one of these cells, it causes a chemical reaction that sends an electrical signal to the brain.
Cone cells give us our detailed color daytime vision. There are 6 million of them in each human eye. Most of them are located in the central retina - macula fovea area. There are three types of cone cells: one sensitive to red light, another to green light, and the third sensitive to blue light.
Rod cells are about 500 times more sensitive to light then cone cells; they give us our dim light or night vision. They are also more sensitive to motion then cone cells. There are 120 million rod cells in the human eye. Most rod cells are located in our peripheral or side vision.
Posterior Chamber
The space between the iris and the front of the lens filled with Aqueous Humor.
Pupil
The pupil is the hole in the center of the iris that light passes through. The iris muscles control its size.
Retina
The retina is the film of the eye. It converts light rays into electrical signals and sends them to the brain through the optic nerve. The sides of the retina are responsible for our peripheral vision. The center area, called the macula, is used for our fine central vision and color vision. The retina is where most the problems leading to vision loss Occur. Three of the leading causes of blindness, from retina damage, are Retinitis Pigmentosa, Macular Degeneration and Diabetic Retinopathy.
Retinal Blood Vessels
A doctor can see the blood vessels that supply the retina when he looks into your eyes. These vessels are in the choroid just beneath the retina. Abnormal blood vessel growth and leaking blood vessels are the cause of vision loss in eye conditions like, Diabetic Retinopathy, ROP, and Macular Degeneration.
Retinal Pigment Epithelium - (RPE)
The RPE is a layer of cells between the retina and choroid. The inside of a camera is panted black to absorb scattered and reflected light. The black pigment known as melanin in the RPE dose the same job for the eye. The RPE gets rid of waste products produced by the photoreceptor cells. As we age, the RPE can sometimes lose its ability to process this waste. Deposits of this waste, called drusen, can distort and damage the retina leading to an eye condition called dry macular degeneration.
Sclera
The sclera is the white, tough wall of the eye. It along with internal fluid pressure keeps the eyes shape and protects its delicate internal parts.
Uvea
The uvea is the middle Vascular layer of the eye. It is made up of three parts: the iris, ciliary body and chorid. Uveitis is the inflammation (or swelling) of these parts of the eye.
Visual Axis
The Visual Axis is an imaginary line drawn through the center of the pupil to the center of the Fovea. The orbital muscles keep the visual axis of both eyes aligned on the center of what you are looking at (fixation point). An eye condition called Strabismus - (misaligned eyes) results when the orbital muscles fail to keep the eyes in alignment. Any damage to eye structures along this axis leads to severe vision loss.
Visual Cortex
The part of the brain that processes and combines visual information from both eyes and converts it into sight. Damage to the visual cortex results in a condition called cortical blindness.
Visual Fields
The retina of each eye has two sections the nasal retina - (nose side) and temporal retina - (ear side). For example: with your right eye, you see the right half of the world with your nasal retina; you see the left half of the world with your temporal retina. The picture your eye takes is flipped left for right and upside down; its up to the brain to sort things out.
Vitreous Cavity
The space between the lens and retina filled with the gel like Vitreous Humor.
Vitreous Humor
The vitreous humor is a jelly like liquid that fills most of the eye (from the lens back). As we age it changes from a gel to a liquid and gradually shrinks separating from the retina. This is when people start seeing floaters, dark specs in their vision. This is a normal sign of aging, but in a few cases the retina can become detached as the vitreous separates.
Zonules
Zonules are hundreds of string like fibers that hold the lens suspended in position and enable it to change shape for near or distant vision.
  • 1
What are you looking for?