Gives us binocular vision (depth perception- Fusion of both inages in the visual cortex)
A cone shaped body cavity that protects the eye. Padded with fatty tissue that allows the eye to move easily.
Six miscles that 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
Protect the eyes from particles that may injure the,. Keep dust and insects out. Anything touching them triggers the eyelids to blink.
Eyelashes and Eyebrows
Protect and lubricate our eyes. Small oil-producing glands line the inner edge of these. These oils mix with aqueous part, keeping the eye moist, protected, and clean.
Releases tears onto the surface of they eye. It lubricates and keeps the cornea from being dehydrated.
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. We literally swollow our tears.
A thin, clear membrane covering the front of the eye and inner eyelids. Has cells that produce mucous to help eye lubriction. Is a protection against infection. Inflammation of this membrane is called conjunctivitis, or pink eye
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. No blood vessels. Tears and aqueous humor keep it nourished. Tears also keep it lubricated.
The colored part of the eye. 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. Helps protect the sensitive retina. Has a sympahetic response which dilates the pupil through contractions of the radial fibers. A parasympathetic response constricts the pupil through contractions of circular fibers of the oculomotor nerve.
The space between the cornea and iris filled with Aqueous Humor.
A water like fluid, produced by the ciliary body and is in the anterior chamber. It provides the cornea and lens with oxygen and nutrients. It drains back into the blood stream through the canals of Schlemm.
The space between the iris and the front of the lens filled with Aqueous Humor.
The hole in the center of the iris that light passes through. The iris muscles control its size. Pupillary construction is a reflex that protects the retina from intense light or permits more accurate vision.
The white, tough wall of the eye. It along with the internal fluid pressure keeps the eyes shape and protects its delicate internal parts.
The space between the lens and retina filled with the gel like Vitreous Humor.
A jelly like liquid that fills most of he 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. This is a normal sign of aging, but in a few cases the retina can become detached as the vitreous separates.
This is where the Aqueous Humor is produced.
Canals located around the perimeter of the iris. They allow aqueous fluid to frain back into the blood stream, The Trabeular Meshwork along with these regulate the eye's internal pressure. In certain types of glaucoma, these canals become blocked leading to increased pressure. The increased pressure destroys the optic nerve.
Canals of Schlemm
This changes the shape of the lens (known as accomodation). It relaxes to flatten the lens for distance vision; for close work it contracts. Everywhere will develop an eye condition called presbyopia. As we age, this muscle and crystalline lens lose their elasticity, causeing the need for eyeglasses for near.
It works like the adjustable lens in a camera. It adjusts its shape for clear distance and near vision according to the distance and size of the object. If it clouds it is a cataract. Unfortunatly, in developing countries, cataracts are still a cause of blindness.
During modern cataract surgery the outer membrane of the lens is left in place. The artificial intraocular lens is placed in this sack.
Hundreds of string like fibers that hold the lens suspended in position and enable it to change shape for near or distanc vision.
The film of the eye. It converts light rays into electrical signals and sends them to the brain through the optic nerve, The sides are responsible for peripheral vision. The center area, called the macula, is used for our fine central vision and color vision, This is where most of the problems leading to vision loss occur. Three of the leading causes of blindness due to this are Retinitis Pigmentosa, Macular Degeneration and Diabetic Retinopathy.
The retina is composed of two types of these cells. When light falls on one of these cells, it causes a chemical reaction that sends an electrical signal to the brain.
Give us our detailed color daytime vision, There are 6 million of them in each human eye. Most of them are located are located in the central retina- mocula fovea area. There are three types of these cells. One sensitive to red light, another to green light, and the third sensitive to blue light.
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 of these cells in the human eye. Most are located in our peripheral or side vision.
A doctor can see the blood vessels that supply the retina when he looks into your eyes. These vessels are in the choriod 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.
Retina Blood Vessels
A layer of cells between the retina and the choriod. The inside of a camera is panted black to absorb scattered and reflected light. The black pigment known as melanin in the RPE foes the same job for the eye. This gets rid of waste products produced by the photorecepter cells. As we age, this can sometimes loses 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.
Retina Pigmented Epithelium
Is an indentation in the center of the macula. Its diameter is only 1.5 mm or about 1/16 of an inch. Is responsible for the higest visual acuity. It is the center of our central vision.
This part of the retina is most sensitive. Its diameter is only 7 mm, or about 1/4 inch. Is responsible for our central, or reading vision. This part of the retina gives us 20/20 vision. without this, you would be blind, legally blind that is. People with diseases like Macular Degeneration have vision from 20/200 to 20/800.
Macula- (yellow spot)
Layer of blood vessels between the retina and sclera and supply blood to the retina. In the disease called Exudative Macular Degeneration, abnormal blood vessels grow into the space between the retina and choriod damaging the macula.
The middle vascular layer of the eye. It is made up of three parts: The iris, the ciliary body, and the choriod. Uveitis is the inflammation (or swelling) of these parts of the eye.
Is the cable connecting the eye to the brain. Each has 1.2 million nerve fibers.
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 mission information.
The nerves that connect the optic chiasm to the LGN. If one of these tracts is damaged, vision will be lost in one side of each eye.
The first part of the brain to receive visual input. Each eye takes a slightly different picture of the world. Here, 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.
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 lead to severe vision loss.
The retina of each eye has two sections, the nasal retina (nose side) and the temporal retina (ear side). For example: with your right eye- you see the right half of he workd with your nasal retina. You see the left half of the workd 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.
Optic nerve takes signals into the visual cortex and processed as vision. Damage to the visual cortes or visual pathway can lead to vision loss. 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, pupilary light reflex, and circadian rhythms. Damage to these parts of the brain often lead to vision disorders too.
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.
Lateral Geniculate Nucleus (LGN)
The orbit houses and protects the eyeball which is formed by the: