THE EYE The eye is an amazing and important part of the body. Eyes allow us to see the shape, size, colour, and depth of the world around us. Of all the information that our brain receives from our five senses, an estimated 80 percent is received through the eyes. http://www.youtube.com/watch?v=15P8q35vNHw

THE HUMAN EYE CORNEA AQUEOUS HUMOR PUPIL VITREOUS HUMOR OPTIC NERVE IRIS BLIND SPOT RETINA SCLERA CILIARY BODY LENS Year 9 Biology

VITREOUS HUMOR HOME The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye. It is of rather similar composition to the cornea. 98-99% of the vitreous humor is water with salts, sugars, a network of collagen type fibers, and a wide array of proteins making up the other 2% in micro amounts. Vitreous Humor YOU ARE HERE

OPTIC NERVE HOME The optic nerve sends signals from the eye to the different parts of the brain where the signals are interpreted into images. The optic nerve consists of about 1,000,000 nerve threads. The optic nerves from both eyes are reconnected behind the eyes so that everything that is seen in the right field of vision is sent to the left cerebral hemisphere and vice versa. OPTIC NERVE YOU ARE HERE

IRIS HOME The iris is the part of the eye that regulates the amount of light that enters the eye. With strong light, the iris sphincter muscles will contract the pupil. In darkness, the iris opens the pupil using the dilator muscles. When focusing on near objects, the pupil decreases in diameter, but it will expand when focusing on distant objects. A person’s eye colour actually refers to the amount and type of pigments in his/her iris. IRIS YOU ARE HERE

SCLERA HOME The sclera is a membrane of tendon in the eye, also known as the white of the eye. The sclera works to protect the inner, more sensitive parts of the eye. It is about 0.03 of an inch thick. Directly on top of the sclera, the episclera is located. The episclera contains blood vessels that nourish the sclera with oxygen and nutrients. These vessels are visible on the surface of the white of the eye. SCLERA YOU ARE HERE

AQUEOUS HUMOR HOME The aqueous humour is the clear, watery fluid that fills the complex space in the front of the eye. The Aqueous Humor fills the front part of the eye, between the lens and the cornea. This fluid is produced at the back of the ciliary body, then seeps through the pupil. The aqueous fluid's main function is to supply the cornea and the lens with nutrients and oxygen, and to help maintain the round shape of the cornea. AQUEOUS HUMOR YOU ARE HERE

BLIND SPOT HOME The blind spot is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells of the retina, where the optic nerve passes through it. Since there are no cells to detect light, a part of the field of vision is not perceived. The brain fills in this blind spot with surrounding detail and with information from the opposite eye, thus the blind spot is not normally perceived. BLIND SPOT YOU ARE HERE

PUPIL HOME The pupil is the opening in the centre of the eye. Light enters through the pupil and goes through the lens, which focuses the image on the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. The size of the pupil is controlled by muscles. When more light is needed, the pupil is made larger. In brighter light, the pupil is made smaller. When pupils appear red in photos it is actually the colour of the retina that is reflected. YOU ARE HERE PUPIL

LENS HOME The eye's 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. The lens is a clear, flexible structure filled with crystalline protein and enables us to change the focus of our vision according to different distances, e.g. when we change focus from a TV screen across the living room to a newspaper in our hand. LENS YOU ARE HERE

RETINA HOME The Retina refers to the light sensitive tissue in the back of the eyeball. The retina absorbs light that ultimately is sent as visual signals to the brain via the optic nerve. The retina contains two kinds of light receptors, the cones and the rods. The cones, which are colour sensitive, are located in the centre of the retina and mainly absorb stronger light. The rods absorb softer light in black and white. RETINA YOU ARE HERE

CORNEA HOME The cornea is the transparent structure located in the front of the eye, protecting the iris, pupil, and the internal components of the eye. The cornea is supplied with oxygen and nutrients through tear-fluid and not through blood vessels, explaining why the cornea is so clear. The cornea plays the initial role in making an image on the retina by bending the light as it passes through. CORNEA YOU ARE HERE

CILIARY BODY HOME The ciliary body contains the ciliary muscle, the muscle that controls the vision accommodation reflex. The ciliary body also produces aqueous humor and is a point of attachment for the zonula threads that hold the lens. CILIARY BODY YOU ARE HERE LENS