The lids are essentially folds of tissue covering the front of the orbit and, when the eye is open, leaving an almond-shaped aperture. The lids have the additional function of preventing injuries from foreign bodies, through the operation of the blink reflex. This is achieved by the eyelids, which during waking hours sweep the secretions of the lacrimal apparatus and other glands over the surface at regular intervals and which during sleep cover the eyes and prevent evaporation. It is vitally important that the front surface of the eyeball, the cornea, remain moist. Is it true that we only use ten percent of our brain? Is the retina the lens at the front of the eye? Dissect these questions and learn more about human organs. The protrusion of the eyeballs-proptosis-in exophthalmic goitre is caused by the collection of fluid in the orbital fatty tissue.
The eyeball and its functional muscles are surrounded by a layer of orbital fat that acts much like a cushion, permitting a smooth rotation of the eyeball about a virtually fixed point, the centre of rotation. There are other fissures and canals transmitting nerves and blood vessels. These nerves may carry nonvisual sensory messages-e.g., pain-or they may be motor nerves controlling the muscles of the eye. The optic foramen, the opening through which the optic nerve runs back into the brain and the large ophthalmic artery enters the orbit, is at the nasal side of the apex the superior orbital fissure is a larger hole through which pass large veins and nerves. Thus, the floor of the orbit is made up of parts of the maxilla, zygomatic, and palatine bones, while the roof is made up of the orbital plate of the frontal bone and, behind this, by the lesser wing of the sphenoid.
The eye is protected from mechanical injury by being enclosed in a socket, or orbit, which is made up of portions of several of the bones of the skull to form a four-sided pyramid, the apex of which points back into the head. Anatomy of the visual apparatus Structures auxiliary to the eye The orbit Human eye, in humans, specialized sense organ capable of receiving visual images, which are then carried to the brain. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.