WHAT IS THE STRUCTURE OF THE EYE?

The eyes are complex sensory organs. About 85% of the total sensory input to our brains originates from our sense of sight, while the other 15% comes from the other four senses of hearing, smell, touch, and taste. The eyes are designed to optimize vision under conditions of varying light. Their location, on the outside of the face, makes them susceptible to trauma, environmental chemicals and particles, and infectious agents. The eyelids and the position of the eye within the bony orbital cavity are the major protective mechanism for the eye.

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The eye itself has the shape of a sphere measuring about 1 inch in diameter. It consists of a clear, transparent dome at the front (the cornea) that is surrounded by the white of the eyeball (the sclera). The iris of the eye is the circular, colored portion within the eye, and behind the cornea, and the pupil is the central opening within the iris. Behind the iris and pupil is the eye's lens. The space behind the back of the cornea and the front of the lens is called the anterior chamber and is filled with the aqueous fluid. Behind the lens is a large space that is filled by the transparent vitreous gel. The inside of the back of the eye is lined by the retina, the thin, light-sensitive tissue that changes light images to electrical signals via a chemical reaction. These electrical signals generated by the retina are sent to our brain through the optic nerve. Our brain interprets what our eyes see.
The inner sides of the eyelids, which touch the front surface of surface of the eye, are covered by a thin membrane (the palpebral conjunctiva) that produces mucus to lubricate the eye. This thin membrane folds back on itself and covers the visible sclera of the eyeball. (This continuation of the palpebral conjunctiva is called the bulbar conjunctiva.) Natural oil for the tears is produced by tiny glands located at the edges of the eyelids, providing additional lubrication for the eye. The main component of tears are formed by the lacrimal gland located under the upper lid at the outer corner of the eye. The tears are composed of a combination of the substances produced by the lacrimal gland, the oil glands, and the mucus glands. Tears flow toward the nasal side of the eye and drain into the lacrimal sac in the area between the eye and the side of the nose.