sight / sīt/ • n. 1. the faculty or power of seeing: Joseph lost his sight as a baby| [as adj.] a sight test. ∎  the action or fact of seeing someone or something: I've always been scared of the sight of blood. ∎  the area or distance within which someone can see or something can be seen: he now refused to let Rose out of his sight. ∎ dated a person's view or consideration: we are all equal in the sight of God.2. a thing that one sees or that can be seen: John was a familiar sight in the bar for many years he was getting used to seeing unpleasant sights. ∎  (sights) places of interest to tourists and visitors in a city, town, or other place: she offered to show me the sights. ∎  (a sight) inf. a person or thing having a ridiculous, repulsive, or disheveled appearance: “I must look a frightful sight,” she said.3. (usu. sights) a device on a gun or optical instrument used for assisting a person's precise aim or observation.• v. 1. [tr.] manage to see or observe (someone or something); catch an initial glimpse of: tell me when you sight London Bridge| [as n.] (sighting) the unseasonal sighting of a cuckoo. 2. [intr.] take aim by looking through the sights of a gun: she sighted down the barrel. ∎  take a detailed visual measurement of something with or as with a sight. ∎  [tr.] adjust the sight of (a firearm or optical instrument).PHRASES: at first sight on first seeing or meeting someone: it was love at first sight. ∎  after an initial impression (which is then found to be different from what is actually the case): the debate is more complex than it seems at first sight.catch (or get a) sight of glimpse for a moment; suddenly notice: when she caught sight of him she smiled.in sight visible: no other vehicle was in sight. ∎  near at hand; close to being achieved or realized: the minister insisted that agreement was in sight.in (or within) sight of so as to see or be seen from: I climbed the hill and came in sight of the house. ∎  within reach of; close to attaining: he was safe for the moment and in sight of victory.in (or within) one's sights visible, esp. through the sights of one's gun. ∎  within the scope of one's ambitions or expectations: he had the prize firmly in his sights.lose sight of be no longer able to see. ∎  fail to consider, be aware of, or remember: we should not lose sight of the fact that the issues involved are moral ones.not a pretty sight inf. not a pleasant spectacle or situation.on (or at) sight as soon as someone or something has been seen: in Africa, paramilitary game wardens shoot poachers on sight.out of sight1. not visible: she saw them off, waving until the car was out of sight.2. (also out·a·sight) [often as interj.] inf. extremely good; excellent: [as adj.] these stereophones are an out-of-sight choice. (get) out of my sight! go away at once!raise (or lower) one's sights become more (or less) ambitious; increase (or lower) one's expectations.set one's sights on have as an ambition; hope strongly to achieve or reach: Katherine set her sights on college.a sight —— inf. or dial. used to indicate that something is so described to a considerable extent: the old lady is a sight cleverer than Sarah he's a sight too full of himself.a sight for sore eyes inf. a person or thing that one is extremely pleased or relieved to see.a sight to behold a person or thing that is particularly impressive or worth seeing.DERIVATIVES: sight·er n.

Sight

Sight, or vision, is the sense that enables an organism to detect light. It serves mainly to allow an organism to see and move about its environment. As one of the five senses, the ability to see is critically important to the independence of the individual. Sight affects all aspects of an organism's survival.

Not all organisms that have receptors for light can actually see. Some of the simplest light-sensitive organisms (like certain cnidarians such as the jellyfish, or flatworms) have eyespots that detect light but cannot see objects. The best their light-sensitive cells can do is determine the direction and intensity of a light. Being able to form an effective image requires a much more complex organ. This organ is called an eye, usually with a lens.

Besides having a lens, which concentrates light for the photoreceptors, a complete system of sight needs a brain that can interpret the light images it receives. In the animal world, there are basically two types of eyes. These include the "camera" eye of vertebrates (animals with a backbone), and the compound eye of arthropods (a phylum that includes insects).

SIGHT IN HUMANS

As vertebrates, humans naturally have the "camera" eye common to higher animals. It is described as a camera because it has an adjustable lens. The human visual system consists of two eyes located in the front of the head, thus allowing both to be focused on the same object. Called "binocular vision," this creates an overlap of information that allows people to judge distance and depth accurately.

Sight begins when rays of light hit an object and bounce back, entering the eye through the cornea. This front part of the eye is a thin, transparent membrane. This membrane refracts, or bends, the incoming light through a watery fluid called "aqueous humor" and then through the lens. The elliptical, or egg-shaped, lens has muscles on either side of it that allow it to adjust its shape by expanding or contracting (according to whether the object is close or distant). The lens serves to focus this incoming light onto the retina at the back of the eye.

Once light reaches the retina, it is absorbed by its more than 100,000,000 photoreceptor cells. These are called cones and rods. Rods are very sensitive to light and enable people to see even in dim light. Cones need more light to work, but they allow people to see colors. These specialized light receptor cells generate electrical impulses that stimulate the optic nerve. The optic nerve carries the impulses to the visual cortex at the back of the brain. At this point, the brain decodes and integrates all this information and produces an image, or a picture.

SIGHT IN ANIMALS

The vertebrate eye is made so it will form sharp images. However, not all vertebrates see the same thing when they look at an object. Each animal species sees in a way that best helps it to survive. For example, animals that hunt at night, like cats or owls, have many more rods than cones, making them capable of night vision. They cannot, however, distinguish color. Such night hunters also have a type of pigment in their eyes that reflects any available light into their photoreceptor cells, explaining why a cat's eyes shine in the dark. Birds and primates who hunt by day need sharp vision. Birds that soar high above their prey have phenomenally sharp sight.

Unlike vertebrates whose eye has a single lens, the compound eye of arthropods (crustaceans and insects) is made up of thousands of separate, little lenses. Each lens is covered by its own cornea. A dragonfly has about 28,000. Each one of these receives light from a narrow field of view. The animal's brain puts these all together to form a single image. This type of vision is not geared to giving a clear, sharp image. Instead, it detects the slightest movement in a very wide field of view. Some insects can see an area as wide as 180 degrees without moving their eyes or their head.

THE BRAIN IS ESSENTIAL TO SIGHT

Like the other four senses that necessarily involve the brain, vision would not work if the brain was unable to tell a person what his or her eyes are seeing. If the part of the brain that processes visual information is damaged, a person may not be able to recognize a visual object despite having a pair of healthy eyes. Real blindness can result from an injury or disease of the eyeball, the optic nerve, or the nerve connections to the brain.

EYE DISORDERS

A common eye condition that is correctable is nearsightedness, or myopia. In this case, the lens bends the light too much so that it focuses before it reaches the retina. Another condition is farsightedness, which is also correctable, and happens when the lens does not bend the light enough. As a result, the light reaches the retina before it is focused. Astigmatism results in blurred vision caused by a misshapen cornea. Glasses, contact lenses, and laser surgery can help these problems.

Cataracts, or a clouding of the lens, common among elderly people, and can be corrected by surgery. Glaucoma, which is a type of high blood pressure in the eye, can cause blindness, although it is controllable. It is not true that one's vision can be damaged by reading in poor light or by sitting too close to a television, but these habits can tire the eyes and make them sore.

[See alsoOrgan; Sense Organ ]

sight thing seen, spectacle OE.; eyesight, vision; show, display, (hence) lot XIV; device to guide the eye XVI. OE. sihō, more usu. ġesihō, ġesiht (see Y-), corr. to OS. gisiht, MLG. sichte, MDu. sicht (Du. zicht), OHG., MHG. (ge)sicht (G. gesicht) sight, vision, face, appearance; WGmc. deriv. of *se(w)- SEE1; see -T1.
Hence sightly †visible; pleasing to the sight. XVI. See -LY1; now more freq. in UNSIGHTLY.

sight out of sight, out of mind one soon forgets people or things that are no longer visible or present. Proverbial; current in this form since the mid 16th century.

See also in vain the net is spread in the sight of the bird, second sight.

sight Sense by which form, colour, size, movement, and distance of objects are perceived. Essentially, it is the detection of light by the eye, enabling the formation of visual images.