1. A ground or molded piece of glass, plastic, or other transparent material with opposite surfaces either or both of which are curved, by means of which light rays are refracted so that they converge or diverge to form an image.
2. A combination of two or more such pieces, sometimes with other optical devices such as prisms, used to form an image for viewing or photographing. Also called "compound lens".
3. A device that causes radiation other than light to converge or diverge by an action analogous to that of an optical lens.
4. A transparent, biconvex body of the eye between the iris and the vitreous humor that focuses light rays entering through the pupil of the eye to form an image on the retina.
5. The transparent part of the eye, behind the pupil.

The lens was named after the lentil bean because it resembled it in shape and size

A lens is the transparent structure inside the eye that focuses light rays onto the retina which is the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain.

In addition to the lens, the eye has a number of other components including the cornea, iris, pupil, retina, macula, optic nerve, and vitreous.

• The cornea is the clear front window of the eye that transmits and focuses light into the eye.
• The iris is the colored part of the eye that helps regulate the amount of light that enters the eye.
• The pupil is the dark aperture in the iris that determines how much light is let into the eye.
• The retina is the nerve layer that lines the back of the eye, senses light and creates impulses that travel through the optic nerve to the brain.
• The macula is a small area in the retina that contains special light-sensitive cells and allows us to see fine details clearly.
• The optic nerve is the nerve that connects the eye to the brain and carries the impulses formed by the retina to the visual cortex of the brain.
• The vitreous humor is a clear, jelly-like substance that fills the middle of the eye.

In optics, a lens often used in eyeglasses, designed to absorb certain wavelengths in order to inhibit their passage through the lens.

A compound lens made of two or more lenses having different indices of refraction, so correlated as to minimize chromatic aberration.

In ultrasonography, a lens used to focus or to diverge a sound beam which may be simulated by the electronic manipulations of signals: Acoustic lenses are made of a material by which the speed of sound differs from that in the surrounding medium and the acoustic lenses may be solid, liquid, or gas.

A lens that produces different magnifications along lines in different directions in the image plane.

A lens used in cases of presbyopia, in which one portion is suited for distant vision, the other for reading and close work in general: The reading addition of a bifocal lens may be cemented to the lens, fused to the front surface, or ground into a one-piece form.

Other bifocal lenses are the flat-top Franklin type, or blended invisibly.

An optic system of two or more lenses.

A lens is one with one concave and one convex face.

1. A device, consisting of four electrodes arranged in alternating polarity, which focuses a beam of charged particles.
2. An instrument for focusing beams of charged particles which has four electrodes with alternately positive and negative polarity; used in electron microscopes and particle accelerators.
3. An apparatus that uses four electrodes set in an alternating positive-negative polarity series to focus the beams of charged particles employed in electron microscopes and particle accelerators.

A system composed of several waveguides that are symmetrically arranged with a related excitation medium in order to become excited with equal amplitudes and phases to in order to provide a net gain in energy.

1. An electron lens in which electron beams are focused by an electromagnetic field.
2. An electromagnet designed to produce a suitably shaped magnetic field for the focusing and deflection of electrons or other charged particles in electron optical instruments.
3. An electron lens consisting of a homogeneous axial electric field and a magnetic field, used in high-quality image tubes for high Modulation Transfer Function (MTF, a measurement of monitor sharpness) and small geometrical distortion requirements.

An electrostatic apparatus which uses an electric potential barrier to allow the transmission of electrons at or above a set level of energy while stopping the passage of those electrons below that set level of energy.

1. Electronic equipment that uses a magnetic or electric field in order to focus a beam of electrons.
2. An electric or magnetic field, or a combination of such, that acts upon an electron beam in a manner similar to that in which an optical lens acts upon a light beam.
3. A tool which uses an electromagnetic field to refract an electron beam in a manner similar to the refraction of light by an optical lens.
4. A system of deflecting electrodes or coils designed to produce an electric field which influences a beam of electrons in the same manner that a lens affects a light beam.
5. An electric field used to focus a stream of electrons on a target.

1. A collection of plates or cylinders with electrostatic properties which cause an electron beam to refract in a manner similar to the refraction of light by an optical lens.
2. An arrangement of electrostatic fields that acts upon beams of charged particles similar to the way a glass lens acts on light beams.
3. An electrostatic field with axial (a line of symmetry of an optical system, such as the line passing through the center of a lens) or a plane symmetry which acts upon beams of charged particles of uniform velocity; such as, glass lenses act on light beams.

The action of electrostatic fields with axial symmetry is similar to that of spherical glass lenses, whereas the action of electrostatic fields with plane symmetry is like that of cylindrical glass lenses.

A tool for controlling beams of electrons or other charged particles, consisting of eight electrodes arranged in a circular pattern with alternating polarities.

It is commonly used to correct a condition that causes a blurring and loss of clearness in the images produced by lenses or mirrors of quadrupole lens systems.

A tool for focusing beams of electrons or other charged particles, consisting of four electrodes arranged in a circular pattern with alternating polarities.

An artificial lens made of plastic, silicone, acrylic, or other material that is implanted inside the eye during cataract surgery.

Removal of the cataract and insertion of the intraocular lens typically takes about an hour and does not require hospitalization.

The intraocular lens is implanted within the capsule, which provides permanent support for the lens. It is never handled or adjusted, as a contact lens might be.

The highly modified epithelial cells that form the main mass of the lens of the eye.

The ectodermal anlage of the lens of the eye; its formation is induced by the presence of the underlying optic vesicle.

The starlike arrangement of the lens sutures, having three to nine rays, produced by the growth of the lens fibers.

Elements in a single viewing aperture in which there are curvature centers on both of its surfaces: The meniscus lenses may lie on the same side of the lens so that both arched areas are concave or both are convex or the meniscus lens have a spherical concave curve on one side and a spherical convex curve on the other side.

1. A lens for near and distant vision in which the reading portion is a continuously variable curve.
2. A lens whose power increases continuously and regularly in a downward direction, avoiding the discontinuity of bifocal and trifocal lenses.

A spectacle (reading glass) lens corrected for distortion and curvature of the periphery.

Intraocular inflammation: Phacoanaphylactic uveitis can occur after an extracapsular cataract extraction, which is believed to be an immune reaction to the patient's liberated lenticular proteins.

A light-sensitive spectacle lens that reduces light transmission in sunlight and increases transmission in reduced light.

1. Flat on one side and concave on the other side, usually referring to a lens of that shape.
2. Pertaining to or noting a lens that is plane on one side and concave on the other side.

1. A lens having one surface that is a part of a sphere, while the other is a part of a cylinder.
2. A lens ghat has one spherical surface and one cylindrical surface.

A lens having one surface that is a part of a sphere, while the other is a part of a torus (a doughnut-shaped geometric surface generated by rotating a circle around a line in the same plane as the circle but not intersecting it).

A lens used to test one's vision.

A lens with three parts of different refracting powers: the upper for distant sights, the middle for intermediate views, and the lower for near visions.