aberration /ab·er·ra·tion/ (-shun)
chromatic aberration
1. deviation from the normal or usual.
2. unequal refraction or focalization of a lens.
3. in cardiology, aberrant conduction.
chromatic aberration unequal refraction of light rays of different wavelength, producing a blurred image with fringes of color.
chromosome aberration an irregularity in the number or structure of chromosomes, usually a gain, loss, exchange, or alteration of sequence of genetic material, which often alters embryonic development.
intraventricular aberration aberrant conduction within the ventricles of an impulse generated in the supraventricular region, excluding abnormalities due to fixed organic defects in conduction.
mental aberration any pathological deviation from normal mental activity, usually limited to a circumscribed deviation in an otherwise adapted individual.
| chromatic aberration n. Color distortion in an image produced by a lens, caused by the inability of the lens to bring the various colors of light to focus at a single point. Also called chromatism. |
aberration
1. deviation from the normal or usual.
2. imperfect refraction or focalization of a lens, e.g. the lens of the eye.
chromatic aberration
inability to focus a pencil of light through a lens because of the different refrangibilities of the colored constituents of white light. In an optical instrument such as a microscope this represents an error in the lens system.
spherical aberration
that due to failure of a spherical mirror to focus all the light rays at one point; a fault of construction in an optical instrument.
adaptation
1. Process by which a sensory organ (e.g. the eye) adjusts to its environment (e.g. to luminance, colour or contact lens wear).
2. The reduction in sensitivity to continuous sensory stimulation. The neurophysiological correlate corresponds to a decrease in the frequency of action potentials fired by a neuron, despite a stimulus of constant magnitude. Visual adaptation is prevented from occurring by the continuous involuntary movements of the eyes. See fixation movements; action potential; stabilized retinal image.
chromatic adaptation Apparent changes in hue and saturation after prolonged exposure to a field of a specific colour.
dark adaptation Adjustment of the eye (particularly regeneration of visual pigments and dilatation of the pupil), such that, after observation in the dark, the sensitivity to light is greatly increased, i.e. the threshold response to light is decreased. This is a much slower process than light adaptation. Older people usually take longer to adapt to darkness and only reach a higher threshold than young people. See adaptometer; hemeralopia; visual pigment; duplicity theory.
light adaptation Adjustment of the eye (particularly bleaching of visual pigments and constriction of the pupil), such that, after observation of a bright field, the sensitivity to light is diminished, i.e. the threshold of luminance is increased. See duplicity theory.
prism adaptation See vergence adaptation.
sensory adaptation Mechanism by which the visual system adjusts to avoid confusion and diplopia of the perceptual impression due to an abnormal motor condition (e.g. strabismus).
vergence adaptation A process by which the eyes return to their condition of habitual heterophoria or orthophoria after a heterophoria has been induced by prisms (prism adaptation) in front of one or both eyes (as, for example, when lens centration does not coincide with the interpupillary distance), or by spherical lenses, or due to changes in the orbital contents with increasing age. This adaptation process may be related to the phenomenon of orthophorization. People who have symptomatic binocular vision anomalies do not, or only partially, show vergence adaptation to prisms. Vergence adaptation decreases with increasing age.
chromatic adaptation Apparent changes in hue and saturation after prolonged exposure to a field of a specific colour.
dark adaptation Adjustment of the eye (particularly regeneration of visual pigments and dilatation of the pupil), such that, after observation in the dark, the sensitivity to light is greatly increased, i.e. the threshold response to light is decreased. This is a much slower process than light adaptation. Older people usually take longer to adapt to darkness and only reach a higher threshold than young people. See adaptometer; hemeralopia; visual pigment; duplicity theory.
light adaptation Adjustment of the eye (particularly bleaching of visual pigments and constriction of the pupil), such that, after observation of a bright field, the sensitivity to light is diminished, i.e. the threshold of luminance is increased. See duplicity theory.
prism adaptation See vergence adaptation.
sensory adaptation Mechanism by which the visual system adjusts to avoid confusion and diplopia of the perceptual impression due to an abnormal motor condition (e.g. strabismus).
vergence adaptation A process by which the eyes return to their condition of habitual heterophoria or orthophoria after a heterophoria has been induced by prisms (prism adaptation) in front of one or both eyes (as, for example, when lens centration does not coincide with the interpupillary distance), or by spherical lenses, or due to changes in the orbital contents with increasing age. This adaptation process may be related to the phenomenon of orthophorization. People who have symptomatic binocular vision anomalies do not, or only partially, show vergence adaptation to prisms. Vergence adaptation decreases with increasing age.
dispersion
Phenomenon of the change in velocity of propagation of radiation in a medium, as a function of its frequency, which causes a separation of the monochromatic components of a complex radiation. All optical media cause dispersion by virtue of their variation of refractive index with wavelengths. Dispersion is specified by the difference in the refractive index of the medium for two wavelengths. The difference between the blue F (486.1 nm) and the red C (656.3 nm) spectral lines is called the mean dispersion, i.e. nF − nC. Dispersion is usually represented by its dispersive power ω or relative dispersion which is equal to the mean dispersion divided by the excess refractive index of the helium d (587.6 nm) spectral line (nd − 1), often called the refractivity of the material,
ω = nF − nC/nd − 1
The reciprocal of the dispersive power is called the Abbé's number or constringence (Fig. D8). See aberration longitudinal chromatic; achromatic axis; Fraunhoffer's lines; achromatic prism.)
Fig. D8 Dispersion of a white beam of light by a prism
parallax
Apparent displacement of an object viewed from two different points not on a straight line with the object.
binocular parallax The difference in angle subtended at each eye by an object that is viewed first with one eye and then with the other.
chromatic parallax Apparent lateral displacement of two monochromatic sources (e.g. a blue object and a red object) when observed through a disc with a pinhole placed near the edge of the pupil. When the pupil is centred on the achromatic axis (in some people the pinhole may have to be placed away from the centre of the pupil), the two images appear superimposed. The relative displacement of the two images becomes reversed when the pinhole is on the other side of that axis. This phenomenon is attributed to the chromatic aberration of the eye. See chromostereopsis; longitudinal chromatic aberration.
monocular parallax The apparent change in the relative position of an object when the eye is moved from one position to another.
motion parallax Apparent difference in the direction of movement or speed produced when the subject moves relative to his environment (Fig. P2). Example: when viewing the landscape through the window of a moving train near objects appear to move much more quickly than distant objects. See depth perception; stereopsis.
relative binocular parallax See stereoscopic visual acuity.
binocular parallax The difference in angle subtended at each eye by an object that is viewed first with one eye and then with the other.
chromatic parallax Apparent lateral displacement of two monochromatic sources (e.g. a blue object and a red object) when observed through a disc with a pinhole placed near the edge of the pupil. When the pupil is centred on the achromatic axis (in some people the pinhole may have to be placed away from the centre of the pupil), the two images appear superimposed. The relative displacement of the two images becomes reversed when the pinhole is on the other side of that axis. This phenomenon is attributed to the chromatic aberration of the eye. See chromostereopsis; longitudinal chromatic aberration.
monocular parallax The apparent change in the relative position of an object when the eye is moved from one position to another.
motion parallax Apparent difference in the direction of movement or speed produced when the subject moves relative to his environment (Fig. P2). Example: when viewing the landscape through the window of a moving train near objects appear to move much more quickly than distant objects. See depth perception; stereopsis.
relative binocular parallax See stereoscopic visual acuity.
)
Fig. P2 An example of motion parallax
chromatic aberration
Optics The differences in the focal points when multiple wave lengths–colors of light–eg, those of white light, pass through a lens system
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