pe·rim·e·ter (p -r m -tr)n. 1. The outer limits of an area; circumference. 2. An instrument used to measure field of vision. |
perimeter
[pərim′ətər]
Etymology: Gk, peri, around, metron, measure
1 the circumference, outer edge, or periphery of an object.
2 an instrument for measuring visual fields.
3 an instrument for measuring the circumference of teeth.
perimeter
An instrument for measuring the angular extent and the characteristics (e.g. presence of scotoma) of the visual field. See campimeter; visual field; isopter; tangent screen.
arc perimeter Perimeter consisting of a semicircular arc, the inside surface of which is painted matt black or grey. The patient's head is placed such that the eye under investigation is located at the centre of curvature of the arc. The visual field is determined by moving a target along the black surface of the perimeter until the patient either just sees it or just no longer sees it. The targets are small discs of varying colour and size attached to the end of black wands or may be projected on the arc, which can be rotated around the fixation point located at its centre. Thus the visual field can be tested along any meridian.
automated perimeter An instrument to test the visual field in which the presentation of the stimuli and the recording are carried out electronically and under the control of a built-in computer. There exist many types (e.g. Henson CFA, Humphrey Field Analyzer, Octopus, Dicon). Computerized perimeters have the following advantages: the examination strategy is reproducible; they can be operated by non-specialists; the testing routine (e.g. number of stimuli or their location) can be altered by modifying the program; each instrument can contain several examination routines aimed at testing various pathologies (e.g. one for glaucoma and another for hemianopic defects); the computer capacity can be used for quantifying the results as, for example, in the Henson CFA where the visual fields can be classified as normal, suspect or defective on the basis of a system included in the instrument (Fig. P7). Syn. computerized perimetry. See Swedish Interactive Thresholding Algorithm; frequency doubling perimetry; short wavelength automated perimetry; Esterman test.
bowl perimeter See Goldmann perimeter.
Goldmann perimeter Perimeter consisting of a hemispherical bowl, the inside radius of which is 30 cm. Targets of varying intensity and size are projected onto the inside white surface. The background luminance of the bowl is also controlled. In addition there is a telescope attached to the back of the bowl through which the practitioner can verify that the patient maintains fixation. Goldmann perimeter can be used either for kinetic or static perimetry, although it is more appropriately designed for the former. Syn. bowl perimeter. See kinetic perimetry; static perimetry.
projection perimeter A perimeter in which the target is projected either onto an arc or a bowl such as the Goldmann perimeter.
arc perimeter Perimeter consisting of a semicircular arc, the inside surface of which is painted matt black or grey. The patient's head is placed such that the eye under investigation is located at the centre of curvature of the arc. The visual field is determined by moving a target along the black surface of the perimeter until the patient either just sees it or just no longer sees it. The targets are small discs of varying colour and size attached to the end of black wands or may be projected on the arc, which can be rotated around the fixation point located at its centre. Thus the visual field can be tested along any meridian.
automated perimeter An instrument to test the visual field in which the presentation of the stimuli and the recording are carried out electronically and under the control of a built-in computer. There exist many types (e.g. Henson CFA, Humphrey Field Analyzer, Octopus, Dicon). Computerized perimeters have the following advantages: the examination strategy is reproducible; they can be operated by non-specialists; the testing routine (e.g. number of stimuli or their location) can be altered by modifying the program; each instrument can contain several examination routines aimed at testing various pathologies (e.g. one for glaucoma and another for hemianopic defects); the computer capacity can be used for quantifying the results as, for example, in the Henson CFA where the visual fields can be classified as normal, suspect or defective on the basis of a system included in the instrument (Fig. P7). Syn. computerized perimetry. See Swedish Interactive Thresholding Algorithm; frequency doubling perimetry; short wavelength automated perimetry; Esterman test.
bowl perimeter See Goldmann perimeter.
Goldmann perimeter Perimeter consisting of a hemispherical bowl, the inside radius of which is 30 cm. Targets of varying intensity and size are projected onto the inside white surface. The background luminance of the bowl is also controlled. In addition there is a telescope attached to the back of the bowl through which the practitioner can verify that the patient maintains fixation. Goldmann perimeter can be used either for kinetic or static perimetry, although it is more appropriately designed for the former. Syn. bowl perimeter. See kinetic perimetry; static perimetry.
projection perimeter A perimeter in which the target is projected either onto an arc or a bowl such as the Goldmann perimeter.
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Fig. P7 Computerized perimeter. (Humphrey Field Analyzer, Humphrey Instruments, Inc
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