optometer


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Related to optometer: pupilloscope

optometer

 [op-tom´ĕ-ter]
a device for measuring ocular refraction.

op·tom·e·ter

(op-tom'ĕ-tĕr),
An instrument for determining the refraction of the eye.
[opto- + G. metron, measure]

op·tom·e·ter

(op-tom'ĕ-tĕr)
An instrument for determining the refraction of the eye.
[opto- + G. metron, measure]

optometer

An automatic machine for determining the REFRACTION of the eye. Also known as a refractometer.

optometer 

Instrument for measuring the refractive state of the eye. There are two main types of optometers: subjective and objective. Subjective optometers rely upon the subject's judgment of sharpness or blurredness of a test object while objective ones contain an optical system which determines the vergence of light reflected from the subject's retina. Electronic optometers in which all data appear digitally within a brief period of time after the operator has activated a signal can be of either type. Objective types (also called autorefractors or autorefractometers) have become very popular and several of these autorefractors are now providing both objective and subjective systems within the same instrument. Syn. refractometer. See objective accommodation; Humphrey Vision Analyser; autorefraction; infrared optometer; photorefraction; refractive error.
Badal's optometer A simple, subjective optometer consisting of a single positive lens and a movable target. The vergence of light from the target, after refraction through the lens, depends upon the position of the target. The patient is instructed to move the target towards the lens from a position where it appears blurred until it becomes clear. That point (converted in dioptric value) represents the refraction of the patient's eye. This is a crude and inaccurate instrument, in which the measurement is marred by accommodation, variation in retinal image size with target distance, large depth of focus, non-linearity of the scale, etc. Badal's improvement was to place the lens so that its focal point coincides with either the nodal point of the eye or the anterior focal point of the eye or the entrance pupil of the eye, thus overcoming the problems of the non-linear scale and the changing retinal image size (Fig. O3).
optometer of Fincham, coincidence An objective optometer which forms the image of an illuminated fine line target on the retina by passing through a small, peripheral portion of the pupil. The examiner views through a telescope with an optical doubling system, which splits the visual field into two. If the incident beam of light is not in focus on the retina, the reflected beam will not be along the optical axis and the two half-lines will be seen out of alignment. Adjusting the dioptric value of the target in order to obtain alignment gives a measure of the ametropia.
infrared optometer An optometer that uses infrared light rather than visible light. This is done so that the target used in the optometer is invisible to the patient. Otherwise when it is altered it tends to become a stimulus to accommodation. However, the instrument must be corrected for the chromatic aberration of the eye. Most modern optometers use infrared light. They are based on one of three principles: (1) retinoscopy, (2) Scheiner's experiment, (3) ophthalmoscopy (indirect).
objective optometer; subjective optometer See optometer.
Young's optometer A simple optometer consisting of a single positive lens and using the Scheiner's disc principle. The target is either a single point of light or a thread, which is moved back and forth until it is seen singly by the observer. When the target is out of focus, it is seen double and slightly blurred. See Scheiner's experiment.
Fig. O3 Optical principle of the Badal optometer ( F , F ′, first and second principal focus of the lens; F e , anterior focal point of the eye; T, target)enlarge picture
Fig. O3 Optical principle of the Badal optometer (F, F′, first and second principal focus of the lens; Fe, anterior focal point of the eye; T, target)
References in periodicals archive ?
In experiments with absolute intensity measurements, it was necessary to detach the recording electrodes and move the preparation so the optometer detector could be placed in the same position as the preparation.
(b) Irradiance was measured using a Daavlin X96, P9710 optometer (accuracy, [+ or -] 5%).
Measurements of cylindrical irradiance were made using a GigaHertz-Optik model P9710 optometer and a model ROD-360-UV 18-2 cylindrical UV sensor (Puchheim, Germany).
One possible interpretation of this discrepancy is that measures from infrared optometers are more valid because they are not contaminated by subjective factors (such as perception of nearness; Rosenfield & Ciuffreda, 1991) that may be idiosyncratic to the laser optometer.
The LDM-9810 modularly designed viewer module is combined with the PD-16VI011 plug-in photometric detector and any proprietary optometer, forming an luminance measurement system that features a viewable and sizeable target spot A wide achromatically corrected 50-mm lens aperture objective and focusing feature satisfies the tightest requirements for the suppression of stray light and image formation.
Dr Fowler was a third-year optometry student when he first found a way to integrate his mechanical engineering skills into the optical sector by building an objective optometer. After developing this first instrument, the academic support officer went onto build, amongst other things, a progressive lens measurement machine that he patented, and a scanning focimeter which second-year optometry students at Aston University use today.
Irradiance was controlled with a neutral density wheel under computer control, calibrated in units of photons [cm.sup.-2] [S.sup.-1] with a UDT Optometer (Model S370) and a radiometric probe placed 3 mm from the tip of the light guide.
Accommodation and convergence were measured with a dynamic infrared optometer (Cornsweet and Crane, 1970) and a dual-Purkinje image infrared eyetracker (Crane and Steele, 1985), respectively.
Irradiance was controlled with a neutral-density wheel driven by a stepper motor under computer control, and calibrated with a UDT optometer (United Detector Technology Model S370) and radiometric probe with point calibrations provided by UDT.
Initially, in the mid-1910s, monocular optometers were used as opposed to phoropters binocular refracting devices that could also measure ducitons, phorias and other traits of binocularity.
* Use of hand-held air-puff tonometers to measure intraocular pressure (IOP); Use of hand-held optometers (Nikon, Retinomax) for objective refraction.