optometer

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optometer

 [op-tom´ĕ-ter]
a device for measuring ocular refraction.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

op·tom·e·ter

(op-tom'ĕ-tĕr),
An instrument for determining the refraction of the eye.
[opto- + G. metron, measure]
Farlex Partner Medical Dictionary © Farlex 2012

op·tom·e·ter

(op-tom'ĕ-tĕr)
An instrument for determining the refraction of the eye.
[opto- + G. metron, measure]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

optometer

An automatic machine for determining the REFRACTION of the eye. Also known as a refractometer.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

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)
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
References in periodicals archive ?
Based on device, the market is classified into slit lamp, biometer, perimeter, tonometer, optical coherence tomography (oct) scanner, fundus camera, autorefractor & keratometer, and other devices.
Smart Vision Labs has developed a commercially available smartphone-based autorefractor, the SVOne, to enable accurate and fast mobile vision exams anywhere and anytime.
Monocular subjective refraction was performed based on subjective refinement of the autorefractor readings until the best-corrected visual acuity was achieved.
The static accommodation responses were measured using the WAM-5500 infrared open-field autorefractor (Grand Seiko Co Ltd; Hiroshima, Japan) [18].
It does the job of a $5,000 instrument called an autorefractor.
The results of this procedure determine the strength of lens needed to give you the best vision in each eye and should tally with the autorefractor and retinoscope results.
Members of year 3 are pictured with teacher Caroline Howarth, optometrist Azhar Iqbal and an autorefractor (PW110711Ceyes-01)
For the 1999-2000, 2001-2002, and 2003-2004 surveys, participants also were asked questions regarding vision function, and the physical examination included a vision examination in which visual acuity was measured before and after an objective autorefraction test (optical correction measured by all autorefractor).
Accommodation was measured using a Canon R1 infrared autorefractor. A laser optometer mounted atop the Canon R1 was positioned so that participants could perform the laser task (the active viewing condition) while their accommodation was assessed with the Canon R1.
So the vertex distance was set as zero during autorefractor examination and TA was given in the autorefractor output.

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