JPH0471531B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a visual fatigue measuring device that objectively measures visual fatigue.

[Background Art] With the spread of VDTs (Visual Display Terminals: computer terminals with screen display devices), the number of people who use them for long hours every day has rapidly increased, leading to complaints of various visual impairments.

Traditionally, the methods for measuring fatigue associated with such work are:
Visual acuity, periapsis, Fritzker measurement, etc. are performed using subjective measurements based on the subject's subjective responses, which has the problem of poor measurement accuracy and long measurement times.

However, recently, an optical device called a dynamic refractometer, as shown in Figure 3, has been developed that can measure dynamic changes in the refractive power of the eye lens instantaneously, continuously, and objectively. was developed. An example of such a dynamic refractometer is introduced, for example, in "Physiological Optics" edited by the Optics Conference of the Japan Society of Applied Physics, Asakura Publishing, pp. 117-120.

To explain the outline of this device, as can be seen from Fig. 3, the light of the infrared light emitting diode LED that emits alternately passes through lenses L1, L2 and beam splitter BS1, and then passes through two thin beams obtained by an aperture D. The image from the beam is projected onto the retina,
The reflected light of the image is focused through beam splitter BS1, lens L3, beam splitter BS2, and lenses L4 to L7, and a second image is created on photocell PC. To utilize these images, the aperture D and lens L6 are servo-controlled to match the two images on the retina.

Refractive power is measured using the fact that the distance between two beams on the retina changes as the refractive power of the eye lens changes. Specifically, it is calculated from the amount of movement of the diaphragm D when the position of the diaphragm D is changed so that two light spots on the retina given through the diaphragm D coincide.

The mask in the figure removes the reflected light from the cornea and directs the reflected light from the retina of the eye to the photo cell PC.
This is to enable measurement.

The optical system including lenses L3, L8, L9, etc. constitutes an optotype presentation device that provides accommodation stimulation to the subject based on instructions from the optotype, and provides the subject with an image of the optotype moving on the visual axis. Used to perform adjustment operations. These lenses L3, L8 and L9 constitute a Badal lens system, in which the size of the optotype image on the retina is kept constant,
The lenses were placed so that the subject was given only information about the blur.

In addition, the optical system consisting of lenses L10, L11, reticle, beam splitter BS3, TV monitor TV, etc. constitutes an eye monitor for setting. It is used to place the object at a specific distance.

FIG. 4 shows a typical accommodation response when the visual target is slowly moved from far to near using such an optical device.

The diopter D on the vertical axis in the figure is the focal length (-
It is defined as the reciprocal of f(m)), and when used for the subject's eye, the distance from the corneal vertex is
It is defined as -1D at 1m and -2D at 0.5m. In the diagram
OH indicates the response before work, and 3H indicates the response after 3 hours of continuous VDT work.

Figure 5 shows the accommodation response when the visual target was moved in steps, and similarly, before work and for 3 hours.
The response after VDT work is shown as OH, 3H. The shaded area in the figure is the adjustment area (described later) after 3 hours of VDT work, and the decrease in this adjustment area is most noticeable in the second waveform in the figure.

According to these measurement results, the response to gradual changes in the optotype (ramp response) as shown in Figure 4 does not show any obvious changes before and after the VDT task, but the response as shown in Figure 5 shows no obvious change. , various characteristic changes appear in the response to a sudden change in the visual target (step response).

Note that the far point is the farthest point from the person that can be seen with the human eye.

The following six characteristic changes can be summarized.
It becomes a point.

(A) Increase in dead time, (B) Increase in rise time, (C) Increase in number of times it becomes difficult to maintain accommodation near the near point, (D) Increase in accommodation error, (E) Increase in blinks, (F) Movement of the far point to the nearer side.In general, human reactions have large individual differences and temporal fluctuations, so if the measured values of (A) to (F) above are directly used, the measured values will have large variations. This makes it difficult to use.

[Problems to be Solved by the Invention] The present invention solves the problems (A) to (A) that appear randomly with respect to integral values for a specific area as indicated by hatching in the fourth waveform in FIG. Focusing on the fact that all of the characteristic waveforms in F) act to decrease their integral values, the present invention aims to provide a visual fatigue measuring device that expresses visual fatigue as a stable measurement value by decreasing its integral value. It is.

[Means for Solving the Problems] In order to achieve the above object, the visual fatigue measuring device of the present invention uses an optical system shown in FIG. 3 for measuring dynamic changes in the refractive power of the eye in real time. The falling and response waveforms of the optotype as shown in the fourth waveform in FIG. It is constructed by connecting an integrating means for obtaining a value corresponding to the area surrounded by (this is referred to as an adjustment area) by integration, and further providing a display device for displaying the calculation result.

[Function] According to the visual fatigue measuring device of the present invention having the above-mentioned configuration, from the output of the dynamic refractometer, the accommodation area, that is, the average value of the far point in several step responses is set as the bottom, and the fall of the visual target is determined. Visual fatigue can be objectively, quantitatively, and stably measured and displayed as a value corresponding to the area surrounded by the response waveform and the response waveform.

[Example] FIG. 1 shows an example of the visual fatigue measuring device according to the present invention. This visual fatigue measuring device uses the accommodation area, that is, the average value of the far point in several step responses measured before work as the shaded area of the fourth waveform in Figure 5, to the base 1, and the visual target. The characteristic waveforms (A) to (F) that appear randomly due to fatigue associated with VDT work are all in that area with respect to the area surrounded by the falling edge 2 and response waveform 3. Focusing on the fact that it acts to reduce
Visual fatigue is expressed objectively and quantitatively as a stable measurement value by reducing its area.
Its structure and operation will be explained below.

First, as a dynamic refractometer that measures dynamic changes in the refractive power of the eye in real time, a conventionally known dynamic refractometer as illustrated in Fig. 3 is used, and its output, the refractive power, is It is sent to the integrator through the gate. Based on the gate signal from the dynamic refractometer, the gate opens immediately after the optotype rises, and closes in response to the fall of the optotype, as shown in the timing chart of Figure 2. .

The output of the refractometer sent to the integrator through this gate is integrated using the average value of the far point in several step responses measured in advance as the base.
In order to include the effect of (F), it is necessary to compare the previous far point and the average far point at the reference time, and if the previous far point is closer to the subject, it is necessary to change the base of the integral. be.

The comparator in FIG. 1 is for performing the above comparison, controlling the DC power supply based on the result, and adding a voltage corresponding to changing the base of the integral to the output of the refractometer. Figure 2 shows how the base of the integral is changed. Specifically, in the above comparator, the output of the refractor at the time of the rise of the optotype in FIG. If the value is changed and it is smaller than base 1 of the standard,
It is set to base 1 of the standard.

The output of the above integrator objectively and quantitatively represents eye strain. If necessary, an averaging circuit is provided to perform the averaging, and a divider is further provided to divide the output into the stimulation width. Standardize by dividing by , and display the result on the display. The integrator, display, etc. are reset at the timing shown in FIG. 2 by a reset signal from the dynamic refractometer.

Note that the above-mentioned measurement circuit can also be easily realized by using a microcomputer.

[Effects of the Invention] As is clear from the detailed description above, the visual fatigue measuring device of the present invention can measure and display visual fatigue objectively, quantitatively, and stably.

[Brief explanation of the drawing]

Fig. 1 is a block configuration diagram of a visual fatigue measuring device according to the present invention, Fig. 2 is a timing chart of signals in the measuring device of Fig. 1, Fig. 3 is an explanatory diagram of a dynamic refractometer, and Fig. 4 The figure and FIG. 5 are diagrams showing the measurement results by the refractometer shown in FIG. 3. 1...The base of the integral consisting of the average value of the far point, 2...
Falling target, 3...Response waveform.

Claims (1)

[Claims] 1. A dynamic refractometer that measures dynamic changes in the refractive power of the eye in real time is used for its output, with the average value at the far point of several step responses as the bottom, and the fall and response of the optotype. 1. A visual fatigue measuring device, characterized in that it is connected to an integrating means for obtaining a value corresponding to an area surrounded by a waveform by integration, and is further provided with a display device for displaying the calculation result.