DE3143949A1 - Method and device for vision tests dependent on contrast - Google Patents

Abstract

The invention relates to a method and a device for vision tests dependent on contrast. It can be applied in the field of ophthalmology in vision tests under defined and variable contrast conditions. It is the object of the invention to detect anomalies in vision at a reduced contrast and to reveal false conclusions about the vision. For this, the contrast of the visual symbols is varied in physiologically meaningful steps by switching of grey filters of predetermined, stepped transmission degrees into the projection beam path of a projector having a defined initial contrast.

Description

Method and device for contrast-dependent

Visual acuity testing The invention is in the field of ophthalmology when testing visual performance under defined and variable contrast conditions Use. It is used to measure the contrast dependence of visual performance as well the detection of consciously or unconsciously incorrect information on visual performance.

In connection with the visual performance test using a visual projection projector the contrast dependence of the visual acuity has not yet been measured. The well-known technical Solutions dispense with an objective control of the contrast ratios in chart projectors. They assume that the prescribed illuminance of the The area around the optotypes on the projection screen, the image quality is adequate of the projector and the quality of the projected slides Isa (W. Straub, "Die Opthalmological investigation method, Verlag F. Enke, Stuttgart 1976).

With regard to the projection conditions, especially the conditions There are regulations and recommendations for brightness and contrast (E. Aalhorn u. a .: Commission proposals for the coordination of visual acuity measurement devices of the German Ophthalmological Society) These become present taken into account according to a subjective assessment and without quantltateve measurement.

A chart projector with a contrast warning device ensures security a built-in luminance meter with threshold value display a specified Minimum contrast and thus compliance with constant test conditions. Defined Contrast levels are achieved with this device described in WP A61B / 219373 not possible.

Adaptation testing equipment is only available to a very limited extent Extensive statements about visual acuity values are possible, since the repertoire of signs and examination distance are not are optimized for this purpose (CH 566766) The aim of the invention is, for a chart projector, which is combined with a device for measuring the contrast of the projected optotypes is to create a method for measuring the contrast dependence of the visual acuity value, which at the same time allows false statements about visual performance about this contrast dependency can be ascertained in a quick and convenient examination.

The invention is based on the object of a method and a device for contrast-dependent visual acuity check and error elimination when determining the To create visual performance in which the test subject also recognizes the visual signs can be presented with a gradual reduction in contrast. The gradation is physiological sensibly designed so that there is a visual acuity reduction of about 0.1 per level. The examination situation remains for the test subject in comparison with the usual one Visus tests unchanged, in particular the same will be the same on the visus test station Optotypes that are used in normal visual acuity testing are presented.

A chart projector for checking visual acuity with a defined reduction in contrast consists of a chart projector combined with a device for measuring the luminance of the projection field. According to the invention, the Sehzeichenprojek tor also has a neutral density filter that can be switched into the projection beam path, through which the luminance density generated by the projector on the projection screen and thus the contrast generated are changed in suitable steps. The well-known effect of light weakening by gray filters is used. If the presentation takes place by projection, which in the bright environment around an optotype shows the illuminance E and in the area of the sign the illuminance @O results from the contrast definition: For an absolutely black character (Ez = 0) the contrast is Ko = 1.

In fact, the test conditions are such that the visual test is moderate bright surroundings, reducing the illuminance in the area of the sign E> 0 and the contrast drops to values E <1. Because of this reduction in contrast the apparent visual performance of the test person is influenced.

The visual performance of a test person, which is the visual acuity value when the contrast K = 1 When V = 1 is reached, it decreases when the illuminance from the projector is constant generated illuminance E is reduced. This dependence that occurs with normal According to the invention, visual acuity testing is disruptive and is used to detect pathological changes the visual performance with poor contrast or to make false statements about the Recognize the test person by giving him the visual signs of the last read visual acuity value be presented in a defined reduced contrast. Can the character even then are read, the actual visual acuity value is better than the original than the lower one Detectability limit specified.

After switching on the projector, an optotype is projected without the interposition of a gray filter and presented to the test person with the contrast Ko. Then a gray filter with a transmittance of # 1 is placed in the beam path, which causes the character to have reduced contrast appears.

The transmittance of the individual neutral density filters is calculated according to the formula calculated so that the contrast levels Kn a Kn + 1 + 1 according to the empirical relationship between visual acuity value and contrast (HodamS fortelsammlung and book of tables of technical optics, VEB Verlag Tachnik, Berlin 1974, p. 183, table 2.60) defined visual acuity value levels Vn - Vn + 1 correspond to # 0.1. An initial contrast Ko = 0.85, which is generated by additional lighting and is still permissible for the usual visual acuity test, is assumed.

The invention is explained below with reference to the schematic drawing explained in more detail.

It shows a device for carrying out the invention Procedure.

A light source 1, a condenser 2 and an objective 4 represent symbolically a projector 5, which an optotype slide positive 3 on a usually round projection surface 6 depicts. A second lens 7, a pinhole 8 and a photoelectric receiver 9 form a luminance meter 15 with a display device 10. The test subject's eye 12 is in the direction of view of the projection surface 6. A lamp 14 enables the room lighting and thus the additional lighting to be varied the projection surface 6. A neutral density filter 13 can optionally be placed in the projection beam path be switched on, advantageously a plurality not shown here of filters is provided. When the projector 5 is switched off, the luminance meter is used 11 the luminance on the projection surface 6 measured2 which of the through the Light source 14 generated illuminance Ez originates. The display device 10 signals when a previously set threshold value for the illuminance Ez is reached, which in the projection of the optotypes a for the usual visual acuity test causes an impermissible reduction in contrast.

After switching on the projector, it becomes positive on the chart 3 located characters are projected without the interposition of a gray filter 13 and A gray filter is then presented to the test person with the existing contrast 13 with the transmittance # 1 1 switched into the beam path, where by the sign appears with reduced contrast. As already described, the reduction in contrast has result in a change in visual acuity. Does the measured change give way to a test person? of the visual acuity value in the case of contrast reduction from the physiologically justified and empirical one known normal state, this is an indication of pathological changes or incorrect information provided by the test person.

By successively switching on several gray filters 13 with graded The degree of transmission, the visual acuity value can be precisely determined depending on the contrast.

Claims (3)

Claims: 1. Method for contrast-dependent visual acuity test and error elimination when determining the visual performance in the one subject Optotypes under defined contrast ratios and successively down to the lower one The limit of the recognition can be presented, characterized in that after reaching the lower limit of the recognizability of the contrast gradually reduced and thereby preferably a visual acuity reduction of about 0.1 a level is brought about. 2. Device for performing the method according to Ansporuch 1, consisting from a chart projector for visual acuity testing with built-in measuring and display device to measure the luminance of the projection field and to display if it is exceeded a minimum contrast, characterized in that at least one gray filter is optional is arranged switchable in the projection beam path 3. Device according to claim 2, characterized in that the gray filters have graduated degrees of transmission.