Apparatus and method for testing night vision

Abstract

A method and an apparatus for testing night vision are disclosed. At least one visual mark is presented to a test person having an open pupil from a distance of several meters. The visual mark is configured as a light point, and a visual impression of the test person is determined by means of the visual mark. The apparatus comprises means for opening a pupil of a test person, in particular a darkened room. An examination position for the test person and a presentation apparatus for visual marks arranged at a distance of several meters from the examination position are also provided. The presentation apparatus comprises at least one point-shaped light source. A light beam thereof is directed towards the examination position. Means are provided for determining a visual impression of the test person with the help of the visual marks.

Claims

1. A method of testing the night vision of a test person by determining the visual acuity or visual correction needs of the test person, comprising the steps of: placing the test person in a completely dark enclosure so that a pupil of the test person is fully open for testing, directing an isolated light point from a distance of several meters onto the open pupil of the test person, such that the light from the light point is the only light presented to the test person, so that a test person with defective night vision sees the light point with enlarged circular or elliptical contours with laterally falling flanges.

2. The method of claim 1, wherein the diameter of the light point is 0.9 millimeters and the distance from the light point to the test person is 6 meters.

3. The method of claim 1, further including the step of determining an optimum visual acuity correction of the test person by selectively placing different spectacle lens in front of the test person and identifying when the test person no longer perceives laterally falling flanges in the test person's image of the light point.

4. A method of testing the night vision of a test person and determining the optimum correction needs of the test person, comprising the steps of: placing the test person in a completely dark enclosure so that a pupil of the test person is fully open for testing, directing an isolated light point from a distance of several meters onto the open pupil of an eye of the test person, such that the light from the light point is the only light presented to the test person, selectively placing different spectacle lens in front of the eye of the test person, and identifying when the test person's image of the light point is the smallest with no perceived laterally falling flanges.

5. The method of claim 4, wherein the diameter of the light point is less than 1 mm.

6. The method of claim 1, wherein the light point comprises a continuously illuminated light point.

7. The method of claim 4, wherein the light point comprises a continuously illuminated light point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are explained in more detail in the following description and are represented in the drawings, in which:

(2) FIG. 1 shows a highly schematic side elevational view of an embodiment of an inventive apparatus;

(3) FIG. 2 shows a front elevational view of a presentation apparatus used in the apparatus of FIG. 1;

(4) FIG. 3 shows a first embodiment of a visual mark used for the present invention and having the shape of a light point;

(5) FIG. 4 shows the point-shaped visual mark of FIG. 3, as perceived by a test person with defective vision;

(6) FIG. 5 shows a second embodiment of a visual mark used for the present invention and having the shape of a pair of light points;

(7) FIG. 6 shows a third embodiment of a visual mark used for the present invention and having the shape of several pairs of light points; and

(8) FIG. 7 shows a fourth embodiment of a visual mark used for the present invention and having the shape of several rows of light points.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) In FIG. 1, reference numeral 10 designates as a whole an embodiment of an apparatus for checking night visual acuity according to the present invention with which the method according to the present invention may be executed.

(10) For the present invention it is important that the pupils of the test person be open. For that purpose, apparatus 10 comprises a preferably darkened room 12. The term “darkened” is to be understood to mean that the room is light-tight to the exterior and is totally dark after an ambient or point-shaped orientation illumination has been switched off. This does, of course, not exclude that a certain brightness may be set within room 12 and that the pupils are opened artificially by administering an appropriate agent (atropine drops). The preferred operational mode, however, is the total darkness because the test person then has fully open pupils after a certain adaptation time.

(11) At the right hand end of FIG. 1, there is provided within room 12 an examination position 14 for a test person 16, in the simplest embodiment a chair. In FIG. 1 an eye of test person 16 is shown at 18. Test person 16 wears a test spectacle 20 of conventional design into which an examination person may insert different test spectacle lenses.

(12) At the left hand end of FIG. 1 there is provided within room 12 a presentation apparatus 30 for visual marks. Presentation apparatus 30 is located at a distance “a” from examination position 14. Distance “a” shall be as long as possible and, in practice, shall be of the order of several meters, for example 6 meters.

(13) Presentation apparatus 30 is provided with a base 32 supporting a visual mark source 34. Visual mark source 34 may be configured in various ways.

(14) In the embodiment shown in FIG. 1, visual mark source 34 consists of an aperture 36 having a central opening 38. A lamp means 40 is located behind opening 38. In this way, a point-shaped light source 41 or a light point is generated as a visual mark, as is shown in the front elevational view of FIG. 2. Point-shaped light source 41 emits a light beam 42 directed towards examination position 14 and falling into eye 18 of test person 16.

(15) FIGS. 2 and 3 show that point-shaped light source 41 or light point is located on an axis 44. Light point 41 has a diameter “d” being smaller than 1 mm. A diameter of 0.9 mm is preferred. This value is appropriate at a distance “a” of about 6 m for a test person 16 having a visual acuity of 2 (40/20). Other visual marks may also be generated relative to axis 44, as will be explained further below with reference to FIGS. 5 to 7.

(16) Within room 12, there is, further, provided an indirect illumination 46. Indirect illumination 46 may be located on the rear side of presentation apparatus 30, and may be adapted to be set that a certain brightness is generated within room 12 for measuring or orientation purposes. Illumination 46 may also be configured and located such that it is appropriate for flaring test person 16 for a short period of time for simulating flare situations as may occur during night driving.

(17) Moreover, there is also provided within room 12 a magazine 50 for test spectacle lenses in the vicinity of examination position 14 for enabling an examination person to insert test spectacle lenses 52 one after another into test spectacle 20 worn by test person 16, as already explained. An orientation illumination may also be provided there (not shown).

(18) FIG. 4 shows a visual mark 58 as perceived by a test person 16 having defective vision. Perceived visual mark 58 has a circular or elliptic contour with a transition into laterally falling flanges 59. This shape of perceived visual mark 58 is caused by the so-called point spread function (PSF) already discussed at the outset.

(19) As already mentioned, the PSF causes for an ideal, i.e. aberration-free system focused to infinity that the light distribution in the image of a point-shaped (diameter d) light source 41 being at a distance “a” has an intensity function in the shape of a first order Bessel function with a narrow tip and laterally falling flanges in a radial direction away from the center. In the case of a myopia or a hyperopia of test person 16 the PSF's reaction is quite sensitive and obtains the shape of a circle instead a narrow tip, the diameter of the circle being an indication for the defective vision; in the case of an astigmatism the shape becomes elliptic.

(20) In any event the laterally falling flanges remain and their magnitude as perceived by test person 16 is an indication to which extent the defective vision was already corrected by inserting respective test spectacle lenses 52 into test spectacle 20, namely with wide open pupils within the surrounding darkness. With increasing correction perceived visual mark 58 in FIG. 4, therefore, becomes narrower until, ideally, it assumes the shape of a narrow tip with minimum lateral flanges 59. This constitutes a major advantage of the invention because the measurement within a dark room 12 has the effect that test person 16 can very well recognize laterally falling flanges 59 which is already no longer possible at low ambient light.

(21) FIG. 5 shows an alternate embodiment in which several pairs 60a, 60b, 60c, and 60d are arranged parallel to one another along axis 44, wherein pairs 60a, 60b, 60c, and 60d have increasing distances D.sub.1, D.sub.2, D.sub.3, and D.sub.4. Such patterns allow to determine the visual acuity particularly well, similar to prior art visual marks having the shape of Landolt rings.

(22) Finally, FIG. 7 shows another alternate embodiment with four rows 72a, 72b, 72c, and 72d of six light points, rows 72a, 72b, 72c, and 72d being normally oriented differently and, in the embodiment shown, intersect at an intersection point 74 under equal angles of 45°. This arrangement allows to additionally examine the astigmatism of test person 16.

(23) As already mentioned above, various practical designs come into consideration for point-shaped light source 41. Besides the backlighted aperture arrangement of FIG. 1 one can, preferably, also work with light emitting diodes (LED). Light emitting diodes are nowadays available in very small dimensions (diameter down to 0.200 μm including socket). Its brightness may easily be set by adjusting the supply current. They need only a small supply voltage of typically 5 V and have a high efficiency.

(24) In particular for the generation of patterns of light points (FIGS. 5 to 7), planar displays of high brightness are appropriate. These displays may be LED displays, in particular OLED displays utilizing organic light emitting diodes and having a particularly large area. As an alternative one can also use a backlighted planar display being provided with a controllable aperture device, for example a liquid crystal device (LCD) which allows to optically switch on or off individual pixels by selective shadowing.