GB2245982A

GB2245982A - An optical test device for measuring eye convergence

Info

Publication number: GB2245982A
Application number: GB9015153A
Authority: GB
Inventors: Richard James Scaddan
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1990-07-10
Filing date: 1990-07-10
Publication date: 1992-01-15
Also published as: GB9015153D0

Abstract

An optical test device, particularly suitable for measuring eye convergence, includes two substantially co-planar positive lens means 1 spaced apart at substantially the inter-ocular spacing x of a human being, marker and/or scale means 2. 3 located on the side of the lens means 1 remote from a viewer, which means 2, 3 are located one in the field of view of each lens means 1, spaced apart at the same distance x and located at or lust inside the focal length of each lens means 1 and means for illuminating the marker and/or scale means 2, 3. The degree of eye convergence of a viewer looking at and through the lens means 1 is indicated by the apparent position of the marker and/or scale means 2, 3 to provide an indication of the optical characteristic being tested. Optional beam splitter means is shown at 8 mounted on wall 7. <IMAGE>

Description

AN OPTICAL TEST DEVICE This invention relates to an optical test device particularly, but not exclusively, suitable for testing the eye convergence of a human viewer.

It is often necessary to measure the degree of convergence of the eyes of a human being, for example in psychology or human factors experiments. Alternatively it may be necessary to check that the eyes of a viewer are focused on a particular distance. This is particularly necessary for aircraft pilots whose attention may wander or relax such that their eyes become focused in the middle or short distance rather than at long distances or infinity so that they do not see the approach of an oncoming aircraft until too late to take satisfactory avoiding action.

There is thus a need for a relatively simple passive optical device which can provide a quick indication of an optical characteristic such as the degree of eye convergence, to a viewer.

According to the present invention there is provided an optical test device, including two substantially co-planar positive lens means spaced apart at substantially the inter-ocular spacing of a human being for viewing from one side by a human being, marker andlor scale means located on the other side of the lens means remote from the viewer, which marker andlor scale means are located one in the field of view of each lens means, spaced apart at substantially the inter-ocular spacing of a human being and located at or just inside the focal length of each lens means, and means for illuminating the marker and! our scale means so that the degree of eye convergence of a viewer looking at the lens means is indicated by the apparent position of the marker and/or scale means to provide an indication of the optical characteristic being tested.

Preferably the device includes beam splitter means located, in use, between the eyes of a viewer and the lens means and operative so that the viewer may view a scene and the marker andlor scale means simultaneously.

Conveniently the device includes a substantially rectangular housing having two spaced apart walls in one of which the lens means are located and in the other of which the marker and/or scale means are located, and a further wall extended at substantially 450 to the lens means containing wall, in which further wall the beam splitter is located.

Advantageously the beam splitter is in the form of a sheet or window of semi-reflecting, at least semi-transparent, material, operative such that the viewer can look through the beam splitter at an angle of substantially 450 thereto and see the marker and! our scale means displayed or projected thereon by the illuminating means.

Preferably the marker and! our scale means consist of one marker means in the form of one triangle, and one scale means in the form of a scale, with the triangle and scale means being located such that when the viewer is focusing at infinity the triangle appears to be set at the zero convergence or infinity point of the scale and to move across the scale as the viewer focuses and converges on progressively nearer vision points.

Conveniently the marker and/or scale means consist of two marker means each in the form of a triangle, with the two triangles being located such that they appear to be aligned apex to apex when the viewer is focusing at a set distance.

Advantageously the scale means is calibrated in convergence angle or viewing distance.

Preferably the illumination means islare located to illuminate the marker andlor scale means from the side thereof remote from the lens means.

Alternatively the illumination means is /are located to illuminate the marker andlor scale means from the side thereof nearest to the lens means.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a general perspective view of an optical test device according to a first embodiment of the invention, Figure 2 is a schematic plan view of the general operation of the device shown in Figure 1, and Figure 3 is a diagrammatic view of the eye line vision of a viewer looking through the device of Figure 1 in an inverted position.

An optical test device of the invention basically includes two substantially co-planar positive lens means which preferably are individual positive lens 1 spaced apart at substantially the inter-ocular spacing x of a human being for viewing from one side by a human being such as shown in Figures 1, 2 and 3.

The device also includes marker and/or scale means, preferably in the form of marker means 2 and scale means 3 located on the other side of the lens means 1 remote from the eyes 4 of a viewer.

The marker and/or scale means 2, 3 are located one in the field of view of each lens 1, spaced apart at substantially the inter-ocular spacing x and located at or just inside the focal length of each lens 1. Also forming part of the device are means 5 for illuminating the marker andlor scale means 2, 3 as shown in Figure 2. The degree of eye convergence of the eyes 4 of the viewer looking at the lens 1 is indicated by the apparent position of the marker and! our scale means 2, 3 to provide an indication of the optical characteristic being tested.

Such a device is extremely simple and relatively easy to construct and operate in contrast to existing complex photo-electronic devices for measuring the pointing direction of each eye and for calculating the convergence of the eyes. An additional disadvantage of such conventional photo-electronic devices is that the user has to wear part of the apparatus in front of the eyes with a separate display being necessary.

In the embodiment of the invention illustrated in Figures 1, 2 and 3 the device is simple, passive, inexpensive, compact and light. Preferably the device includes a substantially rectangular housing 6, as shown in Figure 1, having two spaced a part walls 6a and 6b in one of which 6a the lens 1 are located and in the other 6b of which the marker means 2 and scale means 3 are located. The housing 6 also includes a further wall 7 extending at substantially 450 to the wall 6a in which an optional beam splitter means is located between the eyes 4 and the lens 1 and operative so that the viewer may view a scene 9 and the marker andlor scale means 2, 3 simultaneously.The beam splitter means is in the form of a sheet or window 8 of semi-reflecting, at least semi-transparent, material operative such that the viewer can look through the beam splitter material 8 at an angle of substantially 450 thereto and see the marker andlor scale means 2, 3 displayed or projected thereon by the illuminating means 5.

This is illustrated more clearly in Figure 3 where the eyes 4 are shown looking through the beam splitter material 8 at a scene generally indicated at 9.

In the illustrated embodiment there is one marker means 2 and one scale means 3. The marker means 2 is in the form of one triangle 10. The scale means 3 is in the form of a scale 11 located such that when the viewer is focusing at infinity the triangle 10 appears to be set at the zero convergence or infinity point of the scale 11 and to move across the scale 11 as the viewer focuses and converges on progressively nearer vision points. The scale 11 may be calibrated in convergence angle or in viewing distance as required.

Alternatively in the case of an optical test device required to indicate a set convergence angle or distance, the marker and scale means 2, 3 may be replaced by two triangles (not shown) located one in each focal plane which appear to be aligned apex to apex when the viewer is viewing at the set distance.

The illumination means 5 islare located to illuminate the marker and/or scale means 2, 3 from the side thereof remote from the lens means as shown in Figure 2. Alternatively the illumination means 5 may be located to illuminate the marker and/or scale means 2, 3 from the side thereof nearer to the lens 1.

The optical test device of the present invention may be tailored for many uses such as, for example, to provide a focus monitor for the pilot of an aircraft. When a pilot is flying in a featureless sky his eye focus may relax to a distance of only two or three metres and he may not see other aircraft or may misjudge the distance to them. In this case a device such as that shown in Figures 1, 2 and 3 may be placed at the top of the instrument panel of an aircraft or may be viewed through a head up display or incorporated in a helmet mounted display.

The pilot can periodically check that he is focused on infinity by means of the test device. The test device of the invention may easily be adapted to further uses such as for checking the alignment, calibration or other optical characteristics of optical instruments such as binoculars. Moreover the focal lengths of the lenses 1 can be chosen to give more or less sensitivity to change in eye convergence.

Claims

1. An optical test device, including two substantially co-planar positive lens means spaced apart at substantially the inter-ocular spacing of a human being for viewing from one side by a human being, marker and/or scale means located on the other side of the lens means remote from the viewer, which marker andlor scale means are located one in the field of view of each lens means, spaced apart at substantially the inter-ocular spacing of a human being and located at or just inside the focal length of each lens means, and means for illuminating the marker and/or scale means, so that the degree of eye convergence of a viewer looking at the lens means is indicated by the apparent position of the marker andlor scale means to provide an indication of the optical characteristic being tested.

2. A device according to Claim 1, including beam splitter means located so as to be in operation between the eyes of a viewer and the lens means and operative so that the viewer may view a scene and the marker and/or scale means simultaneously.

3. A device according to Claim 2, including a substantially rectangular housing having two spaced apart walls in one of which the lens means are located and in the other of which the marker and/or scale means are located, and a further wall extending at substantially 450 to the lens means containing wall, in which further wall the beam splitter is located.

4. A device according to Claim 3, wherein the beam splitter is in the form of a sheet or window of semi-reflecting, at least semi-transparent, material operative such that the viewer can look through the beam splitter at an angle of substantially 450 thereto and see the marker and/or scale means displayed or projected thereon by the illumination means.

5. A device according to Claim 4, wherein the marker and! our scale means consist of one marker means in the form of one triangle, and one scale scale means in the form of a scale, with the triangle and scale being located such that when the viewer is focusing at infinity the triangle appears to be set at the zero convergence or infinity point of the scale and to move across the scale as the viewer focuses and converges on progressively nearer vision points.

6. A device according to Claim 4, wherein the marker and/or scale means consist of two marker means each in the form of a triangle, with the two triangles being located such that they appear to be aligned apex to apex when the viewer is focusing at a set distance.

7. A device according to Claim 5, wherein the scale means is calibrated in convergence angle or viewing distance.

8. A device according to Claim 7, wherein the illumination means is/are located to illuminate the marker and/or scale means from the side thereof remote from the lens means.

9. A device according to Claim 7, wherein the illumination means is/are located to illuminate the marker and/or scale means from the side thereof nearest to the lens means.

10. An optical test device substantially as hereinbefore described and as illustrated in Figures 1, 2 and 3 of the accompanying drawings.