GB2300487A - Apparatus for testing eye alignment - Google Patents

Abstract

An eye testing apparatus (16, Fig 2) is provided having an image generator (20, Fig 2) for producing an alignment image upon a display (18, Fig 2). The alignment image is viewed by a test subject with a Maddox lens 8 in front of one eye 4. The alignment image may include a white bar 24 that is transformed into a line image 34 by the Maddox lens. The line image 34 and the alignment image viewed directly by the other eye are dissociated allowing a test for eye alignment to be made. A background image (26, Fig 3) may be provided together with the bar to assist in fixation and dissociation. Markings (28, Fig 3) may be provided on the alignment image to give a quantitative assessment of eye alignment. 36 is the composite image perceived by the test subject.

Description

APPARATUS FOR TESTING EYESIGHT This invention relates to an apparatus for testing eyesight. More particularly, this invention relates to an apparatus for testing eye alignment.

The correct alignment of a subject's eye is important to healthy vision. One effective known technique for assessing such alignment utilises a red tinted Maddox lens held in front of one eye whilst viewing a point light source, such as a spotlight, in a darkened room. An example of this technique is illustrated in Figure 1 of the accompanying drawings. A test subject observes a point light source 2 with both a first eye 4 and a second eye 6. A Maddox lens 8 is positioned in front of the first eye 4. The Maddox lens is formed of a series of parallel rod lenses and has the function of making a point light source appear as a line.

Accordingly, if the Maddox lens 8 is tinted red, then the first eye 4 sees a red line and the second eye 6 sees the point light source 2 directly. The effect of the different appearance of the images seen by the first eye 4 and the second eye 6 is to disassociate the two eyes such that they adopt their natural alignment. The image perceived by the test subject is illustrated in region 12 and comprises a view of the line image 10 and the point light source 2. If the first eye 4 and the second eye 6 are correctly aligned, then the line image 10 will pass through the point light source 2.

However, if the first eye 4 and the second eye 6 have some degree of misalignment, then the line image 10 will be displaced to one side or the other of the point light source 2, as is illustrated in Figure 1.

As shown in Figure 1, the Maddox lens 8 is oriented to test the horizontal alignment of the first eye 4 and the second eye 6. If the Maddox lens 8 is rotated through 90 , then the vertical alignment of the first eye 4 and the second eye 6 may also be checked.

It is also known to provide eyesight testing apparatus that utilises general purpose computing equipment (such as personal computers) to display test images.

An example of such a computerised eyesight testing apparatus is described in British Published Patent Application GB-A-2 267 159. Such systems provide increased flexibility in the nature of the images that may be produced, for example randomly changing the letters on an acuity testing chart, as well as providing the possibility for the computer to directly receive user responses to the testing images and perform screening analysis upon the responses.

A problem with the above described computerised testing systems is that the brightness of the test images that may be displayed is severely restricted by the brightness possible on the computer display output. A particular example of this is that it is not possible to produce a sufficiently bright point on a computer display to mimic the point light source 2 used in the eye alignment test discussed in relation to Figure 1.

According to the invention there is provided apparatus for testing eyesight, said apparatus comprising: an image generator for generating images to be viewed by a test subject; a display coupled to said image generator for displaying said images; and a Maddox lens for producing a line image of a spot source; wherein said image generator generates an alignment image for testing eye alignment, said alignment image having a bar such that when said alignment image is viewed with said Maddox lens in front of a first eye of said test subject and not in front of a second eye of said test subject, said test subject sees through said first eye a line image of said bar disassociated from the image of said bar seen by said test subject through said second eye.

The invention solves the problem of conducting an eye alignment test with a Maddox lens using a display coupled to an image generator by replacing the point light source with a bar. Providing a larger area on the alignment image from which light will be transformed by the Maddox lens into a line image allows the brightness of the line image to be advantageously increased to a level where a reliable eye alignment test may be provided. The fact that the bar spatially extends in a direction parallel to the line image that is produced by the Maddox lens does not have any significant disadvantage since it is the alignment in a direction transverse to the bar that is being tested.

It will be appreciated that the bar could take many different colours. However, in order to maximise the brightness of the bar it is advantageous that the bar is white.

In order to assist the dissociation of the first eye and the second eye, it is advantageous that said Maddox lens is coloured such that said line image is a different colour from said bar.

The increased flexibility that an image generator and display arrangement provides over the traditional technique illustrated in Figure 1 may be advantageously exploited in embodiments in which said alignment image includes a background pattern.

Such a background patent assists the test subject in fixing the image of the alignment image seen through the second eye and so improves the dissociation of the eyes.

This effect is further enhanced when said background image is coloured so as to not be visible through said Maddox lens. As an example, the Maddox lens may be red and the background image may be green.

An additional feature that may be provided by the alignment image is that said background pattern includes markings for the quantitative assessment of eye alignment.

This additional feature exploits the ability of the image generator and display to produce more complicated images to provide an additional function over and above the standard test.

It will be appreciated that the display could take a number of forms, such as a standard television receiver, but will preferably comprise a computer display.

Computer displays are relatively inexpensive and yet are capable of producing good quality images.

The computer display could take one of many different forms, such as an LCD panel, a projection display or preferably a cathode ray tube monitor. A cathode ray tube monitor can produce a bright display relatively inexpensively.

The image generator could be a special purpose piece of electronic hardware.

However, preferably the image generator is a programmable computer. Such programmable computers offer a great deal of flexibility and convenience of use at a relatively low cost.

When using such a programmable computer, a particular advantage is that the programmable computer may generate further test images for testing further aspects of said test subject's eyesight.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates a known eye alignment test utilising a Maddox lens; Figure 2 illustrates a computerised eyesight testing apparatus; Figure 3 illustrates an alignment image for use with the apparatus of Figure 2; and Figure 4 illustrates how the test subject views the alignment image of Figure 3.

Figure 2 illustrates a test subject 14 utilising an eyesight testing apparatus 16 comprising a cathode ray tube monitor as a display 18 and a general purpose programmable computer as an image generator 20.

The test subject 14 will typically be placed in a darkened room looking at the display 18. A user input device, in this case schematically illustrated as a keyboard 22, is provided such that the user may directly input their responses to the display test images for screening analysis by the computer, which displays a sequence of differing test images to test differing aspects of the test subject's eyesight..

Figure 3 illustrates an alignment image to be displayed upon the display 18.

The alignment image comprises a white coloured bar 24 surrounded with a green coloured background image 26 in the form of a cross. Markings 28 are provided to assist in the quantitative measurement of eye alignment. The corner regions 30 of the image are black.

Figure 4 corresponds to Figure 1 and illustrates the testing of a subject's eye alignment using the alignment image of Figure 3 and the testing apparatus of Figure 2. The alignment image 32 of Figure 3 is displayed upon the display 18 and viewed by both the first eye 4 and the second eye 6 of the test subject. The Maddox lens 8 in front of the first eye of the test subject serves to filter out the background image 26 and the markings 28. The white bar 24 is seen as a line image 34 by the first eye 4 of the test subject due to the action of the Maddox lens 8. This line image 34 will be red by virtue of a red tint of the Maddox lens 8.

The test subject's second eye 6 directly views the alignment image 32. The difference in colour and appearance of the images seen by the first eye 4 and the second eye 6 will assist in the dissociation of these images allowing the test subject's eyes to relax and a true measurement of eye alignment to be made.

The composite image perceived by the test subject is illustrated in area 36.

Assuming the eyes are misaligned in the same way as in Figure 1, the line image 34 will appear off-set from the bar 24 viewed directly by the second eye 6. A quantitative measurement of the degree of misalignment may be read by the test subject from the markings 28.

Claims (11)

1. Apparatus for testing eyesight, said apparatus comprising: an image generator for generating images to be viewed by a test subject; a display coupled to said image generator for displaying said images; and a Maddox lens for producing a line image of a spot source; wherein said image generator generates an alignment image for testing eye alignment, said alignment image having a bar such that when said alignment image is viewed with said Maddox lens in front of a first eye of said test subject and not in front of a second eye of said test subject, said test subject sees through said first eye a line image of said bar disassociated from the image of said bar seen by said test subject through said second eye.

2. Apparatus as claimed in claim 1, wherein said bar is white.

3. Apparatus as claimed in any one of claims 1 and 2, wherein said Maddox lens is coloured such that said line image is a different colour from said bar.

4. Apparatus as claimed in any one of the preceding claims, wherein said alignment image includes a background pattern.

5. Apparatus as claimed in claims 3 and 4, wherein said background image is coloured so as to not be visible through said Maddox lens.

6. Apparatus as claimed in any one of claims 4 and 5, wherein said background pattern includes markings for the quantitative assessment of eye alignment.

7. Apparatus as claimed in any one of the preceding claims, wherein said display is a computer display.

8. Apparatus as claimed in claim 7, wherein said computer display is a cathode ray tube monitor.

9. Apparatus as claimed in any one of the preceding claims, wherein said image generator is a programmable computer.

10. Apparatus as claimed in claim 9, wherein said programmable computer generates further test images for testing further aspects of said test subject's eyesight.

11. Apparatus for testing eyesight substantially as hereinbefore described with reference to the accompanying drawings.