GB2266386A

GB2266386A - Subjective eyesight and visual display unit visibility test

Info

Publication number: GB2266386A
Application number: GB9308322A
Authority: GB
Inventors: Ian James Murray; Neil Robert Alan Parry
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-04-22
Filing date: 1993-04-22
Publication date: 1993-10-27
Also published as: GB9208679D0; GB9308322D0

Abstract

A computer-based procedure uses a combination of software and ancillary equipment to test various aspects of the computer user's eyesight and screen quality. Test patterns are presented on the screen 2 while the ancillary equipment (e.g. linear polarising filters 5, 6 mounted on the screen 2 and 3, 4 in front of the user's eyes) allows control over which pans of the test patterns are seen by each eye. By determining the smallest size of test pattern that can reliably be identified, monocular or binocular visual acuity can be estimated. By detecting misalignment of detail seen by each eye, ocular co-ordination can be estimated. The visibility of detail on the screen can be assessed by presenting targets at various screen locations. Areas where the user cannot accurately identify detail indicate localised impairment of visibility, due to such factors as on-screen glare from light sources, or poor or uneven screen quality. <IMAGE>

Description

VISUAL DISPLAY UNIT VISIBILITY TEST This invention allows Visual Display Unit (VDU) users to: a) test their eyes and spectacles whilst viewing the screen they use in their everyday work.

b) ensure the screen is optimally adjusted so that image quality is not compromised by inappropriate environmental or display characteristics.

It is well known that people using VDUs experience discomfort in and around their eyes. For this reason, and because longterm viewing of computer screens creates specific difficulties for the human eye, it has been recommended that individuals using VDUs should have their eyes examined regularly. A recent European Community (EC) Directive (90/270/EEC) provides guidelines for visual examinations. In Great Britain this has been implemented in the Health and Safety (Display Screen Equipment) Regulations 1992. Eye examinations and screening procedures are, however, expensive and may be inadequate because they do not test vision at the intermediate viewing distance used for VDU screens. Furthermore, they may not identify the source of an observer's problem because they are not performed under true working conditions.For example, glare sources on and around the VDU screen may cause as many problems as inappropriate spectacles. The invention would have three main advantages: 1) economy when large numbers of individuals need to be assessed quickly without leaving their place of work; 2) efficiency in that eyes and equipment can be tested simultaneously; 3) the ability to identify individuals with potential eyesight difficulties, who should therefore seek specialist advice.

According to the first part of the invention there is a VDUbased procedure which measures the finest visually resolvable detail in a pattern or other target presented on the screen, both when the eyes are working independently (monocular vision) and when they are working together (binocular vision).

According to the second part of the invention there is a VDUbased procedure which assesses how well the eyes work together. When viewing a VDU binocularly, the eyes must be well co-ordinated; to test this, the invention utilises a procedure which reveals the misalignment of viewing direction.

In addition to the computer software required to generate these tests on the user's computer, both the visual ability test and the binocular co-ordination test require some physical means of controlling which parts of the screen are seen by each eye. This device forms an integral part of the invention.

According to the third part of the invention there is a procedure for assessing the extent to which visibility of detail on all or part of the VDU screen is degraded by the display characteristics. This includes any aspect of image generation and any environmental factors, but particularly onscreen reflections and screen cleanliness.

A specific example of the invention will now be described with reference to the accompanying drawings.

Figs 1 and 2 illustrate the crossed polaroid filter principle.

Fig 3 illustrates a target for assessing binocular coordination.

Fig 4 illustrates a target for assessing visual ability.

Fig 5 illustrates an alternative target for assessing visual ability.

ability.

The crossed polaroidlprinciple is a method of controlling the information that is presented to each eye. It is illustrated in figs 1 and 2. The observer (1), views the screen (2) with two linear polarising filters, one in front of each eye. One of the filters (3) vertically polarises the incident light and the other (4) horizontally polarises incident light. A divided linear polarising filter is mounted on the screen such that one part (5) transmits only vertically polarised light whilst another part (6) transmits only horizontally polarised light.

This means that selected parts of the screen are seen exclusively by one or the other eye as depicted by the fields of view (7) and (8) in fig 1. The vertical and horizontal boundaries between the differently polarised areas of the screen are indicated by (9) and (10) in fig.2. Hence, in this example, the right upper quadrant of the display area is seen only by the right eye and the rest of the display area is seen only by the left eye. This configuration is only an example and the filters may be arranged in any way which allows the two eyes to view different parts of the screen. The display area is defined as the part of the screen which is seen through the filters.

Fig. 3 depicts the polarising filters mounted in a frame (11).

This frame bears flaps of highly plasticised PVC (12) to allow it to be fixed temporarily on a glass display screen. Bars (13) bisect the filter assembly horizontally and vertically to form four windows. Areas of the screen behind the upper right window are in this example only visible to the right eye and those behind the other three windows are only visible to the left eye. The bars are viewed binocularly and therefore promote simultaneous perception by the two eyes. Fixation disparity, which is a means of testing binocular stability, is tested by utilising the crossed polaroids described above to present one part of a square (14) to the left eye and the other part (15 and 16) to the right eye, as indicated in fig 3. The part of the square seen by the left eye (14) remains static throughout the procedure.The horizontal (15) and vertical (16) parts of the square seen by the right eye are ndependently movable and their positions can be controlled by pressing certain keys on the computer keyboard. The observers task is to align the moveable parts of the target so that they perceive a complete square. Errors in this procedure indicate the direction and severity of fixation disparity.

Fig. 4 illustrates the target used for assessing visual ability. A gap (17) is presented either at the top or bottom of a circle (18). Because the display device imposes a minimum limit on the size of the gap it is sometimes necessary to present additional patterns to make the gap detection task more difficult. In this example, the test circle (18) is surrounded by a larger patterned ring (19) and inside it is a smaller circle (20).

In order to measure visual ability of the eyes the target is presented to the left or right eye by appearing in the upper left or upper right window as seen in fig. 3. The observer reports whether or not he sees the gap (17) which appears randomly either at the top or bottom of the circle (18). Gap position is indicated by the observer as top or bottom by pressing one of two keys on the computer keyboard. If no gap is seen the observer presses a third key. When the observer responds the target disappears, to be replaced after an interval by a new target with a different gap size and position. The objective is to determine, from the observer's responses, the smallest gap which can be reliably detected using each eye. In order to check observer reliability, there are some 'blank' presentations in which no gap occurs.

Fig. 5 illustrates an alternative target for assessing visual ability. A horizontal line (21) with a central gap (22) is presented at a selected location on the display screen. A vertical line (23) passes through the gap (22) and itself contains a gap (24). The vertical line (23) depicted in fig.

5 is not centrally positioned in the gap (22) but is displaced towards the left. In other presentations the vertical line (23) can be positioned towards the right of the gap (22) or centrally so that the target is bilaterally symmetrical. The size of the pattern can be adjusted, keeping the proportional size of the gaps (22) and (24) and the lines (21) and (23) constant.

In order to measure the visual ability of the eyes the target is presented to the left eye or the right eye by appearing in the upper left or upper right window as seen in fig. 3. The line (23) appears randomly to the left of, to the right of, or centrally within the gap (22), and the observer reports what he or she can see by pressing one of a selection of keys on the keyboard. One key indicates that offset to the left is seen, and another indicates that offset to the right is seen.

If no offset is seen, either because the target is too small for the observer to detect the offset, or because the line (23) is in the middle of the gap (22), this is signalled by pressing another key. When the observer has responded, the target disappears, to be replaced after an interval by another arget. The objective is to determine the smallest size of line and gap for which the observer can reliably detect an offset.

An alternative means of assessing visual ability with this invention is to present one or more alphanumeric or other characters to one or both eyes, and to determine by the observer's responses the smallest size character or characters which can be correctly identified. These characters can be presented in one of several orientations.

The effect on visibility of display characteristics is investigated using a visual ability target as illustrated in fig. 3 or fig. 4, or described in the paragraph immediately preceding this paragraph. The polarising filter assemblies are not used for this procedure. Gap, line or character size is fixed and is chosen to be close to the limit of visibility of the observer under ideal conditions. A single target is presented on an otherwise blank screen. The target is manipulated in the manner described in the appropriate paragraph such that the observer must attempt to identify its configuration. The observer responds in the same manner as described in the relevant paragraph. The procedure is repeated several times with the target at different positions, so that visibility at selected locations over the entire screen can be assessed. The locations where the target is not correctly identified detected are indicated graphically at the end of the procedure by means of brightness or colour changes at those locations. The user can then adjust the room lighting or the position and settings of the monitor to optimise visibility on all parts of the screen.

Claims

1 A computer-based procedure which comprises a computer program and ancillary equipment and which presents test patterns on the computer's display screen, enabling various aspects of the user's eyesight and screen visibility to be assessed.

2 A computer-based screen visibility test as claimed in claim 1 wherein ancillary equipment provides a means of dissociating the screen information seen by the user's two eyes such that only certain information on the screen is visible to each eye, allowing each eye to be tested independently or for the two eyes to be tested together.

3 A computer-based screen visibility test as claimed in claim 1 or claim 2, wherein control over what each eye sees on the displavjscreen is provided by means of the crossed polaroidprrincipal by which a piece or pieces of linear polarising filter are placed in front of the display screen and further linear polarising filters are placed in front of the user's eyes such that a particular area of the screen is virtually invisible to one eye if the polarising filter covering that area has its axis of polarisation perpendicular to that of the filter in front of the eye.

4 A computer-based screen visibility test as claimed in claim 2 or claim 3 wherein the dissociating material is mounted in a window arrangement such that there are 4 panes in a two-by-two array, and one eye sees the display screen through one pane while the other eye sees the display screen through the other three panes.

5 A computer-based screen visibility test as claimed in claim 1 or claim 2 or claim 3 or claim 4 wherein a target is presented on the display screen, to one or both eyes, in order to determine by the user's responses the smallest target in which detail can be reliably seen by the user, thus allowing monocular or binocular visual acuity to be estimated.

6 A computer-based screen visibility test as claimed in claim 5 wherein the visual task is a gap detection task in which the user has to report the position of a gap in the target.

7 A computer-based screen visibility test as claimed in claim 5 wherein the visual task is a gap offset task wherein the user has to detect whether detail is lined up with the centre of the gap or has been displaced to one or other side.

8 A computer-based screen visibility test as claimed in claim 5 wherein the visual task is a character identification task in which the user has to identify which letter or letters or other alphanumeric information has been presented.

9 A computer-based screen visibility test as claimed in claim 1 or claim 2 or claim 3 or claim 4 or claim 5 in which the alignment of viewing direction of the user's two eyes when dissociated is assessed by presenting a target or targets on the display screen such that certain parts of the target or targets are presented to the left eye and other parts of the target or targets are presented to the right eye in order that any misalignment can be reported by the user.

10 A computer-based screen visibility test as claimed in claim 1 or claim 2 or claim 3 or claim 4 or claim 5 in which the alignment of viewing direction of the user's two eyes when dissociated is assessed by presenting a target or targets on the display screen such that certain parts of the target or targets are presented to the left eye and other parts of the target or targets are presented to the right eye in order that any misalignment can be adjusted by the user so that the parts of the target appear aligned.

11 A computer-based screen visibility test as claimed in claim 4 and claim 10 wherein the test pattern is a square 3 of whose corners are seen through 3 window panes and are thus presented to one eye and the fourth corner is seen through the other window pane and is thus presented to the other eye, the whole target therefore being used to simultaneously assess horizontal and vertical misalignment of the two eyes when dissociated by allowing the user to adjust the test pattern until it is perceived as a complete square.

12 A computer-based screen visibility test as claimed in claim 1 or claim 5 or claim 6 or claim 7 or claim 8 wherein a visual acuity target is presented at various locations on the display screen, the user being tested at each presentation as to whether he or she can correctly identify the relevant detail thus revealing areas of the display screen where visibility is impaired by glare, poor screen quality or any other means.

13 A computer-based screen visibility test as claimed in claim 1 such that any permutation or combination of claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9, claim 10, claim 11 or claim 12 are employed to produce an array of tests.